The Speed Limits of the Biosphere

Climate policy focuses heavily on fixed targets such as the Paris Agreement’s 1.5°C target. However, natural systems do not respond exclusively to absolute values, it’s now becoming clear that in many cases they respond to rates of change, specifically how fast the planet is warming. This is particularly relevant at the moment as a number of studies and reports confirm that the rate of warming is currently accelerating.

The previous background rate of warming was widely agreed to be in the region of 0.18°C per decade. This had been the case from the 1980 to the start of this century. Work by Foster and Rahmstorf however showed that over the last decade this rate has increased to ~0.35°C per decade.1 Lower-tropospheric temperature is warming even faster, with a recent (preprint) paper putting it at up to 0.48°C per decade.2 Adding in the effect of El Niño jumps they conclude that there is potential for an additional 0.5–1.0°C of warming within the next decade.

The driving cause for this acceleration in warming, is primarily due to the increase in Earth’s Energy Imbalance or EEI. Between 2003 and 2025 the net flux has increased from 0.35W/m² to 1.45W/m² (a four-fold increase). This increase in the rate of energy accumulation by the Earth system drives acceleration across every other measure.

A recent study by Gervana Gyuleva et al. from the Institute of Atmospheric and Climate Science at ETH Zurich has linked this increase in EEI to higher rates of Transient Climate Response (TCR).3

Transient Climate Response is different from Equilibrium Climate Sensitivity, which I normally discuss. TCR measures warming at the exact moment atmospheric CO₂ doubles, based on a gradual increase of 1% per year over 70 years. It captures the immediate, short-term surface warming while the deep ocean is still actively absorbing heat. Equilibrium Climate Sensitivity (ECS) measures the ultimate, long-term warming after atmospheric CO₂ doubles and the fast feedbacks have stabilised, remaining constant until the climate system reaches full thermal equilibrium. This process takes years to decades because of the inertia of the system. TCR is therefore very relevant to fast warming responses to our emissions.

In their study, the team were able to use the EEI observational data to better constrain the likely range of TCR. Previous work not using EEI, but based on temperature measurements, had the range between 1.2°- 2.4°C. Their work suggests 1.9°- 2.6°C. This raises the lower bound by 46% and increases the upper bound which means that the immediate effects of continued emissions happen faster, agreeing with the observed acceleration in warming observations.

As seen in the geological and palaeontology records, biological and physical Earth systems have always adapted well to gradual change, but poorly to rapid change. A system can easily handle a +2.0°C world if it has centuries or millennia to adapt. But exposing that same system to a warming velocity of >0.3°C per decade strips away its structural adaptation capacity, triggering rate-dependent tipping points long before theoretical stable temperature limits are reached. The great extinction events of the deep past are all linked to sudden change.

Rate-Dependent Tipping Points

Put simply, a tipping element is a system that has more than one stable state and that the state in which it resides in is determined by some outside force or effect. Consider a simple chair. It has a few stable states but two of them as standing upright on four legs and laying on its back. When it is on all four legs, it can be rocked backwards slightly and it will return to the stable state, perhaps overshooting a bit before settling back to a static position. If it is pushed back quite a lot, it will still return to upright, but if we push it just a tiny bit more, it will pass a balance threshold and rather than return to upright, it will accelerate to the fallen over state. Once there it is again stable, pushing it up a bit will return it to the same fallen position. You have to push it all the way past the balance threshold again to get it to move back to the upright state. The balance point is the tipping point of the system.

There are two forms of tipping behaviour that are relevant here.

• Threshold Tipping (B-Tipping): Pushing a parameter (e.g., total greenhouse gas concentrations) past a critical boundary where the background equilibrium state disappears in favour of an alternative equilibrium on the other side of the tipping point. An example of this would be the altitude effect on the Greenland ice sheet. As the ice melts it drops in altitude into warmer air, speeding up the melting. A temperature threshold exists whereby even if it doesn’t get any hotter, the ice will continue to melt away once the lower altitude is reached. Here the rate of warming is not important, the final temperature is.

• Rate Tipping (R-Tipping): The background equilibrium moves faster than the system’s internal relaxation time. Even if a safe equilibrium exists at a higher temperature, the system fails to track it and collapses en route. A forest system can migrate to a cooler latitude over centuries unless the warming rate is so fast that the lower latitude trees die out in the heat, before the higher latitude trees are able to colonise high latitude lands.

Expressed mathematically provides us with an Adaptation Deficit function

Where τ_system is the internal timescale of the Earth system (e.g., deep-ocean mixing, forest migration rates) and dT/dt is the rate of warming (dT is the temperature change, dt is the time). If this product exceeds the system’s basin of attraction (range of stability), tipping occurs.

Case Studies: Systems Vulnerable to Speed

Ocean Circulation: AMOC and Deep-Convection Failure

A recent study that has attracted a lot of attention involves the Atlantic Meridional Overturning Circulation or AMOC. This is the ocean current that brings warm waters into the North Atlantic maintaining northern Europe’s temperate climate. Without it, the climate would be very different leading to UK winters down to as low as -20°C but still warming in the summers. The AMOC is driven by changes in water density as the current moves northwards. It sheds heat to the atmosphere, which aided by evaporation from the surface increases the density of the salty water allowing it to sink to the abyss and return south. The AMOC is a tipping element however. As the climate changes, the temperature gradients change and fresh meltwater from Greenland interferes with the surface waters impeding the overturning or sinking of the waters. With no sinking, the current slows and eventually stops, leading to hugely significant climate and sea level changes, both in Europe and globally.

The new paper from René van Westen et al. from Utrecht University has shown that the AMOC’s tipping behaviour is highly dependent on the rate of warming, and by extension, the rate of greenhouse gas emissions.4 In fact a slow warming driven by CO₂ levels only increasing by 0.5ppm per year, shows AMOC stability all the way up to more than 5.5°C above pre-industrial levels. However increasing CO₂ levels by 2.5ppm per year shows collapse at just 2°C above pre-industrial. The rapid warming (>0.3°C/decade) prevents deep-water columns from releasing heat efficiently, causing an AMOC shutdown at significantly lower absolute temperatures than slowly paced warming scenarios. This is extremely worrying since the average rate of CO₂ increase over the last 5 years was 2.64ppm, and on our current accelerating trajectory, 2°C could be reached as early as 2036!

Ecological Disconnect: The Amazon & Boreal Forest Migration

Ecosystems adapt through evolutionary adaptation or geographic migration. Natural tree migration rates top out around 1–5 km/year. Current shifts in climate envelopes require velocities of >10 km/year. Dieback occurs not because trees cannot survive at +2°C, but because the transition rate creates severe physiological drought stress and fire-feedback cycles faster than the ecosystem can restructure.

There can also be a mismatch between different elements and species within an ecosystem. Bark beetles can migrate faster than trees can adapt. In Europe this is a big problem as beetles no longer die off in the winters as temperatures do not get low enough any more to kill them off. Trees however lack the evolutionary time required to develop protection strategies. Migrating birds are struggling to adapt as they start their migrations to higher latitudes based on day length, but when they arrive the spring food resources they were expecting and relying on have been and gone, weeks earlier. This has a knock-on effect for the vegetation as the lack of both predators of plant eating insects and seed dispersal symbionts are missing when needed.

Energy accumulation: Marine Heatwaves and Storms

Heat enters the oceans from the sun from above. Mixing of the water column and the transfer of heat to the deeper water layers occurs quite slowly. When the temperature rise at the surface is slow, the ocean currents, gyres and mixing mechanisms have time to spread the heat to deeper waters, slowing the accumulation of heat at the surface. When the warming rate is fast however, these mixing mechanisms break down, heat gets trapped at the surface when the water’s density drops, making it more buoyant and less able to sink and mix. This traps the warm water at the surface where it continues to warm in a feedback loop. This then creates an increasingly stratified ocean water column (figure 2).

Other mechanisms join in to create a marine heatwave. These include reducing the amount of cloud cover (allowing more solar radiation to reach the surface) and a lowering of the surface winds over the warm area. Both of which allow more heat to accumulate.5

The occurrence of these marine heatwaves is increasing rapidly. So fast in fact that the term was not even coined until 10 years ago, but in 2024, 91% of the ocean surface experienced at least one event.

The trapped energy eventually has to go somewhere. As ever more heat is accumulating within the top layers of the sea, more of it escapes into the atmosphere as water vapour, turning the air into a high-octane fuel for storms.

The 2024 Valencia flooding provided a grim “proof of concept.” With Mediterranean sea surface temperatures at record highs, the storm didn’t just follow standard physics; it exhibited Super-Clausius-Clapeyron scaling. Instead of the expected 7% increase in rain per degree of warming, rainfall intensity jumped by 20%. The result was a year’s worth of rain (771.8mm or 32 inches) in just 16 hours. The flooding claimed 230 lives and caused huge economic losses.6

These kinds of storms are strongly related to rate dependent warming. A higher temperature but under slower warming would allow the heat to be mixed to deeper layers in the ocean, preventing these huge accumulations of potential storm energy.

Moving Beyond Global Mean Surface Temperature (GMST)

These findings, together with the acknowledged acceleration in warming, mean that instead of focusing solely on temperature anomalies, we should also track the following metrics to evaluate the velocity hazard:

Policy & Mitigation Blindspots

Now that stopping warming exceeding 1.5°C, as stipulated by the Paris Agreement, is impossible to achieve, the concept of Overshoot is becoming accepted. This implies that the temperature threshold can be ‘temporarily’ exceeded and brought back down again by removing CO₂ from the atmosphere in future decades and centuries.

Rate dependent changes and tipping elements invalidate this hypothesis. Rapid warming during the upward leg of an overshoot risks crossing rate-dependent limits. Reversing the temperature later cannot un-tip a collapsed ocean current or restore a dead biome.

This means that slowing down is as crucial as stopping. This dramatically increases the importance of near-term mitigation efforts (e.g., rapid methane abatement) buying vital time by flattening the warming curve, even if ultimate long-term carbon targets remain unchanged.

In another recent study from ETH Zurich, Konstantin Weber et al. examine the practicalities of achieving a safe return through an overshoot period, finding that current financial and governance capacity is simply not capable of achieving the levels of negative emissions required. They used the highly ambitious SSP1-1.9 scenario, which is now widely accepted as unachievable, to show that even a delay of 20 years until the start of strong mitigation work led to the overshoot lasting over 250 years. That assumes no tipping points are reached despite long term temperature averages of over 2°C.

What are the options?

These recent studies, backed as they are by observations and real world data, show that the current warming rate is highly dangerous and getting worse. This needs just as much attention as the fact that we are about to breach 1.5°C of warming, if we haven’t done so already.

The main takeaway is that it is increasingly important to limit the rate of warming, even if the eventual peak is higher than hoped for. This means quick win actions like methane emission reduction are essential. Methane is a very powerful greenhouse gas, but short lived, so reductions have a fast effect. Our methane emissions are currently responsible for about 30% of the current warming, so cutting them would go a long way to reducing the warming rate. The good news is that a lot can be done to achieve this, often at very low cost, as I reported recently.7

It also means that any delays in achieving net-zero emissions, adds disproportionately to the risks we face in the near future. We need to bend the emissions curve down as soon as possible.

There are also other ways we could slow the warming rate. Solar radiation modification is moving out of the shadows and starting to be discussed openly and seriously. There is even government funded research underway in the UK. It maybe that the only way the world, still addicted to fossil fuels (and bullied by the US hegemony if they talk of rehabilitation), can escape catastrophic tipping elements such as the collapse of the AMOC or death of the rainforests and other essential ecosystems. Technologies that could cool the planet, or even just reduce the rate of warming, by reflecting some of the sun’s radiation back out into space, could be a last hope, and may need to be implemented sooner than most people would like.8

Conclusions

We must urgently shift the public and policy discourse from “How hot will it get?” to “How fast are we warming?”

Earth’s systems can withstand remarkable shifts given geological timescales, but they cannot withstand our current velocity of forcing. Slowing down the rate of warming through near-term methane abatement and atmospheric stabilisation is no longer just a secondary goal—it is the primary defence against systemic collapse.

We may need to deploy solar radiation modification if the warming rate does not come down in order to avoid truly devastating tipping points. This effort requires more urgent government level funding to ensure that enough is known about the potential downsides and side effects. Governance structures and public acceptance is also a high priority, all of which will require considerable effort, but other realistic choices are eroding in the mean time.

It’s not just that bad things are on the horizon, its that the horizon is accelerating towards us.

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I am delighted to be joined by Mark Roberts from 4Hunger.org for this article. Mark has a long and distinguished career as an environmental lawyer, international climate and anti-deforestation advocate. His recent focus is on hunger and aid policy. I highly recommend his Substack and hope you subscribe for more of his highly insightful and relevant content.

Physics sets the shock. Policy sets how many people go hungry. Slowly though food insecurity, chronically through lack of calories, and acutely through the starvation that kills. Every number and figure we cover below carries a source, and a confidence level wherever the source states one, because the impacts on global and domestic hunger in a 2°C world due to climate change does not need to be exaggerated, the truth is scary enough.

The 2ºC Dinner Table is Already Being Set

In 2025, for the first time in the history of the world’s hunger monitor, famine was confirmed in two countries in the same year. Parts of Gaza. Parts of Sudan, with four more countries on the brink of famine. Across six countries, 1.4 million people ended 2025 in the category the international humanitarian classification calls Catastrophe, the level at which starvation and death are no longer projected but counted body by body. That figure is nine times higher than it was a decade ago.

All of that happened at about 1.4°C of warming, in a world that still had a functioning humanitarian system.

Those are figures for acute hunger, the crisis level measured by the Integrated Food Security Phase Classification, where a shock strips a household of everything between it and starvation, and where famines are declared. It is not the same thing as the lower chronic hunger category, the slow shortfall of calories and nutrients the UN Food and Agriculture Organization (FAO) counts at roughly 645 million people worldwide. Nor is it food insecurity, the broadest of the three levels, where people have had to skip meals or go without food for a day or two. The three categories are tallied by different systems and can move in opposite directions: the chronic count can drift downward in the very year the acute count climbs. This article tracks all three, and is careful not to let the reassuring number stand in for the dangerous one.

The threshold this article discusses is what happens to hunger when the world reaches 2°C above the historic (1850-1900) baseline, and the fact that this is no longer a problem of the 2050s. With the rate of warming now measured rather than modelled, 2°C could arrive as early as 2036. That is inside the working career of every official who will decide how to prepare for it, inside the term of most mortgages held by the people reading this, and before the high school graduation of a child about to start their eduction this autumn.

So the question is not whether a hotter world makes more people hungry. That was answered in Somalia in 2022, where a drought that human warming made roughly a hundred times more likely killed an estimated 43,000 people, about half of them children under five. The question now is how many more, where, and whether anybody with the power to change the answer has the courage and the empathy to do something about it in the short time that remains.

The published answers are neither reassuring nor agreed. Estimates of how many additional people will go chronically hungry in a 2°C world run from roughly one million to roughly 183 million.12 That is not a scientific inaccuracy or a rounding disagreement. It is a spread of nearly two orders of magnitude, due to the single most important fact in this article. The choice of how many people will go hungry depends on the policy choices our leaders make right now.

A range that wide usually means the underlying science is immature. Here it means something else, and that difference matters more than any single number in this article. The models producing the low end and the high end broadly agree on the physics. They agree on how much heat a maize plant can tolerate during pollination, where rainfall belts are shifting, and what a hotter atmosphere does to evaporative demand. What they disagree about is what we and our leaders will do about it: whether trade stays open when exporters take fright of a food shortage, whether smallholders can access credit and improved seed, whether safety nets hold through the price spikes that are coming, and whether adaptation finance arrives before the shock or only in the wreckage, hunger and famine after it. Numbers of this size are easy to read as fate. They are not. For once the climate change story is not about ever increasing suffering, at least it needn’t be.

2°C sets the size of the shock. Policy choices decide how much of the shock becomes hunger.

These projections need a baseline. The FAO’s 2026 edition of The State of Food Security and Nutrition in the World puts the number of people facing chronic hunger at approximately 645 million in 2025.3 This article uses that as a level but does not treat the reported direction of where hunger is going as established.4

The Horizon: When 2ºC Arrives

The last IPCC assessment, AR6 published in 2023, working from evidence published up to 2019, indicated that under a moderate emissions pathway (SSP2-4.5) the 2°C threshold would not be breached for several decades, most likely in the 2050s. That estimate has aged badly, and it has aged badly for reasons of scientific measurements rather than politics.

The most compelling new evidence concerns the Earth’s Energy Imbalance (EEI): the difference between the solar energy arriving at the top of the atmosphere and the energy radiating back to space. It is the cleanest single indicator of whether the planet is accumulating heat, and how fast. NASA’s CERES satellite record now shows an approximately fourfold increase in the rate at which the Earth system is accumulating energy since 2003, and independent analysis finds the imbalance has more than doubled in recent decades.5 Observed accumulation is running above the projection for RCP8.5, the high-emissions scenario in the IPCC latest report, even though human emissions are following a lower path than RCP8.5 assumed. Warming is faster than anticipated. Impacts are arriving decades earlier than hoped.

A large part of the explanation is a better understanding of cloud feedbacks. Earlier assessments could not determine whether clouds would amplify warming or restrain it; by AR6 the sign was clear, and it was amplification, though the uncertainty band remained wide. Work by James Hansen and colleagues indicates the feedback is strongly positive and is the primary driver of the rise in EEI: the planet is dimming, losing cloud cover while the clouds that remains have grown less reflective. On this analysis, the climate’s sensitivity to greenhouse gasses sits at the high end of the IPCC’s likely range.6

Since the EEI is a rate of accumulation, rather than a measure of the stock already accumulated, a rising EEI means that the energy available to warm the planet is itself accelerating. That acceleration is now visible in every downstream measure: surface air temperature, sea surface temperature, ice melt, sea level rise, ocean heat content, atmospheric relative humidity and the intensity of extreme weather events.

A 2026 analysis by Foster and Rahmstorf7 found that global temperature is accelerating even after accounting for natural variability, including the El Niño–Southern Oscillation. Their analysis places the crossing of the 1.5°C threshold between 2026 and 2028. Extrapolating the emerging warming rate puts the crossing of the 2°C threshold as early as 2036. That is approximately two decades earlier than the IPCC’s last estimate, and that temperature increase is now close to unavoidable.

The consequence is that everything downstream of the changes in climate arrive faster. But plant breeding programs take years to move a trait from the trial plot to the farmer’s field. Irrigation schemes, grain reserves and cold chains take even longer to finance and construct. Trade agreements take longer still. On the timeline the physical evidence now supports for increasing global temperatures, 2°C arrives with very little warning and very little room for us to prepare.

The Calories That Quietly Disappear

The most useful single number in the agricultural literature comes from Hultgren and colleagues (2025), an eight-year study of six staple crops across 12,658 regions, capturing two-thirds of global crop calories. For every degree of global warming, the world loses approximately 120 kilocalories per person per day, about 4.4% of daily consumption. Critically, that estimate is net of adaptation: it already assumes farmers change cultivars, shift planting dates and adjust management in response to the climate they experience, despite the fact that farmers notoriously resist changes to their farming practices.8 In the West this temperature change and reduction in crop production mostly arrives as higher grocery prices. In the Global South it arrives as food insecurity and acute hunger.

The timeline matters as much as the magnitude. The same study, written before the energy-imbalance work by James Hansen and colleagues described above, puts the global calorie loss at roughly 7.4% by 2050 and 11.2% by 2100 under moderate emissions once adaptation is included, and 24% by 2100 on a high-emissions pathway. The 24% figure is the one the media picks up; the mid-century figure is the one that should be of immediate concern, especially as it’s timing is on the optimistic side. It sits inside the planning horizon of every finance ministry, development bank and grain trader now operating, and is far harder to dismiss as a future scenario.

Adaptation’s contribution can be stated precisely: adaptation and income growth together offset 23% of global losses in 2050, rising to about a third by 2100. That is real mitigation. But it is also a ceiling, and even with the adaptation fully implemented, it leaves the majority of the loss standing in a model already generous about how quickly temperatures will rise and farmers will adjust. The offset is also wildly uneven. In Africa it reduces projected end-of-century losses from 16.0 to 11.6%; in North America, from 21.0 to 20.8%, which is within rounding of nothing at all. The regions with the most agronomic capital have the least room left to improve, because they already farm close to the optimum.

The distributional result inside the same study is worth stating, because it cuts against the intuition that climate damage is a poor-country problem. Projected end-of-century crop yield losses average 41% in the wealthiest regions and 28% in the lowest-income regions. The steepest damage falls at both extremes of the agricultural economy: on modern breadbaskets currently enjoying the world’s best growing conditions, and on subsistence communities depending on small harvests of cassava and millet.

Behind the smooth averages sits a distinctly un-smooth implementation mechanism. Tropical staples such as maize, sorghum and rice are already grown close to their ceiling temperatures. Yield does not decline gently as the thermometer rises; it holds, and then collapses, because the damage is concentrated in a narrow reproductive window. Agronomists have measured the critical thresholds for seed set at flowering with unsettling precision: roughly 37.2°C for rice, 37.9°C for maize and just 27.3°C for wheat.9 Above those threshold during the flowering period leads to sterilised pollen and failed fertilisation. Grain filling is also reduced, so even a handful of hot days can destroy a whole crop. In this context, averages hide the real hunger smallholders in the Global South and smaller farmers in the Global North will experience.

The nutrients that go missing too

There is a second loss inside the first, and it does not appear in tonnage of food harvested. Elevated atmospheric CO₂ makes staple plants grow more and nourish less. Wheat grown under the concentrations of CO₂ expected in the atmosphere later this century lose approximately 9.3% of its zinc, 6.3% of its protein and 5.1% of its iron. Up to 35% of the global population depend on these crops for the bulk of those nutrients.

Translated into people rather than percentages, the effect is huge. Smith and Myers (2018) estimate that elevated CO₂ could push an additional 175 million people into zinc deficiency and 122 million into protein deficiency, while 1.4 billion women of childbearing age and young children, precisely the groups for whom iron status matters most, would lose more than 4% of their dietary iron by 2050. The burden of these nutrient losses concentrates in some particular countries rather than being spread: in India alone, the same analysis finds roughly 50 million people newly zinc-deficient, 38 million newly protein-deficient, and 502 million women and children in the iron-vulnerable group.

The IPCC’s Sixth Assessment reaches compatible conclusions and assigns them high confidence: protein content in rice, wheat, barley and potatoes falls by 6–14%, placing an additional 150 million people at risk of protein deficiency; zinc dilution adds 150–220 million to the zinc-deficient population and worsens deficiency in more than a billion people who are already deficient.10

A harvest can arrive exactly on target and still carry less nourishment than the same harvest did twenty years ago. The one number everybody watches is the weight of grain harvested, but weight of grain does not say how nutritious it is.

The outcomes show up in clinics, rather than on commodity exchanges, as stunted growth, impaired immune function, complications in pregnancy and higher child mortality. Hidden hunger is a term of art, but the hiding is literal. The metric everyone watches is the weight of grain, and the weight of grain is the one thing that does not change, how nutritious the grain is, on the other hand, does.

A One-Percent Grain Shortfall Becomes a Six-Percent Price Shock

Between a lost calorie and a hungry person sits a market, and markets for staple foods are peculiar. Demand is highly inelastic: people do not respond to a bad harvest by eating less bread. Supply is equally unresponsive within a season, because when one crop fails another cannot be planted for immediate replacement. The entire adjustment therefore falls on price.

The elasticities estimated by Roberts and Schlenker give the standard result.11 Their framework identifies demand using current-period yield shocks and supply using past shocks working through inventories, and finds commodity demand to be extremely inelastic. A shortfall of roughly 1% in global caloric availability (a shortfall of corn, rice, wheat, sorghum or cassava) therefore produces a price movement several times larger, on the order of 6%. A 2% crop reduction becomes roughly 12% price increase, 5% shortfall of grains becomes a 30% increase in price, and a 10% crop reduction becomes a 60% price increase⁸ (Some UK farmers are already reporting a 20% drop in wheat yield this year due to the unprecedented 2026 drought and heat). Realised responses depend on stocks-to-use ratios, trade policy, export restrictions and speculative positioning, all of which can push the multiplier higher. This is not a market failure. It is what a well-functioning market does when neither supply or demand can adjust. The impacts are real though.

Until recently this was a modelled claim. It is now an observed one. Kotz and colleagues (2025) document 16 cases across 18 countries between 2022 and 2024 in which extreme heat, drought or rainfall drove measurable food-price spikes, many following weather beyond all historical precedent prior to 2020.12 Olive oil across the European Union rose by around 50%. Japanese rice rose by around 48%. U.S. vegetable producer prices rose about 80% after drought across California and Arizona. Cocoa rose roughly 280% after a February 2024 West African heatwave that attribution analysis found had been made approximately 4°C hotter by climate change.

The persistence of the increase matters as much as the spike. Earlier work by Kotz and co-authors, a collaboration between the Potsdam Institute and the European Central Bank, found that higher temperatures and related crop shocks raise food and headline inflation persistently for roughly 12 months after the event.13 A single hot season is not a single bad month at the checkout. It is a year of elevated prices working through processing, retail and wage bargaining and landing on those least able to pay.

Then comes the political amplifier. Faced with domestic price pressure, exporting governments often restrict exports. Each restriction is locally rational and globally destructive: it removes supply from the world market at precisely the moment the world market is short, prompting the next exporter to do the same. The food price crises of 2007–08 and 2010–11 both followed this pattern, and both did more damage through policy cascade than through the underlying weather events.

For a household in a wealthy country spending a tenth of its income on food, a 6% rise in staple crop prices is an irritation. For a household spending half or more of its income on food, which describes a large share of the population in the regions covered below, it is the difference between three meals a day and two, or two meals a day and just one.

When the Breadbaskets Fail Together

World grain trade rests on a small number of exporting regions: the US Midwest, the Southern Cone of South America, the Black Sea and eastern China, with Australia and India significant in wheat and rice. Five regional breadbaskets account for roughly 60% of global grain production. The system’s implicit insurance policy has always been that these regions do not fail in the same year: their weather has historically been close to uncorrelated, so a drought in one is covered by a surplus in another.

The system’s insurance policy has always been that the breadbaskets do not fail in the same year. Climate change is quietly cancelling this policy.

Work by Gaupp and colleagues shows that warming erodes exactly this assumption.14 Amplified Rossby wave patterns and hemispheric heat extremes couple the growing seasons of distant regions, converting independent risks into correlated ones.15 The probability of simultaneous failure does not rise gently with temperature; it ratchets up. The return period for simultaneous climate risk across all five maize breadbaskets falls from roughly every 16 years historically to under every 2 years in a world at 2°C.

Tigchelaar and colleagues put the same risk in the units a trader watches. The top four maize exporters are the United States, Brazil, Argentina and Ukraine, and between them they account for 87% of global maize exports. The probability that all four suffer simultaneous production losses greater than 10% in a given year is presently close to zero; at 2°C it rises to 7%, and at 4°C to 86%. At 2°C the projected decline across those four amounts to some 53 million tonnes, equivalent to 43% of current global maize export volume.16

The McKinsey Global Institute’s 2020 analysis puts the same risk in the units a planner uses. The probability of a greater than 15% global grain production shock roughly doubles by 2030, from about 1-in-100 to about 1-in-50 in any given year, giving an 18% chance of occurrence between now and 2035. A smaller but still severe shock of a 10% loss, moves from a 6% to an 11% annual probability, and from a 46 to a 69% chance of occurring at least once in the next decade.17 That is the decade in which 2°C plausibly arrives.

A 2024 study by Zhang and colleagues puts numbers on the physical mechanism. At approximately 2°C, the likelihood that the world’s breadbaskets concurrently expose more than half their cropland to at least five days of extreme heat during the reproductive window in a typical year, not an exceptional one, rises from virtually zero in the 1984–2013 baseline to 43% for maize, 33% for rice and soybean, and 27% for wheat.18

The Limits of What Adaptation Can Do to Protect Crops

The World Bank’s Turn Down the Heat assessment contains a threshold that is easy to skim past: below roughly 2°C, adaptation offsets a substantial share of agricultural losses; above it, it becomes rapidly harder and covers only a shrinking fraction of the damage caused by the increasing temperature. 2°C is where the returns bend downward. The same report finds that at 2°C, South Asian crop production may fall by at least 12%, requiring more than twice the imports to meet per-capita demand, with childhood stunting rising by around 35% by 2050.19 The IPCC projects soft adaptation limits for multiple staple crops in many growing areas at 2°C, particularly in the tropics.

The Hultgren figure quantifies this from the other direction: adaptation and income growth together offset 23% of global losses at mid-century. Call that the best available estimate of what a farming system doing its rational best can recover. Note what ‘adaptation’ means inside these models. It means switching cultivar, shifting a planting date, drilling a well, installing drip irrigation. Every one of these requires capital, credit, information, secure land tenure and, frequently, a water right. Smallholders who lack the reserves do not adapt the way the model predicts. At 2°C their adaptation increasingly means land abandonment and migration, which the models score as adaptation and the households experience as catastrophic loss.

A result that points the other way

Honesty requires including one finding that cuts the other way. Zhao and colleagues (2025) analysed 92,096 hybrid-trial observations across the US Corn Belt between 2000 and 2020 and found that modern breeding delivered both yield gains and improved drought resistance; the trade-off breeders had long assumed would bind progress did not. Projected forward, continued genetic improvement of this kind could cut drought-related yield losses by approximately 17.8% by 2100 relative to older hybrids.20

The caveats are substantial and belong in the same breath. This is one crop, in one region, against one stressor. It addresses drought during grain filling, not extreme heat during pollination, which is the mechanism that does most of the damage to crops. It assumes the historical rate of developing genetic gains continues, and that farmers can afford the improved hybrids, fertilisers and other inputs that go with the new hybrids each season. It does not overturn Hultgren, whose estimates are already net of adaptation, and it does nothing for maize, sorghum or millet farmers in the Sahel or rest of the Global South.

A Map of Who Pays First

The additional hunger caused by a 2°C world does not distribute itself evenly, and the concentrations of damage and hunger are severe. South Asia carries roughly 33 million additional people at risk of hunger. Sub-Saharan Africa carries roughly 15 million additional hungry, plus approximately 43 million pushed below the poverty line. Across Sub-Saharan Africa, South Asia and Southeast Asia together sits around 80% of total exposure to additional hunger.

The reasons compound rather than merely accumulate. These regions have the highest dependence on rain-fed agriculture and the thinnest irrigation coverage. They spend the largest share of household income on food, so the price channel of crop loss to price increase described above hits them hardest. Their staples are already grown nearest to their thermal ceilings, so a given increment of warming does more damage. Their safety nets are thinnest and their fiscal space to expand them smallest. Their populations are also the youngest, which means the nutritional deficits fall during the developmental window in which they may do permanent harm.

An independent analysis by Oxfam approaches the same map from the opposite end. Rather than ranking by modelled exposure, it ranks by revealed damage: the ten countries with the most extreme-weather-linked UN humanitarian appeals since 2000, where climate was assessed as a major contributor. They are Somalia, Haiti, Djibouti, Kenya, Niger, Afghanistan, Guatemala, Madagascar, Burkina Faso and Zimbabwe. Across those ten, acute hunger rose from 21.3 million people in 2016 to 47.5 million in 2021, a 123% increase in six years, with 18 million at emergency levels of hunger or worse.21

The same analysis supplies the arithmetic of responsibility that the modelling literature tends to leave out. Those ten countries account for roughly 0.13% of cumulative global carbon emissions. The G20 accounts for around 77%. The distribution of the damage is close to the inverse of the distribution of the cause, and no adaptation figure anywhere in this article alters that ratio. So far, the G20 are not fully meeting funding pledges to pay for adaptation in low income countries hit hardest by climate change.

That is where the nutrition findings and the geography findings meet. The populations most exposed to calorie loss are, to a close approximation, the same populations carrying the nutrient losses described earlier. The same households absorb both shocks.

A third layer then sits on top: heat attacks food after harvest as well as before it. Higher temperatures accelerate spoilage and raise the risk of mycotoxin contamination, above all aflatoxin, a carcinogenic mould toxin in maize and groundnuts that worsens under exactly the combination of heat and drought stress a 2°C world delivers. Food-borne pathogen risks rise wherever cold chains are absent. Calories can be grown, harvested and delivered, and still not be safely eaten. Utilisation is the pillar of food security that receives the least attention and is among the most temperature-sensitive.

The Broad Base: Food Insecurity Now and at 2ºC

Next to chronic and acute hunger sits the third measure, and it is the broadest. The FAO’s Food Insecurity Experience Scale asks people directly whether, in the past year, they have had to eat less, skip meals, or go without food entirely for lack of money. By that measure roughly 2.3 billion people, about 28% of humanity, were moderately or severely food insecure in 2024, several hundred million of them severely food insecure, meaning they had at times run out of food or gone whole days without eating. The figure has barely moved since 2020 and sits roughly 680 million higher than in 2015. In sub-Saharan Africa it exceeds 58%, more than one person in two do not know where their next meal is coming from.22

Food insecurity measures access, not calories or crisis, and that is what makes it the base of the other two measures of hunger: chronic hunger and acute hunger. It captures the enormous population living one shock away from starvation: not necessarily undernourished on the calorie accounting, not yet inside the IPC’s crisis phases, but unable to count on enough safe and nutritious food from one day to the next. Roughly 2.6 billion people already cannot afford a healthy diet at all, before any further warming arrives.

2°C carries no published headcount for this measure, for the same reason it carries none for acute hunger: food insecurity is observed in surveys, not projected by crop models. But its transmission belt has already been traced. Access is governed by price, and a 1% shortfall becomes a price rise several times larger, with a single hot season lifting food inflation for a year afterwards. A durable rise in staple prices does not simply tighten budgets; it moves people down the scale, and from severe insecurity into the acute pipeline the next section describes. A world that lets food insecurity spread is quietly filling the reservoir from which the next decade’s famines will be drawn.

The Sharp End: Will Acute Hunger Get Worse?

Everything modelled so far is chronic hunger: the slow arithmetic of calories per person per day, nutrient density, prices and purchasing power. That is what the crop literature is built to produce, and it is the measure behind the one million to 183 million range. It is not the measure that produces famines. Acute crisis tracks shocks rather than averages: what happens when a harvest fails, a currency collapses, a road closes or a war starts, and a household with no reserves has nothing between it and hunger or even famine.

How much of this is already climate related?

The honest answer is: a large and rapidly growing share of acute hunger is caused by climate change, but not the largest share. In 2025 conflict and insecurity were the primary driver for 147.4 million people across 19 countries, that is 56% of the total. Weather extremes were the primary driver for 87.5 million people across 16 countries in 2025, about a third of the total acutely hungry people in the world.23

The trend inside that second number is the one to watch, especially in the context of 2°C of warming. As a primary driver of acute food insecurity, weather extremes accounted for 15.7 million people in 2020 and 87.5 million in 2025, a fivefold rise over a period in which global mean temperature moved by a fraction of a degree. Much of it traces to the 2023–24 El Niño, which devastated southern Africa, but this only temporarily rose temperatures to 1.6°C. A near-certain super El Niño for 2026–27 is already in the FAO and WFP hotspot outlook, which warns of deterioration across 13 countries and territories, with northeast Nigeria and Somalia joining Sudan, South Sudan, Yemen and Palestine at the highest level of concern.24

For the causal link itself, the closest thing to a controlled experiment is the Horn of Africa. Between late 2020 and 2022, five consecutive rainy seasons failed across southern Ethiopia, Somalia and eastern Kenya, the worst drought in four decades. Attribution analysis found the agricultural drought was made roughly 100 times more likely by human-caused global warming, and that an event of that severity would not have occurred in a climate 1.2°C cooler.25 More than 20 million people were pushed into Crisis or worse, and in Somalia an estimated 43,000 excess deaths occurred in 2022 alone, about half of them children under five.26

A child stunted in a famine year is stunted permanently. There is no later harvest that gives those years of nutrition back. Stunting causes a lifetime of physical, metabolic, and cognitive challenges.

What 2°C does to the shock machinery

No published study puts a number on how many people will be in acute hunger or famine in a 2°C world. The IPC classifies observed conditions rather than projecting them, and the humanitarian and conflict variables that dominate it are not forecastable on a multi-decade horizon. Anyone offering a precise figure is extrapolating past the evidence. What can be done instead is to ask, driver by driver, whether the machinery that generates acute crises runs more often at 2°C. On every input for which projections exist, it does, meaning it is much more likely that acute hunger will increase in a 2°C world.

• Drought exposure rises. The IPCC’s assessment finds an additional 350 million urban residents exposed to water scarcity from severe drought at 1.5°C, rising to 410.7 million at 2°C; across all populations the additional exposure roughly doubles between the two thresholds. Drying is amplified in the tropics, which is where the protracted crises already exist.27

• Extreme heat exposure rises far faster. Around 700 million people, approximately 9% of the world, would face extreme heatwaves at least once every twenty years at 1.5°C. At 2°C the figure is more than 2 billion, or 28% of the world.28 Heat does not only cut yields; it destroys the casual agricultural labor that landless households in crisis contexts depend on for the income to buy food.

• Shocks become more correlated and more frequent. The breadbasket evidence above is the machinery of acute crisis stated in physical units. A correlated shock is worse for acute hunger than for chronic hunger, because the mechanism that normally rescues a failed region, imports from one that did not fail, is exactly what a correlated shock removes.

• The price channel is an acute-hunger channel. The twelve-month persistence of heat-driven food price inflation matters far more to a household in Phase 2 hunger than to one in a wealthy country. Phase 2 acute hunger is where the people who fall into Phase 3 severe acute hunger come from, and a year of elevated prices is how they get there.

• Recovery capacity is not being rebuilt. The same 33 countries have appeared in every edition of the crisis report since 2016, and more than 80% of the severely food-insecure now live in protracted crisis contexts. These are places where a bad harvest is no longer a setback but a cumulative loss, because the resilience that used to absorb it has gone. Each new shock lands on the residue of the last.

The estimate, and its uncertainty

Setting those pieces together supports a directional judgement rather than a point estimate, and it should be labelled as such: this is inference from the drivers, not a projection anyone has published.

Acute food insecurity will almost certainly be worse at 2°C than it is now, and the mechanism will be frequency in addition to the then level of the acute hunger crises. The expectation is not that the world settles at a permanently higher number, but that the peaks come closer together. A bad year arrives before the previous one has been absorbed. Setting the El Niño impacts beside a fivefold rise in weather-driven acute hunger over five years and a fraction of a degree of warming, and a doubling of the weather-attributable component by mid-century reads as conservative. Whether the total number of people suffering from acute hunger doubles depends overwhelmingly on conflict, which nobody can forecast and which can be expected to worsen where there is less food. Conflict, climate and the cost of food are the three factors driving rates of hunger around the world.

The number that deserves the closest watch is not the headline count but the Catastrophe population. It has risen ninefold since 2016 to 1.4 million people in 2025, and famine was confirmed in two places in the same year in 2025 for the first time. Catastrophe is where a shock meets the absence of a response, which makes it the most sensitive indicator of both trends at once: hazards increasing, humanitarian capacity contracting. The 2026 crisis report expects no improvement, reporting the fall in humanitarian food-sector funding at around 39% since 2024, with development assistance down at least 15%. In the past, peoples of the world rallied to provide food to people in famines, remember Live Aid, and the fact that this did not happen to any great extent in 2025 does not bode well for the hungry people when 2°C arrives.

All of this points at the conclusion the chronic analysis reached, arriving from the other direction. The increase in acute hunger in a 2°C world is real, already growing, and already measurable in mortality rates - people are dying. But the difference between a bad decade and a catastrophic one still runs through whether anyone is funded to respond, whether trade stays open when the shock lands, and whether countries in permanent crisis are given any means of rebuilding the buffer that used to absorb the next crisis. WFP puts the return on taking anticipatory action at three to seven dollars saved for every dollar spent. 2°C decides how often the shock arrives. It does not decide how many people it kills.

What It Means in America, Britain and Australia

Crops do not fail gradually. The relationship between temperature and yield established by Schlenker and Roberts is sharply asymmetric and piecewise: below a crop-specific threshold, around 29°C for maize, 30°C for soybean, 32°C for cotton, additional warmth is mildly beneficial; above it, damage accumulates several times faster.29 Warming does not drive a smooth curve. It moves more of the growing season onto the wrong side of a hard biological edge.

The modelled consequences for the United States are stark: reductions of 30 to 46% in maize, soy and cotton yields by 2100 under slower warming, and 63 to 82% under unmitigated warming. Hultgren’s global analysis projects maize losses of up to 40% for mid-latitude grain belts even after farmers adapt, and separate work by Liu and Basso projects net US soybean yields will be 26 to 57% lower by 2050.30 The climate is already moving underneath the system: roughly half the country shifted a half-zone warmer between the 2012 and 2023 revisions of the USDA Plant Hardiness Zone Map.31

American hunger from climate change nevertheless arrives through a different door than in Malawi or Bangladesh. The United States is a net exporter with deep reserves and a highly capitalised farm sector; supermarket shelves will not go empty. What changes are the prices on the shelf and, upstream, crop insurance costs, farm incomes, land values and the fiscal exposure of federal support programs. Low-water events on the Mississippi already interrupt grain movement in drought years. There is also a trade dimension the Hultgren authors state bluntly: as northern latitudes gain and mid-latitudes lose, agricultural advantage is going to transfer to Canada, Russia and China.

The households that feel these price rises are the ones already spending a high share of their income on food, and they feel it in the same year that public budgets are absorbing disaster and insurance costs. It is the price elasticity described earlier, operating inside a wealthy country: a modest availability shock, a multiplied price response, and the impact concentrated on the poor and working classes.

Britain’s exposure is structurally different, because Britain is a net importer of food. It is the case where the correlated-failure mechanism described earlier lands directly on a wealthy population. Two of the three worst UK wheat harvests on record have occurred this decade, in 2020 and 2024, both caused by relentless rainfall. Wheat self-sufficiency fell from 96% in 2023 to 79% in 2024, with imports the following autumn running at double the five-year average. Across 2020 to 2024 the cumulative shortfall exceeded seven million tonnes. Then the 2025 crop failed from the opposite direction, in one of the hottest and driest springs and summers on record. 2026 looks like being even worse. A country short of wheat in a wet year and short again in successive dry ones is not having bad luck. It is experiencing climate disruption; both extremes can be bad, and are expected to get worse as 2°C is reached.32

The second half of that exposure is that Britain’s suppliers sit in the regions this article has already identified as losing when the temperature rises to 2°C. More than 90% of imported vegetables come from the Mediterranean, with Spain being the largest single supplier. Spain has been in a historic drought. Headline self-sufficiency across all farming sectors has fallen from 86 to 78%. Domestic shortfall and supplier shortfall are not independent events; they are two expressions of the same warming, which is the correlation problem operating at the scale of one country’s shopping basket.33 Europe is also the fastest warming continent on Earth, meaning the effects of warming arrive here first.

Australia sits between the two, and supplies the longest-running natural experiment. It’s wheat yields stopped rising in 1990. Hochman and colleagues simulated 50 representative sites across the grain zone and found that water-limited yield potential fell 27% between 1990 and 2015, driven by declining rainfall and rising maximum temperatures, with elevated CO₂ preventing a further 4% loss. National yields nonetheless held flat, because technology closed the gap between what farmers achieved and what the climate permitted, lifting relative yields from 39 to 55% of potential.34

There is a qualification here that cuts both ways. The Zhao breeding result is a Corn Belt study, and if any agricultural region on Earth has the pipeline, the capital and the agronomic data to bend its own curve, it is this one. That is the strongest reason to think the American numbers may land nearer the optimistic end of their range. The Australian record is what taking a bet on agriculture looks like after twenty-five years: it paid, and it paid by spending the yield gap it was closing, which is why Hochman’s authors end by asking whether the gains can continue. Neither case is a reason to expect the same in the Sahel or the rest of the Global South.

The Window That Is Still Open

If most of the distance between one million and 183 million is policy, then the policies that should be implemented need exploring. Four fronts carry most of the leverage.

First, keep the grain moving

This is the largest single lever in the literature and the cheapest to implement. The difference between a world in which staple crop trade stays open during a crop price shock and one in which exporters close their borders is a swing of approximately 53 million people at risk of hunger. It requires no new technology, no infrastructure and no transfer of funds. It requires only that governments refrain from doing the thing they are most tempted to do at the worst possible moment. The temptation is strongest when the stakes are highest and price shocks and grain availability are at their worst. The mechanism by which countries agree not to close their borders has to be built in advance: pre-commitments against export bans, exemptions for humanitarian purchases, and regional reserves. Such an agreement takes negotiation and time. The process to agree to open borders must start now, before the crisis really starts to gain momentum.

Second, breed for nutrition and break the monoculture

Bio-fortification now has a hard target rather than a general aspiration, and the nutrient figures above state exactly what it is up against. Zinc-bio-fortified wheat and rice, high-iron beans and pearl millet, and quality-protein maize are existing technologies with existing delivery channels. What they lack is scale.

Alongside bio-fortification sits diversification away from over-reliance on just four dominant monocultures. Millets, sorghum, cassava and legumes carry higher thermal tolerance and, in several cases, better micronutrient density than the crops they were displaced by. Rebuilding seed systems, agronomic knowledge and consumer demand for them is slow work, which is an argument for starting now rather than for postponing, given we may have only a decade to work with.

Third, fund the response before the failure, not after it

The compressed timeline established at the start of this article is the whole argument here. If 2°C plausibly arrives in the mid-2030s rather than the 2050s, then adaptation finance disbursed in the 2040s is finance disbursed after the event. Irrigation, on-farm and regional storage, decentralised solar-powered cold chains, processing hubs close to production, extension services and seed systems all take the better part of a decade to plan, fund and build. Front-loading is not a preference about spending profiles. It is arithmetic about lead times.

Fourth, build safety nets that trigger on a forecast, not on a famine

The FAO’s 2026 affordability data provided this warning: approximately 2.6–2.7 billion people, 31.3 to 32.5% of the world, already cannot afford a healthy diet before any 2°C shock arrives.35 A 6% staple price move applied to a household already priced out of adequate nutrition does not produce belt-tightening. It produces substitution into cheaper, less nutritious calories, which compounds the dilution effect described earlier.

The design feature that matters is automaticity. Safety nets that expand by discretionary political decision expand late, after the harm is done and after the politics have hardened. Safety nets indexed to observable triggers, such as food price indices, rainfall deficits, satellite-observed vegetation stress which release resources when certain thresholds are crossed. The technology for this exists and such systems are in operation in several countries. Expansion of these systems is a question of coverage and financing, and getting countries to allow these inventions. Linking safety net response to climate signals such as Earth’s Energy Imbalance may even provide an outlook away from natural variability in weather.

Every famine that follows a forecast drought is a policy choice made a year earlier, by people who had the forecast and failed to act.

The direction of travel

Everything above is written as though these four fronts were open. But we do not live in an ideal rational world. Three of them are currently closing, not through climate stress but by political choice.

2025 brought the largest single-year contraction in development assistance ever recorded. Aid from OECD donors fell 23.1% in real terms to $174.3 billion dollars, back to roughly where it stood in 2015 when the 2030 Agenda was adopted. The United States drove three-quarters of the fall, cutting its own aid by 56.9%, the largest reduction by any provider in any year on record, with Germany, France, the United Kingdom and Japan all cutting foreign aid as well. Humanitarian assistance fell 35.8%, and core contributions to the UN system fell 27%. A further 5.8% fall is projected for 2026.36

The incidence is not evenly spread, and the geography should look familiar. The OECD projects bilateral aid to the least developed countries falling by 13 to 25%, and to sub-Saharan Africa by 16 to 28%. That is the same map as the 80% of climate exposure described earlier, and the same as the 60% of the 2030 chronic-hunger projection that sits in Africa.

The operational consequences are already measurable. In Uganda, donor shortfalls forced the suspension of food assistance for a million refugees and ration cuts of up to 80%, alongside a rise in global acute malnutrition among refugees from 5.5% at the end of 2024 to 7.7% in late 2025.37 Peer-reviewed modelling of the US cuts alone projects more than 14 million additional deaths by 2030 across 133 countries, including 4.5 million children under five.38 None of those cuts were forced by anything other than a political choice to effectively cause a genocide.

None of this makes the four fronts wrong. It makes three of them counterfactual. Front-loaded adaptation finance and automatically triggered safety nets are the levers that set the multiplier between one million and 183 million, and both are being dismantled in precisely the years before 2°C arrives, which raises the standing of the one lever that costs nothing. Keeping staple trade open is the only front that does not require money that is no longer there, and on the accelerated timeline it may be the only one that can still be built in time.

Conclusions - The 2ºC Warning

Food is not merely an economic commodity. It is the baseline condition on which every other form of order rests. Governments survive inflation in most things; they survive it in bread less often. The historical record of price spikes in staple grains is also a record of unrest, of conflict, of migration, of state capacity failing under a load it was not designed to carry. When the harvest fails in several places at once, the consequences do not stay agricultural for long.

The instinct in wealthy countries is to treat this as somebody else’s emergency, buffered by distance and purchasing power. That instinct misreads the system twice over. A globally integrated food network transmits scarcity through price, and price reaches everywhere the network reaches. And the modelling does not even grant wealthy agriculture the protection it assumes: the steepest projected losses fall on today’s best growing regions, because they have the least headroom left. Wealth buys position in the queue. It does not buy exemption from the queue.

Which returns the argument to where it began. One million or 183 million. The physics that sets the shock is now largely determined; the acceleration in the energy imbalance has taken the choice about whether 2°C arrives, and much of the choice about when, out of our hands. What remains entirely in our hands is the multiplier: whether borders stay open, whether nets hold during food price shocks, whether the money arrives before the harvest fails rather than after.

The 2°C dinner table is being set. What ends up on it, and who is seated, is still, for now, ours to decide. It will not be for much longer.

Action you can take

The choices remaining are narrowing as 2°C approaches faster than anyone anticipated and are therefore far more consequential. They are being made now, in budget lines and trade rules and appropriations votes, by people who will not do anything about it unless somebody demands that they do. So, ask them.

The aid contraction described above was not a natural disaster; it was a set of votes and decisions made by representatives. Votes can be taken again to reverse those decisions. The trade commitments that keep grain moving in a crisis are negotiated in advance or not at all. The safety nets that decide whether a price spike becomes hunger are written into domestic law by legislators who answer to constituents.

• Call your representatives, at all levels, and ask what they intend to do about food security before the shock arrives rather than after it.

• Ask what they are doing to restore humanitarian and development funding. Ask whether they will commit, publicly and now, against export bans in the next crisis.

• In the UK, demand that the full Government national security assessment on ‘Global Biodiversity Loss, Ecosystem Collapse and National Security’ be made public and ask your MP to support a televised emergency briefing to properly inform the public.

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A note on the evidence used

The figures in this article come from three classes of evidence, and they do not deserve equal weight. Observed and attributed is the strongest: the price cases documented by Kotz and colleagues, the USDA hardiness-zone revision, the UK harvest record and the rise in the Earth’s energy imbalance are all measurements of events that happened. Assessed with stated confidence covers the IPCC’s nutrient-dilution findings, which carry an explicit high confidence label. Modelled projections, which include Hultgren, Smith and Myers, Gaupp, Tigchelaar, Zhang, Zhao, Hochman and the McKinsey analysis, are conditional on assumptions about emissions, adaptation speed, trade and income growth, and the conditions are the argument.

This is why the headline range is so wide. Studies at the low end assume open trade, effective adaptation and continued income growth; studies at the high end assume the opposite. Neither is wrong. They answer different questions, and reporting the range honestly is more useful than selecting a point estimate that flatters a position. Three things would move the numbers toward the optimistic end: sustained genetic gains of the kind Zhao documents, a durable regime holding staple trade open through a synchronised shock, and bio-fortification reaching scale faster than dilution accumulates. Three would move it the other way: a synchronised breadbasket failure arriving before adaptation finance does, a cascade of export restrictions, and the contraction in assistance persisting through the 2030s.

5

4Hunger.org

MILLIONS OF PEOPLE ARE STARVING

The major media headlines says global hunger is falling. Third year in a row. The number from the 2026 Global Report on Food Crises they are quoting describes last year’s rate of hunger, rests on the thinnest data in a decade (eighteen countries and territories aren’t even included…

Read more

a month ago · 7 likes · 3 comments · Mark Roberts

Here is the link to the Youtube recording and below are a copy of the slide deck.

For nearly a decade, the Paris Agreement’s 1.5°C and 2°C temperature thresholds were treated primarily as political north stars—aspirational, voluntary targets designed to encourage incremental national ambitions. That era is over.

Through landmark advisory opinions from the world’s highest judicial bodies—most notably the International Court of Justice (ICJ) and the International Tribunal for the Law of the Sea (ITLOS)—those numbers have been stripped of their soft-law flexibility. They have been codified as objective, binding baselines under customary international law. Crossing them is no longer framed merely as a tragic political failure, it is increasingly defined as a trigger for international legal liability.

Yet, just as global jurisprudence acquires the teeth to hold high-emitting states accountable, a quiet accounting crisis threatens to undermine the entire architecture. International climate science relies on multi-decadal moving averages to formally declare when a threshold has been crossed. This statistical smoothing creates a decade-long enforcement vacuum—a legal immunity zone where states can claim compliance while real-world physical damages are being accrued.

Paris Targets as Hard Legal Standards

The transition from voluntary pledge to statutory standard occurred through two major judicial developments. First, ITLOS unanimously established that anthropogenic greenhouse gas emissions constitute marine pollution under Article 192 of the UN Convention on the Law of the Sea (UNCLOS).12 Because the oceans absorb the vast majority (89%) of excess heat accumulation, failing to curb emissions to stay within Paris-aligned pathways places states in direct breach of their statutory duties to protect the marine environment.

Shortly after that, the ICJ addressed the core mechanics of state responsibility.3 The Court ruled that states have a binding duty of due diligence to prevent transboundary environmental harm under customary international law. Crucially, the Court removed much of the discretion states previously claimed when designing their Nationally Determined Contributions (NDCs), emissions reduction policies developed by the signatory states of the Paris Agreement, updated every 5 years.

Under this updated standard:

• NDCs must strictly align with the best available science—specifically Intergovernmental Panel on Climate Change (IPCC) pathways targeting 1.5°C.

• Customary law applies universally. Even if a government formally withdraws from the Paris Agreement (like the US), its legal obligation to prevent dangerous warming remains intact.

• Failing to exercise due diligence constitutes an Internationally Wrongful Act4, triggering the Law of State Responsibility, which requires offending states to cease harmful conduct and provide financial reparations for attributable loss and damage.5

The Measurement Trap: The Decadal Hindsight Gap

While the legal theory is now robust, its practical application hits a major hurdle: how we actually measure global temperature and warming.

Under standard IPCC and World Meteorological Organisation (WMO) protocols, a “breach” of the Paris Agreement is not defined by an individual hot month or a single anomalous year (such as 2024). To filter out internal climate variability—like El Niño-Southern Oscillation (ENSO) cycles, the scientific consensus requires a ‘multi-decadal’ global mean surface temperature average.

However, the Paris Agreement text doesn’t define precisely how many decades is meant by ‘multi-decadal.’ The IPCC AR6 Summary for Policy Makers published in 2023 states in a note: “Global warming (see Annex I: Glossary) is here reported as running 20-year averages, unless stated otherwise, relative to 1850–1900.” Checking the glossary, it states: “Global warming refers to the increase in global surface temperature relative to a baseline reference period, averaging over a period sufficient to remove interannual variations (e.g., 20 or 30 years). A common choice for the baseline is 1850–1900 (the earliest period of reliable observations with sufficient geographic coverage), with more modern baselines used depending upon the application.”6

However a different approach was used in December 2023 for the first Global Stocktake7, a report required by the Paris Agreement to track progress every 5 years, with the first in 2023. The report stated the temperature situation in one sentence: “Earth’s global average surface temperature in 2011–2020 was around 1.1°C higher than the pre-industrial average.” This suggests a 10 year historic average approach, not 20 or 30 years. It was also 3 years out of date, since they took the number from the last IPCC report, rather than the modern data sources.

Even if a period could be agreed upon, there is still a significant difference between a historic and a centred average approach. The Global Stocktake used a historic approach. The IPCC AR6 WP1 states “20-year running average”, but then goes on to infer a centred average whereby the temperature for a specific year uses 10 years historic and 10 years future trend as the average.

However both a 10 year historic and a 20-year centred average require ten years of data after a given point to confirm the mid-point temperature. Science faces an inherent lag: we cannot formally confirm that we have crossed 1.5°C until roughly a decade after the physical reality has occurred.

Looking at the most up to date data trend (figure 1), the differences are clear. 2025 was either 1.12°C on a 20 year historic average, 1.30°C on a 10 year historic average, or 1.5°C on a centred average projecting forward the current 45 year polynomial trend. That’s a big difference because of the rapid rate of increase. In a more stable climate there would be hardly any difference, but that is clearly no longer the case.

The next bone of contention is how the future should be treated; linearly, but over what period; polynomially; model based on emissions pledges; model based on current policy; include or exclude likely tipping elements… Agreement from a legal perspective is unlikely.

The Physical and Legal Fallout of Delayed Recognition

This statistical delay creates a dangerous mismatch between environmental physics and legal accountability. Since it was used in the case in the Global Stocktake, it’s fair to assume a 10 year historic average will be used in the future, but based on data from the last IPCC report (hence 2020 data in the 2023 stocktake). The next IPCC report, AR7 may be available in time for the 2028 stocktake, but the method that employs is anyone’s guess at this stage.

Meanwhile the planet actually sails through 1.5°C on its way to possible 2°C by the time 1.5° is finally legally acknowledged.

Non-Linear Physics vs. Linear Accounting

Earth systems do not respond to 20-year rolling averages; they respond to real-time thermal stress and atmospheric carbon concentrations. Critical tipping elements, especially those that result in further GHG emissions or significant harm, such as the thaw of boreal permafrost, or the destabilisation of the West Antarctic Ice Sheet, can be triggered by acute, multi-year temperature spikes. By the time a 20-year average formally logs the breach, the physical feedback loops will already be self-sustaining.

It also creates a false impression that there is a ‘remaining carbon budget’ to stay below temperature thresholds.

The Legal Shield

This lag provides high-emitting states and corporate actors with a potent defence in court. When sued by climate-vulnerable nations, youth groups, or NGOs for failing to cut emissions, state defence teams can point to the multi-decadal metric and argue that the Paris Agreement has not technically been breached yet. This allows states to justify ongoing fossil fuel licensing during the exact window when rapid decarbonisation is physically required. A position not helped by repeated claims that there is still a remaining carbon budget for 1.5° which is clearly not the case.8

Retrospective Reparations

Triggering the breach makes responsible states liable for damages and reparations, but if these are un-justly delayed by a decade or more, those real-world damages, caused by the realty of 1.5°C will go unanswered.

When international courts finally confirm a breach a decade late, the Law of State Responsibility will apply to a landscape of permanent loss. Financial compensation cannot restore melted glaciers or submerged low-lying island territories. The measurement lag converts proactive legal prevention into post-mortem accounting.

Cascading Into Domestic Courts

Despite the statistical delay, domestic courts are increasingly becoming the arena where this tension is fought out. Litigants are using the ICJ and ITLOS findings to challenge national policies using real-time scientific indicators rather than waiting for retrospective confirmation.

Aligning Law with Real-Time Physics

To prevent the Paris Agreement’s legal teeth from being blunted by this statistical lag, both scientific and legal communities need to refine how climate compliance is assessed.

Courts should not rely exclusively on long retrospective averages to evaluate whether a state is fulfilling its due diligence obligations. Instead, legal accountability could be tied to real-time indicators of human-induced warming—such as tracking atmospheric greenhouse gas concentrations, Earth’s Energy Imbalance, radiative forcing, and annual carbon emissions against IPCC-aligned pathways.

If a state’s current emissions trajectory is mathematically incompatible with staying under 1.5°C, and lets face it, that includes just about every state on the planet, the breach of due diligence is occurring now, regardless of when the 20-year temperature curve catches up with reality.

The New Horizon of Climate Law

International jurisprudence has established a vital precedent: temperature targets are binding legal boundaries, and violating them carries real consequences under international law.

However, law is only as effective as the metrics used to enforce it. If international institutions allow multi-decadal smoothing to delay the formal recognition of threshold breaches, they grant high-emitting nations a temporary legal free pass precisely when action is most urgent.

To give global climate law real power, we must measure the crime in real time—before the damage becomes irreversible. This should be discussed and agreed at the next COP meeting, adopted by the IPCC (preferably ahead of AR7 and the 2028 Global Stocktake) and ratified by the courts. We no longer live in a world defined by averages, but in a world defined by standard deviations. The science needs to adapt to it in order to protect both humanity and the ecosystem we utterly rely on.

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Methane (CH₄) is a powerful greenhouse gas, much more so than carbon dioxide, but has a much shorter lifespan in the atmosphere, oxidising in about 12 years. It’s concentration in the air has more than doubled since pre-industrial times, causing roughly 30% of recent global warming. The methane cycle includes natural sources and sinks but human activity is behind the dramatic increase. Methane is emitted from landfill sites as garbage rots, from fossil fuel infrastructure including leaky natural gas pipelines, abandoned wells and mines, from beef, dairy and lamb agriculture and from rice cultivation. Fortunately, there are viable economic solutions to most of these human sources, making methane action an achievable ambition with a fast climate response. Like any little brother though, it has the capability to wreak havoc as temperatures rise. Natural stockpiles are waiting to erupt which could push accelerating warming even higher.

Trends in Atmospheric Methane Rise

Pre-industrial atmospheric methane was 729 ppb, but according to the latest NOAA data, this has climbed to 1,937 ppb as of March 2026.1 That’s over 2.6 times higher. During the late 20th century the rise was due to rapid expansion of agriculture and fossil fuel extraction but through clean air initiatives, reductions in gas flaring and other efficiency improvements, this levelled off to an equilibrium after the turn of the century (figure 1). From 2006 however, the trend started to rise again as natural emissions increase due to global warming, changing ecosystems and increases in human emissions. This is confirmed by isotopic analysis of atmospheric methane, which can be used to trace the sources of the airborne gas. Human caused emissions represent 76% of the growth however, so mitigation action can still have a significant impact.

Greenhouse Gas Potential

Methane has a steady state lifetime in the atmosphere of about 12 years. 90% of the loss in the atmosphere occurs through reaction with hydroxyl radicals (OH) in the lower atmosphere, 5% by bacterial soil oxidation and the rest through chemical reactions in the upper atmosphere.

When it is first emitted, over the first year methane has a CO₂ equivalent value (CO₂e) of 120. This means that 1 tonne of methane in the air traps 120 times as much heat as 1 tonne of CO₂ during that first year. Due to its limited lifespan however, after 20 years most of it has been converted or absorbed, so this value drops to 84 averaged over the 20 years. Over 100 years, the value has dropped further to just 28.

You’ll have noticed that concentrations are measured in parts per billion (ppb) for methane as opposed to parts per million (ppm) for CO₂. It’s this very high greenhouse gas potential that makes it important though. Since the pre-industrial, methane has risen 1.2ppm compared to CO₂’s 152ppm, but factoring in the stronger potential, this equates to 102ppm CO₂e over 20 years. The IPCC calculate that methane has been responsible for 30% of the warming over recent decades, due to both the sharp rise in concentration and its high greenhouse gas potential.

Adding the increases in CO₂ and methane together is equivalent to a 254ppm increase in CO₂ which is almost double the concentration in the pre-industrial (278ppm). Climate sensitivity is a measure of the climate’s response to a doubling of CO₂ with a temperature rise of between 3° and 4.5°C (likely to be at the higher end). It’s clear from this that keeping temperatures below 2°C as mandated by the Paris Agreement cannot be achieved without addressing both methane and carbon dioxide emissions.

Detecting methane emissions

Methane’s ability to absorb high levels of long wave radiation coupled with the fact that most human caused emissions are point sources such as pipeline leaks, waste facilities, intensive farming sites etc. means that locating sources of methane emissions can now be carried out with satellites. Just as smoke from a forest fire can be seen in the visible spectrum, obscuring the land beneath it, methane clouds can be seen in infrared. Not because they are warm in themselves but they obscure the warm surfaces beneath the plume.

This makes large emission sources much easier to detect. 25 satellite missions can currently detect methane point sources using infrared imaging and even handheld devices are used to detect and report leaks from pipelines, extinguished flares and abandoned wells.

Figure 2 is part of a report from MethaneSAT covering observations of the San Joaquin area of California. The findings show that the oil and gas industry is emitting roughly 9% of its marketed gas production into the atmosphere. Not only is this 20% higher than reported in the US EPA directory, but it is significantly greater than the widely stated goal of just 0.2% by 2030, which the industry had adopted. This is obviously damaging from a pollution and climate perspective, but it is also significant revenue loss for the operators. What sane person would voluntarily waste 9% of their hard earned productivity?

Human Emissions and Opportunities

Recognising the importance of methane emissions, the Global Methane Pledge2 was launched at the Glasgow COP26 in 2021 and has now been signed by 160 countries. The participants have agreed to take voluntary actions to contribute to a collective effort to reduce global methane emissions at least 30 percent from 2020 levels by 2030. This is a global, not a national reduction target. Half way through the period however, few countries or companies have formulated real plans that match the commitments with very few verifiable reductions. Under-reporting appears systemic too, which doesn’t help.

The Energy Sector

The energy sector, including oil, natural gas (which is methane), coal and biomass accounts for 35% of human methane emissions according to the International Energy Agency 2026 Global Methane Tracker report3, which found “no sign that methane emissions from fossil fuel operations are falling, despite well-known and proven mitigation pathways.” Record production of oil, gas and coal, combined with limited mitigation efforts, has kept emissions above 124 million tonnes (Mt) annually.

Oil production is the largest source at 45 Mt, followed by coal at 43 Mt, and natural gas at 36 Mt. Abandoned wells and mines contributed around 7% to these emissions in 2024. Bioenergy production and consumption results in a further 20 Mt of methane, largely from the incomplete combustion of traditional biomass used in cooking and heating in developing economies.

Methane emissions from the sector are often under-reported though as a 2025 study of Canadian abandoned fossil fuel facilities demonstrated.4 The study found that actual emissions from non-producing wells were seven times higher than reported. There are roughly 8 million abandoned mines and wells globally emitting an estimated 8 Mt of methane each year. Plugging these leaks would be the equivalent of removing 7.7 million petrol cars from the road.

The good news is that all the technology required to detect and fix 70% of fossil fuel related leaks already exists and is proven to work. This is evident in the disparity of emissions across different regions. Norway for example, has very low leakage compared to Turkmenistan. The IEA estimate that 35Mt of emissions could be avoided at no net cost since the costs of abatement measures are less than the market value of the additional methane gas captured and sold or used (Equivalent to removing 33.5 million petrol cars from the road, and for free).

Policy is a key requirement to drive change. Lost potential profits from leakage is one driver, but mitigation efforts are slower than required to meet the Global Methane Pledge. Perhaps leakage fees, fines for inaction following notification of a detected leak or quality requirements based on whole supply chain leakage need to be implemented more widely to force the necessary action.

Now that satellite observations have been operational for a few years, global analysis of fossil fuel industry emissions are emerging. They show that overall oil and gas methane emissions as measured by MethaneSAT were 50 percent higher than reported in the widely cited Emissions Database for Global Atmospheric Research and U.S. EPA’s Greenhouse Gas Inventory. Figure 3 shows the oil and gas emissions across global production fields. Although the Permian in the US is the worst, it it one of the largest, so figure 4 shows a normalised picture with emissions as a proportion of marketed gas production. On this scale the top 3 are in Iraq and Russia. Following the widespread destruction of infrastructure in the Middle East and Russia this year, the picture may well be far worse today than even this 2025 data suggests.

Agriculture

Agricultural emissions are principally from two sectors, ruminant animal farming which includes beef, dairy, lamb and wool, and water-based crops, mainly rice cultivation.

Ruminants like cattle and sheep have a digestive track that ferments their food before passing to the rest of the gut. This fermentation results in methane production which the animals belch to the air. The cattle population has been growing globally to 1.58 billion animals by 2024,5 but follows a mainly linear trend this century, so does not account for the acceleration seen in figure 1. It is still a major contributor to human methane emissions, reaching over 110Mt per year by 2023. (Equivalent to over 100 million petrol cars)

Efforts have been made to use modified feedstocks which don’t require as much fermentation and significantly reduce this methane belching. The economics are interesting. In dairy production, the fats, proteins and carbohydrates in the milk are made principally of Carbon, Hydrogen and Oxygen. Lactose for example has the chemical formula C₁₂H₂₂O₁₁. All the CH₄ that is being wasted in burps, could therefore be going into milk production if it passed through the gut more efficiently. A dairy cow will burp up to 700L per day of methane accounting for up to 13% of the digestible feed.6 The same principle applies with fat and muscle growth for beef and lamb. Research into methane inhibiting feed additives and alternatives is therefore vital. There is some interest in using Asparagopsis, a type of red seaweed that can be cropped or grown in tanks, as a methane mitigating feed additive because it can be naturally sourced and is “generally recognised as safe” by some regulatory authorities.

The other end of the cattle is also an issue. Cow dung emits methane as it decomposes especially if carried out anaerobically. Methods are being developed to deal with these emissions by trapping the gas and either converting it to fuel or burning it in a turbine to generate electricity. A 2025 study of such digesters in California reported an 82% reduction in emissions from this source.7

Rice is the world’s third most produced cereal crop at 530 million tonnes last year. Its cultivation is also a major methane emitter accounting for 12% of human emissions. Rice grown in flooded paddy fields creates anoxic conditions in the soil which favours methane producing microbes. Different varieties of rice are associated with different emission levels, so low-methane varieties are being developed, some with far less water requirements. A 2024 study showed methane reductions of 70% suggesting that further hybridisation has the potential for both higher yields and lower emissions. Another win win for the producers.

An additional problem with rice cultivation is the remaining stubble and straw, roughly the same weight as the harvested rice. Currently, to clear fields for future crops, farmers either burn the rice straw, which results in significant carbon dioxide emissions as well as methane, carbon monoxide, nitrogen oxides, sulphur oxides, and particulate matters, or they flood the field to encourage swift decay, which also leads to extensive additional methane emissions. Better practice utilising the stubble as mulch has been found to reduce emissions by 78% while increasing profits by up to 20% through fewer input costs and increased yields.89

Waste

Landfills used for waste management are the third largest human related methane source in the US, accounting for over 14% according to the EPA.10 In addition to the climate impacts, gasses escaping from landfills is often an unpleasant foul mixture with air quality and public health implications. As the mainly organic matter decomposes, conditions quickly become anoxic promoting the methane emitting microbes. Fortunately through good site construction, this gas can be captured and processed to make fuel and generate electricity.

The situation outside the US is worse. In total, waste generates 20% of human methane globally. Many sites in the developing world and some in the developed world are not capped and so vent their gas straight to the atmosphere.11 Even bulldozing soil over the top would make a substantial difference since soil microbes would convert the leaching methane to CO₂. With proper capping and treatment, gas could be made available to poor communities for energy and cooking.

Progress

In addition to the Global Methane Pledge, China has included methane in its Nationally Determined Contribution emissions targets. This is the first time that all greenhouse gases from all sectors have been included in national targets. For example coal mines need methane extraction for safety reasons in order to avoid explosions. By collecting the methane and burning it, they are using the power to run the extraction pumps, saving money and halving the emissions in the process.

The projected time to net-zero is too slow to leave methane to itself in the hope that it will decrease as our reliance on fossil fuel reduces. More determined policy and initiatives will be required.

Natural methane sources and feedbacks

Whilst human emissions of methane are the main driver of growth, the recent accelerations over the last 20 years is also being partly driven by increased emissions from wetlands and permafrost melt. Both these sources are highly likely to increase as the climate continues to warm.

Methane is thought to be a major contributor in the processes that switch the planet from a glacial state to an interglacial one. These glacial termination events are observed in ice core bubbles and occur with sea level rise and increases in rainfall that swamps low lying plains. Kicked off by the planet’s orbital cycles, the jumps in resulting methane acts as a feedback further accelerating warming and ice melt. The last termination event at the start of the Holocene saw methane concentrations increase abruptly by ~250ppb at rates of up to 6 ppb/year. Todays increase of 1,200 ppb in less than two centuries with a current ten year average increase rate of 11 ppb/year is therefore a major concern as it exceeds even this extreme climate altering natural rate.

Isotopic analysis over the last 2 decades points towards tropical wetlands being a key driver in the accelerating methane concentration. Xin Lin et al. added to this conclusion by showing that concentrations were rising fastest in tropical and boreal water inundated areas of the world.12 Another recent paper however, points towards the rise of shale gas extraction coinciding with the acceleration over the last two decades.13

To find out more about termination events and modern natural methane rises, I can recommend this 2023 paper by Euan Nisbet et al.14

Permafrost emissions comprise both CO₂ and methane and are set to accelerate as warming increases. According to the 2025 State of the Cryosphere report15, recent permafrost emissions rival a top-10 country’s emissions at up to 0.6Gt CO₂e. As the world passes through 1.5°C this increases to 2.6Gt, rivalling India, continuing for the rest of the century. As we pass 2°C next decade, this increases to 3-4Gt, about the same as the 38 countries of the OECD Europe combined. Passing 3°C puts the levels up to rival China and the US, above 5Gt for centuries. This natural feedback loop where temperature increases drive emissions that further increase temperature is extremely dangerous and will likely prevent any stabilisation in temperature even if net-zero is achieved, if it is not reached soon.

Much has been made of the ticking time bomb of Methane Clathrates, vast sub-sea accumulations of methane that could burst to the surface with devastating effect. However, recent research including the IPCC AR6 review concludes that deep-ocean gas hydrate emissions will remain minor throughout the 21st century. However, it identifies shallow subsea permafrost degradation on Arctic continental shelves (shallow waters of less than 100 m depth) as a persistent, long-term positive feedback requiring close monitoring.

Exceeding 2°C of warming poses severe risks to these shallow, highly vulnerable methane deposits, particularly subsea permafrost along polar continental shelves like the East Siberian Arctic Shelf. In these shallower waters, methane bubbles have a short transit time to the surface, bypassing microbial breakdown and venting directly into the atmosphere. Recent empirical studies reveal that warming bottom waters and glacial meltwater intrusion can destabilise shallow deposits much faster than previously assumed.16 While not a singular catastrophic tipping point, sustained warming beyond 2°C risks locking in a chronic, long-term positive feedback loop of elevated methane emissions, driving further global warming, while locally exacerbating ocean acidification and deoxygenation in these fragile polar ecosystems. Methane bubbles have also been observed escaping from shallow water sea beds in Antarctica.17

A new study examining the pan-Arctic methane emissions concludes that current analysis and top down models are underestimating the accelerating rate of Arctic methane emissions.18 Their results suggest much stronger positive methane-climate feedbacks in the pan-Arctic and highlight the urgency of reducing anthropogenic methane emissions to achieve the goals of the Paris Agreement and the Global Methane Pledge.

These natural accelerations increase the need for more urgent action on human caused emissions, since these are the aspects we can do something about quickly. If we fail to do this, the runaway effects are severe and make any future carbon removal work even more challenging.

Conclusions

Methane is an often overlooked greenhouse gas but is a major contributor (30%) to the current accelerating warming. Its very high greenhouse potential makes it extremely potent and fast acting. It’s short lifespan means determined action can have rapid beneficial effects though.

Methane levels are known to be an important amplifying feedback in pushing the climate from glacial to interglacial settings. Today’s levels and the rate of increase are far higher than geologic records shows for these termination events. New evidence even suggests that current estimates are too low and that the feedback cycle in the Arctic through longer melt seasons and wildfires is driving emissions faster than thought.

Human emissions add to this increasing natural emission rate. Nearly all the current human emission sources, including oil and gas infrastructure, abandoned mines and wells, beef and dairy farming, rice cultivation and waste management could easily and cheaply reduce a significant proportion of their emissions. In a great many cases, across all sectors, these approaches would increase revenue and productivity. Leakage levels of up to 20% of marketable product is just insane and would not be tolerated in any other industry. Imagine a farmer that was content if 1 in 5 of his livestock never made it to market. What would you’re company’s board think if you wasted 20% of your inventory, materials or productivity?

Action on methane is a vital part of achieving a more stable climate, let alone the Paris climate goals. Staying under 2°C is impossible without addressing methane emissions. It’s not enough to assume that emissions will naturally drop with fossil fuel reductions, given the emissions from agriculture and waste management, not to mention increasing natural sources as the planet continues to warm.

Reducing methane emissions is not a substitute for reducing CO₂ emissions but it could buy a little time if it is carried out with the haste set out in the Global Methane Pledge. It’s time for countries to start living up to the pledges they have made. Most of the actions are ‘no regret’, so let’s just get on with it.

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Of all the measurements that scientists make to chart the changes in the climate and weather systems, perhaps the most important, at least in terms of understanding the underlying problem, is the examination of the Earth’s Energy Imbalance or EEI. It can tell us a lot about the rate of warming, where the energy goes, how much is reflected and radiated back into space, and critically, what needs to happen for the planet to re-stabilise or even cool back down. This helps us examine the potential tools we have available to promote stability and reduce the risks of irreversible tipping points being crossed, some of which could prove to be existential.

Earth’s Energy Flows

I’ve discussed Earth’s Energy Imbalance (EEI) a lot through Climate Uncovered articles, but in a nutshell: The Earth receives energy from the Sun as short wave radiation. It reflects some of this which bounces back into space from the tops of clouds, from surface ice and in fact any light, relatively reflective surface. That reflectivity, or Albedo, reduces the incoming energy that acts to warm the surface. Responding to this warmth, the surface emits long wave or infra-red radiation back out towards space, balancing the equation of EEI which is Energy In minus Energy Out (figure 1) . Greenhouse gases in the atmosphere trap some of this long wave energy, so to achieve balance, the surface continues to warm, emitting more energy, until a point is reached were the amount of long wave energy successfully leaving the planet balances the absorbed energy coming from the sun. At that average surface temperature the EEI becomes zero and the climate system is balanced.

That all works fine until the level of greenhouse gases in the atmosphere changes. If the level goes down, more long wave radiation makes it out, making the EEI negative. The Earth loses heat, cooling down until the surface radiation drops to a point where the lower level of greenhouse gas can balance the EEI once more. The climate will once again be stable, but at a cooler average temperature. The happens naturally over very long periods of time when natural processes draw down atmospheric CO₂ by sequestering more in the oceans or during periods of mountain building when it is absorbed through rock weathering.

The opposite happens when the level of greenhouse gasses in the atmosphere is increased. This time though, more long wave radiation is trapped, the EEI turns positive and the temperature rises. The accumulating energy warms the surface, which in turn, emits more long wave radiation until a point is reached where it is sufficiently hot that enough long wave radiation can escape the higher greenhouse gas level to balance the EEI. Again, this happens naturally through volcanic venting, ocean de-gassing and other processes, but today it is happening through human activity. By burning massive amounts of fossil fuels, cutting down forests and disrupting ecosystems, we have doubled the effect of greenhouse gases in the atmosphere in a little under two centuries, ten times faster than any previous geological event.

NASA’s CERES project has now delivered over a quarter of a century of data to show exactly what has happened to the EEI as a result. It will come as no surprise that not only is the EEI positive, so leading to the warming we see in every single measure, but it is increasing, leading to the now acknowledged acceleration in every single measure (figures 2 and 3). In fact the EEI has increased by over 400% in just the last 25 years, accumulating almost unimaginable amounts of energy within the Earth’s systems, which are now hunting for a new balance point, a point quite a bit warmer than it has been for millions of years.

The Albedo Problem

Breaking down the CERES data further shows us that the imbalance is not just driven by the accumulation of greenhouse gases trapping the heat, but the amount of short wave radiation being reflected back into space is dropping. The albedo of the Earth is in decline and as a result, the absorbed radiation is increasing markedly (figure 4).

So, why is the Earth dimming? Some of the dimming is due to icy surfaces melting as the planet warms, exposing darker rock or open water beneath. Sea ice extent has been dropping fast, as have mountain glacier and snow-pack area. The main loss in reflectivity however is due to changes in the world’s clouds. They are decreasing in surface area (by an average of 1.5 million square kilometres in 25 years) but also in brightness.

The cloud changes are believed to be a feedback mechanism attached to the warming. As the greenhouse gases warm the climate, fewer clouds are formed, despite there being more water vapour available in the air. Fewer clouds let in more short wave energy and at the same time, the water vapour acts as a powerful greenhouse gas itself, amplifying the warming effect. Cloud cover over the world’s oceans are showing the most abrupt changes, leading to other knock-on effects such as triggering marine heat waves. That’s a whole other story which we covered in The Great Decoupling.

The energy flux ladder

This leads us to the Energy Flux Ladder diagram (figure 5). The diagram shows what has contributed to the rise in EEI between 2000 and 2025. It breaks down the absorbed short wave radiation increase into clear and cloudy sky, and the outgoing long wave radiation in the same way. There has been a slight positive contribution from solar activity through the 25 year period since the Sun’s brightness goes through an 11 year cycle and it just so happens that the 25 year period has contained more peaks than troughs. The net impact however is negligible.

Looking at the short wave bars first, their strongly positive contributions reflect the drop in albedo discussed above. The clear sky bar is driven by the drop in cloud cover as well as the loss of surface reflectivity from ice. The cloudy bar is driven by the drop in cloud brightness as well as a contribution from cloud area loss.

The long wave bars are interesting. The clear sky bar should be strongly negative since the surface of the planet has warmed significantly and will be radiating more long wave Planck radiation as a result. However the increase in greenhouse gases means that none of this additional long wave radiation is getting out of the atmosphere. In fact slightly less is getting out than 25 years ago, despite the increase in surface heat.

The cloudy area long wave decrease is as a result of the clouds becoming warmer and also rising to higher altitudes. As a result their long wave emissions are able to escape the thinner atmosphere more readily, making this the only dampening factor in the EEI growth between 2000 and 2025.

The three levers we have available

Now that we understand the drivers of the current accelerating warming, we can look at the tools available to us to ultimately get control of the EEI and stabilise the planet. The three tools or levers, are decarbonising our activities - stop releasing greenhouse gases into the atmosphere, remove the greenhouse gases we have emitted to bring the level down to a safer concentration, and increase the albedo of the planet with solar geoengineering techniques.

Decarbonisation

This comes in several guises with the most recognisable termed Net-Zero. This involves stopping all human emissions of all greenhouse gases from all sectors of the entire global economy. Where there are emissions that can’t be stopped, they must be accounted for and balanced with some matching greenhouse gas removal activities. There is also a version called True-Zero which does not allow any emissions accounting. It also deals with any natural emissions that have been triggered by other human activities or caused warming, such as permafrost melt. While net-zero stops human emissions, true-zero ensures no further rise in atmospheric concentrations.

Looking at the energy flux ladder, its possible to see what impact decarbonisation would have on the EEI (figure 6). At first glance, it will have no effect on the short wave drivers as the greenhouse gases only affect long wave radiation. However, zero emissions also includes emissions of other pollutants such as aerosols, which actually provide a cooling effect today by reflecting some shortwave radiation and brightening clouds. When zero emissions are achieved therefore, we can expect the short wave side of the diagram to increase slightly.

The effect on the long wave side of the ladder is the objective though. Remembering that decarbonisation won’t reduce the level of the accumulated long lived greenhouse gasses, the effect will be to allow the warming surface to catch up with the greenhouse gas effect. The surface will continue to warm, due to the still positive EEI, until it is warm enough that it can radiate sufficient long wave radiation to escape the atmosphere and balance the increased short wave side. The short wave won’t reduce since it is a temperature feedback, it may even increase with further cloud area losses, but eventually an equilibrium will be established, albeit at a higher temperature than today.

Calculating the amount of temperature rise following true-zero is obviously highly complex involving detailed modelling, however basic physical calculations exist which provide clues for what could be expected. If net-zero was achieved today with the EEI at 1.45 W/m², the additional global average surface heating required for the escaping long wave signal to balance the EEI would be 0.73°C. This does include the feedback effect of additional water vapour in the atmosphere, but does not include any further reduction in cloud area. The eventual stable temperature would therefore be around or above 2.25°C above pre-industrial.

A recent paper1 modelled this process in more detail and found that even if the now unrealistic SSP1-2.6 was followed, EEI would continue to increase, accelerating the warming for 15-20 years until it levelled out. After that the EEI would start to drop, warming would slow down until after about 100 years, the EEI would eventually fall to zero and the climate would stabilise at that point. This assumes that no tipping elements that result in more natural emissions occur in that time, such as permafrost abrupt thaw, tropical rain forest collapse etc. That’s a big if.

In reality net-zero is unlikely to be achieved for at least another 25 years, even in a very optimistic scenario, so extrapolating from this study, temperatures would stabilise somewhere around 4°C by 2150, but probably even higher as permafrost melt would continue to increase greenhouse gas concentrations.

There was a time when net-zero would have been sufficient to control temperatures within the Paris limits, but those days are sadly behind us.

Carbon Dioxide Removal (CDR)

OK, so we’ve missed the boat in terms of being able to stabilise the planet at a safe level with just decarbonisation. The second tool in the box is CDR which actively removes greenhouse gases from the atmosphere. Let’s not mess about, we’re not talking about planting a few million trees here, we’re taking about drawing down the level of CO₂ in the atmosphere to below 350ppm (IPCC recommendation). That was the level in 1990, so yes, in addition to zero future emissions, we need to suck out every tonne of emissions we have dumped into the atmosphere for the last 35 years (as well as all future emissions from today). To be of any use, we also need to suck out all the natural emissions that are now increasing as the planet warms, since there is no accounting here, we’re not trying to just remove our direct emissions, were targeting a specific atmospheric concentration.

This is not new, all the ‘safe’ Paris target comparable scenarios include huge levels of CDR, as do the new CMIP7 emissions scenarios that will be used for the next round of IPCC reports. The new Medium-to-Low scenario, arguably the most likely ‘safe’ scenario involves removing over five trillion tonnes of CO₂ from the atmosphere!2

Although CDR is directly related to CO₂, there are also technologies for removing other greenhouse gases, such as methane and nitrous oxide which are included in this umbrella.

Looking back at the ladder diagram (figure 7), CDR works on the same bar as decarbonisation, but would act more quickly and have a greater stabilising effect since it reduces the amount of surface warming required to generate the level of long wave radiation that can escape the atmosphere and balance the EEI. Since the maximum temperature is lower than just decarbonation, the cloud feedback would also be reduced, meaning it also has the benefit of having less work to do in order to balance the EEI.

CDR is not therefore just a part of achieving net-zero, it becomes an essential tool that needs to be scaled to the point where it can draw down atmospheric concentrations as quickly as possible.

The scale of the challenge is almost unimaginably huge, but it need not all come from technological solutions. It is definitely worth including efforts to rejuvenate nature to help in the task (as well as provide a whole host of other benefits obviously). The oceans could also be encouraged to absorb more carbon with techniques such as iron fertilisation to encourage phytoplankton blooms, and alkalinity enhancement to improve the chemical take-up. There is a risk though that as the atmospheric concentration drops, the oceans may outgas some of their stored carbon to maintain a water-air partial pressure balance, but eventually equilibrium can be reached.

A conservative estimate of the temperature profile would suggest that although temperatures would almost certainly rise above 3°C, if decarbonisation and CDR were scaled quickly enough, with concentrations peaking by 2050 and reducing thereafter, 4°C could probably be avoided.

CDR is the only tool available that can permanently cool the planet. By allowing more long wave radiation to escape than is being accumulated through albedo decline, the EEI could be turned negative, cooling the planet and reversing the cloud feedback. Once a lower level of atmospheric concentration is achieved, CDR could be stopped and the climate could stabilise at a lower safer temperature. Adjustments would still persist for millennia as the ice sheets found an equilibrium within the new climate. This would drive sea level rise but to a much lower extent than just through zero emissions.

Solar Geoengineering

Reducing the short wave bars of the ladder diagram involves trying to increase the planet’s albedo. This would allow more solar radiation to be reflected, reducing the EEI and the warming. For this reason the technologies proposed come under the heading of Solar Radiation Modification (SRM), but the acronym also works for alternative descriptions such as Solar Radiation Management and Sunlight Reflection Methods. They all have the same driver though - Make Earth Shiny Again.

Since the loss of albedo has been due to warming feedbacks - cloud cover and ice loss, as well as aerosol pollution reduction, there is no behavioural change we can make as there is with emissions reduction for the long wave side of the ladder. If we want to increase albedo, we have to do it artificially. We also have to do it continually to maintain the effect. For example if we constructed a huge mirror in space that reflected away enough solar radiation to return the EEI to zero, warming would stop. But as soon as we took down the mirror, the EEI would jump back up and warming would resume. Worse than that though, if we had continued to accumulate greenhouse gases while the mirror was operational, the EEI would jump back to a higher level, and at a rate faster than if the mirror had never been installed in the first place. This is known as termination shock.

Space mirrors are one future approach being discussed, but a more short term plan involves spreading reflective aerosols into the stratosphere. Volcanos occasionally do this naturally and can cool the planet by over 0.5°C for a year or two. Human Stratospheric Aerosol Injection (SAI) could do the same thing. This would reduce the short wave bars, lower the EEI and stabilise the warming.

Looking at the ladder diagram one last time (finger 8), the amount of SRM would determine whether the warming acceleration was stopped - limit EEI growth, the warming rate reduced - lower the EEI, or cool the planet - take EEI negative.

The sooner SRM is deployed the less work it would have to do to avoid dangerous 3°C temperatures and triggered tipping points, but the greater the accumulated termination shock if decarbonisation and CDR were not simultaneously scaled. This is the great dilemma that will be debated increasingly in the coming years. There is a strong moral hazard argument that if SRM is deployed, it will divert attention away from the only permanent solutions, and give cover for continued fossil fuel consumption and emissions. But it’s not like we’ve been doing a great job on that without it either.

Conclusions

It’s becoming obvious that a strategy involving all three levers will be required to stabilise the planet whilst avoiding dangerous levels of warming and the potential for disastrous tipping points being crossed. 3°C or 4°C of warming would not just be unpleasant, they represent levels that are incompatible with our current industrialised civilisation. The Institute and Faculty of Actuaries predict a sigmoid GDP destruction path that would see at least a halving of the world economy at 3°C followed by complete collapse (~2060 on our current trajectory).3 At which point, not only would there be unimaginable starvation, death and destruction, but there would be no economy left to invest in CDR or SRM - although decarbonisation would become automatic.

Due to the short wave component of the EEI being increased through cloud feedbacks, emissions cuts on their own are now insufficient to avoid the disaster which is looming in the not too distant future. Regardless of what we do in the next couple of years, the 2°C point will be crossed in the late 2030s. This in no way means it is pointless, it is the first step on a crucial journey to bring atmospheric greenhouse gas levels back to a safer level.

Carbon dioxide removal is the second step and equally critical since it is the only way of permanently stabilising temperatures and cooling the planet down to a more hospitable level. Technological solutions are available but need to be scaled. Nay-sayers point out that they have not been scaled to date, but there has been no market incentive for them to do so. That needs to change, probably through some progressive carbon tax or carbon reward scheme backed by national or international banks.4

The rate by which the EEI is growing, and with it the warming accelerating, now strongly suggests that the world is entering a zone where dangerous tipping points will be reached. Indeed, tropical coral reef die-off has already been declared as a crossed tipping element. The only short term tool available to avoid these tipping points, and to avoid 3°C of warming, is SRM. It brings risks, both in terms of potential side effects and it will be very difficult to achieve a level of international agreement and collaboration sufficient to regulate and control it.

SRM can only be used as a stopgap and it must be accompanied by a concrete global effort to decarbonise and scale CDR. Otherwise it will ultimately fail as greenhouse gases continue to accumulate, warming continues and tipping points are breached regardless and the resulting economic destruction causes the SRM to be abandoned. At which point the termination shock could be the last nail in our coffin.

The question for the next decade may well be “Should we start SRM now?” At the moment I would say no, it should be vigorously researched but not deployed without solid signs of decarbonisation first, and a far greater understanding of both its positive and negative effects. If it is confirmed that the AMOC is collapsing, or permafrost melt is shown to be approaching its tipping point, then that answer may change. The geopolitics would be highly complex and progress is not currently possible while the US hegemony is putting all its weight behind perpetuating the carbon economy and propping up the petrodollar at all costs. My worry is that by the time the economic damage signals are obvious even to the most ardent petrolhead, it will be too late to do anything about it.

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The talk was recorded and is available on YouTube.

Normal service will resume on Wednesday 29th July.

Outline

The talk will walk through the physics of climate change using the very latest satellite data to show how the planet is out of energy balance, is accumulating energy at an accelerating rate and how this energy is taken up as heat in different Earth systems. The up-coming ‘Goliath’ El Niño effects will be looked at with reference to past events and the phenomena of temperature ratcheting uncovered, leading to predictions for the second half of this decade. Tipping points are the next topic focussing on the ocean currents and Amazon rainforest as well as the economic consequences of the continued warming. The talk will then look at the triad of measures we still have available to combat the predicament - decarbonising the economy, removing greenhouse gases from the atmosphere and deploying solar geoengineering. Finally we’ll try and answer the question of whether this is a new normal.

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When pondering what to write about this week, while sat in a too hot home office with a fan blasting away, as we in Europe endure the third heatwave of the year, the answer seemed obvious. This is an updated edition of an article I posted just over a year ago. Ahh, the coolness of 2025, the last year ever1 when global average temperatures were below +1.5°C.

Saying that either climate change or natural variability caused a particular weather event is often a difficult proposition as there have obviously always been storms, droughts, heatwaves and cold snaps. So how can we determine what is natural variability, what is climate change driven or what proportion of the two contributed to a particular event?

Let’s start easily with a phenomena that nobody should argue with (hopefully). The average July temperature is warmer in southern England than northern Scotland. Even the proudest of Scotsman would agree, having first pointed out that the scenery in the Highlands is far superior to the Cotswolds, that it does tend to be a wee bit nippy.

I’ve downloaded historic weather station data from the UK Met Office website for a station near Gloucester at the top of the Bristol Channel, and from a station near Inverness on the Moray Firth 650km to the north.

The data includes temperature, rainfall, sunshine and frost days all the way back to the 1930s. But to keep it simple, I’ve concentrated on July temperatures and plotted the range temperatures for both sites from the data for 2015 to 2025. This gives us a ten year average to compare. The two curves confirm our hypothesis that it is generally warmer down south. Note however that there is considerable overlap and that it’s perfectly possible, in fact not unlikely, that sometimes it will indeed be warmer in Scotland. That’s not proof that Scotland isn’t cooler than England, it’s a probability that Scotland will be cooler because of its higher latitude.

We can take this a step further and look at the chances of certain temperatures and average temperature differences.

What are the relative chances of having an average July daily temperature of 21°C? It’s well within the normal area of the Bristol Channel with a likelihood of 0.7 (70% chance) but at the high end of temperatures in the Moray Firth with a likelihood of just 0.2 (20% chance). You are therefore three and a half times more likely to enjoy a nice 21°C July in the Bristol Channel than you are in the Moray Firth. In other words, the 650km of latitude makes a 21°C day in the Bristol Channel 3.5 times more likely than in the Moray Firth.

We can look at the temperatures in the same way. An unusually hot (top 20% event) July in the Bristol Channel would be 4°C hotter than an equally unusually hot July in the Moray Firth. Or, because of the latitude difference the same event in the Bristol Channel would be 4°C hotter than the higher latitude.

Just what you’d expect and hopefully no arguments.

OK let’s take a look at climate change. Using the same data source, but this time plotting 2015-2025 July temperatures for the Bristol Channel against the 1965-1975 temperature record from the same weather station. It yields a similar looking graph, but this time the difference is 50 years of global warming. The difference is almost as pronounced and it is clear that the July temperatures are warmer in the last decade than they were 50 years ago.

An unusually hot (0.2) July 50 years ago of 22.5°C is now a 0.5 chance and therefore is two and half times more likely today. And an unusually hot July today is 2.5°C hotter than it was 50 years ago. Unlike the geographic shift between the Bristol Channel and the Moray Firth, this shift is down to global warming. We can confidently say that based on this data, very hot days are much more likely and also hotter due to climate change.

The left hand side of figure 3 is also interesting. The cold events are slightly warmer (by 1.5°C), but the difference is much smaller. In other words, the warm extremes are showing a stronger rate of increase than the general temperature trend. Not only are heatwaves more likely, they are disproportionately hotter. This is why temperature records are being broken so often, and by such large margins.

Downloading the Climate Stripes for Gloucester (figure 4) shows the trend. You can do this for your home town from the Show Your Stripes website.

Interestingly this change in average temperature is higher than the global average surface temperature (SAT) increase between these dates. The July average global SAT between 1965 and 1975 was 0.24°C above pre-industrial and 1.30°C above pre-industrial between 2015 and 2025. A rise of just 1.06°C in 50 years (less than the 1.6°C increase locally). This is consistent with the fact that land surface temperatures are warming faster than the global average since ocean surface temperatures warm more slowly due to better heat absorption and mixing with deeper waters. Europe is also the fastest warming continent.

The Climate Shift Index

This type of analysis can be done for any measure from temperature, rainfall, cloud fraction and so on. Climate Central2, who helped pioneer this form of analysis, use it in their daily Climate Shift Index to show regions of the world where temperatures are made much more or less likely due to climate change. The current heat wave (while writing this on July 9th) is clear to see. Most of the UK, Central Europe, Spain, the Mediterranean and North Africa are experiencing a heatwave made up to 5 times more likely by climate change.

The accompanying marine heat wave on the European coast is even more extreme and one of the reasons this heat is going to last for a good while yet. The sea water in the English Channel is currently 3.3°C hotter than normal which is made at least 600 times more likely due to climate change!

Individual Events

When it comes to examining the climate change contribution to individual events a more sophisticated approach is taken. World Weather Attribution3 is an international consortium of scientists and meteorologists who have been performing this work since 2014. They have performed more than 100 studies on heatwaves, extreme rainfall, drought, floods, wildfires and cold spells around the world.

The method they have developed have been published in a number of peer-reviewed papers as have 30 of the attribution studies.

Once an event has been selected for study, data is collected to determine the geographical boundaries, the duration and the key variables such as maximum temperature or average rainfall. This sets the event definition and parameters.

Next, observational and historic data is collected to determine how often similar events can be expected today and if they are more likely in recent decades than the past, using the basic method described above.

The second part of the study uses climate models to isolate the role of climate change in the specific event. Two ‘worlds’ are created, one with today’s warming and one with pre-industrial conditions - so without the present warming. The results are compared to quantify how the event was influenced.

All the results are then combined to provide the overarching quantitative estimate of the change in intensity and likelihood caused by climate change, together with the statistical significance or confidence in the result.

Here are some examples of their recent studies.

Heatwave

On May 15 2025, Egilsstaðir Airport in Iceland recorded 26.6°C, breaking the previous record for Iceland’s highest May temperature, while regions of the country saw temperatures more than 10°C above average (Icelandic Met Office, 2025). The Ittoqqortoormiit station in Greenland saw temperatures reach 14.3°C on May 19, which is more than 13°C above the May average daily maximum temperature of 0.8°C.

When combining the observation-based analysis with climate models, to quantify the role of climate change in this 7-day heat event, WWA concluded that climate change made the extreme heat about 3°C hotter and about 40 times more likely.4

When global warming of 2.6°C is reached (probably within 25 years), the likelihood and intensity of such events could at least double in likelihood and increasing by a further 2°C in intensity.

Flooding

On October 29th 2024, the city of Valencia in Spain experienced a flood that killed 230 people and caused many billions of Euros of damage. A physical-based attribution study, published earlier this year, assessed the contribution of anthropogenic climate change to the event.5 They found that due to global warming since the pre-industrial period, the one hour rainfall rate was increased by 20% per degree of warming. It intensified the six hour rainfall rate by 21%, amplified the area with total rainfall above 180 mm by 55%, and increased the volume of total rain within the Jucar River catchment by 19%. Without climate change, the damage would have been significantly lower.

Figure 8 breaks down the climate change related increases across the whole storm system, starting with the record heat in the Mediterranean causing an increase of 10.5% in evaporation - the water source for the storm.

Tropical Storms

Two hurricanes hit Florida in 2024 within weeks of each other. Both intensified extremely quickly due to the high sea surface temperatures in the Gulf of Mexico. Heavy rainfall was highly impactful. The rainfall from Hurricane Helene caused considerable damage far inland. A WWA study found that rainfall was about 10% heavier due to climate change, and equivalently the rainfall totals over the 2-day and 3-day maxima were made about 40% and 70% more likely by climate change, respectively. If the world continues to burn fossil fuels, causing global warming to reach 2°C above pre industrial levels (likely late 2030s), devastating rainfall events in both regions will become another 15-25% more likely.6

In the case of Hurricane Milton, the second of the two storms, three out of the four analysed datasets showed that heavy 1-day rainfall events are 20-30% more intense and about twice as likely in today’s climate, than it would have been without human-induced climate change. The fourth dataset showed even larger changes.

By statistically modelling storms in a 1.3°C cooler climate, this model showed that climate change was responsible for an increase of about 40% in the number of storms of this intensity, and equivalently that the maximum wind speeds of similar storms are now about 5 m/s (around 10%) stronger than in a world without climate change. In other words, without climate change Milton would have made landfall as a Category 2 instead of a Category 3 storm.

Using weather forecasting models

World Weather Attribution studies use climate models and often an ensemble of several runs. An alternative approach is to use weather forecasting systems to replay an event from a few days out but constraining temperature data to pre-industrial norms. Alternatively historic storms could be replayed but with modern baseline temperatures to see how much worse they would have been today.

This has been carried out for Storm Ulysses, a severe extratropical storm which hit the UK in 1903.7 In a proof of principal study, a reanalysis reconstruction was made of the original storm benefiting from rescued pressure readings taken at the time and is a credible reconstruction of one of the most extreme windstorms to occur over the British–Irish Isles in the past 120 years. The storm in the warmer-world reanalysis is constrained to be very similar to the original, except for a 2°C increase in sea surface temperature along the storms development path. Specific humidity and surface air temperatures are also higher.

The warmer-world version of the storm generates stronger maximum winds (middle row of figure 9) and increased rain-fall (bottom row) compared to the original event, suggesting that the consequences of the same surface circulation pattern would be more severe in today’s climate. The increase in wind footprint represents a significant increase in damage (> 10 %; roughly related to the cube of the wind speed). The total rainfall over land during the storm would be increased by 26%.

This method could be applied to recent events such as the 2024 hurricane season, or the 2026 European parade of heatwaves but in 2°C and 3°C worlds to inform policy makers and the public of the upcoming threats and probable impacts.

From a policy perspective, a very relevant study subject would be the 1953 North Sea storm that caused devastation from Scotland to Belgium. The scale of the flooding was unprecedented. In England there were 1,200 breaches of sea defences, 140,000 acres of land were flooded, 32,000 people were evacuated, 24,000 properties were damaged, 46,000 livestock were killed, and 307 people died. In the Netherlands, approximately 100,000 people were evacuated, 340,000 acres were flooded, 47,300 buildings were damaged, 30,000 livestock were killed, and 1,836 lives were lost. In addition, there were 17 deaths in Scotland, 22 in West Flanders, Belgium, and 230 in vessels at sea, including the 133 lost on the passenger ferry Princess Victoria. The storm surge peaked at 3.35 meters above the average sea level, and waves of over 4.9 meters were recorded.8

Following the storm, the Dutch repaired and improved their dykes which was a huge project which took 40 years to accomplish. The new dykes are 40cm higher. In the UK, the Thames Barrier was constructed over a 30 year period.

What would the same storm look like in today’s, or tomorrow’s climate? Would the new walls still be high enough? At what point of warming will they now fail? Given current warming rates, how long do the authorities have until a repeat of the 1953 storm would once again be catastrophic? A recent decision was made in the UK to bring forward plans for a new Thames Barrier by 15 years, so maybe someone is thinking about it.

As climate models and weather forecast models develop and become more closely related, this form of analysis will become more common. AI also has a role to play too. They are already proving more accurate than traditional models in predicting tropical cyclone developments, paths and intensities.

Conclusions

Global warming is real despite it still snowing sometimes. It can be seen on every level from global to local trends to daily anomalies. You can get the Climate Stripes for your local city to see how it has affected your region. If you’d like a catchy sound track to go with it, check out the music video we created for Show Your Stripes Day this year.

Attribution studies are widely performed, often just days after an extreme event and provide the change in likelihood and intensity of the event as a result of climate change. I’d like to see this carried out routinely for every named storm or weather warning and included in all weather reports. Imagine if with every yellow or red warning, it was noted that this event is made X% more likely and Y °C/mm/Cat… stronger due to climate change. It would raise public consciousness and if the public got fed up of hearing it, they may start demanding action to do something about it (climate change rather than the broadcasts).

Future studies using weather forecasting systems will be able to replay past events in today’s climate as well as current events in the even warmer climate we are heading into. This could be a big help for both the public and policy makers in planning resilience and adaptation policies and investments.

So what about the current string of heatwaves? According to WWA, the June event smashed the infamous 1976 records by a margin that would not have been possible in 1976. If the weather phenomena that drove the 1976 event were to happen today, it would be 3.5°C hotter during the day and 2.4°C hotter at night.

In the UK especially, 1976 was such an extraordinary event it has become part of the cultural heritage. It did this because it was so extreme, so unprecedented, so freakish, that it defined weather conversations for half a century. That record has gone though, and it will likely tumble down the rankings in the coming decade. No wonder you can’t buy an air conditioner now for love nor money.

If you found this article interesting or useful, please tick the ❤️ button as it helps the algorithm point more people in this direction and gives us feedback on what subjects are most useful. Thank you!

You might also like this recent article on Coastal Protection which looks at preparations for future storm surges linked to sea level rise:

For this article I’m delighted to be joined by Gérard Collin, the Spokesperson for the Collectif Montée Des Eaux in France. The CMDE is campaigning for better coastal protection and planning in France and beyond. I’m honoured to be an International Associate Member of the organisation.

On Saturday 31st January 1953 the first 133 lives were lost to a North Sea storm that would go on to kill over 2,500. The first casualties were from the sinking of the Princess Victoria en route from Scotland to Ireland. The vast majority would die in the devastating floods that swept down the English east coast and on into the Netherlands and Belgium. The funnelling shape of the North Sea, coupled with a high spring tide drove a storm surge which peaked at 3.35m above the average sea level. The wave action caused flooding to reach areas higher than 5m above sea level. In addition to the human lives lost, it is estimated that 75,000 head of livestock was killed, 70,000 properties were damaged and almost 500,000 acres (>200,000 hectares) of farmland was inundated.1

As a result of the storm, protections and warning systems were put into place at huge expense across northern Europe. In the UK the Thames Barrier was built and completed in 1984 along with other coastal protection projects. In the Netherlands the government constructed an ambitious flood defence system beginning in the 1960s. The Delta Works is designed to protect the estuaries of the rivers Rhine, Meuse and Scheldt. The system was completed in 1998, with completion of the storm surge barrier Maeslantkering in the Nieuwe Waterweg, near Rotterdam.

But what if a similar storm were to hit today, with sea levels 25cm (1 foot) higher than in 1953 and with global warming fuelling more extreme weather events? How are countries predicting the future and what preparations are being made for even higher seas later this century? The UK and Netherland defences took over 30 years to build and we haven’t got any faster at these sorts of projects, just look at the UK’s lamentable HS2 project! We should be building now for end of the century threats, so what should that look like?

Sea level rise and climate change risks

There are three basic constituents of sea level rise as it affects coastal infrastructure. There is the fact that as the climate system warms, the oceans’ heat content is rising at an accelerating rate. Water expands as it warms which raises the global sea level baseline. This thermosteric rise will continue even if net-zero is achieved as the heat distributes and mixes with cooler deeper waters. Land water entering the oceans from both the melting of land ice (including from polar regions) and the draining of aquifers (for agriculture, industrial and societal use) is the second component. The third issue is local or regional changes in land height relative to the sea level as some regions subside. This regional steric rise can be through long term rebound following ice mass removal and though the pumping out of aquifers and oil and gas deposits from deep beneath the surface.2 The rise itself is far from uniform, being affected by regional and local variability due to ocean density and circulation changes, atmospheric pressure variations and due to the gravitational, rotational and deformational effects of water and ice mass redistributions as well as vertical land motions that can affect some areas locally.3

For more on the causes of sea level rise I have another article which you can access here.

Implications for coastal infrastructure

There are three main threats to coastal infrastructure linked to sea level rise and climate change; baseline level rise, storm surge height and coastal erosion.

Baseline rise

Figure 2 shows the various model predictions for the different IPCC scenarios out to 2150. The dotted and dashed lines are the low likelihood scenarios if ice sheet stability is lower than hoped for. The solid orange and red lines are a good guide for our current trajectory, but the models used don’t account for ice sheet modelled melting, just a linear trend with temperature. Currently thermal expansion is the main contributor but this will change as Greenland and Antarctica melt rates continue to accelerate. We can therefore bank on it being at least as bad but probably worse than the solid lines.

One important property of sea level rise is that it is fundamentally non linear, subject to many feedback and cascade processes, all of which make prediction difficult. The other characteristic, different from atmospheric temperature rises, is that sea level rise cannot ‘overshoot’: there is no lowering again for millennia. They will only drop again when the next glaciation event starts - and we’ve already cancelled the next one as the CO₂ levels are too high to trigger it through the next orbital cycle.

There are obvious ramifications for coastal infrastructure through this gradual, albeit accelerating, average rise. Ports will need to modify loading facilities to account for ships sitting higher against quays. Saline waters will reach further inland at river mouths increasing the corrosion rate of steel structures and the steel reinforcement within concrete piles and foundations. This form of ‘concrete cancer’ is well known for coastal infrastructure even above the waterline, but a 2017 study found that for a standard coastal concrete structure engineered for a 50-year service life, the combined impact of global warming and SLR slashes that operational lifespan immediately by roughly 5%, requiring earlier and more aggressive structural interventions.4

Of course some properties and facilities may need to be abandoned or raised to avoid inundation during spring tides and so on.

Storm Surge

The real danger though, just like in 1953, comes from storm surges. There are two factors within a storm system that locally raise sea levels. Wind action literally pushes water ahead of the storm where it piles up, and the low atmospheric pressure of the storm pushes down less on the surface allowing it to rise, drawing in water from the surrounding seas. The effects can be huge. The 1953 storm delivered 3.35m of surge but these more recent events were even higher:

• Hurricane Ian (USA) September 2022: Up to 4.6 metres (15 feet)

• Cyclone Idai (Mozambique) March 2019: 4.4 metres (14.4 feet)

• Cyclone Amphan (India & Bangladesh) May 2020: Up to 5 metres (16 feet)

• Hurricane Dorian (The Bahamas) September 2019: 6 to 7.3 metres (20 to 24 feet)

• Typhoon Rai / Odette (Philippines) December 2021: Up to 4 metres (13 feet)

One of the most worrying trends is that storms and tropical cyclones are increasingly “stalling” near coastlines (as seen with Hurricanes Dorian and Ian), meaning the surge is sustained over multiple high-tide cycles rather than striking quickly and receding. A 2018 study analysed global historical data from 1949 to 2016 and found that the translation speed (the speed at which the storm moves forward from place to place) decreased globally by 10% in that time. Crucially from a coastal protection perspective, the slowdown was much more severe when storms crossed over land, leading to a 20% slowdown in the North Atlantic and a 30% slowdown in the Western North Pacific.5 The study links this directly to global warming causing a general weakening of summertime tropical atmospheric circulation (the large-scale “steering winds” that push cyclones along). A second recent study has found that the length of the intense tropical cyclone season has also increased.6 They found a global lengthening of season of 10–14 days/decade across all basins, equivalent to a 7.4–22% increase.

Coming on top of baseline sea level rise, the implications for coastal planning and protection are profound. How much longer do flood protection measures such as the Thames Barrier or the Delta Works have before they are breached and effectively worthless?

Storms are also bringing higher levels of rainfall as the warmer climate allows the air to hold more moisture. Flooding events in coastal regions linked to storms add to the danger from rivers beaching their banks or not being able to drain to seas that are already at a high level. The Valencia tragedy of 2024 is a salient example.

Erosion and saline intrusion

Storms have always eroded coastlines. The famous fossil hunter, Mary Anning took advantage of this fact to look for and discover incredible fossils in the early 1800s on the beaches of Lyme Regis, part of the UK’s Jurassic Coast. She would venture out onto the newly eroded cliffs to examine what the fresh rock falls had revealed. A practice still employed today by amateurs and professionals alike.

When it comes to property and infrastructure at the top of these cliffs, or even behind sand banks and wetlands, erosion brings serious hazards and in many locations, inevitable losses.

Saline intrusion occurs when the rising seas force salt water into coastal aquifers making the ground water increasingly brackish. A 20 year study of the Bengal delta in Bangladesh found that salination was experienced even 200km from the coastline in the low lying delta.7 This has collapsed local agriculture and resulted in more than 10 million people having to abandon their homes and livelihoods and move to slums outside the major cities. Similar problems are likely in other low lying land masses and deltas such as the Nile in Egypt, Norfolk in the UK, Flanders in Belgium and Holland and southern Florida, to name a few.

How much risk is acceptable?

There is inevitably a trade off between the costs of building defences and the costs of potential losses, but first the question has to be asked: What level of sea level rise is it pragmatic to plan for? This is no longer down to scientific or IPCC reports, but political decisions: what must we responsibly prepare for? The decisions need to be based on risk apatite and will vary for different situations.

The Hinkley Point C nuclear power plant being constructed in the UK sits on the coast and is sea water cooled. This is being built with a two level storm surge protection system.8 Firstly a sea wall will extend to 13.5m above current average sea level. The main platform is then at 14m above the current average level. The design criteria was based on a 1-in-10,000 year storm on top of predicted sea level rise for the operational and decommissioning lifespan which could create a surge of 11.5m including wave overtopping. There is therefore an additional 2m of safety margin before the station platform could be inundated. A similar approach is followed for next French nuclear EPR’s.

If future climate tracking shows that actual sea-level rise or storm surges are outpacing the initial projections used for the Hinkley C design, the safety case dictates that the operator must implement engineered modifications. The structural foundations of the sea defences are reinforced so that the height of the wall can be physically raised or supplemented with further barriers in the future if a worst-case, non-linear ice sheet collapse scenario begins to manifest.

What to plan for

That’s all very sensible and reassuring for a new-build nuclear reactor, but what level of rise should be anticipated for existing infrastructure, private property and other less critical building projects?

Different countries are adopting different approaches and measures. The new 2026 Code of Practice on Coastal Protection issued in Singapore9 uses a sea level rise of 2.15m by 2150 as the standard for all coastal protection measures. This applies to new and existing structures alike, with building modifications demanded as appropriate.

In the UK, the Environment Agency and maritime authorities structure their flood risk assessments for critical infrastructure through standard UK planning policy operating on an “Adapt for 2°C, plan for 4°C” approach, leaning on the upper percentiles of the high-emissions scenario (RCP 8.5) and exploring extreme contingency scenarios:

Given the recent acceleration in global warming especially in ocean heat content, this now seems inadequate for a high-end approach. This view is echoed by the Collectif Montée Des Eaux in France who are pressing their government and local authorities to prepare for a sea level rise of 1.20 m by 2100 and 1.50 m by 2125, and 2 m for new private buildings (with reference to pre-industrial ages). Currently French ports are planning for levels well below this pragmatic request. Le Havre is planning for just 0.6m, as is Bordeaux, Cherbourg, Dunkirk and La Rochelle. A new ferry terminal at Brest is only planning for 1m, as is Marseille.

For several years, France has been due to update it’s national reference which currently dates back to 2011 which is still only 0.60 m by 2100. This still applies in particular to new constructions via Plan Local d’ Urbanisme. For planning purposes, most modern countries anticipate over, if not well over, 1 m sea level rise by 2100 and rising after that. 2m is due next century no matter what, so arguing as to when exactly this will occur is a secondary issue. In addition, most modern countries incorporate a multi-layer plan according to the degree of security and to the life span attached to the project. For instance, New Zealand uses a 3-stage plan from + 1,2 m to + 1,7 m by 2130, plus Vertical Land Movement (VLM, subsidence). Similarly, San Francisco is preparing in extremes cases for up to 2.75 m by 2120. Incidentally, VLM is of major concern to many locations as it adds to sea level rise; although for some fortunate regions it can be positive, as is the case of Helsinki and Greenland which ‘surges’ upwards as its glaciers melt. Beyond that, there are differences between oceanic regions, often depending on the source of the water. Melting in Greenland increases levels in the Southern Hemisphere due to a lowering gravitational pull as the ice mass reduces.

Although we’re discussing a global average rise, the rates vary considerably in different parts of the world as the charts in figure 4 show. This is from the official 2025 French Government Sea Level Rise report, based on a 3°C by 2100 trajectory.10 Note the increased rise in the Northwestern Atlantic.

Northern European and east coast US and Canada ports also need to consider the implications of a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), which will increase the rate of rise adding a further 0.5 - 1m of sea level on top of the global average to this regions.11 This won’t be a sudden switch when the current has stopped but a gradual effect as it weakens. Some recent research suggests a 51% reduction in AMOC strength by 2100, so the North Atlantic should be planning for 0.25-0.5m of EXTRA sea level rise this century, on top of the global average. Studies suggest that this will effect the western Atlantic more than the east, but a jump of 40cm could be experienced in the North Sea region following an AMOC collapse.

The scale of the challenge

Practically all of the top 15 global port cities are directly threatened by sea level rise this century. The top port, Shanghai, is perhaps the most notable, including effects on its 27 million inhabitants. In France the three leading ports by annual tonnage, Le Havre, Marseille, and Dunkirk, are all directly threatened.12

In addition to cargo ports, thirteen high traffic global oil ports which take supertankers are also at severe risk at 1m of sea level rise. These are: Houston (US), Ust-Luga (Russia), Rotterdam (Netherlands), Ras Tanura (Saudi Arabia), Khor Fakkan (UAE), Dalian (China), Gwangyang (South Korea), Shanghai (China), Ningbo-Zhoushan (China), Singapore, Galveston (US), Yanbu (Saudi Arabia), Fujairah (UAE).

However well before 2100, the oil industry will have ceased to exist - won’t it?

There are also other chemical and industrial storage and processing facilities close to the 1m line around the world, not to mention fisheries, leisure beaches and marinas. All face the same issues with the same timeline, though with a very wide range of budgets and capabilities.

In terms of domestic property, the UK makes a good case study. By 2100, the scale of exposure across England’s coastal zones expands significantly, covering both direct permanent erosion and frequent tidal inundation.

• Coastal Floodplain Exposure: Today, over 540,000 residential and 72,000 non-residential properties sit within England’s coastal floodplain.13 Even with existing defences considered, tens of thousands remain exposed to high-frequency flooding.

• Properties Threatened by 2100: Estimates from the UK’s Climate Change Risk Assessment (CCRA3) project that approximately 82,000 properties in England are at risk of complete loss due to coastal erosion by the end of the century.14

• The Policy Pressure Point: If global temperatures rise between 2ºC and 4ºC, roughly 1,600 to 1,900 km (around 30%) of England’s shoreline currently designated under a “Hold-the-Line” policy will face unsustainable pressure to realign, directly threatening 120,000 to 160,000 homes and commercial buildings.

• Financial Value: The direct capital value of assets at risk runs into tens of billions of pounds, with annual financial damages from coastal erosion alone projected to rise from historical averages of £15 million to upwards of £126 million under worst-case scenarios.

Adaptation options

There are three main options to manage sea level rise that are being discussed and implemented:

Hold the Line: Build up sea defences to combat sea level rise. This includes raising the height of sea walls, local gates and coastal defences as an incremental engineering task. This mainly involves asset-level protection rather than an all encompassing wall. The exception to this is where large areas need protection such as in Singapore and Manhattan. Ports like Dover and Southampton in the UK are following this approach. London recently brought forward plans for a new line of defence on the Thames by 15 years. Many ports believe they are following this policy, but some are dangerously underestimated rates and levels of rise, as mentioned above.

Managed Realignment: Under this strategy, defences are moved further inland creating natural barriers and buffers that can absorb both wave energy and water level. This has the advantage of creating ecologically rich areas that support wildlife in addition to protecting human infrastructure. These can vary from wetlands to sandbanks and mangrove swamps. Often structures on the old coastline will have to be removed, but they were highly likely to become unusable in the short term anyway.

Retreat (no active intervention): Simply let nature take its course. This is often the case where the assets under threat simply do not warrant the cost of taking any serious action.

The role of Insurance

Like many aspects of the climate crisis the economic impact is likely to hit the insurance sector first. The inability to secure affordable insurance then has a knock-on effect on property prices, asset purchases and the ability of companies and families to secure loans and mortgages.

In the UK, for coastal flooding, the UK insurance industry and government established Flood Re in 2016.15 Flood Re is a public-benefit reinsurance scheme funded by a statutory levy on all UK home insurance policies. It allows insurers to pass the high-risk flood portion of a policy to Flood Re at a capped, subsidised rate, keeping home insurance widely available and affordable for flood-prone households. The scheme is due to run to 2039 and a transition plan is being developed. Interestingly it can’t be used for properties built after 2009 (as they should have known better), but this does not seam to have put off developers who continue to build on flood plains.

In the UK, there is no compensation scheme for property lost through coastal erosion and it is practically impossible to get insurance against it. The best private property owners can hope for is up to £6,000 to cover safe demolition and planning easements for building further inland. There is also no statutory right to compensation for property loss caused by natural coastal erosion or flooding. Landowners are legally considered to bear the historical risk of changing environments.

By contrast, so far France has indemnified owners whose properties had to be moved (e.g. Saint-Pierre-et-Miquelon) or destroyed (Soulac, Treffignac); but the expected longevity of this policy is in doubt. Insurance companies show an increasing reluctance to cover damages which once were assumed to be rare but are now become more and more frequent. As an example, reports indicate that extreme events (storms coinciding with spring tides) will increase by 100 times by the end of the century in the Mont-Saint-Michel Bay; i.e. a centennial event will become annual. Such events threaten both sides of the Channel!

According to CEREMA, the cost of sea level rise in mainland France alone will approach €100 billion by 2100, with nearly 500,000 homes affected. This is without even factoring in private businesses or the costs borne by local authorities: roads, railways, ports and airports, hospitals, schools, etc. And all of this is based on a +1m rise by 2100, which is far from being the worst-case scenario.

Call to Action

In this article we’ve focussed mainly on our home areas of France and the UK. But what plans are in place for your areas of the world? Do you live near the coast, or rely on infrastructure that is within 5m of the current sea level? Have you noticed flood frequency or extent increasing over the time you have lived there? Have you experienced difficulty getting affordable insurance and are their schemes similar to the UK’s Flood Re that lower the costs?

How do you think your coastline will change in the coming decades, and how will your community adapt?

We’d love to hear your thoughts in the comments. If you are based in France and would like to know more about the CMDE, please visit their website and signup for the newsletter.

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For more on the causes of sea level rise, you might like this recent article:

The Barents Seaway is an area of relatively shallow sea between Svalbard, Scandinavia and Novaya Zemlya with access to both the North Atlantic and Arctic Oceans. It has not always been so accessible though, according to a new paper by Kwangchul Jang et al.1 To explain the implications, we need to go back over two and a half million years.

The start of the Quaternary 2.58m years ago saw the start of the current ice age period. Since then, ice sheets have spread and contracted across the northern hemisphere according to the orbital wobbles of the Earth about the Sun. There are three such wobbles known as Eccentricity (the shape of Earths orbit from slightly elliptical to roughly circular), Obliquity (the angle of the Earth’s tilt setting the extent of the tropics) and Precession (the direction of earth’s axis of rotation).

The Eccentricity cycles over about 100,000 years, we are currently living in a time approaching its most circular. Obliquity cycles over about 41,000 years and we are currently about halfway between the minimum and maximum with the tropical lines at 23.4°. The Precession cycles over 25,800 years with the current location of the axis pointing towards the North Star.

These wobbles are more commonly known as Milankovitch Cycles (figure 2). They are important because they control the hemispheric heat input from the sun as the planet moves seasonally farther and closer, facing the sun from subtly different angles. These changes in turn warm and cool the poles, controlling the timing of the glaciations and interglacials of the ice age. Incidentally these cycles have always affected the Earth’s short term climate variations. In warmer states, with higher levels of atmospheric CO₂, the cycles still adjusted how the planet behaved. It was just not cold enough to create a glaciation event.

In previous ice age periods, such as the Carboniferous (359-299Ma) the same glacial, interglacial pattern occurred. In fact the coal seams in the UK’s Forest of Dean, where I live, are layered with shallow marine limestone deposits as the then tropical landscape was alternately a low land forest (where the coal comes from) and a shallow marine basin depositing fossil bivalve rich limestone. During glaciations when the sea level was low, the forest thrived, during the interglacial warm periods the sea levels were higher, inundating the forest and marine deposits took over, burying the woody deposits where they would slowly bake to become coal.

For the first 2 million years of the current Quaternary period the glaciations occurred on a ~41,000 cycle, synchronised to the obliquity of the Earth’s orbit. Then during a period called the Mid-Pleistocene Transition (MPT) between ~1.25 and 0.7 million years ago, this pattern shifted to a ~100,000 year cycle. The causes of this change have been a hot research topic for decades (sorry).

Certainly geological evidence and ice core analysis confirms that the northern ice sheets grew substantially larger and atmospheric CO₂ levels dropped within the glaciated periods to lower levels than they had prior to the MPT, but the reasons for these changes remain debated.

The Ice Age Architect

The new study shows that the Barents Sea was much shallower prior to the start of the ice age, but became progressively deeper as successive ice sheets eroded it away, pushing and washing the sediment into deeper waters. Eventually a tipping point was reached where the seaway was open enough to allow a second opening of the Atlantic into the Arctic alongside the Fram Strait to the west of Svalbard.

The paper suggests that this increased Arctic-Atlantic connectivity reorganised global ocean circulation. In doing so it enhanced deep-ocean carbon storage and increased moisture supply to the Arctic. These two outcomes drew down the atmospheric CO₂ levels and allowed more rain and snow to accumulate on the growing ice sheets. In a classic feedback loop, the larger ice sheets reflected more sunlight back into space, increasing the planet’s albedo, causing the energy imbalance to go negative driving further deeper cooling and triggering altitude feedbacks as the ice sheets gained height. This locked in the glaciations through the 41 kyr boundary allowing them to remain until the 100 kyr eccentricity cycle allowed sufficient sunlight to reach the northern high latitudes to trigger a deglaciation and the start of an interglacial period.

The enhanced carbon storage occurred as more carbon rich water from the south was able to enter the Arctic Ocean where it could be overturned as the waters cooled, taking the carbon to the abyss, locking it away from the atmosphere.

In combination, these feedbacks were enough to tip the planet out of the 41 kyr cycle onto the 100 kyr cycle governed by the orbital eccentricity, that has run until today.

The Arctic’s Overturning Engine

The second recent study from Jakob Dörr et al.2 explains the importance of the Barents Sea to regional climate and its role as the northern most loop of the Atlantic Meridional Overturning Circulation (AMOC).

The deep water formed in the Arctic Ocean is the densest of the southerly flowing deep water produced by the AMOC system. Looking at the map in Figure 1, you might be excused for thinking that the Fram Strait was the key player in the story. It is, but for the deep water flow only, not for surface flow or overturning. The incoming northerly flow and the salty water that overturns to form the deep water flows mainly through the Barents Seaway.

The flat shallow sea allows the winds to very efficiently strip the remaining heat from the southerly sourced water as it flows north, creating dense salty water that then enters the Eurasian Basin, following the St Anna Trough down to the deepest parts of the Arctic. There it joins and re-mixes with the remaining flow from the Fram Strait in a loop following the Lomonosov Ridge south and out of the Fram Strait to join the Atlantic Bottom Water flowing south.

Some of the Barents water skirts past the Ridge and instead takes a long (500 year) circuit around the whole Arctic Ocean mixing with Pacific water from the Bering Strait before eventually flowing out of the Fram Strait as part of the Atlantic Bottom Water.

At various points on both journey routes, the water is freshened as it mixes with fresh river and ice melt supplied water and also made more salty through sea ice formation. The end result is that Atlantic Water is transformed into dense waters at a rate of 3.1Sv and into Polar Water at a rate of 1Sv. Given that the total mean AMOC flow was between 15-17 Sv annually from 2011 to 2020 (down from 18-19 Sv over 2004-08), the Arctic contribution is meaningful at ~20% of the AMOC’s total bottom water formation.

The Barents Sea role not only dominates the deep water formation thought temperature loss, it’s dense waters provide the mixing potential for the Fram Strait waters to also form deep water. 85% of the Fram Strait deep water is formed this way.

In a warming climate, the overturning circulation in the North Atlantic (i.e. the AMOC) is projected to decline as the necessary dense water formation is inhibited by warmer and fresher surface waters. In contrast, in the Arctic Ocean, sea-ice loss might lead to a stronger surface exposure of Atlantic water and hence increased dense water formation, potentially partially stabilising the northern overturning circulation, or at least providing some form of back-stop. This is likely to be well below the typical 5Sv threshold used to indicate a complete collapse of the AMOC, but could still be advantageous during the summer months when the Barents Sea is not covered in sea ice. In previous AMOC collapses during the last glaciation, much of the Barents Sea would still have been ice covered so would not have been able to provide this back-stop.

Closing thought

This is just one example of a relatively innocuous stretch of water on the edge of an ocean basin wielding huge power, not just in the distant past, but in shaping our whole world. How would humans have developed and spread if throughout their entire evolution since before Homo Habilis, there had been no 100,000 year glaciations, just smaller 41,000 year cycles? How might the sea protect northern Europe from a complete AMOC collapse in the decades and centuries to come? What other seemingly unimportant parts of the world affect us in ways we have not even looked into yet?

What an amazing, complex and fascinating world we live in. Pity we don’t respect it more…

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A “cold blob” has developed in the North Atlantic over recent decades, standing out as the only region of the world’s oceans that has stubbornly refused to warm. At the same time, monsoon patterns thousands of miles away have shifted dramatically across India. Northwest India now receives substantially more rain than it once did, while a coincident lack of moisture sends the fertile Indo-Gangetic Plain spiralling toward chronic drought.

Historically, these two phenomena were treated as isolated anomalies. The cold blob is linked to the Atlantic Meridional Overturning Circulation (AMOC) slowing down as less warm water is transported there and melting ice freshens the North Atlantic. The monsoon disruption is tied to shifts in the jet stream, driven by Arctic amplification narrowing the temperature gradient between the tropics and the pole.

However, a groundbreaking study has revealed that these two phenomena are not just parallel symptoms of climate change—the monsoon shift is a direct result of the Atlantic cold blob.1 Linked by a massive atmospheric teleconnection, a wind reconfiguration known as a barotropic governor mechanism strengthens the jet stream’s core while weakening adjacent regions, ultimately redistributing India’s rainfall. As we discover more about the planet’s inner workings, it is becoming clear that our shift from environmental normality is highly interconnected. These networks can provide temporary stability through dampening feedbacks, but they also possess the terrifying capacity to trigger domino-like cascading effects, leading to non-linear accelerations of global impacts.

Jan has a deeper explanation of this paper here.

Whilst we recognised that global warming was intensifying extreme events. We overlooked the main principle behind the amplification of these extremes. It’s intensifying upstream events that enable downstream events to reach new, never seen before intensities. It’s a feedback cascade that operates via the dynamical parts of the system, mutually amplifying and reinforcing downstream events in time and space.2 This chain reaction is behind the recent emergence of awe-inspiring incidents that have started to pop up all over the world. Even more worrisome we are now starting to realise that Earth is an oscillatory system in which oscillations can be forced to synchronise.3

Tipping Cascades

Earth is stabilised by life support systems which appear in various forms. These systems all have important functions that help to keep our climate stable. If these systems tip into another regime they can switch their function from stabilising to destabilising the Earth system. Unfortunately, if one system tips it can bring other systems closer or even past their tipping point. Such cascading tipping behaviour operates via teleconnections that exist between many of the world’s major tipping elements.

This makes the overall system potentially highly unstable, since if one passes it’s point of no return, there is a domino effect that can travel around the world, changing the status of other elements, both positively and negatively.

Figure 2 from Wunderling et al. shows the links between the major tipping elements, red lines indicating destabilising connections and blue indicating stabilising connections.4 (This is from a 2024 paper, so the link between AMOC and Indian monsoon is shown as having limited evidence, this may now be strengthening as discussed above.)

Science is slowly revealing that the Earth is a interlinked system in which changes on one side of the planet can have an effect all the way on the other side. Sea ice retreat interacts with circulation changes around Antarctica that can alter sea surface temperature patterns further north. These emerging ocean-atmosphere patterns then impact the tropical circulation, which can then impact circulation patterns over the Northern Hemisphere, all the way to the Arctic.

Rising and sinking motions in the atmosphere inside rotating atmospheric pressure systems connect with upper and lower air flows that are then able to undergo mutual amplification, being further reinforced by evolving surface extremes (e.g. warmer oceans can couple more strongly with the atmosphere or drying out soils, driving further temperature increases). Hence, circulation changes in one part of the system can affect, for example, surface temperature extremes in the oceans, over the land masses or the ice sheets over large distances, triggering further knock-on effects.

All the discussed tipping elements have one thing in common - that extreme weather events can trigger long lasting impacts on their behaviour. This includes marine heatwaves, or sudden alterations of ocean currents. A striking new signal at the forefront of Earth system change is the emergence of new classes of extreme events, far beyond our historical experience, or model prediction. It’s these exceptional extremes triggered by chain reactions between extreme subsystem states that are now becoming the driving force behind state shifts of important systems, such as Greenland ice mass loss, sea ice declines or the rainforests.5678

New Tipping Elements in the Chain

While major tipping elements like the Greenland ice sheet, the AMOC, and the Amazon rainforest are well known, emerging research continues to uncover hidden vulnerabilities within the biosphere.

A recent 2026 study exposed how retreating Arctic sea ice is triggering an ecological regime shift.9 While increased sunlight was expected to boost marine primary production, scientists discovered that nitrogen availability acts as a strict limiting factor. As vast, shallow continental shelves are exposed to sunlight, it accelerates a process called benthic denitrification, which strips essential nutrients from the seawater. By analysing two decades of data, researchers identified a distinct tipping point passed in 2009: as sea ice collapsed, nitrite levels plummeted in perfect synchrony, triggering a localised ecosystem collapse where fish populations virtually disappeared. As a knock-on, low primary production leads to low aerosol release which then affects cloud formation down-stream, and so on.

In another study just published, the tipping point of the Tibetan Plateau permafrost has been narrowed down to between 2° and 4°C.10 The region is warming 2.5 times faster than the global average, so this is getting close. The problem centers on a delicate balance between two competing processes. Plants initially thrive with a slight increase in temperature resulting in them pulling more CO₂ from the atmosphere through photosynthesis. But it simultaneously accelerates microbial decomposition in the soil, releasing carbon back into the atmosphere. The tipping point exists when the balance breaks irreversibly, with a decline in photosynthesis but an acceleration of soil decomposition. The whole cascade amplifies if fires increase non-linearly across the permafrost regions, for example if driven by soil-moisture-atmosphere feedbacks or sudden summer sea ice losses which greatly enhance their carbon emissions.11 Actually, new assessments predict values that would be near runway warming.12 The region containing 47 billion tonnes of carbon then becomes an massive unstoppable carbon source, accelerating warming in a feedback.

When one system is forced past its point of no return, it sends shockwaves through these interconnected networks, threatening a global domino effect. The danger of accelerating warming is that tipping points of important subsystems could occur within shorter time intervals. Disturbances could therefore greatly increase their interaction with other systems that lose their resilience at the same time, all operating via intensifying “weather” events synchronising at a global scale.131415

The Collapse of the Amazon Moisture Pump

The continents form a major domain of this interconnected network. The world’s forests act as a vital global carbon sink, sequestering roughly 18% of anthropogenic CO₂ emissions annually. Beyond carbon storage, they dictate global climate states through the regional hydrology of the “biotic pump”. Undisturbed forest canopies evaporate water pumped up by deep roots, fuelling moist convection that draws in moist trade winds from the ocean to sustain rainfall far inland.

Severe, recurrent droughts have outpaced the adaptive capacity of the Amazon, leaving over 75% of the ecosystem systematically losing its baseline resilience since the early 2000s.1617 When drought limits root water access, the Soil Moisture-Temperature Cascade engages: latent heat fluxes drop, sensible heat fluxes rise, the air dries, and solar radiation heats the land surface directly.

This elevates the localised Vapour Pressure Deficit (VPD)—the dry air acts like a sponge, demanding exponentially more water to cool down. This prolongs the dry season, breaches the physiological limits of trees, and triggers mass mortality. As the forest dries, intense wildfires spread, and the resulting smoke alters cloud droplet nucleation, further suppressing rainfall.18 Crucially, the breakdown of Amazonian convection stops pulling in Atlantic trade winds. The resulting wind slowdown reduces latent heat loss over the North Tropical Atlantic, causing sea surface temperatures (SSTs) to spike—a condition that naturally induces further drought over South America, locking the Amazon into a self-amplifying loop toward a savanna state.

This situation is expected to tip at around 4°C of global warming, but the impact of deforestation and degradation has lowered this to below 2°C of warming if deforestation reaches 22-28% - today we have already reached 18%.19 Then in 2023/24 an highly exceptional drought, far exceeding previous levels, hit the region. It affected most of the Amazon. The main causes were hot and dry compound events (figure 4).20 You can clearly spot the El Niño years - what will a ‘super’ strong 2026 event bring?This is another example of how extreme weather is starting to become the leading cause of subsystem shifts.

Subterranean Degradation and Pathogen Proliferation

This canopy level biological instability is mirrored underground. Healthy, biodiverse soil ecosystems exhibit a natural control function known as the dilution effect, where diverse microbial and fungal communities naturally suppress the transmission and proliferation of opportunistic pathogens. However, industrial agricultural runoff, pesticide overuse, and micro-plastic pollution are acidifying and contaminating global topsoils, decimating specialised microbial biodiversity.21

When these symbiotic mycorrhizal fungal and bacterial networks collapse, the structural stability of the soil fails, and net primary productivity drops. Combined with compound drought-heatwaves—which raise soil temperatures significantly faster than equivalent air temperatures—the Earth’s microbiome is losing its capacity to regulate biogeochemical flows. The resulting dry, barren topsoil is easily eroded into massive dust storms that transport airborne, heat-adapted pathogens across vast geographic distances, spreading disease to already stressed ecosystems downwind.

Sudden increases in microbial organic matter decomposition driven by hydroclimatic extreme events

The surprise jump in atmospheric CO₂ levels in 2024 by ~3.7ppm (figure 5), could have been driven by a surprise peak in microbial organic matter decomposition (microbial respiration). One study found that hot and moist conditions drove emissions from microbial respiration to new heights, ~4.3 Gt of Carbon (although this needs further confirmation). Such a peak would be near to half our direct CO₂ emissions. They found that grass and shrub lands had been important sources.22 A second study also identified microbial respiration as the main driver. But this time under hot and dry conditions.23 Unfortunately, both studies could have a point as under both, hot/dry and hot/wet conditions, microbial respiration can increase substantially. The emerging common driver could be high temperatures, be it directly24 or indirectly.25 A recent analysis revealed that sudden shifts between wet and dry conditions drive microbial respiration as well.26 Current models could dramatically underestimate warming driven soil carbon losses,272829 as emissions are driven by hydrological extreme events of both flavours.

Temperature related hydrological extreme events driving microbial respiration to new peak heights is another striking example of weather extremes that are now starting to drive important feedback’s. Since the 2000s we have observed how hot and dry compound extremes have increased non-linearly.3031 We see similar developments occurring with extreme precipitation events that also seem to be increasing non-linearly.3233 Furthermore, weather whiplash events - fast transitions from one hydroclimatic extreme into another - show a non-linear trend as well,34 while the abrupt shifts also intensify non-linearly.35 On the planetary scale we are observing how dry and hot3637 and large scale flooding events can become globally synchronised.3839 These synchronisations become strongest during El Niño and La Niña events.40 A recent estimate saw a shift to higher rates of microbial respiration starting in the 80s by 2% per decade. It projects an increase of 40% by the end of the century in a high emission scenario, mostly driven by the Arctic,41 while in reality we could already see it accelerate through lower latitude regional drivers. Hence, if we do indeed here a strong microbial feedback in the making, the 2024 signal will repeat itself as global warming continues to accelerate, driven by the temperature jumps triggered by strong El Niño events.

The Cryosphere: A Pole-to-Pole Tipping Loop

The Earth’s polar cryosphere acts as our primary planetary cooling mechanism, yet a rapid feedback cascade is actively linking the degradation of both poles. Arctic Ocean sea ice volume has declined by up to 50%. Under current trajectories, exceptional extreme weather events could cause the Arctic Ocean to experience its first ice-free summer day (dropping below 1 million km²) as early as 2030, or potentially even sooner.42 In a similar way to other significant events, it is likely that the first ice-free Arctic summer will be linked to other extreme weather events elsewhere.

This rapid melting initiates powerful internal feedbacks:

• The Albedo Effect: As reflective multiyear ice is replaced by open water, the exposed ocean absorbs shortwave radiation, warming the water to undermine the remaining surface ice from below.

• Wildfire Feedback: Diminishing sea ice alters atmospheric pressure, creating persistent blocking configurations that drive severe mid-latitude heatwaves and massive wildfires across the Western US, Canada and Siberia. The resulting wildfire smoke deposits soot directly onto the Arctic ice sheet, darkening its surface and compounding melt rates.

• Cyclonic Destabilisation: Thinner ice lacks mechanical resilience. Open water increases latent heat and moisture transport into the atmosphere, spinning up intense Arctic cyclones that mechanically fracture fragile ice flows.

• The thermal feedback: Sea ice acts like a thermal barrier for downwelling long wave (LR) radiation from the atmosphere and upwelling LR from the oceans. If sea ice thins this barrier weakens. Downward LR can then warm the oceans as well as upward LR is remitted through the ice to the atmosphere driving further ice loses.

• Ice-fire feedback: With declining sea ice area during the summer, water vapour production increases, supporting lighting storms over drying out and warming tundras triggering non-linear increases in fire activity. The emitted soot then deposits over the sea ice, darkening it and fuelling ice algal blooms which further drive sea ice losses, feeding back on the Arctic landscapes increasing fire potential.

A further surprise is that Northern Hemisphere sea ice loss is rapidly synchronising with the Southern Hemisphere sea ice. During 2005 and 2015 warmer, saltier water moved closer to the surface in the Southern Ocean. This shift preconditioned the upper ocean so that in 2015, just one extreme storm season was enough to trigger a regime shift. Storms mixed warmer and saltier water into the upper mixed layer. This then drove surface density looses driving further upward mixing of warm and saline waters melting the sea ice.43

This degradation has rapidly synchronised with the Southern Hemisphere. Since 2016, Antarctica has experienced unprecedented summer sea ice declines, reaching a record low in February 2023 that was 38% below the long-term average due to non-linear ocean-atmosphere coupling.44

Simultaneous ice loss at both poles intensifies the planet’s primary mode of natural variability: the El Niño-Southern Oscillation (ENSO).4546 Dynamic climate modelling reveals that combined polar ice loss induces an El Niño-like warming pattern over the tropical Pacific, driving more frequent and intense El Niño events. In a dangerous closing of the loop, these stronger El Niño regimes transfer heat back toward the poles, accelerating further ice shelf decay and trapping the high-latitude cooling systems in a global death spiral with changes at both poles playing ping pong, disturbing circulation patterns well into the other Hemisphere with each one feeding the other.

Spikes as System Disruptors

We have known all along that Earth is a highly non-linear system in which abrupt changes are not the exception but the norm. If warming rate thresholds are breached, sudden shifts not only occur more often but also intensify. It’s the rate of warming which pushes Earth’s subsystems ever faster away from the climate state they could exist in while more stable. The growing disequilibrium then forces subsystems to shift more abruptly. This principle could be at the core of the non-linearity that is now intensifying rapidly throughout the dynamical subsystems of the Earth, shifting their function from climate stabilisation to destabilisation in multiple domains. The non-linear chain reaction is now working its way upward to the planetary level.

A striking example can be seen in Sea Surface Temperatures (SST), which play a large role in regulating Earth’s climate. They are the interface between the oceans and the atmosphere and regulate the energy fluxes, both into and out of the oceans (e.g. high SSTs reduce cloud cover and fuel storms that undergo rapid intensification). The recent jump in SSTs in 2023 by more than 0.3°C had been driven by a sudden jump in area, intensity, and persistence of Marine Heatwaves (MHW). This jump had been preconditioned by an energy accumulation across the upper oceans in previous years, cloud reductions, and atmospheric circulation patterns triggering MHWs over wide parts of the oceans in 2023.47 This signal persisted into 2024 with two ocean basins - the Atlantic and Indian Ocean running simultaneously hot for some months. From July 2023 to June 2024 surface temperatures spiked at +1.58°C with a record 12 month increase of +0.36°C driven by SSTs going wild.48

All warning signs point to the fact that the oceans are overheating. In 2025 oceans accumulated a record 24 ZJ of energy. This is an eight fold increase above the 1958-1981 average of 2.9 ZJ and equivalent to 200 times the total global human energy generation for the year. The non-linear expansion, intensification, and persistence of MHWs are a warning sign to humanity that we are warming the oceans far too fast.

The warming is concentrating in the upper layers, driving faster stratification, thereby decoupling the upper from the deeper ocean layers, transforming the upper ocean into a highly efficient heat depot which the atmosphere can tap into to drive extreme weather events. MHWs are now becoming prevalent in both Hemispheres with the largest and most intense ones persisting the longest, driven by non-linear upper ocean-atmosphere interactions.49 We reached already at mean warming levels of 1.4°C climatic boundary conditions that just abnormal weak winds are now enough that whole oceans basins and marginal seas alike run hot.5051

Concurrently, we are seeing more extreme events that do not merely break previous records, but utterly smash them. The recent May heatwave in northern Europe and the UK is a stark example: reaching 35.1°C in London did not just creep past the old record; it shattered it by 2.3°C52 (As this article is posted, London is bracing for 40°C heat for the second time in 5 years, something that the Met Office said in 2020 was a 1-in-100 to 300 year event). Rainfall, heat, drought, and fire intensity are all behaving this way with sudden peaks now emerging all over the Earth system with upper ocean heat, extreme SST anomalies, and intensifying SST gradients becoming ever more often the trigger point for feedback cascades of non-linear surface-atmosphere interactions, driving these sudden peaks. These acute spikes are uniquely dangerous because they can instantly nudge a fragile planetary feedback loop beyond a threshold that a steady, linear rate of warming may not have breached until decades later. At the forefront of these are short term variations going off the charts within the time scales that weather operates within.

Critical Slowing Down: Early Warning Signs of System Failure

Predicting the exact moment an interconnected system will tip remains beyond the reach of current historical climate modelling due to complex, non-linear cross-correlations. However, complex systems theory provides distinct mathematical indicators—known as critical slowing down—that can warn that a major state shift is imminent.53

Global empirical observations suggest we are actively approaching this critical threshold. While the long-term climatological average has not yet permanently stabilised above the 1.5°C threshold, the physical Earth system breached this boundary on an annual basis in 2024, with temperatures approaching a 1.6°C warming anomaly relative to pre-industrial baselines. As of the end of May, the average global surface air temperature for the last 42 month period has been above 1.5°C.

As regional tipping elements lose their individual resilience, their internal dynamics begin to align. When local environmental fluctuations synchronise into global mass and energy transfers, the entire biosphere risks shifting from a collection of isolated regional ecosystems into a self-amplifying, domino-like chain reaction.

Temperature Jumps That Do Not Recover

In 2016, following the warming spike of a very strong El Niño event, global temperatures failed to return to the baseline trend during the subsequent La Niña. This was the first clear sign of an Earth system that is no longer buffering heat, but amplifying it with each El Niño spike, forcing the planetary engine into a permanently higher gear.

The exact same phenomenon occurred following the 2023 El Niño. As expected, 2024 was the hottest year on record, but temperatures in 2025 did not drop back to the prior trend line, despite a relatively weak La Niña phase that has run into 2026. The three-year average for 2023–2025 stood over 1.5°C, and 2025 itself was more than 0.25°C warmer than the five years leading up to the 2023 spike.54555657

The world is now bracing itself for another likely very strong El Niño event expected to intensify through the latter months of 2026 and persist into 2027.58 As it develops, we are not just looking at a warm 24-month cycle; we are looking at the discharge of a “loaded” planetary battery. The immense heat accumulated in the Pacific will be released into the atmosphere, driving another permanent jump in global temperatures. A new record of 1.7°C could be reached in 2027—and once again, it may never be recovered from.59

Key Takeaways

Observational data suggests that the coming 2026 El Niño is poised to bring another structural jump in global temperatures, alongside the devastating regional droughts, floods, and storms normally associated with the phenomenon. If temperatures remain permanently elevated afterward—as they did following recent strong events—the world will never again drop below 1.5°C of warming. We will be firmly on the path to 2°C, accelerating the looming cascade of feedbacks and tipping elements that move the planet away from the suitable zone for human civilisation.

Crossing 1.5° and entering what has become known as Overshoot, risks not just extreme events, but engaging feedbacks that push tipping elements over their thresholds, triggering cascades of changes that are unrecoverable on any sensible human time horizon. We also risk triggering natural emissions, such as permafrost, forest die back and ice sheet collapse that render our capabilities of carbon reduction almost meaningless. In short we risk an extinction event tipping threshold that not even we can survive.

The critical functioning of biodiversity across both macro and micro-biomes serves an emergent control function for the planetary climate system. Key recycler species and microbial networks decompose matter, suppress opportunistic pathogens, and regulate soil-moisture-atmosphere coupling. When climate shocks alter these relationships, critical slowing down occurs, increasing network cross-correlations and paving the way for synchronised tipping cascades across the continents, the cryosphere, and the oceans.

The 2023 State of the Climate Report issued a warning in the face of the unfolding catastrophe: “we are entering uncharted territory.”60 The following year’s report stated that we are “on the brink of an irreversible climate disaster.”61 In the 2025 report they added “We are hurtling toward climate chaos. The planet’s vital signs are flashing red. The consequences of human-driven alterations of the climate are no longer future threats but are here now.”62 It was these cascading risks they had in mind when they wrote those words.

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The global warming trend is obvious. For virtually every country, region or city, the stripes turn from mainly blue to mainly red in more recent years, illustrating the rise in average temperatures in that location.

Today, June 20th is Show Your Stripes Day It is a global moment to share our concern about how the climate is changing and the need for urgent action in our local communities and around the world.

This is my little contribution - I hope you enjoy it 🕺, if so please like ❤️ share 🔁 and discuss 💬

If you are new to Climate Uncovered, you may like some of our recent articles:

This article was originally posted on the 17th June 2026, but was updated with the very latest available data on the 22nd August 2026.

The El Niño Southern Oscillation (ENSO) is one of the most impactful climate phenomena on Earth due to its capacity to alter global atmospheric circulation. This, in turn, dictates temperature, precipitation, and extreme weather patterns across the world.

Following a barrage of forecasts and warnings from global meteorological services, the traditional media, as well as social media, has woken up to the looming threat, deploying terms like ‘super’ and even ‘Godzilla’ El Niños as model predictions venture off the charts. The UK Met Office being the latest to issue warmings.1 They are right to do so. If you live in an area heavily influenced by these shifts—such as the Western US, Amazonia, Australasia, South America, the Western Pacific, or sub-Saharan Africa—preparations for the latter half of this year should be made with haste.

However, it is 2027 and beyond that may require our most serious preparations.

How bad are we talking?

The forecasts for the strength of the upcoming El Niño have risen steadily over the last few months, as demonstrated by Professor Eliot Jacobson’s recent model animation on Bluesky.

The latest plume plot from the NOAA (Figure 1) is striking. I have overlaid the peaks reached by the 2015/16 (very strong) and 2023/24 (strong) events for comparison. As of August 22nd, the El Niño event is already at the peak temperature of the 2015/16 event NOAA are also currently forecasting a >80% chance of it being ‘very strong’ through to January.2

Beyond the immediate global disruption these events cause, they leave permanent scars. The 2016 event helped to trigger a structural tipping point in Antarctic sea ice, which had been resiliently stable up to that juncture but has since suffered an accelerated decline.3 Meanwhile, the 2023 event drove 2024 to become the first full calendar year to breach 1.5°C of global warming.

Looking further back, an exceptionally strong El Niño in the early 1940s has been definitively linked to the initial unpinning and retreat of both the Thwaites (‘Doomsday’) Glacier and its neighbour, Pine Island Glacier, in West Antarctica.4 Long after the tropical atmosphere cooled down, the glaciers never re-advanced. The anomaly was temporary; the structural destabilisation was permanent. We are still tracking that continuing retreat via satellites today, in fact the final unpinning of the remaining floating ice sheet is imminent.5

Key takeaway: Situate these historical precedents on top of our current baseline of nearly 1.5°C of global warming, and a ‘super’ El Niño in 2026 transitions from an ecological crisis into a literal killer. The implications for global food security and price inflation, especially coming on the back of fertiliser and fuel shortages caused by the US misadventure in the Strait of Hormuz, cannot be underestimated. Mark Roberts has an excellent analysis here.

The short window since the 2023 event might superficially suggest that the Pacific has less accumulated energy available to fuel a monster event so soon. Historically, very strong El Niños are preceded by prolonged neutral or cool La Niña phases, allowing heat to pool in the western Pacific. This time, however, the ocean is primed early. Rare and extreme ‘annular warming patterns’ emerged across the western, northeastern, and southeastern tropical Pacific in spring 2026, whilst subsurface equatorial heat content remains dangerously above average.6

Furthermore, global ocean heat uptake jumped by a staggering 23 zettajoules (ZJ) in 2025 alone. For context, 23 ZJ is roughly 200 times the total annual electricity generation of the entire human race. The 2025 ocean heat uptake represents an eight-fold increase over the 1958–1985 annual mean baseline (~2.9 ZJ).7

To cap it all off, powerful Kelvin waves continue to charge eastward beneath the equatorial Pacific surface. They are providing a conveyor belt of heat that breaches the surface and releases thermal energy directly into the atmosphere, with subsurface temperature anomalies already exceeding 8°C, less than 100m from the surface (Figure 2).

Immediate Impacts

Numerous commentators have outlined the immediate macroeconomic and humanitarian casualties of a super El Niño event—including a recent summary by The Guardian detailing the risks to the global economy. In a nutshell, we are looking at:

• Widespread droughts and heightened wildfire risks

• Severe rainfall events and catastrophic flash flooding

• Food price shocks (compounded by fertiliser and diesel shortages linked to the ongoing conflicts in the Middle East)

• Coral bleaching and death as well as collapsing fisheries catches and regional famine

• Extreme heatwaves driving a spike in heat-stress mortality

• Surging energy grid demands to power air conditioning

• Range expansion of insect-transmitted diseases such as Dengue

• Elevated geopolitical tensions and civil conflict

• Cats and dogs living together... mass hysteria. (Oh wait, that’s Ghostbusters).

The Warming Ratchet: Phase 1 (2027)

The primary thermodynamic consequence of an El Niño is that it allows the global ocean to exhale. The oceans absorb roughly 90% of the Earth’s Energy Imbalance, so when they release a fraction of that accumulated energy back into the sky, global mean Surface Air Temperatures (SAT) spike.

The magnitude of this atmospheric boost scales with the strength of the ENSO event (Figure 3). By plotting the peak monthly SAT achieved after historical El Niños against the surrounding 18-month mean, the correlation becomes clear: the stronger the oceanic anomaly, the sharper the atmospheric temperature spike.

If we take a linear fit of this historical data and project it out across the ECMWF model plumes from figure 1, we get a sobering look at 2027. By adding these projected monthly peaks to our current pre-event baseline (+1.47°C mean global SAT from January 2025 to May 2026), we can establish a conservative look at the upcoming 2027 temperature peak.

The historical peak monthly anomaly occurred in February 2024 at +1.78°C. The coming event will eclipse this. If the upper-quadrant model projections materialise, 2027 could deliver the first individual month breaching +2.0°C above pre-industrial levels in human history. The full calendar year average for 2027 is highly likely to settle above 1.7°C, shattering 2024’s record by a wide margin.

The Warming Ratchet: Phase 2 (2028–2030)

We have witnessed record-breaking hot years before, but a terrifying systemic pattern has emerged: temperatures no longer drop back down to the pre-existing trend line after the event concludes. Instead, the climate system undergoes a step-change—a warming ratchet that locks in a higher baseline.

Consider the data:

• The average global SAT for 2010–2015 was 0.98°C above pre-industrial levels.

• The 2016 super El Niño spiked temperatures to 1.14°C.

• Crucially, during the subsequent cooling/neutral years (2017–2021), temperatures did not revert to 0.98°C; they ratcheted up to an average baseline of 1.20°C.

We watched this exact mechanism play out again after the 2023 event. The average global temperature from January 2025 to May 2026 sat at 1.47°C—more than a quarter of a degree warmer than the five-year average preceding the 2023 El Niño.

That is not to say that El Niños warm the planet per se, but they release the temperature jumps required to step up global temperatures by the expected 0.2-0.35°C per decade.

The looming danger is that the 2026/27 event will execute the exact same manoeuvre. If it does, 2025 will have been the last year ever* where global average temperatures remained below 1.5°C for a full calendar year. *well for at least 10,000 years anyway!

With 2026 already averaging 1.48°C prior to the onset of the El Niño heat dump, this year should comfortably top 1.5°C by December (aligning with my January prediction of 1.52°C). Interestingly James Hansen is predicting that 2026 will overtake 2024’s record coming in at above 1.6°C for the full calendar year.89 It is most unwise to bet against Jim’s predictions. If he is right, and his logic seems sound, it is a very worrying situation we find ourselves in.

To test his logic very crudely (figure 4) - if we superimpose the August through December 2023 temperature profile onto the 2026 January through July temperatures, then average the year, 2026 would be 1.61°C - indeed just higher than 2024’s 1.60°C.

Following that, 2027 will likely soar to between 1.7°C and 1.8°C for the calendar year average. It will certainly be hotter than whatever 2026 delivers, since the peak SAT temperatures lag the ocean temperature extremes. When the system settles in 2028–2030, our new “cool” baseline will likely hover around 1.55°C to 1.7°C—leaving us perfectly positioned so that the subsequent El Niño introduces the first full calendar year at +2.0°C, depending on when it emerges. Permanently passing 2°C during the 2030s now seems unavoidable.

The planetary impacts locked into the backend of this decade will be severe; there is simply too much thermal energy accumulated in the system for any other outcome. This places the planet squarely in the danger zone for a number of the great tipping elements including the West Antarctic and Greenland Ice Sheets, Boreal Permafrost abrupt thawing, Ocean Current disruption and Amazon collapse.

We can only hope that these upcoming systemic shocks finally jolt global leadership and the voting public into treating the crisis with the structural seriousness it demands.

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8

Climate Uncensored

Yes, 2026 is on Track to be the Hottest Year

James Hansen, Pushker Kharecha, Dylan Morgan and Jasen Vest…

Read more

3 months ago · 101 likes · 23 comments · James Hansen

9

Climate Uncensored

Super-Duper El Nino and the Bigger Problem

James Hansen, Pushker Kharecha, Dylan Morgan and Jasen Vest…

Read more

11 days ago · 273 likes · 52 comments · James Hansen

As we pass through the Paris 1.5°C goal and enter what has been called “Overshoot”, we have to ask: what’s next? Is there a way back, and if not, where are we heading? It’s particularly timely that a new paper from the Potsdam Institute for Climate Impact Research has just been published, projecting some possible futures.1

Have We Passed 1.5°C?

To a certain extent, “1.5” is a state of mind rather than an absolute moment in time. We can say that the average temperature for 2023-2025 was above the 1.5°C pre-industrial baseline, and that 2024 was the first full year where the global average reached 1.6°C, but does that count?

With NOAA projecting a 96% chance of El Niño returning by the end of this year (with a greater than 60% chance of it being strong or very strong), 2026 is looking likely to exceed the threshold once again. Furthermore, 2027 is highly likely to break the 2024 record. We are witnessing a climate ratchet effect: the Earth no longer cools back down to previous baselines during La Niña phases. Instead, it uses each El Niño to jump to a new temperature plateau and stay there.2

However, a precise scientific definition remains elusive. Climatologists typically require a 20-year average to formalise a climate shift. I am quite confident, however, that when we reach 2035 or 2036, the preceding 20 years will indeed have averaged above 1.5°C—making the exact crossing point, well, right about now. The Paris Agreement itself does not provide a clear metric, pointing vaguely to “multi-decadal” averages, but a 20-year window is the most widely accepted interpretation.

The “state of mind” aspect is simply this: we have crossed a Rubicon. Extreme events are breaking records on a weekly basis, seven of the nine Planetary Boundaries have been breached, and every measure of climate change and nature loss is accelerating. The natural systems that have protected and buffered us for thousands of years, cradling our development, are actively breaking down. In short, we are in deep shit, and it’s time we admitted it to ourselves. We are in overshoot.

When overshoot is discussed, two aspects dominate the conversation: peak and duration. The political assumption is that overshoot is temporary. The narrative suggests that if we reach net-zero emissions, and then pump huge volumes of greenhouse gases back out of the atmosphere, we can successfully return to sub-1.5°C temperatures. How quickly we reduce emissions sets the peak temperature reached; how quickly we scale negative emissions defines the duration. Both are incredibly hopeful and ambitious assumptions.

Welcome to the Anthropocene

The new Potsdam paper uses this transition into overshoot to reframe our understanding of the Anthropocene. The International Commission on Stratigraphy may have recently rejected it as a formal geological epoch, but the physical evidence clearly shows that humanity’s impacts on the Earth system will be felt for millennia—perhaps far longer.

The Earth has departed from the stable baseline of the Holocene and entered uncharted territory. Whilst global temperatures and CO₂ concentrations have been this high in the deep geological past, they have never occurred at the same time, and never with this terrifying rate of change. The Earth is profoundly out of balance, violently trying to find a new equilibrium.3

To map out overshoot outcomes, the Potsdam team used three scenarios. Rather than comparing a traditional high-emissions future with a low-emissions one, they focused on a very low pathway (SSP1-1.9) and a medium pathway (SSP2-4.5). The ultra-low SSP1-1.9 scenario has effectively been abandoned in the new CMIP7 models as unrealistically optimistic, given it required global emissions to peak in 2020 and drop by ~7.5% every year since. However, it serves as a useful aspirational baseline here.

The second and third pathways both follow the medium (SSP2-4.5) emissions scenario, but apply different Equilibrium Climate Sensitivities (ECS)—specifically 3°C and 4°C. ECS dictates how much the world warms when atmospheric CO₂ doubles. By altering this, the researchers compared a “helpful” Earth system response against an “unlucky” one. They also evaluated a worst-case variation involving “surprising” Earth system feedbacks, such as rapid carbon sink destruction and cascading tipping points.

These three scenarios fit perfectly into the overshoot realities we face. Pathway 1 shows a limited overshoot with a minimal peak and a short duration before a return to relative safety—albeit in a permanently altered world. Pathways 2 and 3 show our more likely continuous warming scenarios, differing only by the degree of catastrophe.

At this point, it is worth noting that Pathway 2 looks overly optimistic for a medium-emissions future. The Earth’s Energy Imbalance is currently four times what it was just 25 years ago. With accelerated warming making a 2°C breach highly likely in the 2030s, the data points squarely toward the red danger zone of Pathway 3. The paper accepts this reality, noting that ECS is increasingly likely to be higher than the IPCC’s historic 3°C best estimate. Crucially, ECS exhibits “state dependence”—meaning it amplifies and increases as the climate state grows warmer. It may have been closer to 3°C in the 1990s, but it is climbing now, driven partly by secondary stressors like global deforestation.4

A Point of No Return

Whether we follow Pathway 2 or 3, the paper describes a terrifying threshold: the risk point where human emissions take a back seat to Earth system responses. This is the point where hitting net zero no longer controls the peak, and the duration of overshoot stretches far beyond any relevant human time horizon.

While public focus remains fixed on industrial emissions, other human activities are actively dismantling the planet’s resilience. Deforestation and degradation in the Amazon are lowering the temperature thresholds needed to tip the entire rainforest into a dry savanna. Coral reefs, the backbone of marine ecosystems, now face inevitable extinction, which will trigger massive knock-on effects for the ocean’s biological carbon pump. Concurrently, permafrost and oceanic methane clathrates are poised to release greenhouse gases in volumes and at temperatures lower than standard models anticipated. The biosphere’s ability to absorb carbon appears to have peaked back in 2008,5 a reality reflected in the extraordinary jumps in atmospheric CO₂ levels observed recently.

If these natural carbon sources exceed a dangerously low threshold of roughly 5 Gt per year, it could be enough to lock the Earth into a self-sustaining warming state for millennia, regardless of whether human emissions drop to absolute zero.

As the Potsdam authors note:

“A doubling of current cumulative carbon emissions to 1,000 PgC (a value expected to be reached by ∼2070 in SSP2‐4.5) would delay the next glacial inception by 50,000 years. Even after hundreds of thousands of years into the deep future, the Earth system may not return to its natural orbitally driven cycling between glacial and interglacial states...”

If this trajectory is triggered, the Anthropocene will no longer be classified as a mere epoch following the Holocene; it will register on the geological period-scale, representing a permanent departure from the Quaternary conditions that governed human evolution over the past 2.58 million years.

What Are the Options?

Though we are drifting rapidly toward the “unmanageable” red zone of Figure 3, we could theoretically still get away with a merely “dangerous” future if we act immediately and get incredibly lucky with the Earth’s feedback loops.

The choices we make in the next decade will dictate the state of the planet for millennia. These choices will affect our immediate lives, not just those of our grandchildren.

• Option 1: Status Quo. We continue to prioritise short-term economic growth and corporate shareholder value, which remains the functional policy of most major economies. This takes us straight down Pathway 3 toward an unmanageable planet and a near-certain mass extinction event. This might be an acceptable gamble if you are celebrating your 80th birthday soon, but it is a death sentence for the rest of the biosphere.

• Option 2: Managed Damage Control. We openly acknowledge the depth of the crisis, accept collective responsibility, and aggressively pivot. While Pathway 1 is now out of reach, we can still aim for a trajectory that mirrors its curve from a higher baseline—one that caps warming above 2°C but aggressively averts a 3°C or 4°C collapse. The new Medium-to-Low scenario proposed for CMIP7 may represent the absolute best we can realistically achieve.

Interestingly, none of the new CMIP7 emissions scenarios project human emissions continuing forever. Why? Because industrial economies and organized global society likely collapse once global warming exceeds 3-4°C.67 Furthermore, the fossil fuel industry will inevitably hit an energy-return-on-investment (EROI) wall, where extracting the remaining resources costs more energy than they yield. Either way, emissions hit net zero because there is eventually nothing left to burn, and no industrial society left to burn it.

What Is Required?

If we choose Option 2, we must execute two equally critical strategies. Public policy is obsessed with greenhouse gas reductions, but large-scale nature restoration is just as vital.

As Anastasia Makarieva, Theodore Rethers and others have highlighted, restoring the natural biotic pump and water cycle is paramount to lowering local heat stress and facilitating heat dissipation into the upper atmosphere.8 Forests do not just provide shade; through transpiration, trees convert incoming solar radiation into latent heat within water vapour. As this vapour rises, it condenses into clouds, reflecting sunlight back into space and generating rainfall. Crucially, the heat released at high altitudes has far less greenhouse gas pollution to fight through to escape into the vacuum of space. Actual planetary cooling is enhanced.

Methane reduction represents our quickest, most immediate lever. It is entirely achievable with existing technologies, and often highly profitable.9 Methane is responsible for nearly a third of net global warming since the pre-industrial era, and atmospheric levels have soared by 170%. While some sources are natural, a massive portion stems from ruminant agriculture and fossil fuel infrastructure leaks. Plugging these leaks and altering agricultural practices will exert an immediate braking effect on the current rate of temperature rise, buying crucial time.

Simultaneously, the foundational challenge remains the absolute decarbonisation of the global economy. It will be an agonizingly difficult task; all modern mining, heavy manufacturing, agriculture and long-haul transport run almost exclusively on fossil fuels. But it is non-negotiable, we have to wean ourselves off them.

Finally, we must scale negative emissions. Mechanical and biological carbon dioxide removal (CDR) must be built out to multi-gigaton annual capacities to permanently draw down atmospheric CO₂ and eventually bring an end to the overshoot period. There is no long term alternative.

The Climate Wildcard

The nagging question is whether these structural changes can possibly occur fast enough. Given that observational data tracks far closer to Pathway 3 than Pathway 2, we will almost certainly breach 2°C and flirt heavily with 3°C. This risks pushing us past the tipping points that decouple the climate from human control entirely.

Because of this timeline mismatch, solar geoengineering—specifically Stratospheric Aerosol Injection (SAI)—is shifting from a fringe sci-fi concept to an inevitable climate stabilization backstop.10 Injecting reflective aerosols into the stratosphere to mimic volcanic cooling could artificially buy us the critical decades needed to scale carbon removal and roll out global transitions. It carries immense geopolitical, ethical, and termination risks, but if we tread too close to the point of no return, humanity may find itself with no other choice.

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8

Biotic Regulation and Biotic Pump

How natural ecosystems keep our planet habitable

By Anastassia Makarieva

Theodore Rethers

environmental tinker

A new study has been published which reduces the uncertainty of the various contributors to sea level rise since 1960.1 The analysis breaks down the contributions of thermal expansion, ice melt and land water storage. The findings, when linked to other recent studies, suggest the rises we should be planning for are, at best, on the high side of previous predictions.

The rate of sea level rise is accelerating, a paper published in 2024 showed that the rate had more than doubled between 1993 and 2024 - the era of satellite measurements of global sea surface height.2 Figure 1 shows the global sea level rise record. The trend curve in red is a quadratic fit indicating the acceleration. The global mean rise is currently 4.5mm per year, and rising.

Contributions to sea level rise

The new study by Huayi Zheng et al. breaks the contributions of sea level rise into six distinct drivers. The largest single contributor is thermal expansion of the ocean water as its temperature increases. The cryosphere provides three contributors in the form of melting ice from Antarctica, Greenland and continental glaciers and snow pack. Land water storage makes the last contributor, and is surprisingly high. Atmospheric water vapour increases, due to the warming air being able to hold more water vapour, has a slight lowering effect.

Thermal Expansion - Thermosteric rise

As water warms, it expands. As we change the climate though our fossil fuel burning and land use changes, the resultant warming affects the seas as well as the air and land, in fact more so. According to von Shuckmann et al. 89% of the energy the Earth is accumulating is being stored in the oceans.3 This is a huge amount of energy, and its being stored as heat. Only 2% of the energy is warming the air where it is now 1.5°C hotter and driving all the extreme weather events which are unfolding.

The total heat gain of the oceans so far this century is over 300 zetajoules (300 with 21 0s after it). What’s more it is being added to at a rate of nearly 10 Hiroshima bombs worth of heat every single second!

The energy comes form the Earth’s Energy Imbalance (EEI), the difference between the incoming solar energy and the outgoing reflected and radiated energy. This is positive and rising, meaning more and more energy is being accumulated at an accelerating rate. Since 89% is stored in the oceans, they are warming and expanding also at an accelerating rate. The 2005-2023 thermosteric sea level rise was 1.55mm/year and shows an acceleration of 0.115mm/year per year.

An interesting recent study by Douville and Allan4 looked at future EEI trajectories and found that even under a very low emissions scenario (SSP1-2.6), EEI is likely to continue to increase until at least the 2040s and not return to zero for centuries. This implies that even a very low emissions scenario will see future thermosteric expansion for the foreseeable future. A more likely scenario such as SSP2-4.5 or the new CMIP7 Medium will see even faster EEI growth with matching thermosteric sea level rise.

Unfortunately it gets worse than that. Although the oceans absorb 89% of the energy, 52% is in the top 700m of the water column. Only 8% has reached the deep layers 2,000m down so far. Ocean currents and mixing will gradually move this heat to the deeper layers where they too will expand. This in turn allows the surface layers to continue to absorb energy and keep warming. This locks in thermosteric sea level rise for centuries to come.

Glaciers

According to the 2025 State of the Cryosphere Report,5 glacier ice loss around the world is increasing exponentially. Between 2000 and 2023, global glaciers outside of the ice sheets in Greenland and Antarctica lost an average of 273 gigatons each year, with ice loss 36% higher in the second half of that period compared with the first. Relative glacier loss was greatest in Central Europe and the Caucasus, which lost 39% and 35% of their ice, respectively, during this time.

The most recent observations are even more alarming. Since 2020, glaciers in Western Canada and conterminous United States have lost 12% of their mass and those in Switzerland 13% - in just 5 years! Not only have Indonesia’s Puncak Jaya glaciers lost more than 99% of their 1850 surface area, but new satellite imagery from 2023 and 2024 shows the tropical ice masses have lost as much as 64% of the remaining surface area since the most recent survey in 2018.

A new paper by Aaron Cremona et al. found that the glaciers in Switzerland lost 25% of their volume between 2010 and 2024. A loss of over 15 cubic kilometres.6

Zheng et al. have glacial ice melt contributing 0.73mm/year to global sea level rise accelerating at 0.014mm/year per year. These prognosis for accelerating melt as temperatures continue to rise suggest this will also increase for decades until they are gone. A study published last year suggested a peak glacial extinction rate could be crossed in the 2040-50s seeing 4,000 glaciers disappear each year.7 The total glacial contribution to sea level rise is therefore set to continue in the short term but level out as the glaciers disappear.

Ice Sheets

The Greenland and Antarctic ice sheets contribute 0.70 and 0.51mm/year of sea level rise respectively. Interestingly the rates for both have slightly slowed during the 2005-2023 period with decelerations of 0.025mm/year per year. The trend had been acceleration since the 1960, but changes in weather patterns creating more snow have slowed the rate slightly.

Although the mass balance loss each year is the direct link to sea level rise, its important to note that the new ice tends to be added to the high altitude ice sheets, while the losses occur within the glaciers that surround the continent. Tipping points are believed to exist for various glaciers within the continents. Winkelman et al. mapped the risks of the Antarctic ice catchment basins predicting tipping temperatures and sea level rise consequences.8

You’ll notice that the system closest to tipping is the Thwaites and Pine Island Glaciers in the Amundsen Sea. Thwaites, also sometimes called the “Doomsday Glacier” is the widest glacier in the world and is held back by a floating ice shelf which is pinned to a grounding line on the sea floor. Unfortunately satellite recognisance is showing that it is just about to break away from this anchor and collapse.9 This will allow the ice shelf to break up and drift off as ice burgs. The lack of buttressing will then allow the land based glacier to flow faster into the sea, accelerating it’s contribution to sea level rise.

Thwaites is already losing mass 5 times faster than it was in the 1990s. One study predicts it could increase its ice loss rate to 180–200 billion tons of ice per year—roughly equal to all the ice Antarctica loses today, by 2067.10

Greenland is no more stable. A 2026 study showed that the Prudhoe Dome ice cap in the northwest of Greenland, currently covered in 500m of ice, was ice free just 7,000 years ago.11 During that time, summer temperatures in the region were only 3°C to 5°C warmer than pre-industrial levels. This is a critical “mild” warming threshold that is close to being experienced today since Arctic Amplification means the region is warming up to 4 times faster than the global average, which is already at 1.5°C. This is important, since if relatively modest warming was enough to erase a 500 meter thick ice dome in the recent past, it suggests that Northwest Greenland is far more sensitive to temperature increases than previously thought, and prone to imminent melting leading to increased and rapid sea level rise.

Terrestrial water storage

As global patterns of precipitation, evaporation, and streamflow change, terrestrial water storage (TWS), which includes all of the surface water, canopy water, soil moisture, and groundwater stored on land, has been shifting rapidly in response. Shifting patterns of TWS threaten water availability and sustainable water management for people and the environment, putting livelihoods and food security at risk, but also contributing to sea level rise.

Zheng et al. show losses of ground water accounting for 0.35mm/year of sea level rise. A recent study by Chandanpurkar et al. broke the trends down further to separate non-glaciated drying from wetting since some regions are experiencing increasing rainfall while others are drying.12 They found that not only do the losses from drying regions amount to more than retrieved through wetting areas, but by far the largest contribution (68%) to drying region loss was ground water - the water that we pump out of the ground for crops, industry and consumption. This activity is draining aquifers worldwide and literally pumping it into the sea in massive volumes.

A new study just published examined the ground water storage implications of the observed increase in precipitation concentration into fewer, heavier events on the land water balance.13 They project widespread relative TWS reductions from future rainfall concentration alone, with 50% of the global population experiencing drying, in turn forcing more pumping from aquifers and natural ground storage.

Then we can add data centre expansion. The average data centre uses 1.7 litres of cooling water per kilowatt hour of energy consumed. This suggests freshwater usage in 2024 by data centres was 705 million tonnes. This could increase to 1,600 million tonnes by 2030 and potentially more than 2,000 million tonnes by 2035 as the industry expands AI rollout. If you prefer to think in terms of Olympic swimming pools, that equates to a current usage of 775 pools per day in 2024 increasing to 1,750 a day in 2030 and 2,250 a day by 2035. It may only increase ground water use by ~2%, but it all ends up raising sea levels.

Atmospheric water vapour

As the air warms it is able to hold more water vapour. This is in accordance with the Clausius–Clapeyron relation which holds that for every 1°C of temperature increase, the atmosphere can hold 7% more water vapour. Observations and reanalysis confirm that today’s atmosphere does indeed have a growing specific humidity. This is water that is actually reducing sea levels, but before you get too hopeful, the level is just -0.05mm per year.

Projected rises

There are two aspects involved in predicting future sea level rise and therefore informing adaptation and resilience planning. There is the amount of sea level increase that is already committed to and cannot be avoided, and there is future rise rate that is dependent on the rate of global warming and therefore a combination of our emissions trajectory and the climate’s sensitivity.

The Royal Society published a report where the authors assessed the likelihood of lower IPCC sea-level rise scenarios (SSP1–1.9 and SSP1–2.6) in light of current ice-sheet observations and model limitations, alongside today’s emissions trends and current shortfall of climate commitments.14 They concluded that ‘low-end’ projections may underestimate the true pace and magnitude of future sea-level rise and, if we continue on today’s mid-higher emissions pathway (SSP3–7.0), sea-level outcomes of more than 1m by 2100 should be planned for and that rises of more than 2m this century and several metres thereafter are a real possibility.

Whilst this is the global average, due to currents, gravitational and other effects, regional changes may be even greater. For example an AMOC weakening is believed to cause up to 1m of additional sea level rise in the north Atlantic coastlines on top of the global trend.15 Since the latest research points to a 50% weakening within 75 years,16 coastlines of the eastern US, Canada and northern Europe should be planning for at least a 1.5m rise and considering the risks of over 2m this century.

Deep emissions cuts and scaling of carbon removal could help to shave the peak from these projections, but most of the rise is now unescapable regardless of our actions, so adaptation is key. It is also worth noting that the rise to date has been fairly steady, albeit with acceleration. There are however significant jumps ahead, not least in the form of Thwaites losing its ice sheet buttress. This will be followed by many others around Antarctica and Greenland. The sleeping giants are awakening. There is no time to lose.

This is why organisations such as the Collectif Montée Des Eaux are working so hard to draw peoples attention to, and help France prepare for the inescapable sea level rises to come. They advocate planning and preparing now for 1.2m by 2100 and 1.5m by 2125. Given the weight of evidence, this makes perfect sense.

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The climate and Earth system modelling work for IPCC and other reports leans on sets of pathways or scenarios that describe potential climate policy directions. The first set was developed between 2009-2011 and was used for the modelling work in CMIP5. The fifth round of the Coupled Model Intercomparison Project (CMIP). It was called Representative Concentration Pathways (RCPs) and focused strictly on the outcomes of human activity—specifically, atmospheric greenhouse gas concentrations and the resulting radiative forcing (measured in Watts per square meter, W/m²) by the year 2100.

The main pathways were RCP2.6 (low warming), RCP4.5 and RCP6.0 (intermediate warming), and RCP8.5 (high warming/expanding fossil fuel use). RCPs provided the climate models with target physical numbers, but they didn’t explain how society would get there. There were no integrated political, economic, or demographic narratives attached to them.

The next iteration was the development of the Shared Socioeconomic Pathways (SSPs) between 2015 and 2021. These are the pathways currently in use by CMIP6. These introduced five distinct global socioeconomic narratives detailing how population, education, technology, and geopolitics might evolve over the century.

The Core Narratives were:

SSP1: Sustainability (”The Green Road”)
SSP2: Middle of the Road
SSP3: Regional Rivalry (”A Rocky Road”)
SSP4: Inequality (”A Divided Road”)
SSP5: Fossil-fuelled Development

Climate scientists combined these five human storylines with the physical forcing outcomes of the RCPs. For example, SSP5-8.5 represents a world of rapid, fossil-fuelled economic growth resulting in the extreme 8.5W/m² forcing. This SSP framework powered the IPCC’s Sixth Assessment Report (AR6), completed in 2023.

A new set is being developed for CMIP71 which will be used for the next IPCC report (AR7) to be published around 2028-2029. Headlines have focussed on the removal of the old, very high end SSP5-8.5, which is increasingly viewed as implausible given the global rollout of renewable energy and increasing fossil fuel extraction costs. Deniers have pounced on this news, claiming that earlier climate predictions have been over-hyped, which is just not true, but when has that ever stopped them

Instead of just telling climate models what the greenhouse gas concentrations will be, CMIP7 will run more scenarios in an “emission-driven” mode. This allows the models to calculate their own carbon cycle feedbacks, providing a more accurate picture of climate uncertainty. It also allows feedbacks such as permafrost melt to add to the emissions within the models rather than be somehow included in the budgets.

The high end scenario, conveniently named “High”, shows continued emission growth to the end of the century, effectively replacing SSP5-8.5 but at a more realistic level of emissions growth set against current reality. It represents a scenario where current climate policy is rolled-back and fossil fuel burning and deforestation continues to grow.

The goal of the modelling work to come is then to calculate the Earth’s response to these emission trajectories, while reflecting current geopolitical realities, updated economic data, and the landscape of international climate agreements. As such some of the scenarios indicate emission pathways that allow the Paris 2ºC goal to be met. Interestingly none of them constrain temperatures below the 1.5ºC target since that is now basically impossible (without solar radiation modification). The new “Low-Negative” scenario could achieve a return to below 1.5ºC but later in the 22nd century.

The new scenarios

Seven emission scenarios are proposed. These can be divided into baseline scenarios and mitigation scenarios. High and Medium are based on continued emissions consistent with rolling back current policies (High) and a steady state pathway consistent with policies frozen as of 2025 (Medium). These are the baseline scenarios. Both result in more than 3ºC of warming by 2100, continuing to increase thereafter. A new High-to-Low scenario follows the High emissions pathway until after mid-century then a rapid decline to net-zero by the middle of the next century. It tracks a world that reaches 3ºC, then either suffers economic collapse (as suggested by the Institute and Faculty of Actuaries for a 3ºC world2), or humanity makes a collective decision that enough is enough and rapidly cuts emissions voluntarily.

The remaining four scenarios all have varying degrees of ambitious decarbonisation and emissions reduction, striving to meet the Paris goals. These are the mitigation scenarios. Medium-to-Low follows the Medium pathway to 2050 then strives for net-zero CO₂ by 2100. Low strives for 2ºC by 2100 with net-zero GHG (not just CO₂). Very Low strives for 1.5ºC by 2100 with rapid emissions decline and a low overshoot. Finally Low-to-Negative follows the Low scenario but uses more negative emissions to hit 1.5ºC by 2100 but with a higher overshoot than the Very Low scenario.

The keen eyed may have noticed that figure 1 is slightly different from the graphs provided in the Van Vuuren paper, included in the header image. This is due to the paper’s figures being illustrations rather than taken from the latest CMIP7 data files, which were still under development when the paper was submitted.

Where are we now?

All scenarios start at the measured 2025 point in terms of emissions. Incidentally this is another reason for dropping SSP5-8.5. Since its formulation in 2015, emissions have not grown to the extent suggested in the 10 years since then. Temperature have done, as has the radiative forcing which is actually higher than all the SSPs including SSP5-8.5, but that’s for the models using the emissions scenarios to sort out.

Predicting the future is obviously very difficult but it’s probably a fairly safe bet to go along with the IEA 2025 report for Energy related CO₂ emission which suggest very little change out to 2050. This would suggest the Medium scenario is the most likely in the short term. Given current geopolitics and the tightening grip of the fossil fuel lobby supporting right-wing politics in many countries, the chances of a short term switch to Medium-to-Low or Low are slim. The chances of following Very Low or even Low-to-Negative are negligible in the short term.

However, the world continues to change, even in the short time since the IEA analysis and the CMIP7 scenarios were developed. The US-Israeli war on Iran and the subsequent blockades of the Straight of Hormuz will have an impact. According to the IEA May 2026 Oil Market Report3, cumulative oil losses to date exceed 1 billion barrels. 14.4 million barrels a day is shut in. An increase in production in other areas is providing 3.5mb/d with the shortfall coming from stocks and reserves. That rate of reserve extraction is unsustainable though. Price increases and supply problems will soon start to destroy demand, leading to the IEA now forecasting a drop in annual demand in 2026 compared to 2025. Long term, the resultant and inevitable economic recession is likely to push emissions down, possibly to 2005 levels for a decade (similar to the effect of the 1970s oil crises). Many countries are seeing the added security and reliability benefits of switching to renewables too. We could therefore see the blue stated policy scenario in figure 2 play out, without the need for the policies themselves.

Against this is a rise in coal use as gas becomes more expensive and also the continuing rise in AI datacenter expansion, which is increasingly relying on gas for energy generation, both as a stopgap while grid connections are established, and as a long term plan.

On balance, given current circumstances, in my humble opinion, we will be lucky to stick to the Medium scenario with no further increase of annual emissions, but unlikely to follow the High scenario, at least until 2040.

It’s important to note however, that these are just the human emissions. As temperatures rise, natural emissions from permafrost melt and wildfire continue to rise. These will have to be added to the new scenarios within the climate models as feedbacks.

Carbon Dioxide Removal

Current trajectory puts us clearly on the path to a 3ºC world, not just by the end of the century, but by keeping emissions high, the current rate of warming will persist at best, and continue to accelerate at worst. 3ºC by 2060 with 2ºC passed in the 2030s is likely, unless things change radically.4

This brings us neatly to the mitigation scenarios for CMIP7. To follow any of these, varying levels of negative emissions are required. That means to achieve them, humanity needs to develop, scale and deploy Carbon Dioxide Removal. But how much?

Figure 3 shows the negative emissions area on the annual CO₂ emissions scenario graph. It’s substantial to say the least. Even the Very Low scenario passes net-zero by 2055 but then relies on negative emissions ramping to 5Gt a year from 2070 through 2300 - over 200 years, totalling 1,125Gt!

Medium-to-Low, our most likely best chance, requires net-zero by 2100 then ramping to 13Gt/year of removal from 2125 onwards. A total of 5,400Gt.

That is just part of the story though, since in order to get from where we are today with our likely short term emissions locked in, to follow any of these mitigation pathways, CDR will be required to achieve net-zero in the first place.

For example, If we assume we are going to follow the Medium path, plateaued emissions for 25 years then declining to net-zero by 2200, the resulting 4ºC+ warming will be catastrophic. To switch to a different scenarios will require CDR to correct the course down to either the Medium-to-Low, Low, or Low-to-Negative paths. We can simply subtract the path’s emissions data to show the level of CDR that would take.

Figure 4 shows the CDR required to run alongside a Medium emissions scenario but follow the safer trajectories. None of these are going to be easy, but with little hope of survival if we don’t try, what are the options? Even so peaking at over 60Gt a year of CDR does seem a little, um, ambitious???

Proposed methods

The CMIP7 emissions scenarios do not directly account for how the CDR will be implemented, that’s not its role. It is for the following Integrated Assessment Models (IAM) to implement within their Earth System Model runs. The paper does however cover the main forms that are anticipated to be applied.

“Currently, a broad range of CDR methods is being discussed within the policy communities and considered as part of climate action plans. IAMs only represent a subset of these approaches to date however. The main CDR methods represented in IAMs are Bioenergy with Carbon Capture and Storage (BECCS), Direct Air Capture with Carbon Storage (DACCS), and afforestation and reforestation. In addition, IAMs are exploring new CDR methods such as biochar, soil carbon sequestration, enhanced weathering, storage in long-lived materials, agroforestry, improved forest management, and ocean-based CDR, although only a subset of those are included in most scenarios.”

Models will then have to experiment with different methods, locations, scales and feedbacks within the carbon cycle to generate the planet’s response, suggesting scenarios that can inform policy makers.

how the global economy pays for this level of CDR is another question entirely…

Climate Stabilisation and Solar Radiation Modification

The scenarios also show the increasing need for some form of climate stabilisation strategy involving solar radiation management or other forms of geoengineering. If we can’t develop, scale and deploy CDR within the next decade, this will be the only and last chance to avoid 3ºC. It may even be the only chance, given that CDR will take a very long time to have any impact on temperatures, given the long lag times between reduced atmospheric CO₂ concentrations and a slowing of the warming.

Until net-zero is achieved, temperatures will continue to rise, so emissions reduction and CDR to gradually reduce net emissions will only slow the rate of warming, not stabilise temperatures. Meanwhile tipping point risks increase and sea levels continue to rise. The planet also does not care where the emissions come from, so net-zero means all the natural, heat induced emissions too, not just our direct emissions. By mid century, permafrost emissions could rival those of the US, so this is not a trivial addition.

Just as Democracy is the worst form of government apart from all the others, solar geoengineering is the worst thing we can do apart from not doing it and entering a 3ºC world. It’s a conversation we need to have.

Final Thoughts

Some areas of the media and notable deniers have pounced on this paper as a way of saying that the highly warming SSP5-8.5 being dropped shows that the whole climate crisis was overexagerated. This is completely WRONG WRONG WRONG, it shows that efforts to date to slow fossil fuel burning have worked to the extent where our worst case Drill Baby Drill future has been avoided. We are still in deep trouble, but it could have been worse. Having said that the temperature acceleration and rise in Earth’s Energy Imbalance have met and exceeded SSP5-8.5, despite us roughly following SSP2-4.5 for a decade. It could have been a lot lot worse. Figure 5 posted by Prof Ryan Katz-Rosene shows the total effective radiative forcing exceeding all the SSP scenarios.

To me, the new scenarios are, if anything, even more worrying than the old ones however. They show that we have passed the point of ‘easy’ return. Our climate account is massively overdrawn, and huge levels of CDR are now required to avoid disaster. It’s certainly not clear if that is even achievable, which is extremely worrying. In fact, a 3ºC world with everything that entails, is very likely even with hugely ambitious and expensive CDR. Solar Geoengineering is becoming increasingly inevitable.

These new scenarios will promote some interesting modelling in coming years, pointing to the facts of our predicament, the trouble is - facts are soluble in fossil fuel revenues.

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Today, May 22nd 2026, is the UK’s Overshoot Day.1 It is the day we officially “break the bank” of the UK’s share of the Earth’s natural resource budget for the year. But to understand why we hit this limit so early, we have to look past our electricity smart meters and look at our Energy Elephant.

The 3,800-Watt Human

Biologically, you are a 120 Watt organism—about the same as a bright old-fashioned lightbulb. But once you factor in the “Total Consumption Footprint”—the energy required to mine the metals in your phone, grow your food in global greenhouses, and ship your purchases across oceans—your true power rating leaps 32 times to 3,800 Watts.

To keep you functioning as a member of the UK economy, the global energy system must “burn” roughly 78,500 kcal every single day just for you. A huge amount more than the 1,800 kcal you need to maintain your physical presence. Also a huge amount more than the average UK citizen before the Industrial Revolution who lived entirely on 7,250 kcal, equivalent to the metabolic rate of a large dog like a St. Bernard.

The Elephant Equivalent

An adult African Elephant has a metabolic rate of approximately 80,000 kcal/day.

Essentially, every person in the UK is trailed by a “ghost elephant” of energy. We may have closed our coal mines and cleaned up our local grid, but we have replaced that domestic energy with embodied energy imported from abroad. We are effectively a very crowded nation of 70 million people and 69 million invisible elephants.

We are far from the worst though, each US citizen is followed by not one, but 2.6 elephants, or one 40 foot long Sperm Whale.2 This is not just gluttony or waste, logistics are longer, there is more need of AC and homes tend to be larger. The global average is just over 50,000 kcal, so a Bottlenose Dolphin or large Brown Bear. 8.4 billion of them!

The Efficiency Mirage

We often hear that the UK has “decoupled” its growth from energy use. While it is true our domestic energy use has fallen, our consumption-based footprint tells a different story. We are one of the world’s largest net importers of embodied energy. We have offshored the “heavy lifting” to manufacturing hubs like China and Vietnam, but the energy bill—and the ecological impact—still belongs to us.

A New Weight Class

As we cross the threshold into “ecological debt” today, the goal for the next decade isn’t just to swap gas boilers for heat pumps. It’s to address our Total Metabolic Rate and our reliance on energy-heavy global supply chains.

We need to figure out how to maintain our high quality of life while slimming our energy ghosts down from a five-tonne elephant back to something the planet can actually support. More likely we need to downgrade our lifestyle and expectations, but I don’t want to ruin your weekends.

You can look up your country’s overshoot day on this chart, how do you compare?

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A quick heads-up - This article may seem a bit nerdy, but please bear with me, the relevance and importance for future scenarios and indeed our very survival will hopefully come through.

There is a single value in climate science that is more important than all others, but which has a plausible range so large, that policy and planning struggles to rely on reliable risk assessments to take appropriate action. That value is Climate Sensitivity. At its core it is the amount of global average surface warming that will occur if the CO₂ concentration in the atmosphere is doubled.

As the concentration of CO₂ increases in the atmosphere, the planet warms through the trapping of energy by the greenhouse effect, creating a positive energy imbalance. The warming is not instantaneous however, a large number of lags and feedbacks take effect during the warming process. Some are quite fast, like changes in water vapour and cloud behaviour. Others take longer, such as vegetation changes, ocean mixing and heat recycling. Some take millennia, such as the melting of continental ice sheets. Eventually however, the Earth system finds a balance and settles at that new temperature.

That eventual stable temperature increase is referred to as the Earth System Sensitivity (ESS). The relationship is logarithmic, meaning we get the same temperature increase for a CO₂ concentration rise from 250ppm to 500ppm as a rise from 1,000ppm to 2,000ppm. The chart below by Dean Rovang plots the ESS from multiple independent data sources for the last 66 million years.1 ESS is resolved as 8.2 to 9.1ºC for a doubling of CO₂.

ESS however takes tens of millennia to settle out, so using it to predict temperature rises on human timescales is not really much help. Today we have increased the CO₂ concentration by a little more than 50% since pre-industrial times, but temperatures have so far only risen by ~1.5ºC, not the 4.5ºC that ESS would imply.

Instead, scientists turn to something called Equilibrium Climate Sensitivity (ECS). This value is still logarithmic but only includes the fast feedbacks, not the longer term ones. This makes it more useful since it can predict temperature responses on a decadal timescale.

So far so good, but unfortunately it turns out to be very difficult to determine a solid value for ECS. The IPCC’s latest report has the likely range between 2.5º and 4ºC, with a best estimate of 3ºC. Recent works by Tierney2 and Hansen3 have independently arrived at best estimates in the 4.5-6.5ºC range.

To make matters worse, there is some evidence that although ESS stays constant, since the nature of feedbacks change in different climate states, ECS is larger in warmer states than cooler ones, for example a hot house state has no ice to melt. This makes comparisons with paleoclimates difficult. Tierney finds an ECS of 6.5ºC for the hot house PETM but 4.8ºC for the cool house Pliocene.

The difference between the IPCC’s best estimate and those of Hansen and Tierney are stark. They would mean that instead of temperatures stabilising at ~1.5ºC if we stopped emissions today, they would continue to rise to ~2.4ºC in short order. Given that the Institute and Faculty of Actuaries, and others, point to 44-88% GDP destruction at 3ºC4, this is something that needs to be bottomed out, and soon.

There is also evidence that ECS is rate dependent (how fast CO₂ concentrations are rising). Ocean stratification is an example of a phenomena being driven by the rate of heat uptake, trapping heat at the surface where it has a greater influence on air temperatures. Slower warming would allow the heat to be mixed into the deeper ocean, reducing the atmospheric take-up. Same final CO₂ concentration, but different initial temperature response.

As we move deeper into the 21st century, it is becoming clear that ECS is an incomplete yardstick. It treats the Earth as a passive recipient of greenhouse gases, rather than a dynamic system whose very “sensitivity” is not only driven by feedbacks, but also being altered by a range of other human activities.

Anthropogenic Efficacy

As our influence on the planet diversifies, treating the Earth’s response as a singular, CO₂ driven constant is becoming increasingly insufficient. We are simultaneously changing the biosphere and the landscape. We are emitting other pollutants that act to both warm and cool the planet, but these aren’t captured in a simple CO₂ only ECS value. CO₂ Equivalents (CO₂e), which treats other gases as having a relative CO₂ value also fail to capture all these other human influences effectively.

We should instead view climate response through the lens of Anthropogenic Climate Sensitivity (ACS): a framework where the baseline sensitivity of the Earth system is modified by specific human “multipliers.” These dictate how efficiently the Earth responds to the added heat.

In formal thermodynamics, not all units of energy (forcings) are created equal.567 In an ACS framework, a multiplier represents what scientists call an Efficacy Factor. If CO₂ has an efficacy of 1.0, other human activities can be more or less “efficient” at warming the planet per unit of energy they add.

ACS = ECS_baseline × ∑( Forcing_i × μ_i )

Where μ represents the specific multiplier for each anthropogenic driver i. Some have direct radiative effects which can be captured through Effective Radiative Forcing (ERF) but many others escape this method.

The Primary Multipliers

The Cooling Masks: Aerosols and Irrigation

Humanity doesn’t just warm the planet; we also apply “brakes” to that warming, though often unintentionally.

Sulphate Aerosols (μ≈0.6–0.9): Industrial pollution creates a “haze” that reflects sunlight. This acts as a dampening multiplier, masking the true sensitivity of the climate. If these aerosols were removed, the “unmasked” warming would surge. As pollution is reduced, this multiplier will tend towards 1.0 over the coming decades. The reduction of aerosol emissions from shipping fuels is widely believed to be partially responsible for recent ocean warming accelerations.

Agricultural Irrigation (μ≈0.9): By artificially wetting vast tracts of land, we shift energy into latent heat (evaporation) rather than sensible heat (temperature rise), providing a slight regional cooling efficacy. This practice also masks underlying warming. When aquifers run dry and the practice stops, it drives local heat up further, potentially worsening the drought.

The Feedback Primers: Land Use and Soot

Some human activities act as “force multipliers” by directly triggering the planet’s most sensitive feedback loops.

The Bowen Ratio Shift (μ≈1.1–1.3): Deforestation does more than release carbon. By replacing high-transpiration forests with dry pasture or crops, we alter the Bowen Ratio. With less water to evaporate, the surface converts solar energy directly into heat, effectively increasing the local climate sensitivity.

Natural aerosol decline (μ≈1.2–1.8): Aerosols are essential as cloud condensation nuclei but deforestation, changes in farming and land management, and crucially ocean health and pollution are reducing their production. Lower cloud cover and cloud dimming as a result reduces albedo leading to direct warming as well as less rainfall, which in turn reduces evaporation and further Bowen Ratio changes.

Black Carbon on Snow (μ≈1.5–3.0): Soot falling on the Arctic is perhaps the most potent regional multiplier. It doesn’t just trap heat in the air; it darkens the ice, triggering the ice-albedo feedback. This makes soot significantly more “efficient” at driving global melt than an equivalent amount of CO₂. Recent work suggests that micro-plastic pollution also has a similar role, both in the air and within the ocean surface layers.8

The Modern Additions: Aviation, Methane and Ozone

Aviation Contrails (μ≈1.2): High-altitude contrails act as artificial cirrus clouds. While they reflect some sun, their ability to trap outgoing heat gives them a high warming efficacy.9 This is made worse with night flights since the solar reflection aspect is not present. (Not to be confused with so called “chemtrails” which is a baseless conspiracy theory)

Methane’s Chemical Tail (μ≈1.45): Methane is a potent gas, but its multiplier is high because it chemically produces ozone and stratospheric water vapour as it decays. These are both greenhouse gasses so our emissions add “bonus” warming layers to its initial greenhouse impact.

Stratospheric ozone depletion (μ≈0.5-0.8): While ozone depletion is a significant concern, it does create a cooling efficacy since ozone is a greenhouse gas. Its depletion in the stratosphere has historically provided a slight cooling offset, particularly in the Southern Hemisphere, by allowing more long-wave radiation to escape to space.10

Even moving to a green hydrogen economy leads to hydrogen leakage, which inhibits methane destruction in the atmosphere creating an amplifying multiplier if we were to take this path. Fortunately basic economics will likely prevent this.

The Rate and State Problem

Traditional ECS assumes a slow move toward a distant equilibrium. But human influence is fast and messy. There is a rate dependency not just in terms of feedbacks such as ocean warming but also between different emissions. High-efficacy forcings, like aerosols, react in days, while CO₂ reacts over centuries. This creates a transient sensitivity that can look much higher or lower than the theoretical equilibrium.

A pattern effect also exists. Where we act matters. A multiplier isn’t just about what we do, but where. Forcings in the tropics or the Arctic have higher leverage over the global temperature than those in the mid-latitudes since they disproportionally affect evaporation and cloud forming in terms of the tropics and albedo at high latitudes.11

The Socio-Economic Crossroads: SSP2-4.5 vs. SSP3-6.0

The ACS framework also reveals how different socio-economic pathways (SSPs), or emissions scenarios fundamentally change the Earth’s effective sensitivity. This in turn changes the outcomes adding more emphasis for the need to choose the safest trajectories and the right policies to achieve them.

SSP2-4.5 (The Middle Road): This pathway manages a slow unmasking of the dampening multipliers. As we gradually reduce pollution, the aerosol multiplier slowly moves toward 1.0. Because the transition is managed, we hopefully avoid termination shocks with rapid warming and the ACS stays relatively close to the baseline. This pathway also sees methane emissions gradually reduce, lowering this warming multiplier. Land use change also slows, hopefully the Bowen Ratio avoids biosphere tipping points. The end result is a predictable steady climb in temperatures where ACS stays close to baseline ECS.

This is not great though, temperatures continue to rise with all the effects of a growing climate crisis, but without catastrophic rapid changes.

SSP3-6.0 (Regional Rivalry): This is the “Multiplier Trap” since it maximises the amplifying multipliers while keeping the dampening multipliers for longer, masking the true warming. High nationalism leads to dirty energy use, keeping the aerosol mask heavy (μ≈0.65) while methane and deforestation run rampant (μ≈1.45 and 1.3). This creates a “spring-loaded” climate: a massive amount of hidden warming is suppressed by pollution, waiting for a tipping point to release it. This pathway is characterised by significant land-use change and rapid deforestation. This shifts the energy balance toward sensible heat across vast areas (the Amazon, Congo, SE Asia), effectively “priming” the local climate to react more violently to CO₂ increases.

The Net Result is that SSP3-6.0 has a higher “Hidden Sensitivity.” The gap between the observed temperature and the “latent” temperature (what would happen if the aerosols cleared) is much wider than in SSP2-4.5. Both have a time limit where climate damage reaches such a level that humanity is forced to react, either voluntarily, or through collapse. The pathway we take between now and at that point, therefore has a huge impact on the fall out and potential for recovery.

Tipping Points

Humanities choice of pathway also influences tipping point thresholds. These are often not just critical temperature points, but are influenced by other factors, factors that are also multipliers in the ACS framework.

The Amazon is a good example. A recent paper from the Potsdam Institute for Climate Impact shows that deforestation, making changes to the Bowen Ratio multiplier, lowers the temperature threshold for collapse.12 Without deforestation, the Amazon could survive 4ºC of warming, but when a critical level of deforestation (22-28%) is reached, that temperature thresholds drops to less than 2ºC. Essentially the point where the two lines cross spikes the land use multiplier. The energy partition shifts so heavily toward sensible heat that the regional atmosphere dries out, extending the dry season by 4–5 weeks and preventing the forest from recycling moisture. Current levels are about 18%.

Under an SSP2-4.5 scenario, deforestation is curtailed, keeping the multiplier around 1.1 for much longer, possibly forever. Under SSP3-6.0 the multiplier climbs to 1.3+ as deforestation exceeds 25%. This in conjunction with failure to lower methane emissions elevates the ACS to the point where the Amazon collapses in the 2040s under this pathway.

Similar observations affect the southern boreal forest die-back, but it may actually provide a negative feedback for Sahel greening. Increasing CO₂ together with southerly moving monsoon patterns could lead to a greening multiplier of 0.85-0.95 as evapotranspiration and local Bowen ratios improve.

Net-Zero and True-Zero

The ACS framework also creates insights into the net-zero goal. It reveals a fundamental tension in climate policy: the difference between stopping emissions entirely and simply “balancing the books.” In the multiplier framework, these two paths lead to very different “effective” sensitivities during the critical 2030–2050 window.

Net-zero allows for residual emissions such as aviation, cement and heavy industry as long as they are balanced by Carbon Dioxide Removal (CDR) such as direct air capture and reforestation. The danger highlighted by this framework is that replacing 1 tonne of CO₂ emission with 1 tonne of removal may not balance the multipliers. The CO₂ may be balanced, but aerosol and soot emissions may continue that are not accounted for. The results would be a smooth temperature curve with less volatility, but a higher risk of “sensitivity creep” if the high-multiplier gases (Methane, Soot) aren’t prioritised over simple CO₂ math.

True-zero or an absolute clean up implies a total cessation of all human emissions with no offsets, no carbon removal, no excuses. Depending on the rate of achieving it, the reduction in aerosols would match the reduction in methane so ACS could fairly quickly revert to baseline ECS. This is because both aerosols and methane are short-lived climate pollutants, an absolute halt to emissions causes both multipliers to drop out simultaneously, preventing a catastrophic thermal spike. This is more of a total civilisational collapse scenario than a managed transition though.

Net-zero will be a delicate balancing act where we must ensure the high-multiplier influences (like methane and deforestation) are phased out faster than the low-multiplier ones (like aerosols) to avoid a sensitivity-driven overshoot. ACS provides a metric for this that simple carbon reduction accounting misses.

Overshoot and CDR

Now that it is obvious to everyone that the lower Paris 1.5ºC target will be breached, the conversation has moved to overshoot and recovery. How little time can we spend above 1.5º, what maximum temperature will be encountered and how do we get back below it? To that end the new pathways for CMIP7 and the next IPCC round of reports have been suggested.13 There are seven in total that replace the SSP range discussed above. All but two of them include huge levels of Carbon Dioxide Removal (CDR) as they are designed to limit temperatures to within the Paris goals (2ºC by 2100).

The ACS framework introduces a vital aspect to this recovery, that of the asymmetry of cooling.

When we pull carbon out of the atmosphere using Carbon Dioxide Removal, the planet does not simply reverse the warming track it took on the way up. The multipliers behave differently when emissions are net-negative compared to when they were rising. This asymmetry is central to calculating how hard, fast, and long we have to deploy negative emissions to stabilise or lower global temperatures.

Through the lens of ACS, we can extract several critical insights regarding overshoot recovery:

The Hysteresis Trap: Multiplier Asymmetry

The assumption built into many simple climate models is that if you remove 1 ppm of CO₂, you undo the exact amount of warming that 1 ppm caused. In reality, Earth system components exhibit hysteresis—a lag or permanent change in response.

In the ACS framework, the multipliers are state-dependent. On the way down, the “initial climate state” has been altered by the peak of the overshoot:

The Carbon Sink Weakening Multiplier (μsink >1.0 on the way down): When CO₂ was rising, the ocean and land biosphere absorbed roughly half our emissions (the solubility and fertilisation pumps). During net-negative emissions, however, the ocean and land start releasing stored CO₂ back into the atmosphere to maintain equilibrium. CDR has to work twice as hard because it is fighting a “burping” planet.

The Albedo Memory Loss (μalbedo >1.0 on the way down): If an overshoot melts a major ice sheet or thins the Arctic pack ice, lowering the temperature via negative emissions does not instantly refreeze that ice. The dark ocean or land remains exposed, meaning the albedo multiplier stays stubbornly high long after the CO₂ concentration drops.

The Bowen Ratio Permanence (The Irreversible Amazon Shift)

If an overshoot triggers a tipping point, like the 22%–28% deforestation limit in the Amazon or a major Boreal dieback, the regional multiplier changes permanently. During Rising Emissions, μland_use creeps up as forest is cleared, converting latent heat to sensible heat. During Net-Negative Operations, even if we deploy high-tech Direct Air Capture (DAC) to lower global CO₂, it doesn’t automatically replant the Amazon or heal a scorched Siberian Taiga. The biome has permanently shifted to a savanna or steppe state.

The lesson from ACS is that a permanently damaged biome fixes the regional Bowen Ratio multiplier at a high level. Thus, the post-overshoot ACS remains higher than the pre-overshoot baseline, meaning the planet will remain warmer for a given level of CO₂ than it was in the 20th century. The IPCC suggest returning to 350ppm of CO₂ will create a safe climate, ACS begs to differ, if anything levels even lower than the pre-industrial 280ppm may be required for a significant period to return the cryosphere to a stable state.

CDR Strategy: Matching Method to Multiplier

Not all net-negative strategies are equal. The ACS framework implies that instead of just pulling generic carbon equivalents out of the sky, CDR must target specific, high-leverage multipliers to optimise cooling such as:

High-Efficacy Methane Removal: Because methane dictates short-term rate dependencies and has an expanded chemical efficacy multiplier, targeted atmospheric methane destruction yields immediate dividends. Stripping a ton of methane drops the effective ACS much faster during an overshoot than stripping an equivalent radiative unit of CO₂.

Enhanced Ocean Alkalinity, when applied directly to the ocean, or on large coastal agricultural scales this changes ocean alkalinity allowing it to absorb more CO₂. This directly counteracts the weakening ocean sink multiplier (μsink ), preventing the ocean from outgassing its stored carbon back into the atmosphere during the ramp-down phase.

Bio-Energy with Carbon Capture and Storage (BECCS) removes CO₂ by growing crops which are then processed and burned for power generation, but with the emissions captured and permanently sequestered. This would have a positive influence on ACS since any Bowen ratio improvement through crop evapotranspiration would be in addition to the CO₂ removal. This is assuming that the land to grow the crops was not cleared forest. In fact the multiplier would have to be based on the alternative use for the land. More cooling may be achieved through reforestation than using the land for BECCS, regardless of the CO₂ reduction.

Designing the Overshoot Recovery Equation

Using ACS for overshoot analysis teaches us that “cooling is not simply warming in reverse.” The paths are asymmetrical, and a temporary thermal overshoot leaves permanent scars on the Earth’s feedback mechanisms, meaning the planet we return to will possess a fundamentally altered climate sensitivity.

Even more complexity could be added if we resort to Solar Radiation Management as an emergency cooling measure. That too will have to be carefully managed to ensure the multipliers are considered as part of the design and monitoring.

Conclusions

Climate change is often discussed in terms of how much carbon. The ACS framework argues it is also a matter of how much sensitivity. The ECS is a vital theoretical yardstick, but the Anthropogenic Climate Sensitivity, the ECS as modified by our specific suite of multipliers, is what we actually live through. By quantifying these factors, we move away from a world where we simply “wait and see” how the planet warms, and into a world where we can precisely identify which human levers are the most dangerous to pull and manage their release in an orderly transition.

By understanding that our actions—from the way we farm to the altitude at which we fly—directly tune the Earth’s responsiveness, we gain a more nuanced view of the risks ahead.

Due to current aerosol emissions and lags within the system, we are currently in a climate debt, apparently unaware of the true balance of our account. The ACS framework provides a way of attributing this and other multipliers to calculate the value of this subsidy, and how to pay it back.

We are not just changing the temperature; we are changing the very rules by which the Earth’s climate operates. To navigate the 21st century, we may need to manage the multipliers as aggressively as we manage the emissions.

So what is the result? Proper data needs to be collected to calculate each multiplier, but a back of the envelope estimate, based on the numbers shown above suggest an ACS of ~1.8 x ECS. So using IPCC’s 3ºC gives us a current ACS of ~5.4ºC. That suggests a stable temperature of +2.7ºC for our emissions and actions to date, once the energy balances out. That’s not unreasonable given how hard the Earth is trying to warm as the energy imbalance continues to climb. If we were to achieve net or true zero, however the methane and aerosol multipliers would slide back to 1.0 leaving legacy deforestation and other long term pollutants alone. Temperatures could then settle out at ~1.7ºC. Food for thought.

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After decades of bucking the melting trend, the huge ice masses of Antarctica are now in trouble. Sea ice is receding, weakening the ice buttress effect, warmer water is creeping under the floating ice and ice canyons are forming that amplify the melting from below. Astonishing glacier retreat is also being observed, all of which speeds up the flow of land ice into the oceans, raising sea levels at an accelerating rate.

A set of new peer reviewed papers paint a worrying picture for the future of coastal cities and low lying communities around the world.

First, a little bit of terminology: Large area of ice on land are called “ice sheets”. At their edges, they flow in ice rivers down towards the ocean in “glaciers”. When they reach the shoreline and start to float, they are called “ice shelves”, small ones are called “ice tongues.” “Sea ice” is not from the land at all, it is frozen sea water which grows and recedes with the seasons. Sea ice does not affect sea level but land ice entering the ocean does.

Sea ice loss since 2016

Sea ice is critical to ice flow in Antarctica. Since the continent is so cold, it doesn’t melt from the top as the Arctic is doing. Instead glacial flow is regulated by a combination of a buttressing effect from the sea, holding the ice on land, and from sub-surface melting when the ice floats offshore and is exposed to warm water beneath it.

Figure 1 below shows the Antarctic sea ice anomaly. From the mid 1990s the sea ice extent was actually slowly growing, until something radically changed in 2015/16. That sudden drop has not recovered in the decade since then. A new paper has uncovered a triple whammy of causes that drove this decline and now prevents any chance of recovery.

The new paper, led by Dr. Aditya Narayanan1, shows that three critical changes drove the collapse of the sea ice, a collapse so great that the area now missing since 2016 is equivalent to the land area of Greenland.

Firstly around 2013, strengthening winds began pulling warm, salty water from the deep ocean, known as Circumpolar Deep Water, closer to the surface. Then in 2015, intense winds mixed the deeper heat directly into the surface layer, rapidly melting the sea ice, particularly in East Antarctica. Since 2018 the ice-ocean system has become trapped in a cycle where, with less ice to melt, the surface remains salty and warm, inhibiting new ice from forming.

In addition to this, the old ice regime was reflecting a lot of the sun’s incoming energy back out to space, whereas now the exposed ocean absorbs it, warming it further, also inhibiting the freezing process. Lower sea ice area also allows ocean waves to reach further towards the ice shelves which have the potential to stress the ice, enabling faster crack formation, fractures and collapse.

The study also found a striking asymmetry in how the ice is retreating across the continent, with East Antarctic loss almost entirely ocean-driven, fuelled by an upward surge of warmer deep water. While, in West Antarctica, heat was trapped in the ocean by intense cloud cover, which was funnelled by warm air from the subtropics down to the pole, melting the sea ice during the summers of 2016 and 2019 especially.

The Circumpolar Deep Water

Antarctica sits in the centre of the vast network of ocean currents that link all the ocean basins together. Figure 2 illustrates this showing the Circumpolar Deep Water (CDW) in the centre. The CDW upwells as the waters above it overturn and form deep dense waters that flow down to the abyss. As it upwells it brings nutrients and carbon to the surface, fuelling biological productivity and influencing air-sea carbon exchange. It also brings heat. Not that you’d want to swim in it, but warm enough above 0ºC to allow the ice floating in it to melt.

A newly published study by Joshua Latham et al.2 used two sets of independent measurements to track the latitudinal position of the CDW as it has changed over recent decades. They examined data from repeated ship-based transit observations and ARGO float studies. The ARGO project is an international collaboration involving thousands of autonomous “floats” which dive to depth to track current strengths and take temperature, salinity and other measurements as they return to the surface before beaming their data via satellite.

Both these independent analyses revealed an increase in upper 2,000m warm water thickness near Antarctica, consistent with a poleward shift of the upper Circumpolar Deep Water core of 1.26km per year. This shift brings more heat towards the Antarctic shelf, where it influences sea ice as described earlier but also allows heat to flow beneath the floating ice shelves melting them from below.

Under the ice

The stability of Antarctic ice shelves, which regulate the flow of grounded ice into the ocean, depends critically on ocean-driven basal melting, since the air above is too cold to melt the ice exposed to the air. The intrusion of the CDW warm waters beneath the ice is therefore critically important. However the topology of the underwater ice is also a factor. A smooth, level, underwater surface allows a stable cold zone to be created, insulating the ice from the warmer waters only slightly beneath it. Basal cracks, crevices and channels, all widespread features beneath many ice shelves, however heavily influence ice-shelf basal melt rates and influence ice-shelf stability.

A new study by Qin Zhou et al.3 examined the influence of these underwater ice features on the Fimbulisen Ice Shelf in Eastern Antarctica. They found that channel features in the base of the ice generate localised eddies and overturning that traps the intruding warm Circumpolar Deep Water beneath the ice, amplifying melt rates by an order of magnitude within the channels. This ocean-driven process significantly enhances the sensitivity of the ice shelf to ocean warming. There is also a feedback mechanism whereby the resulting differential melting promotes channel growth, enhancing the localised melting even further. This then has the potential to undermine the structural integrity of the deeper part of the ice shelf making it more susceptible to wave and tidal stresses. Their results reveal a key mechanism for basal channel evolution and indicate that even modest CDW intrusions could have important implications for the stability of even the coldest of Antarctic ice shelves.

The Hektoria warning

The Hektoria Glacier on the Eastern Antarctic Peninsula underwent an unprecedented retreat of ~25 km from January 2022 to March 2023. At the peak of the retreat, it lost 8km in just two months. A pre-print paper by Naomi Ochwat explains the process.4

Famous examples of ice shelf collapse include the Larsen A, Larsen B and Wilkins Ice shelves. These all acted as buttresses holding back land ice which has since accelerated. Hektoria is linked to the Larsen B collapse but characterised by a flatter seabed base. The loss of the ice buttress caused the glacier to increase in speed by 6 times. This resulted in a thinning of the ice by a massive 40 times. Thinning rates of 80m per year were recorded. Eventually the ice was so thin that it left the bedrock to float in the sea water. The water penetrating beneath the ice worked on cracks and channels as described earlier, wearing the shelf allowing it to crack and calve buoyancy driven burgs rather than the previous tabular burgs. The resulting retreat was an order of magnitude faster than any reported in the modern record.

The Antarctic Peninsula is warming faster than the rest of the continent so it provides a living laboratory to study future melting and collapse mechanisms around the continent. Observations like this are therefore extremely worrying.

Paleo evidence of rapid melting

We know from Paleo records that extensive Antarctic melt happened in previous interglacial periods. During the Eemian, 125,000 years ago, temperatures were between 0.5 and 1.5ºC above pre-industrial, roughly where we are today. Sea levels were up to 10m higher than today though, which suggests much more melting from Greenland and Antarctica than we have yet to experience. A now famous study from 2023 confirmed that much of the West Antarctic Ice Sheet melted away at this time through the tracing of Octopus DNA.5

They found compelling evidence of gene flow between Antarctic Octopus populations in the Weddell Sea and Ross Sea that could only have occurred if transcontinental open water existed between them during previous interglacials. A region currently completely locked in by ice all the way to the bedrock.

A 2025 study by Karen Vyverberg et al.6 tracked sea level rise rates from the Eemian using fossilised coral reefs in the Seychelles. They tracked abrupt changes in Eemian sea levels to episodes of ice loss and regrowth that were out of sync with each other in the northern and southern hemispheres. The rates of change detected implied greater temperature sensitivity of the ice sheets than currently inferred or modelled.

Implications for sea level rise

These past changes during the Eemian and other interglacials occurred in a climate similar to todays, but cooler than the temperatures we are rapidly heading towards. Evidence from Greenland also shows complete ice sheet collapse in previous interglacials, such as radiometrically dated pollen and seeds at the bottom of 3km deep ice cores from the centre of the continent.7 By 2050, the world is highly likely to be warmer than at any time during these previous warm spells. The implications for ice melt and therefore sea level rise are obvious.

Figure 3 from the IPCC report of 2023 shows the projected sea level rise against the range of emission pathways. Obviously the higher the emissions, the faster the rise, but note that even the very low scenario, where net-zero is achieved and temperatures stabilised, shows a continuing rise in sea levels that we have already locked in. This is due to the huge inertia involved in melting the world’s ice sheets. If we want to stop the melting completely, we don’t just need to keep temperatures below 1.5ºC we need to reduce them all the way back to the pre-industrial, or 0.5ºC at the most.

The dashed line in the IPCC graphic presents the low likelihood rise including many of the phenomena now described as being observed above. It is also worth noting that although we are currently following the “intermediate” path in terms of our emissions, warming and Earth’s Energy Imbalance are following or even exceeding the very high model trajectories. Rapid and accelerating sea level rise is becoming more and more likely in the coming decades.

Figure 4 from the Universe of Colorado tracks current sea level rise rate and rate of acceleration.

Figure 5 is a NASA data plot showing the mass of ice on Antarctica declining this century. All that mass of ice is now in the sea adding to the sea level. These new studies suggest this mass loss will accelerate in the coming decades, leading to accelerating sea level rise affecting hundreds of coastal cities and communities, affecting billions of lives.

The question is not if sea levels will continue to rise, but how quickly.

The following maps in figure 6 from Climate Central show the land area expected to be below annual flood level by 2050. Follow the link to look up your area.

What happens in Antarctica, doesn’t stay in Antarctica.

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I occasionally receive comments stating that CO₂ is not warming the planet or driving climate change, but its water vapour that is to blame. Proponents of this view point out that water vapour is the “number one” greenhouse gas since there is a lot more of it in the atmosphere than CO₂ and it has a much higher green house gas potential. While these facts are certainly true, they are far from the whole story. This article explains how water vapour acts as a warming amplifier, but is not responsible for setting the baseline temperature. There is no escaping CO₂’s role and ultimate control, despite what well funded disinformation campaigns would have you believe.

CO₂ and water vapour play very different roles within global warming. The former is a forcing, while the latter is a feedback. As CO₂ rises, it creates the baseline forcing to raise temperatures and, critically, keep them elevated. This allows an increase in water vapour to exist in the air through something called the Clausius-Clapeyron relationship. This increase in specific humidity acts as a feedback, magnifying the warming, but not in a runaway fashion, since it only stays in the atmosphere for a very short amount of time.

Furthermore, the way water is cycled through the climate and biosphere system adds other feedbacks and complexities with far reaching consequences, both for cooling and warming.

The Feedback Mechanism (The Amplifier)

To separate the forcing and feedback roles, first lets compare what would happen if we were to instantly double the concentration of the two gases in the atmosphere.

If we doubled CO₂ (we’ve already increased it by more than 50%), the gas behaves, as they both do, as a greenhouse gas trapping infrared surface radiation in the atmosphere, preventing it from escaping to outer space and therefore maintaining a positive energy imbalance. This warms the planet. Since CO₂ stays in the atmosphere for tens of thousands of years, this warming is essentially permanent - setting the baseline temperature. This extra energy gets stored in the oceans, it melts the world’s ice, changes the climate and so on. Warming only stops when the surface becomes hot enough to radiate sufficient infrared to escape the atmosphere and balance the energy flow from the sun. That new equilibrium temperature is then maintained for millennia until the CO₂ is removed from the atmosphere. The relationship between CO₂ and equilibrium temperature is logarithmic and has been understood for over 200 years. Depending on the time period being addressed it’s referred to as Equilibrium Climate Sensitivity or Earth System Sensitivity.

If on the other hand, we instantly doubled the amount of water vapour in the atmosphere, the same trapping of infrared would occur, but only initially. Water vapour has a very short residence time, remaining in the atmosphere for only about 9 days. Such an increase would rain out almost immediately as the air reached cooler altitudes. We would experience a fortnight of “biblical” floods until the natural carrying capacity of the air was reached. Within weeks, the water content of the air, and the temperature, would return to previous levels. The Valencia 2024 flood is an example of this process, but on a small regional scale.1 The super-saturated air dumped all its water, a years worth of rain in just 16 hours, killing 230 people in the process.

The reason water vapour acts as an amplifier is due to the Clausius-Clapeyron relationship. This states that for every 1ºC increase in temperature, the air can hold 7% more water vapour before it condenses out. So when we pump enough CO₂ into the atmosphere to raise temperatures by 1ºC, the air can hold 7% more water vapour, fed by increased evaporation from the surface. The increase in stable vapour adds to the greenhouse effect, increasing the warming, quickly finding an equilibrium.

Figure 1 shows that specific humidity tracks the observed temperature rise, while Figure 2 shows that relative humidity (the saturation level) has remained constant. Water vapour follows the warming; it does not drive it.

The effect is significant though. About half the warming we currently experience is due to this water vapour increase effect. Without the Clausius-Clapeyron relationship, the climate would be a lot less sensitive to CO₂.

Energy Transport: Latent Heat & High Altitudes

Water vapour also moves heat around the whole climate system. On the surface, either over water or land, evaporation acts as a coolant. You feel this when you sweat. Energy is absorbed when water changes from a liquid state to a gas state. This is why forests feel cool, each tree is evaporating tonnes of water a day from their leaves, drawing energy from its surroundings.

This cooling effect can have a large benefit in keeping urban areas cool too. A 2025 study in London found that streets without trees were 4ºC hotter than streets with tree cover during heatwave events.2 Urban planting is a great way of adapting to rising heatwaves and urban heat islands.

Since warmer air can hold more water vapour, land surfaces lose moisture more quickly as temperatures rise. Once dry and as vegetation cooling capacity drops (either through plant stress or land use change), this can lead to faster land area warming and more intense heatwaves. This effect also dries out soil moisture leading to agricultural drought and higher fire risk.

As water vapour rises higher in the air column it cools and eventually condenses into clouds, in doing so it releases that stored latent heat into the upper troposphere. These convection dynamics are a primary engine for atmospheric circulation and weather patterns.

As more heat is transferred to higher altitude clouds in a warming world, the temperature of clouds is also increasing. The CERES satellite mission has detected both an increase in cloud effective temperature and a corresponding increase in the infrared radiation from the tops of clouds. Due to their high altitude, this radiation has less distance to travel through the atmosphere’s GHGs so can more easily escape to space. In fact, the only cooling element of the Earth’s Energy Imbalance today is the long-wave radiation increase from cloudy areas, despite a drop in cloud area. Between 2000 and 2025, this effect has increased by 0.87W/m², helping to offset the 1.84W/m² increase in absorbed radiation due to albedo losses and GHG increases shown in figure 3.3

The Dual Nature of Clouds

When water vapour condenses at altitude, it changes from the gas state to a liquid or solid state (depending on the temperature). Clouds have varying effects on warming depending on their properties. One of the main effects is that they reflect more sunlight back into space since they are brighter with a higher albedo than the land or ocean surfaces beneath them. This is a significant aspect of global warming since as temperatures have risen, cloud area and brightness have dropped. Since 2000, there has been a drop of over 1.5m km² of global average cloud cover. To put that area into context its the land area of Mongolia.

Cloud cover can also add to the greenhouse effect by trapping outgoing infrared radiation below it. This is especially true with high level cirrus clouds. The effect is so strong that the warming from aircraft vapour trails accounts for half of the aviation industries warming effect, equalling their carbon emissions impact.

In a related note, human-made aerosol pollution, through the burning of coal and dirty fuels as well as industrial processes, changes cloud properties too. Sulphate aerosols promote smaller cloud droplets that are brighter, so have a higher albedo, and last longer. In cleaning up air pollution, we are simultaneously contributing to the albedo loss, speeding up warming even further. That’s not to say air pollution reduction should not be pursued, it kills approximately 8 million people a year. At the same time we are destroying natural ecosystems which also naturally release aerosols into the atmosphere driving cloud propagation.

The Biotic Pump & Land-Atmosphere Interaction

The water cycle is heavily influenced by the biosphere, forests in particular. Moist air coming off the oceans can only carry that water inland so far. Since the land surface warms more quickly than open water, warm air currents rise carrying the moist ocean air to higher, cooler altitudes where they condense and rain out. Without any additional water being available, moisture can only travel a few hundred kilometres inland. When the land is covered in forest however, the trees draw the rain water from the soil and re-transmit it to the air through transpiration by their leaves. This cools the air, reducing the air pressure which draws in more moist air from the ocean. This process repeats further and further inland, allowing tropical forests such as the Amazon and Congo to reach thousands of kilometres inland, remaining moist and providing water in what would otherwise be an arid desert or savanna. The process is known as the Biotic Pump.

It is believed that northern Australia was covered in dense rainforest since fossil evidence of tree dwelling animals are found in the now desert. Early humans settled on the coast when they reached the continent and burned their way inland, clearing the forest until the connection to the ocean was lost and the inland forest collapsed.

For more on the biotic pump, I can recommend Dr Anastassia Makarieva’s excellent substack:

Biotic Regulation and Biotic Pump

How natural ecosystems keep our planet habitable

By Anastassia Makarieva

Removing forests through deforestation doesn’t just stop CO₂ sequestration; it breaks this inland water flow, leading to regional drying and higher local temperatures. The Amazon is believed to have a tipping point of 4ºC of warming to see it collapse into a savanna. Deforestation of 25% is enough to see this threshold drop to below 2ºC of warming. Today deforestation and disturbance has reached 21%.

Deforestation, loss of mangroves, wetlands and disruption of marine plankton ecosystems also disturbs this movement of heat from the surface to high altitude clouds. A critical, often overlooked factor in regional warming is the Bowen Ratio—the mathematical relationship between “sensible heat” (the heat you feel) and “latent heat” (the energy used for evaporation). In a healthy forest, the Bowen Ratio is low; most of the sun’s energy is channeled into evaporating water, which carries heat into the upper atmosphere as latent energy. Deforestation and other land drying practices break this cooling mechanism. Without trees to transpire, the energy that once fueled evaporation now has nowhere to go but directly into heating the air and the soil. This shifts the Bowen Ratio upwards, turning the area into a localised radiator. Because dry, bare ground lacks the moisture to create the vertical convection elevator provided by latent heat release, less energy is transported to higher altitudes where it could more easily escape to space. Instead, the heat remains trapped at the surface with the full GHG laden air column above it.

As the land surfaces of the world dry out and we continue to squander the resource by pumping water from deep aquifers, land water storage levels are dropping fast. According to Chandanpurkar et al. “Continental drying is having profound global impacts. Since 2002, 75% of the population lives in 101 countries that have been losing freshwater water. Furthermore, the continents now contribute more freshwater to sea level rise than the ice sheets, and drying regions now contribute more than land glaciers and ice caps.”4

Stratospheric Water Vapour

The stratosphere is naturally very dry because most water freezes out as it passes through the extremely cold upper troposphere. However, methane can bypass this trap, passing into the stratosphere easily. Once there, it undergoes a series of chemical reactions, primarily with hydroxyl radicals that result in it breaking down into CO₂ and water vapour. Here it behaves as a green house gas trapping energy escaping from the surface.

The IPCC AR65 explicitly categorises stratospheric water vapour from methane oxidation as an indirect radiative forcing of methane. They estimate that water vapour produced from methane oxidation adds about 15% to 20% to the direct warming effect of the methane itself. Given that methane concentrations have increased by 245% since the pre-industrial, humans are actually ‘injecting’ water vapour into the upper atmosphere indirectly by emitting methane. This bypasses the natural water cycle and creates a warming effect that wouldn’t otherwise exist.6

Conclusions

Water vapour is an important greenhouse gas but it is not in control. It acts to amplify warming in a feedback effect driven by increases in other greenhouse gases that are more longer lived. The residence time of water vapour in the atmosphere prevents it from driving warming since any increase is rapidly removed through condensation and rained out.

Its feedback effect however is significant. Without it, the Earth would be a lot less sensitive to CO₂ emissions. Temperatures would be a lot lower and the climate a lot less agitated. By allowing more water into the atmosphere through our burning of fossil fuels and land use changes, we’ve created the conditions for a more intense water cycle, creating bigger storms bringing more intense floods, and deeper droughts that dry out soils and biomes more rapidly.

By continued deforestation we are cutting off both the biotic pump, preventing moist ocean air from reaching inland, and reducing the cooling effects of vegetative evaporation and heat transfer. This further amplifies global surface warming as well as puts huge areas of land at risk of aridification and significant ecological change, not just effecting the ecosystem, but our crops and water sources.

By taking action to re-forest and re-wild areas of the land, we would not only be restoring the ecosystem or sequestering carbon, but actively cooling the planet. A re-forested area would lower the Bowen ratio, driving more transpiration and evaporation, allowing more heat to be transferred to high altitudes a latent heat where it can be lost to space. Whether on a small scale such as city street planting, or in new forests, the benefits are significant.

Whilst we control the CO₂ thermostat, hitting the boost button with our land use changes, water vapour determines how much the planet actually heats up.

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