This is the reason Blue Lines exists. Contrail avoidance will not fix the climate. But it is one of the very few levers that can remove 1–2% of human-caused warming within years rather than decades, at low cost, with technology that already works. Summers like this one are reminders of why we are doing this and a nudge to act now.

🇬🇧 Operation Blue Skies: the biggest contrail trial yet

The UK just announced what is likely to be the most ambitious contrail avoidance trial to date.

Operation Blue Skies is the first trial to test contrail avoidance across an entire oceanic airspace. It takes place in Shanwick, the eastern half of the North Atlantic, which is controlled by the UK’s air navigation service provider, NATS. More than 1,000 flights a day pass through Shanwick, and the region alone accounts for roughly 5% of global contrail warming.

Contrail forecasts will be fed directly into the air traffic control system, and aircraft will make small altitude changes on 20 to 40 test days during each of two winter windows (2026–27 and 2027–28). Google’s satellite imagery and machine learning will then check whether predicted contrails form.

The consortium is a strong one: NATS, Google, Contrails.org, the UK Met Office, Imperial College London and the University of Cambridge, with the UK Department for Transport funding just over half of the £5 million program.

If you want the full picture of where this trial fits in, we have just updated our list of every publicly announced contrail avoidance trial (involving more than 10 flights) past and present, on the Blue Lines website: blue-lines.org/trials. If we are missing one, let us know.

🇪🇺 The EU puts a price on contrails — but is it enough?

On 17 July, the European Commission published its proposal for revising the EU Emissions Trading System for aviation. For the first time, it contains a mechanism specifically designed to reward contrail avoidance.

The headline number is impressive: a reserve of up to 3 million ETS allowances through 2033, worth around €255 million at today’s allowance price of roughly €85, for airlines that use contrail forecasting in their flight planning. An additional small bonus goes to airlines that report non-CO2 effects using in-flight measured data.

We were excited when we first read it. Then our friends at Nexus Lab and Estuaire ran the actual numbers, and the excitement cooled.

The mechanism pays airlines allowances equal to 0.1% of their verified emissions (plus 0.02% for the measured data). Apply that to the 2025 verified emissions of all 584 operators in the EU ETS, and the total comes to about €5.6 million per year — not the €35 million per year the reserve’s annual cap would allow, and nowhere near the €255 million headline.

Comparing these allowances to yearly revenue numbers, Ryanair’s €1.26 million a year is only equivalent to 0.0081% of the airline’s €15.5B revenue. SAS would receive around €203,000, which is 0.0045% of its annual revenue. Many operators would be well below €10,000 in annual allowances. And from that money, airlines would have to pay for software integration, internal work, any external assistance, and extra fuel burned during avoidance maneuvers.

To put the whole thing in perspective: European airlines made a collective net profit of around €11 billion last year, according to IATA. The entire contrail incentive (€5.6M per year) is half a promille of that.

We welcome the principle and the people behind it. But a contrail incentive worth about what a mid-size airline spends on coffee is unlikely to change how anyone flies. If the EU wants this mechanism used, something closer to 0.5% of verified emissions would be a reasonable starting point. That is still well within the reserve and enough for airlines to begin to notice. We hope the EU will take a close look at that one figure.

🌅 One tip before you book your next flight

Finally, a reminder for everyone now back at their desks and already planning the next trip.

Not all flights are equal when it comes to contrail warming. During the day, a contrail reflects sunlight back into space as well as trapping heat from below, and the two effects partly cancel out. At night, there is no sunlight to reflect, so the contrail only traps heat.

We have posted this graph from RMI before: while persistent contrails from early morning flights are likely to have a slight cooling effect, flights departing in the late afternoon or evening are far more likely to produce warming contrails.

So, until airlines do the avoiding for us: if you have the choice between the 7 am departure and the 7 pm one, the early bird is the better climate choice.

Thanks for reading Blue Lines. Please share with someone who could be interested in aviation and the climate.

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Interested in knowing what it takes to implement contrail avoidance (trials) as an airline? We have put together a free guide with support from Contrails.org. It is called Contrail Avoidance in Practice: A Playbook for Airlines, and it is the first comprehensive, practitioner-built guide to getting started, covering governance, tools, dispatch workflows, pilot engagement, cost management, and funding. It can be downloaded here.

To new Blue Lines followers: Welcome.

In 2025, we added 33% more subscribers. It is always a pleasure to have more people interested in the progress of contrail avoidance – the most promising solution to lower aviation’s climate impact and potentially one of the fastest ways to reduce global warming overall.

Go to Blue Lines’ website to explore contrails in depth.

See you soon.

Joachim Majholm,

Blue Lines

A small number of airlines, American Airlines, Amelia, TUIfly, Air France, and others, have been running contrail avoidance trials in the past few years. They’ve figured out how to build internal buy-in, integrate contrail data into dispatch workflows, set guardrails that keep costs manageable, and bring pilots along on something that feels counterintuitive at first: flying slightly less efficiently to reduce a much larger climate impact. Until now, almost none of that experience has been documented outside of scientific research papers.

Contrail Avoidance in Practice: A Playbook for Airlines changes that. Published this month by Blue Lines with support from Contrails.org, it is the first comprehensive, practitioner-built guide to getting started, covering governance, tools, dispatch workflows, pilot engagement, cost management, and funding.

Getting started doesn’t require large-scale change. Airlines can begin by analyzing their existing flights, focusing on the very warming contrail flights (big hits!), and do that with a limited internal budget.

The playbook is free. If you work in aviation, pass this along to your sustainability team members.

DOWNLOAD THE FREE PLAYBOOK →
blue-lines.org/contrail-avoidance-in-practice-a-playbook-for-airlines

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To new Blue Lines followers: Welcome.

In 2025, we added 33% more subscribers. It is always a pleasure to have more people interested in the progress of contrail avoidance – the most promising solution to lower aviation’s climate impact and potentially one of the fastest ways to reduce global warming overall.

Go to Blue Lines’ website to explore contrails in depth.

See you soon.

Joachim Majholm,

Blue Lines

Today, Blue Lines releases Contrail Avoidance in Practice: A Playbook for Airlines — a free guide to implementing contrail avoidance trials at an airline.

Contrail warming is one of aviation’s largest climate problems and one of the most addressable. But for airlines interested in mitigating contrail warming, it can be overwhelming to figure out the Who, What, Where, When, Why & How of contrail avoidance.

What has been missing is a clear, practical starting point for the people inside airlines who need to make it happen. The playbook is based on interviews with early-adopter airline sustainability leads, dispatchers, pilots, and consultants, who share their knowledge and experience with implementing contrail avoidance in trials.

Here is some of what the playbook covers:

A readiness checklist. What needs to be in place before an airline can run a contrail avoidance trial: data access, software integration, flight operations, crew briefings, and internal stakeholder alignment

Cost and risk management. The extra fuel burn required for contrail avoidance is small but real. The playbook walks through how early movers have handled the business case, what the actual cost exposure looks like, and how to manage it operationally.

First-mover advantage. EU non-CO₂ monitoring and reporting is already in force. Pricing of non-CO₂ warming effects may follow in 2027. Airlines that have run trials are better positioned to influence policymaking and be ready when incentives are introduced.

A six-phase rollout. Based on how airlines have actually done this, from initial data assessment through to a live operation, including the decisions, the stumbling blocks, and what to do when the forecast is uncertain.

The playbook is created with the support of Contrails.org and was reviewed by the International Council on Clean Transportation (ICCT), Transport & Environment (T&E), Green Transition Denmark (RGO), and other kind contributors.

DOWNLOAD THE FREE PLAYBOOK →

💰 New funding for contrail policy

Wren, a climate-focused public benefit corporation, has launched a policy grants program with special emphasis on contrails. They are offering $100K–$500K to organizations pushing for research and policy on aviation's non-CO₂ warming effects, with MRV protocol development highlighted as an example. If you're working on this and need funding, expressions of interest are open on a rolling basis until June 30.

🛠️ New tool to study historic contrail impact data

Contrails.org just launched the Impact Explorer (explore.contrails.org), a new tool that makes it easy to look up the climate impact of commercial flights going back to 2024 (and eventually to 2019).

The idea is to present a dataset based on the best available estimates of per-flight contrail impacts. Airlines can request access to dive deep into their own data, studying high-impact routes, individual flights that produce outsized contrail warming, differences between summer and winter, etc.

Non-airline users can study the big picture: intra-EU flights versus all EU flights, contrail warming month-by-month, impact per airport/country/continent, but also the flights that produce more than 2000 tons of CO2e in contrail warming from a single flight.

For some flights, a basic contrail avoidance simulator is also built in, giving a first sense of how rerouting a given flight might have avoided warming.

Still, for frequent flyers or companies wanting to estimate the total climate impact of their flights (including CO₂, contrails, and other non-CO2 impacts), it is very difficult to do so. In the future, it would be great to have a tool where anyone can upload their travel itineraries and get the best available estimate of the total climate impact - everything included. The Impact Explorer is a big step in the right direction.

To new Blue Lines followers: Welcome.

In 2025, we added 33% more subscribers. It is always a pleasure to have more people interested in the progress of contrail avoidance – the most promising solution to lower aviation’s climate impact and potentially one of the fastest ways to reduce global warming overall.

Go to Blue Lines’ website to explore contrails in depth.

See you soon.

Joachim Majholm,

Blue Lines

The results of the first year of the European Union’s mandatory reporting of contrail warming (and other non-CO₂ effects) should soon be made public. For the first time, airlines are required to report the full climate impact of flying, not just CO₂.

Next year, the EU’s non-CO₂ Monitoring, Reporting, and Verification (MRV) system will expand from covering only intra-European flights to include international flights as well. At the same time, the European Commission is expected to consider whether (and how) non-CO₂ impacts should be incentivized or regulated.

So, the next 18 months will be critical to how quickly contrail avoidance moves toward real-world implementation.

Meet us at SF Climate Week

The importance of the next 18 months is one of the topics we will discuss at SF Climate Week next Tuesday.

In 2024, Blue Lines was the first organization to bring contrails into the conversation at SF Climate Week. Back then, we did it in collaboration with Contrails.org and the ICCT. This year, we have teamed up with Omar Nuruzade from Nexus Lab, which helps airlines forecast and validate contrails.

We’ll focus on how AI and satellite data are now being used to predict and verify contrail impact in real operations.

It’s free to attend, and all are welcome. We already have a strong mix of participants from academia, civil society, tech, and the aviation industry—and we’re aiming for a highly interactive discussion.

📍 Kantine, 1906 Market Street, San Francisco

🕓 April 21, 4:00 PM – 5:30 PM

🎟️ Limited spots

🔗 Register here: https://luma.com/xm53775w (in-person only)

And if you are in town next week, consider signing up for the other contrail event that takes place this year: Understanding Contrails: The Hidden Climate Impact of Flight.

New contrail avoidance trials added

It was only five years ago that the first, larger contrail avoidance trial took place (MUAC/DLR, 2021).

Since then, we have tracked a total of 13 publicly announced, larger trials in our updated database at blue-lines.org. The list has just been refreshed.

As always, if we are missing a publicly announced trial, please let us know.

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Check the full climate impact of your favorite airline

Which airlines produce the most CO2 and contrail warming? And which routes matter most?

Estuaire has once again analyzed millions of flights to publish the 2025 Contrail Opportunity Index. The French company also recently announced a collaboration with Air France to help one of Europe’s largest airlines address contrails.

To all the new Blue Lines followers: Welcome.

In 2025, we added 33% more subscribers. It is always a pleasure to have more people interested in the progress of contrail avoidance – the most promising solution to lower aviation’s climate impact and potentially one of the fastest ways to reduce global warming overall.

Go to Blue Lines’ website to explore contrails in depth.

See you soon.

Joachim Majholm,

Blue Lines

The trial involved American Airlines, one of the world’s largest airlines by passengers and fleet size. Over a 17-week period in early 2025, researchers and technology providers worked with the airline to test contrail-aware flight planning on more than 2,400 transatlantic flights. About half of these flights were randomly assigned to test contrail-aware planning, while the others served as a control group.

Using flight planning software from Flightkeys with integrated contrail avoidance, dispatchers planning overnight flights from the United States to Europe could see a contrail-optimized flight plan designed to avoid atmospheric regions where contrails are likely to form. They could then decide whether to release that flight plan to the crew.

To measure the impact, the study used satellite observations to detect contrails and attribute them to individual flights, enabling researchers to assess whether observed contrail formation changed in the real world.

69% reduction in contrail warming

Across the full experiment, flights where contrail-aware planning was introduced produced 11.6% fewer observable contrails than the control group.

But the effect became much clearer when the optimized routes were actually flown. For flights that followed the contrail-optimized plan, observable contrail formation fell by about 62%, with an estimated 69% reduction in contrail warming.

Just as important, the trial found no statistically significant increase in fuel use.

A large trial, but still a small fraction of avoidance flights flown

Despite the experiment’s scale, the number of flights that actually flew contrail-optimized routes was relatively small: Out of more than 1,200 flights eligible for contrail avoidance, dispatchers released contrail-optimized flight plans for about 15% of them, and only 112 flights ultimately flew the optimized plan.

Participation in the trial was voluntary, meaning dispatchers could simply proceed with a standard flight plan if operational priorities required it. In interviews conducted after the trial, dispatchers cited several operational reasons for not using the contrail plans more often, including workload, turbulence and weather considerations, preference to stay within the North Atlantic organized track system, and limitations in the flight-planning interface.

Measuring only the contrails we can see

Another important caveat is that the study measured observable contrails detected in satellite imagery. Not all contrails are visible to geostationary satellites, meaning the total climate impact reduction may differ from the reduction in observable contrail length.

However, larger and more persistent contrails — which may account for a disproportionate share of warming — are also more likely to be detected by satellites. The researchers therefore believe the results capture a significant portion of the contrails most relevant to climate warming.

How quickly can we scale contrail avoidance

In 2023, American Airlines worked with the same group of researchers from Contrails.org, Imperial College London, and Google Research to conduct its first small trial. One future focus area could be to enhance dispatchers’ confidence in choosing the contrail-optimized flight plan to get a much higher adoption rate than in this trial.

As we wrote about last month, a new study shows that the biggest contrail climate risk is to do nothing. And with one of the world’s largest airlines actively testing contrail avoidance at scale, the question is becoming less whether the approach can work, and more how quickly it can be scaled.

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Contrail impact explained: The blanket effect and the mirror effect

As a communicator, I am always on the lookout for explanations that feel logical, easy to remember, and simple to communicate. This is why I want to highlight this LinkedIn post by Gular Ismayilova, Co-founder of Nexus Lab, a contrail-avoidance tech provider, which distinguishes between warming blanket-effect contrails and cooling mirror-effect contrails. Great way of wording it.

To all the new Blue Lines followers: Welcome.

In 2025, we added 33% more subscribers. It is always a pleasure to have more people interested in the progress of contrail avoidance – the most promising solution to lower aviation’s climate impact and potentially one of the fastest ways to reduce global warming overall.

Go to Blue Lines’ website to explore contrails in depth.

See you soon.

Joachim Majholm,

Blue Lines

Four recent papers tell some interesting stories about contrail avoidance right now:

Transport & Environment’s new report shows how concentrated contrail warming really is. Less than 3% of flights generate about 80% of the climate impact, and a quarter of Europe’s contrail warming occurs in just 10% of traffic - mainly fall and winter night flights.

In congested traffic it can be difficult to change altitude to avoid the areas of cold and humid air where persistent contrails are created. But Europe seems to have an opportunity to begin contrail avoidance at scale during the low density night time traffic.

However, that is not the opinion of the European airline lobbying organization, Airlines for Europe (A4E) in it’s non-CO2 positioning paper. In 2027, the EU commission has to decide whether to incentivice airlines to minimize their contrail warming by pricing non-CO2 climate impact from aviation. A4E argues that uncertainty, data and software problems makes it too early for the EU to hold airlines accountable for non-CO2 warming.

This narrative fits the airline strategy outlined in a new paper (Gössling et. al, 2026) analysing airline sustainability messaging: Aviation’s sustainability discourse systematically pushes meaningful mitigation into the future. It’s a rhetorical strategy (“future soothing”) that allows the sector to acknowledge that they are doing harm while justifying continued growth and postponing real mitigation.

Which brings us back to the risk of doing nothing. A new Nature Communications study finds that by 2050 contrails alone could warm the planet more than aviation CO₂ . If we begin global avoidance at scale in the next decade, we could recover roughly 9% of the remaining 2 °C temperature budget. But delaying action by another decade reduces that to about 2%. The greatest climate risk of contrail avoidance is inaction.

Weight loss drugs could help pay for contrail avoidance

The success of Ozempic and other GLP-1 weight-loss drugs may have a surprising side effect: lighter passengers mean lighter aircraft, which in turn lead to lower fuel burn, lower CO₂ emissions, and lower operating costs.

A Jefferies analysis cited by the New York Times estimates that reduced passenger weight could cut U.S. airline fuel use by about 1.5%, saving roughly $580 million per year for the four largest U.S. carriers alone.

That amount is very close to what Contrails.org estimates the cost of scaling navigational contrail avoidance to be. They estimate an annual cost to operators of $732M, meaning the slimmer passenger of the four largest U.S. airlines alone could largely fund worldwide contrail avoidance at scale.

Is your airline or geographical area involved in contrail trials?

It can be really difficult to find public information about privately or publicly funded contrail avoidance trials. Information can be sporadic or hard to find due to political head winds or shifts in internal policies. So at Blue Lines, we decided to create and host a list of bigger, publicly announced contrail avoidance trials where aircraft are actively trying to avoid forming contrails. You can check if your area or local airline is active here. For a complete list of airlines having publicly acknowledged contrail avoidance or participated in scientific studies or trials, check Blue Lines’ Airline Contrail Index.

As always, if we are missing a publicly announced trial, please contact us.

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To all the new Blue Lines followers: Welcome.

In 2025, we added 33% more subscribers. It is always a pleasure to have more people interested in the progress of contrail avoidance – the most promising solution to lower aviation’s climate impact and potentially one of the fastest ways to reduce global warming overall.

Go to Blue Lines’ website to explore contrails in depth.

See you soon.

Joachim Majholm,

Blue Lines

At the beginning of 2025, we predicted:

1. Corporations will want better contrail warming estimates. For many large software and consulting companies, Scope 3 emissions from air travel are some of their highest emissions. What companies are doing now to also account for the non-CO2 impacts of air travel (including contrails) is multiplying their CO2 emissions by a factor of 1.7x. However, with contrail prediction models and accurate corporate travel data, it should be possible to calculate the warming created by each flight taken by an employee and get much more actionable data.

   RESULT: ✅ Until last week, not much had happened. But then RMI, Estuaire, BCG, and Roland Berger released a groundbreaking report on corporate accounting of non-CO2 effects and how these impacts can be calculated and reported more accurately. The work began at our Copenhagen Contrails Conference in March, and the report has already sparked interest among new large corporations.

   

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2. The EU will sponsor at least one new contrail avoidance trial. I am not talking about the ongoing large EU-supported projects like CICONIA or CONCERTO, but the EU’s Innovation Fund has specifically requested contrail / non-CO2 projects it can support. In 2024, a handful of airlines partnered with flight planners, tech companies, and scientists to form a consortium aiming to conduct thousands of contrail avoidance flights over the coming years. The project was denied funding, but hopefully, someone will be successful in 2025.

   RESULT: 🛑 We are not aware of any new trials receiving funding from the EU Innovation Fund this year. Maybe next year?

3. New climate organizations will start focusing on contrails. Several climate- or policy-nonprofits focusing on transportation are involved in contrail management. However, many more general climate-focused NGOs haven’t yet identified this climate opportunity (I am looking at you, Greenpeace). Maybe one or two new organizations will get involved in 2025.

   RESULT: ✅ Yes to this one. I have personally been in contrail-meetings with representatives from Greenpeace UK, in communication networks where new nonprofits are learning about contrails, and there was a big, coordinated NGO push for focus on contrails at the recent COP30 in Brazil.

I must also highlight another accurate (though delayed) prediction from the beginning of 2024, when we predicted:

4. First fleet-wide testing. In 2024, we will see the first airline(s) testing contrail management on their entire fleet. This means analyzing all their flights daily to identify the few flights that can be diverted to save thousands of tons of CO2e.

   RESULT: ✅ Yes, in 2025, the first fleet-wide testing is finally happening. Two European airlines are currently analyzing all their flights for contrail warming and adjusting flight plans to avoid the worst contrail warming. However, this has not yet been publicly communicated.

We filmed this plane flying parallel to us over the North Pacific in November 2025. Though the contrails looked substantial, we could see that they were dissolving fast, likely not creating significant warming (or cooling).

Here’s what the crystal ball is telling us for 2026

1. A lot more public focus on contrails in 2026 compared to 2025. After a relatively quiet contrail year in 2025 - due to less political focus on climate - 2026 will see a renewed interest in mitigating the warming effect of contrails. One driver will be the results of the new Monitoring, Reporting, and Verification of aviation non-CO2 in Europe, which will require all airlines flying within Europe to report all their climate impacts, including contrails, in 2026.

2. In 2026, the largest contrail trial in history will take place. We still need to conduct additional experiments or live trials to determine how to roll out contrail avoidance at scale. In the UK, the government has set aside multiple millions of pounds to conduct ambitious trials over the North Atlantic. It could also be that larger airlines decide to implement contrail avoidance at scale.

3. Contrails will enter at least one airline’s public climate targets. Blue Lines’ Airline Contrail Index monitors airlines’ public messaging around contrails. One thing we have been tracking over the years is whether any airline sets public contrail-reduction targets. Delta Air Lines did it three years ago, but seems to have retracted the goals since (they have never been repeated). In 2026, we predict that at least one airline will set public contrail climate goals (and hopefully stick to them).

We promise to follow up with you in 12 months to see if any of this materializes.

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Fun, informative, and entertaining contrail video

Communicating about contrails and the climate in an engaging way can be really challenging. The topic can get complicated, a bit dry, and somewhat geeky. But not in the hands of content creator Simon Clarke (who also happens to have a PhD in Atmospheric Physics). His new contrail video features Professor Marc Stettler from Imperial College London and is the best (longer) video I have ever watched on contrails and the climate.

Your favorite contrail story

The most-read newsletter we published this year was our July 31 post featuring Dr. Paul Hodgson debunking the top 10 excuses some airlines use for ignoring the climate impact of contrails and avoiding taking action. This story was also recorded for short LinkedIn videos that we ran over the summer. You can find them all here.

Over the past year, our audience has grown by 68%. Thank you for reading our newsletters and for spreading the word. Please share with someone who could be interested in aviation and the climate.

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Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

Yesterday, the Bill Gates-funded nonprofit Contrails.org released a new interactive calculator that allows users to adjust key assumptions like implementation expenses, ongoing expenses, the price of fuel, etc. It outputs both a cost per ton of CO₂e avoided and an average cost per flight.

The tool allows the user to adjust each lever or select a preset nominal, optimistic, or pessimistic scenario. Even under the pessimistic scenario, contrail avoidance remains highly cost-effective at roughly $14 per ton CO₂e (GWP100). Compared with other aviation climate solutions that routinely cost hundreds of dollars per ton CO₂e avoided, the economic case for contrail avoidance remains exceptionally compelling.

Corporations might have overestimated their climate footprint for years

Many large companies now report their Scope 3 emissions, and for office-based firms in particular, employee air travel accounts for a large share of their climate footprint. To account for non-CO₂ effects such as contrails, companies apply a one-size-fits-all multiplier (typically 1.7x) to their CO₂ emissions. Some organizations even purchase carbon credits to offset this estimated non-CO₂ impact.

A new report from RMI, released yesterday and based on multiple corporate pilot studies, suggests this approach has significantly overestimated real-world impacts. Using flight-specific modeling, RMI and partners Roland Berger, BCG, and Estuaire find that average non-CO₂ impacts from business air travel are closer to 1.3× CO₂, not 1.7×. This implies that many companies’ reported aviation climate footprints and associated offsets have likely been inflated for years.

Two new approaches to corporate contrail accounting

RMI proposes two alternatives to the traditional multiplier-based Baseline Approach: The Differentiated Default Approach maintains simplicity but adjusts the non-CO₂ factor based on broad operational conditions such as region, season, and time of day, better reflecting actual contrail risk.

The more advanced Bottom-Up Approach estimates non-CO₂ impacts at the level of individual flights using real trajectory data and atmospheric conditions. This replaces broad averages with flight-specific estimates, enabling both more accurate reporting and targeted contrail mitigation.

The corporate pilots also confirm the highly uneven nature of contrail warming: roughly 2% of bookings cause around 80% of total contrail impact. This makes broad averaging a poor guide for action and highlights the value of identifying and targeting high-impact flights for intervention.

The studies further show that contrail risk is strongly linked to season and time of day. In the Northern Hemisphere, February flights cause about 10 times as much warming as July flights. Therefore, scheduling the company’s annual all-hands meeting in summer rather than winter can significantly reduce its climate impact.

When possible, prioritize early-morning departures. Flights taking off in the early morning are unlikely to generate contrails that persist into the dark hours, when their warming effect is strongest. In the study, flights departing between 6 and 8 a.m. even showed a net cooling effect from their contrails, while afternoon and nighttime flights produced substantial warming.

Why is aviation such a hard sector to clean up?

The illustration above shows why it is so difficult to reduce aviation’s climate impact. Most highly polluting industries can connect new, clean infrastructure around their facilities to effectively lower their climate impact. But most of aviation’s climate-warming activities take place 35000 feet up in the air, where there are no solar farms, wind power parks, clean nuclear plants, or geothermal projects to support a clean, green transition.

Four years ago, BCG estimated that aviation’s share of global emissions could grow from around 3% today to 20% of total global emissions in 2050. That projection underscores both the scale of the challenge and the urgency of deploying all viable solutions, including contrail management.

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

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🪚 Popular London contrail workshop 🔨

Let’s begin with some good news: A couple of weeks ago, Contrails.org hosted the third annual Contrail Science Workshop, this time at Imperial College London.

• In 2023, about 80 people participated.

• Last year, we were around 100.

• This year, registration had to be capped at 140 - the community is growing, and there is clearly more attention on contrail management today.

The two-day event was packed with the latest scientific findings, workshops, and discussions; what happened during the coffee breaks, over lunch, or at the social mixers was just as important. I am sure many new collaborations and ideas emerged from that event.

🙈 The FAA can’t say “climate” anymore 🙊

Over the summer, the US Federal Aviation Administration’s (FAA) contrails webpage was quietly scrubbed of words like “warming” and “climate.” Now it simply informs visitors that contrails need to be studied further, but not why. The why, of course, is because they trap heat and drive roughly half of aviation’s total warming impact.

However, on the same website, the FAA still hosts the FAA/NASA/NOAA Contrails Research Roadmap (Jan 2025). That report, commissioned under the Biden administration and publicized just as the Trump administration took office, couldn’t be clearer. Line two of the executive summary reads: “Current models indicate that persistent spreading contrail cirrus has a significant net warming impact on the global climate.”

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To be very clear: Contrails impact the climate. This is not a matter of opinion but a scientific fact.

🙉 No climate problem, no reporting

In early September, another US institution, the EPA, proposed rolling back emissions reporting requirements for America’s largest polluters, including oil refineries, power plants, and heavy industries, which would mean they may no longer be required to monitor and disclose their carbon dioxide emissions. Whether that could ultimately apply to airlines remains an open question. Ironically, EPA stands for Environmental Protection Agency.

🌍 ICCT: Contrails are aviation’s biggest climate lever before 2050 🛬

The International Council on Clean Transportation has released a new study confirming what many in the field already suspected: avoiding warming contrails is the single most effective way to cut aviation’s climate impact in the near and medium term.

ICCT estimates that mitigation could cost as little as $5–$25 per tonne of CO₂-equivalent avoided, compared with $300 or more for today’s SAF. In its “Full Breakthrough” scenario, contrail avoidance alone cuts more than 40 percent of aviation’s additional warming by 2050 — making it clear that without contrail action, the industry won’t be able to significantly lower its climate impact by 2050.

The study was released ahead of the 42nd ICAO Assembly, where progress on aviation climate action is on the agenda.

🎯 Delta Air Lines: Still a leader, or backtracking?

In 2023, Delta Air Lines became the first airline to announce contrail reduction targets: an 80% cut of addressable contrails by 2035, and 100% by 2050. That was bold, and it earned them a Platinum tier in Blue Lines’ Airline Contrail Index as the first and only airline.

But two years on, under new sustainability leadership, those targets have not been repeated, reaffirmed, or updated. The special sustainability report from 2023 where the contrails reduction goal was first mentioned, have since been removed from Delta’s website, but a presentation can still be found there.

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As a consequence of the two-year-long silence, we assume that Delta Air Lines no longer stands by its contrail reduction goals and has downgraded them from the Platinum tier to the Gold tier in the Airline Contrail Index (leaving the top tier empty).

Delta, please prove us wrong.

It’s not too late to be amongst the first 🥇

Speaking about taking action on contrails, airlines still have the chance to be a first mover on contrail avoidance. Here are some advantages:

• Regulatory head start: anticipate compliance instead of scrambling later

• Operational edge: build experience with forecasting tools and dispatch protocols before they’re mandated

• Investor and customer trust: demonstrate measurable climate impact reduction now, not just in 2050

• Reputation advantage: claim leadership on one of aviation’s most addressable climate problems

This window won’t stay open forever.

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

That’s why independent legal experts, commissioned by NGOs, Transport & Environment (T&E) and Opportunity Green, reviewed the Paris framework and concluded that countries are legally obliged to address aviation’s non-CO₂ effects – mainly consisting of contrails – in their national climate plans (NDCs). These updated NDCs are due ahead of COP30 in Brazil this November.

If governments follow the advice, contrails could finally move from being an overlooked problem to a core part of climate strategy.

How to compare short-lived contrail warming with eternal CO2 warming

A common problem when talking about the climate impact from aviation is how to compare the warming created from contrails which only lasts a few hours with the warming created by burning jet fuel and releasing CO2, that hangs in the atmosphere for centuries.

Contrails.org released a fresh take: Instead of trying to calculate Global Warming Potential (or similar metric) values over 20, 50, or 100 years, we can instead think of contrails as a camera’s flash 📸 – a contrail can produce very high warming but it dissipates within a few hours – and think of CO2 as a dim LED light left on – CO2 produce minimal warming but it stays in the atmosphere for centuries, even millenia.

What Contrails.org suggests is, that we look over time at when the accumulated warming from CO2 (all those dimmed LED lights) exceeds the instant warming burst from the contrails (the camera flash). Will it take 30, 70, or 120 years before the warming from the CO2 exceeds the contrail warming? This can be valuable to be aware of.

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More US politicians are passing anti “chemtrails” laws

It’s 2025, and instead of addressing aviation’s real climate problem, more US lawmakers are busy outlawing chemtrails (a conspiracy theory). Florida now makes “geoengineering” a criminal offense, Tennessee has banned the “release of chemicals” for weather control, and Louisiana wants state agencies to report chemtrail “sightings” to the Air National Guard. At the federal level, Representative Marjorie Taylor Greene (Republican) is pushing a similar bill in Congress.

The US Environmental Protection Agency has had to step in with a “facts page” to inform the public of basic science: contrails are condensation trails, not government spraying programs.

Laws built on conspiracy theories legitimize misinformation and waste political energy at the same time as contrails, the real climate issue, should receive serious attention. However, if politicians and the public are talking about “chemtrails,” there’s an opening to steer the conversation toward the science of contrails and their warming impact.

Learn about how EU is going to Monitor, Report and Verify (MRV) contrail warming

Nexus Labs, a tech provider that develops contrails avoidance software for airlines and others, has launched a series of talks about contrail-related topics.

The next one (tomorrow, September 10!) is particularly interesting since they invited Dimitar Nikov from the European Commission’s DG Klima. Dimitar is leading EU’s efforts in introducing the aviation non-CO2 Monitoring, Reporting and Verification (MRV) system this year. It will be very interesting to hear what he has to say about getting the MRV systems ready for airline monitoring and reporting of contrails (and the other non-CO2 effects), how to incentivize airlines to do accurate reporting when there are no consequences for not doing so, and much more.

Sign up and read more here.

Meet us in London, New York

September is an exciting month for advancing contrails progress. We’re excited to be attending the Aircraft Contrail Analysis Workshop 2025 in London, and contrail events at Climate Week in New York.

Let’s connect if you’re there!

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

Over the summer on LinkedIn, we launched a 10‑part mini‑series featuring aviation sustainability expert Dr. Paul Hodgson, who methodically dismantles the top ten excuses airlines lean on to justify doing nothing about contrails. From “the science is uncertain” to “there’s no customer or regulatory pressure,” every excuse gets a sharp, evidence‑based response from Paul. The goal: to strip away clouded narratives and expose the truth:

• Yes, there is uncertainty about the climate impact of contrails, but that is no excuse for inaction.

• Prediction tools are not perfect, but good enough for meaningful trials.

• Fuel burn penalties are minimal compared to the climate benefits.

• Contrail avoidance is operationally feasible and we should try it out to learn more.

• Lack of regulation is no reason for inaction - it’s coming and better be prepared.

These bite‑sized videos (2–3 minutes each) dropped weekly on LinkedIn. Here are the top ten excuses:

1. “The science is uncertain"
2. "Contrail prediction models are inaccurate"
3. “Verification is impossible”
4. “Adding more fuel and CO₂ is unacceptable”
5. “Operational implementation is too complex”
6. “Air traffic control cannot support contrail avoidance”
7. “There's no regulation or contrail pricing forcing us to take action”
8. “There are no incentives for voluntary action”
9. “There is no pressure from customers or the general population”
10. “Acknowledging contrails would admit a bigger climate problem”

If you haven’t seen the videos yet, they’re well worth the watch. (LinkedIn, blue-lines.org)

Paul’s core message? Contrails are a solvable problem. We must not let myths stand in the way of action. Aviation can and must move faster. (LinkedIn)

✳️ Which airlines are actually doing something?

Blue Lines’ Airline Contrail Index, updated as of May 2025, tracks those airlines that have moved beyond excuses and started taking real contrail‑reduction action. As of now, 38 airlines feature in the Index, across four tiers: Platinum, Gold, Silver, and Bronze, ranked by their level of ambition, from mentioning the bare existence of climate warming from non-CO2 emissions (including contrails) to participating in trials.(blue-lines.org)

🏆 Platinum tier (the standout)

• Delta Air Lines stands alone in Platinum: collaborating with MIT and Google Research, Delta is targeting an 80% reduction in addressable contrails by 2035, with 100% by 2050.

  However, these first-in-the-world contrail targets were announced in 2022 as a part of a special sustainability plan that Delta has since removed from its website. And the airline’s contrail-pioneering Chief Sustainability Officer Pam Fletcher is no longer with the airline.

  We still hope that keeping Delta Air Lines’ contrail targets in the Airline Contrail Index’ Platinum tier, can inspire other airlines to set targets and remind Delta of a promise they seem to have forgotten.(blue-lines.org)

🥇 Gold Tier (active research & trials)

These airlines have publicly launched trials or are collaborating with scientists to understand and curb contrails:

• Air Canada, Air France, Amelia, American Airlines, Cathay Pacific, China Airlines, Discover Airlines, easyJet, Etihad Airways, Hawaiian Airlines, Iberia, Icelandair, KLM, Lufthansa, Southwest, Swiss Air, TUI, and United Airlines.(blue-lines.org)

  Thanks for reading Blue Lines! This post is public so feel free to share it.

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Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

To raise awareness, we recently asked the contrails community on LinkedIn:

“What’s the best metaphor to describe contrails—the artificial clouds that heat the planet?”

Here’s how you voted:

🔥 Heat traps (54%)
Contrails act like invisible blankets, trapping warmth and accelerating climate change. If we look up and think of each contrail as a heat trap that stops the planet from cooling down, that could be effective.

😨 Scars in the sky (25%)
Contrails leave behind trails like scars: unwanted, human-inflicted wounds on an otherwise natural sky. It is something we want to eliminate or conceal. Scars don’t belong in the sky. On a clear blue day, contrails mar the beauty of the sky, and these scars can serve as a reminder of their climate impact.

🛫 Plane exhaust (17%)
Just like the exhaust from gas-powered cars on a cold day, contrails are the visible "exhaust" of planes. Aircraft leave behind both invisible CO2 and visible contrails, which contribute to warming in a way we should no longer ignore.

👻 Ghost clouds (4%)
Contrails haunt the sky. They are not like natural clouds but can change shape, spread out, and turn into climate-warming clouds. We can’t see them at night, but that is when their heating effect is at its highest. After a while, they vanish like ghosts and leave behind a hotter planet. It's pretty scary.

Thanks for all your votes! Does “heat traps” make sense as a metaphor for contrails, or can we come up with something even better?

🎥 Video series coming soon: 10 excuses airlines use to justify why they don’t take action on contrails.

In the coming days, we will be launching a 10-part video series featuring aviation sustainability expert Dr. Paul Hodgson. Together, we will examine some of the most common reasons airlines cite for avoiding action on contrail warming — and why these excuses don’t always hold water.

Each video will be short (2–3 minutes), direct, and designed for sharing. We’ll tackle excuses like:

• “It’s too early - the science is uncertain,”

• “Contrails prediction models are wrong half the time,” and

• “Adding more fuel and CO2 is unacceptable.”

Expect myth-busting, clarity, and some punchy metaphors. Here’s a taster:

Make sure you follow Blue Lines on LinkedIn to get the video in your feed.

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

A big thank you to the Blue Lines reader who directed our attention to these first additions to the Airline Contrail Index since May last year! If you know of any public resources mentioning airlines that are not yet in the index, we are eager to hear from you.

No More Chemtrails Over Florida

A couple of weeks ago, Florida became the second US state (after Tennessee) to pass a law banning “chemtrails”, the popular conspiracy theory claiming that persistent contrails are created because evil people are adding chemicals to jet fuel to manipulate and control the weather, our minds, or the population.

Chemtrails are, of course, just contrails, which are created by condensation from the jet engines. They do impact the climate (which, sadly, is also a secret to many people), but are formed due to atmospheric conditions, not sprayed for nefarious purposes.

Nevertheless, (republican) politicians in more than 20 US states have introduced bills aimed at banning chemtrails, which, if taken to the extreme, could work out in favor of the climate if chemtrails (in reality, climate-warming contrails) were to be banned altogether.

The Florida bill also includes a hotline for citizens to report any weather-manipulating activity to the Department of Environmental Protection. This could prove to cost the local authorities a lot of wasted hours, the next time the air over Florida is cold and humid enough for passing planes to produce consistent contrails.

While the bill was born out of concern for the impact of chemtrails, it does not mention the term “chemtrails”. The new law is aimed at protecting Floridians from geoengineering and weather modification, which is precisely what the UK government recently set aside £50M for scientists to study (in case we are in desperate need to cool down the Earth sometime in the future).

Masterclass in contrails and their climate impact

“Masterclass: What are contrails, how do they impact the climate, and what can be done to stop them?” This is the title of what appears to be the most popular video from the Copenhagen Contrails Conference. Professor Marc Stettler from Imperial College London led this excellent masterclass, and we want more people to watch it. So here are two short video appetizers:

Globally, around 5% of flight distance forms persistent contrails — but in the North Atlantic, it’s more like 10%.

“This gives an indication of where we want to focus any mitigation activities of contrails. Seemingly, the North Atlantic with a very high proportion of flight distance flown forming persistent contrails would be an area to target.”

We need to move from the lab to real-world demonstrations

“We need to work towards real-world demonstrations to tackle complexity in the aviation system and uncertainty head-on. It’s not until we actually try to do it that we understand all the issues that might pop up.”

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

Some highlights in the first 24 months of Blue Lines:

• Created the educational website blue-lines.org

• Created and still maintains the Airline Contrails Index, tracking airline involvement with contrails

• Co-authored and co-edited the RMI-report, Understanding Contrail Management

• Started and grew Blue Lines’ contrails newsletter (and LinkedIn profile) to currently well over 1000 subscribers

• Co-founded and co-organized the Copenhagen Contrails Conference

• Worked on contrail-related communication and tools with Breakthrough Energy / Contrails.org, Google, and others.

• Plus: Has spoken and moderated contrail-related sessions at aviation conferences and events in the US and Europe, co-launched a contrails communications group, and tirelessly attempted to make journalists cover contrails, their climate impact, and the solutions to avoid them.

This list clearly shows that collaboration and cooperation are key. Only a few people work in the contrail space (compared to, for example, SAF), so working together and helping each other are key.

Looking forward, the coming year is very interesting. At Blue Lines, we are especially interested in two tracks:

1. How do we ensure the climate solution of contrails gets on more people’s radars? Especially when the results of the European Monitoring, Reporting, and Verification (MRV) of contrail warming (and other non-CO2 effects) are publicised in early 2026, meaning that travelers will “discover” that the climate impact of flying is even greater than they thought.

2. How do we get airline executives to participate in contrail avoidance trials at scale? As it is now, airlines are incentivized to do nothing (more about this in a later newsletter). We need to change that.

If these two questions are something you are working on, I would love to get in contact and collaborate.

Video appetizers from the Copenhagen Contrails Conference

A couple of weeks ago, we started posting small video bites on LinkedIn of key messages from some of our best speakers at the Copenhagen Contrails Conference. This could act like a teaser for folks to watch the entire talk (all day 1 talks from the conference were filmed and are available here) and get more people engaged in contrail mitigation.

Below you can watch the first three contrail snacks:

Why might contrails be the most visible effect humans have on climate?

Professor Marc Stettler broke it down in his excellent contrails masterclass at
the Copenhagen Contrails Conference.

Watch the entire presentation here.

Contrail warming is at least 100 times bigger than the CO2 emissions from the extra fuel needed to eliminate most contrails

One persistent myth in contrail management is that the CO2 emissions from the extra fuel needed to fly around the contrail-prone areas could outweigh the climate benefit of avoiding those contrails.

In this clip from the Copenhagen Contrails Conference, AIA director Paul Hodgson explains why the fuel burn penalty (around 1% extra fuel) is at least 100 times smaller than the contrail warming.

Let’s stop treating a rounding error as a roadblock.

Watch the entire presentation here.

The 5️⃣ steps to communicating contrails to anyone

🛫 Contrails are complicated. But here is a brilliant, five-step narrative that can be used to tell family, media, or even policymakers about contrails. This recipe was presented by Diane Vitry, interim aviation director at T&E, at the Copenhagen Contrails Conference:

1. Contrails are a visible problem 👀
2. They warm the planet significantly 🔥
3. Their climate impact can be explained ❄️
4. Contrails can largely be avoided 🛩️
5. Fixing them is inexpensive 💰

Watch the entire presentation here.

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

Likewise, speakers and participants have been posting their impressions on LinkedIn after the conference, and what stands out is not just how many angles people are working from—science, policy, tech, operations—but how aligned they are on the need to move forward toward action.

Here are a few quotes that stuck with me.

On Urgency, Momentum, and Myth-Busting 🚀

Paul Hodgson of the Aviation Impact Accelerator at the University of Cambridge spoke about AIA’s Operation Blue Skies contrail plan at the conference. He used his LinkedIn post to break down some persistent myths that he believes should no longer hold us back:

"We must not allow myths and excuses to stand in the way of progress. Contrails are a solvable problem — and it is imperative that we do so.

Myth 1: “Aviation can only move slowly.” But Boeing went from concept to Entry-Into-Service on the 747 in just 4 years and 5 months.

Myth 2: “The risk of CO₂ from fuel burn penalties outweighing contrail savings.” Our report shows the fuel penalty is orders of magnitude smaller in warming than the contrail savings.

Myth 3: “Contrails are just too complicated.” We’ve pumped aviation full of the best & brightest for generations. It would be a betrayal of that talent if we don’t act."

On Policy and Political Will 🏛️

Dimitar Nikov, Policy Officer at DG CLIMA within the European Commission, offered a structured summary of his takeaways:

"What I take out of this conference is that the EU political will on addressing aviation non-CO₂ needs to remain strong and stable.

Uncertainties do exist, but they are not a showstopper. Not all contrails are created equal, and a robust, risk-based approach can move us forward.

We don't need to wait for humidity sensors to begin mitigation — though more sensors would improve our dataset.

The EU MRV system is already launching with millions of flights/year. It’s a perfect playground to test contrail avoidance — and build the case for champion airlines and ATC.

Let’s act now, not later."

Nuala Doyle from Opportunity Green also emphasized the policy gap — and the opportunity to close it:

"Right now, the majority of non-CO₂ impacts of aviation go unregulated. Crucially, the aviation industry isn't paying for its non-CO₂ climate impacts — something they are responsible for under the Polluter Pays Principle.

The upcoming revision of the EU ETS is a good place to start. Can we also set a near-term target for reducing the climate impact of contrails?"

On Technology and Trials 📊🔧

Several voices highlighted the real-world progress that’s already happening. Alejandra Martín Frías of Flightkeys wrote:

"It was a wonderful opportunity to reconnect with old friends and forge new connections in the ongoing contrail discussion. I look forward to continuing these important conversations."

Maxime Meijers, CEO of Estuaire, was enthusiastic:

"Contrails are aviation-induced clouds warming the planet at night. They are one of the cheapest ways for aviation to fix its climate impact.

It started with an insightful discussion with Sebnem Erzan from Google on informing passengers about contrails on Google Flights, and updates to the Travel Impact Model.

Time for our message to resonate beyond the aficionados!"

On Regulation and Readiness 🛫

Jan Lueckhof from DHL used his post to call out what’s missing — and what’s needed next:

"We need to mitigate contrails on a system level — not just EU ETS flights.

To do so, we need a real Single European Sky. Air Traffic Management will need to play a decisive role, and we should start equipping them with the necessary funding now.

Also, the Science Based Targets initiative needs to focus more on contrail mitigation so that voluntary action becomes possible right away."

On Community and Collaboration 🤝

Many participants expressed gratitude for the atmosphere and shared purpose in the room.

Vincent de Haes from To70 excellently led the panel discussion on uncertainty. He described the event as:

"The mother of all bubbles… Two days of focus on contrail awareness, understanding, and action."

Yes, it was a two-day bubble, and everyone inside it caught what was quickly dubbed the “Contrail Virus.” The next step will be to spread this virus in broader circles and get more scientists, airlines, climate organizations, and politicians involved.

Get the presentations and watch the videos.

We had a professional video crew filming and editing all the sessions on the first day of the conference. You can find the videos on the Copenhagen Contrails Conference YouTube channel.

The presentations (and the videos) can also be found on the conference website under the submenus, Agenda Day 1 and Agenda Day 2.

We only share the presentations and video recordings we received the speaker’s permission to share.

Blue Lines reach 1100 subscribers.

Thank you for your continuous support.

Last month, we reached 1,000 subscribers and received this fine illustration from Substack.

This month, we passed 1,100 subscribers.

It’s the plan to keep the Blue Lines newsletters free, so please share them with aviation or climate-interested folks in your network. We are pleased that so many people are reading these newsletters. Thanks again!

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

🌍 Marc Stettler (Imperial College London) will kick us off with a contrail masterclass, so we’re all on the same page from the start.

🛩️ Christiane Voigt (DLR) will examine how cleaner fuels can help mitigate contrails.

📡 Paul Hodgson (AIA, University of Cambridge) will outline the vision for scaling contrail management over the next 5-10 years.

But it doesn’t stop there! Airlines are already testing contrail mitigation strategies—we’ll hear firsthand from TUI Airline, DHL, and others about how they’re piloting these new ways of flying.

For the policy-minded folks, we’re diving into some of the biggest questions:

🛑 How do we manage uncertainty in contrail impact modeling?

🔎 Carrot or stick? What’s the right approach for regulating contrails?

Expect great discussions from leaders at top climate organizations, including:

💡 Andrew Chen (RMI)

💡 Diane Vitry & Carlos López de la Osa (T&E)

💡 Jayant Mukhopadhaya (ICCT)

💡 Matteo Mirolo (Breakthrough Energy)

💡 Aoife O’Leary (Opportunity Green)

💡 Anna Stratton (ClimateWorks Foundation)

And we can’t forget the tech innovators shaping the future of contrail management:

🛰️ Adam Durant (Satavia)

🛫 Alejandra Martin Frias & Raimund Zopp (Flightkeys)

📡 Julien Lopez (Thales)

💡 Maxime Meijers (Estuaire)

🌍 Nikhil Sachdeva (Roland Berger)

💡 Sebnem Erzan (Google)

🛫 Vincent de Haes (to70)

🚀 Plus, a special policy perspective from Dimitar Nikov, Policy Officer at EU’s DG CLIMA.

🔥 This is the conversation the aviation industry needs to have. And this is just a glimpse of what’s in store! There are many more speakers and sessions covering everything from operational strategies to cutting-edge modeling.

👉 Check out the full program and register now at copenhagencontrails.org

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

1. First fleet-wide testing: In 2024, we will see the first airline(s) testing contrail management on their entire fleet. This means analyzing all their flights daily to single out those few flights that can easily be diverted to save thousands of tons of CO2e. This will also give us a better understanding of the costs of managing contrails.

   RESULT: 🛑 Nah, we haven’t really seen fleet-wide testing in 2024 - at least not publicly. Dear reader, please correct me if I’m wrong!

   Thanks for reading Blue Lines! Subscribe for free to receive new posts and support our work.

2. Airline involvement will double: We will see many more airlines getting involved with contrail management – or at least acknowledging the problem, especially in Europe, where all airlines must report their non-CO2 emissions – including contrails – from 2025. At Blue Lines, we track these frontrunners in our Contrail Airline Index. At the time of writing, there are 17 airlines in the index. By the end of the year, I predict this number will double.

   RESULT: ✅ Yes, this actually did happen. In the first half of 2024, more airlines went public on their contrail mitigation efforts, and the Contrail Airline Index went from 17 airlines to 35. Nothing much has changed over the past 6-8 months, though.

3. First public contrail campaign: We will see an airline, airport, or other organization launch the world’s first public contrail campaign. This could be an informational or marketing campaign announcing an airline's total commitment to managing the warming from contrails. I am excited to see who is going to be first.

   RESULT: 🟡 It wasn’t everywhere, but T&E launched a small contrail awareness campaign in parallel with the release of their well-researched contrail report in November 2024.

1 1/2 hits and 1 1/2 misses. Here’s what the crystal ball is telling us for 2025:

1. Corporations will want better contrail warming estimates. For many large software and consulting companies, their Scope 3 emissions from air travel are some of their highest emissions. What companies are doing now to also account for the non-CO2 impacts of air travel (including contrails) is multiplying their CO2 emissions by a factor of 1.7 or 1.9. However, with contrail prediction models and accurate corporate travel data, it should be possible to calculate the warming created by each flight taken by an employee and get much more actionable data.

2. The EU will sponsor at least one new contrail avoidance trial. I am not talking about the ongoing big EU-supported projects like CESAR or CONCERTO, but the EU’s Innovation Fund has specifically requested contrail / non-CO2 projects they can support. In 2024, a handful of airlines got together with flight planners, tech companies, and scientists to form a consortium looking to do thousands of contrail avoidance flights over the next years. The project was denied funding, but hopefully, someone will be successful in 2025.

3. New climate organizations will start focusing on contrails. Several climate or policy nonprofit organizations focusing on transportation are involved in contrail management work. However, many - more general climate-focused - NGOs don’t have their eyes open for this climate opportunity yet (I am looking at you, Greenpeace). Maybe one or two new organizations will get involved.

Okay, now I will stop making up stuff and stay with the facts. We promise to follow up on the predictions in 2026.

✈️🌍 Registration is now OPEN for the Copenhagen Contrail Conference! 🔥📅

Contrails are one of aviation’s biggest climate challenges—but solutions are within reach. At #CopenhagenContrails, we’re bringing together the brightest minds from academia, the aviation industry, tech companies, and civil society to turn knowledge into impact.

🚀 Join us on March 25-26, 2025, to explore:

✅ Practical solutions for reducing contrail warming

✅ Insights from leading contrail experts across sectors

✅ Collaboration opportunities to scale up action

📍 Scandic Copenhagen, hotel in Copenhagen, Denmark

⚡ Limited spots available!

🌐 Register now at copenhagencontrails.org.

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter know, contrails are the thin white streaks that airplanes sometimes leave behind in the sky, created from water vapor and engine soot. Some of these condensation trails can spread out and form high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space while also trapping outgoing energy in the atmosphere, leading to a net warming of our planet equivalent to 1-2% of human-induced global warming. However, studies and trials indicate that it is relatively simple to avoid most warming contrails by flying around areas in the atmosphere that are prone to contrails. This climate solution—often referred to as contrail management or contrail avoidance—is what Blue Lines advocates for and hopes to see implemented globally.)

See you soon.

Joachim Majholm,

Blue Lines

What is the Copenhagen Contrails Conference?

The Copenhagen Contrails Conference 2025 is a first-of-its-kind global gathering focused exclusively on addressing the climate impact of aviation contrails. On March 25-26, 2025, at the Scandic Copenhagen, the conference will bring together leaders from aviation, climate organizations, policymaking, and corporate sustainability to drive actionable solutions for mitigating contrail-induced climate warming. The conference takes place in Copenhagen, three months before Denmark takes over the Presidency of the Council of the EU.

Why This Matters

Contrails (condensation trails) are aviation's most considerable non-CO2 climate impact, yet they remain under-recognized in global climate action efforts. This conference aims to turn contrails science into real-world strategies for meaningful climate mitigation by leveraging the latest scientific insights and gathering first-mover stakeholders.

Key Objectives

The conference seeks to:

• Raise Awareness: Enable aviation stakeholders, climate leaders, corporates, and others to build a clear understanding of the opportunities connected to contrails.

• Foster Collaboration: Connect policymakers, industry, scientists, sustainability managers, and climate advocates to accelerate contrail-focused solutions.

• Inspire Action: Launch discussions on implementing contrails avoidance measures and targets while inspiring future political action.

2025: A Landmark Year

In January 2025, the European Union introduced new regulations targeting contrails and other non-CO2 aviation emissions, and in July 2025, Denmark will assume the Presidency of the Council of the EU, offering a unique opportunity to shape the policy agenda.

Core Themes

Contrails Science: What are the scientific facts? What is the impact of contrails? How do we handle the scientific uncertainty? What are the main challenges?

Scalable Solutions: Exploring cost-effective and practical strategies for contrails avoidance and how to make large-scale avoidance trials operational.

Policy and regulation: The EU has just introduced a new Monitoring, Reporting, and Verification system. What is it aiming to do? How could it make a difference?

Collaboration and Innovation: Partnerships between aviation stakeholders, climate and tech organizations, corporations, and policymakers to accelerate change.

Target Audience

The conference will bring together:

• Scientists and researchers: Experts in contrails science, aviation, and climate impact.

• Airline industry: Airlines, aerospace companies, tech companies, and other aviation-related organizations.

• Policymakers: Regulators, government officials, and climate policy advisors.

• Sustainability managers: Corporate leaders looking to reduce scope 3 emissions.

• Climate organizations: NGOs and advocacy groups working on aviation and climate issues.

• Climate-concerned individuals: Individuals engaged in the impacts of aviation.

• Press and Media: Journalists covering climate, aviation, and sustainability topics.

Save the date: March 25-26, 2025
Location: Scandic Copenhagen, Denmark

📅 Mark your calendars and join our interest list to receive updates, agenda details, and registration information.

🌐 Visit us at copenhagencontrails.org.

🔗 Keep yourself updated here.

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter will know, contrails are the wispy white stripes that airplanes sometimes leave behind in the sky (made from water vapor and engine soot). Some of these condensation trails can spread out and become high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space but also trap outgoing energy in the atmosphere, resulting in a net heating of our planet equivalent to 1-2% of human-induced global warming. However, we can relatively easily avoid most warming contrails by flying around the contrail-prone areas in the atmosphere. This climate solution – often called contrail management or contrail avoidance – is what Blue Lines promotes and wants to see spread worldwide.)

See you soon.

Joachim Majholm,

Blue Lines

🥇 The newsletter with the most reads was our April 3rd edition, New research: contrail management is a very inexpensive climate solution, which was all about a new study simulating contrail avoidance on almost 85,000 American Airlines flights in near real-time for four weeks in 2023/24. The conclusion was that contrail management at scale will require minimal additional cost (0.08%) and fuel (0.11%) investments to avoid 73% of the climate warming.

🥈 Second top story was a similar November 3rd post, Contrail Avoidance is Cheaper Than a Cup of Airport Coffee, summarizing a recent T&E meta-study where they analyzed expenses related to contrails management and concluded it will only cost passengers 1-4 euros extra per ticket to avoid the majority of the climate impact.

🥉 Finishing off the top three is our September 3 post, One Airline is Leading the Way and Has Committed to Contrail Reduction Targets 🏆, focusing on Blue Lines’ Airlines Contrail Index, where Delta Airlines currently is the only airline at the platinum tier which requires airlines to have contrail reduction targets. Delta is promising to reduce contrail warming by 80% in 2035 and by 100% in 2050 🎉. These targets are admirable and, we believe, obtainable, and more airlines should follow Delta Air Lines’ fine example.

Happy new year everyone, and here’s to a 2025 with less warming contrails, more trials, more climate action, and lots of engagement from airlines, ANSPs, corporates, climate orgs and climate concerned flyers!

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter will know, contrails are the wispy white stripes that airplanes sometimes leave behind in the sky (made from water vapor and engine soot). Some of these condensation trails can spread out and become high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space but also trap outgoing energy in the atmosphere, resulting in a net heating of our planet equivalent to 1-2% of human-induced global warming. However, we can relatively easily avoid most warming contrails by flying around the contrail-prone areas in the atmosphere. This climate solution – often called contrail management or contrail avoidance – is what Blue Lines promotes and wants to see spread worldwide.)

See you soon.

Joachim Majholm,

Blue Lines

As readers of this Substack will know, contrail avoidance is an inexpensive, relatively easy way to eliminate 1-2% of human-induced global warming. Nevertheless, the aviation industry, in general, has not been proactive in dealing with the contrail problem.

“Recognising the impact of non-CO2 effects, particularly contrails, on our warming climate and the urgent need for action, we, aviation and climate scientists, call upon global decision makers to implement solutions to tackle non-CO2 effects of aviation on top of decarbonization efforts,” the letter reads and calls for awareness-raising of the general public on contrails’ climate impact.

The scientists - from all over Europe, including the German Aerospace Center (DLR) and universities like Sorbonne, Cambridge, Oxford, and Imperial College London - also urge policymakers to require companies to report the full climate impact of their business travel while also calling for large-scale contrail avoidance trails. Finally, the scientists ask for “a policy framework, underpinned by a robust monitoring system, to reduce warming contrails and other non-CO2 effects. This will ensure that mitigation measures are quickly adopted, as soon as they are ready.”

Here is the press release from T&E accompanying the letter.

One Day Left! Take Photos of Contrails and Win a Trip to Europe

The E-Contrail project and Breakthrough Energy (contrails) are collaborating to collect more ground observation photos of contrails for research (Deadline is November 24).

Therefore, E-Contrail has launched a competition, which is very simple: Sign up on this webpage, download the contrail observer app (Apple, Android), and take photos with the app of contrails in the sky. That’s all you need to enter the competition and help researchers advance contrail climate science ❤️‍🔥.

🏆 The prize for the best contrail photo is a trip to “Europe” - the E-Contrail folks have not yet decided where to hold their next meeting - it could be Madrid, Brussels, you name it. This is a great way to help the climate. Thank you! 🙏

Go to Blue Lines’ educational website to explore contrails in depth.

(As regular readers of the Blue Lines newsletter will know, contrails are the wispy white stripes that airplanes sometimes leave behind in the sky (made from water vapor and engine soot). Some of these condensation trails can spread out and become high-altitude ice clouds (cirrus), which reflect some of the sun’s energy back into space but also trap outgoing energy in the atmosphere, resulting in a net heating of our planet equivalent to 1-2% of human-induced global warming. However, we can relatively easily avoid most warming contrails by flying around the contrail-prone areas in the atmosphere. This climate solution – often called contrail management or contrail avoidance – is what Blue Lines promotes and wants to see spread worldwide.)

See you soon.

Joachim Majholm,

Blue Lines