Europe has been hit by several climate change-fueled heatwaves this summer, estimated to have killed more than 10,000 people in June 2026 alone. That number will surely climb as the extreme heat continues and new mortality numbers come in. But the subject that drew the most media attention wasn’t early warning systems, cooling centers, or protections for outdoor workers. It was air conditioning.

Nearly every interview I did on European heatwaves this summer had the same question: should Europe adopt air conditioning like the United States? My first answer is that, as a planner, I think the people and their policymakers across Europe living through the heatwaves are the ones who should decide how they cool themselves.

But I also think the question is framed wrong. It assumes indoor cooling is something a country can easily decide to either adopt or not, and it assumes the American standard for indoor cooling should be the goal. Roughly 90% of American households have air conditioning, the highest rate in the world, compared to about 27% globally and about 20% across Europe. The United States is the outlier, not the standard. And extreme heat is still our #1 weather-related killer, despite our high air conditioning adoption rates.

Why Europe has hesitated on AC

The debate over the role of air conditioning in Europe has received a lot of coverage. The hesitation to simply adopt it carte blanche isn’t irrational, though; there are real constraints behind it.

The first is that much of the European building stock is very well designed for its historic climate. Europe’s housing is older, with a whole host of regional adaptations that allowed buildings to work for their inhabitants well pre-air conditioning. The older building stock also often predates modern ductwork, and retrofits can be prohibitively expensive.

The second is emissions targets. European countries have mandated greenhouse gas cuts, and adding millions of air conditioning units runs against those commitments. All of those new air conditioners would also dump additional waste heat into their surroundings, increasing the urban heat island effect.

The third is local practices and beliefs, which have to be taken as seriously as the buildings themselves. Opening windows at night to flush the day’s heat is a deeply ingrained method in many places, as are ideas about how air conditioning harms health.

It’s not like Europe has ignored extreme heat as a threat. One of the earliest examples of a heat plan is France’s National Heatwave Plan, implemented after the catastrophic 2003 heatwave that killed 14,802. The national plan focused on improving public health surveillance, early heat warnings, and local emergency responses and is attributed to saving more than 4,000 lives during a heatwave in 2006, all without increases in air conditioning. More recently, European cities have adopted heat action plans (HAPs) and implemented both heat mitigation strategies to reduce the urban heat island and heat management strategies to prepare for and respond to heat that can’t be prevented.

What Europe can learn from the United States

Here’s the lesson United States air conditioner adoption rates actually teach, and it isn’t the one Americans usually offer. Widespread air conditioning doesn’t protect everyone from extreme heat.

Air conditioning protects people who can afford to run it. Energy costs are rising, and many households respond by rationing cooling, setting thermostats higher than is safe to prevent losing service to shutoffs. A tragic share of indoor heat deaths in Arizona occur in homes that have air conditioning but where the unit isn’t working or isn’t being operated for cost concerns.

Air conditioning protects people only while the power holds. A house designed entirely on the assumption of mechanical cooling can become an oven within hours of an energy grid failure, and grids can fail during heatwaves, when demand peaks.

So the United States’ lesson for Europe isn’t simply “install units.” It’s that our high adoption rate measures equipment, not necessarily protection, and a country can reach 90% and still not protect everyone. Those who can install air conditioning in Europe and across the world will increasingly do so, so let’s make sure we don’t leave behind those who cannot.

What the United States can learn from Europe

The exchange runs the other way too. Europe’s older buildings utilize passive cooling strategies we have designed out of ours in the United States: thermal mass, external shutters and shading, cross ventilation, building orientation, tall ceilings, and courtyards. These passive design strategies work with the local climate instead of against it, and keep working even when the grid doesn’t.

The problem raising the air conditioning question is that the passive design strategies no longer match the climate Europe is now experiencing, and are likely not enough on their own to keep buildings thermally safe anymore.

In the United States, our building codes assume mechanical cooling will always be available, which is now one of our weaker links in heat resilience. Passive design, just like air conditioning, isn’t a silver bullet. I certainly wouldn’t survive a Tucson summer in a building with only passive design and no AC.

Practically speaking, though, there are real benefits. Passive design reduces how much mechanical cooling a building needs and makes buildings more resilient when energy grids fail. And the co-benefits of the energy efficiency gained are reducing greenhouse gas emissions that cause climate change and reducing the waste heat that increases the urban heat island effect.

Retrofit buildings, but cool the public ones first

The United States and Europe actually share two challenges. The first is that retrofitting the built environment, for either air conditioning or passive design, is slow and expensive. The second is that both are struggling with treating public cooling as infrastructure. Neither continent has a plan, funding mechanism, or problem owner for doing both at the speed and scale that extreme heat requires.

What’s the solution?

First, retrofit the built environment for the climate we’re now experiencing and will face in the near future. In both the United States and Europe, there is no one-size-fits-all prescription to retrofit buildings and cities. Regional climate, geographic, cultural, and building differences require local approaches that accommodate more indoor cooling and passive design.

Second, treat public cooling as a serious infrastructure investment rather than an emergency response tactic to be activated during heatwaves. This means cooling government buildings, libraries, schools, clinics, community centers, transit stations, trains, and buses. Public cooling scales faster than retrofitting millions of housing units, and spreads the cost instead of leaving it all to individuals.

If you’ve worked on either side of this, in a European city weighing air conditioning or an American one weighing its building code, I’d like to hear what you’re seeing.

— Ladd

Subscribe now

Our cities were built for a climate that no longer exists.

That’s the sentence I’ve been repeating in media interviews, in public and academic talks, and in discussions with policymakers. It’s also why I’m starting this newsletter.

Extreme heat is the deadliest weather hazard in the United States. It kills more people than hurricanes, floods, and tornadoes. Yet the world is less prepared for extreme heat than for other hazards, even though heat risk is rapidly increasing due to both climate change and how we plan and build our cities.

One reason we’re unprepared for extreme heat is that it’s a largely invisible hazard. Its impacts are less visually dramatic than hazards like wildfires or floods. These hazards also have hazard zones we can plan for: floods have floodplains and wildfires have wildland urban interface areas.

Another reason is that regional planning decisions that increase the urban heat island span jurisdictional boundaries. Similarly, when heatwaves occur, their impacts often span city, region, state, and even national borders, often exceeding our capacity to respond.

Until recently, there were also no dedicated heat plans, policies, or officials responsible for addressing it. The nascent efforts to address heat risk have historically been siloed off in professions like urban planning, public health, and emergency management. Compare this to other hazards, for which there are entire dedicated professions and government structures for protecting communities.

The causes of extreme heat exceed political boundaries, and the solutions to address it must span sectors and levels of government.

That is what a “heatshed” names. It’s the physical and policy scale at which heat actually operates, and therefore the scale at which it has to be planned for and governed.

heat·shed | /ˈhētˌshed/ | noun

1. The spatial and policy area across which extreme heat must be understood and governed as a shared condition — crossing city, regional, and national boundaries, as a watershed does for water. A heatshed does not stop at jurisdictional boundaries, and neither do the solutions required to address it.

2. A critical turning point at which extreme heat must be rapidly addressed to protect health and livelihoods worldwide. We are living through a heatshed moment.

— After watershed, which holds both senses: the land where all water drains and the critical moment things change forever.

Where the term “heatshed” came from

I first used “heatshed moment” in my TEDx talk, referring to a critical turning point where heat has to be addressed as urgently as any other climate risk. I then made the case for the “heatshed moment” in a commentary with Sara Meerow in the Journal of Urban Affairs, which also builds on our earlier work defining heat resilience and heat governance.

Ironically, I think the spatial and policy area comparison of a heatshed to a watershed is the more useful part of the term. We already accept that no city manages its water in isolation. We have interstate compacts, regional authorities, and decades of case law around the basic fact that water crosses jurisdictional lines. Nobody argues that a river or floodplain should respect a city boundary.

Heat behaves the same way, but we plan for and govern it as though it doesn’t.

What this newsletter is

It's summer in the Northern Hemisphere, and climate change is reliably breaking temperature records again. Most of the coverage on extreme heat still repeats the same beats I see year after year, with more headlines on how many temperature records were broken and how many people died. That’s necessary, but it’s not enough. The harder questions are the ones after that. How will we better prepare for the next inevitable record-breaking heatwave? How do we plan our cities better to reduce the urban heat that is within our local control? What lessons can we learn from the places that have already started addressing heat?

That’s what I work on, and that’s what this newsletter will be about: how we plan for and govern extreme heat. Sometimes from my research, sometimes from observations of policymaking, sometimes from the field.

What to expect

I’m an academic, and let’s be honest, I’m used to having my writing thoroughly peer reviewed and published at the speed of peer review (hint: not fast). This is my attempt to experiment with the opposite — to think in public and at the speed at which extreme heat is actually happening.

Some posts will be a full-fledged argument. More often, they will be my response to a timely extreme heat topic, a snippet from something longer I’m working on, or a question I don’t have an answer to yet.

I’ll aim to post monthly, for now.

It’s free, and it will stay free.

If that sounds useful, subscribe below. And if you know someone who wants to address the challenge of extreme heat, send it their way.

— Ladd