Climate change caused 16,469 deaths in European cities this summer, new research estimates.
This summer was the fourth hottest in European history, and its effects on the continent’s population have been widely reported. Spain experienced its most intense heat wave in history in August 2025. Türkiye saw its highest recorded temperature ever (50.5°C, or 122.9°F). Finland saw an “unprecedented” three straight weeks of 30°C heat.
A new, rapid-analysis study by researchers at Imperial College London (ICL) and the London School of Hygiene & Tropical Medicine estimated that 24,400 people across 854 European cities and urban centers died from heat-related causes between June and August 2025. Using climate models and a comparison of this figure with how many heat-related deaths would have occurred in a 1.3°C cooler world, the researchers estimated that climate change was responsible for 68% of these deaths.
“In other words, it could have tripled the death toll,” said Garyfallos Konstantinoudis, a biostatistician at ICL’s Grantham Institute – Climate Change and the Environment.
Though the planet has warmed about 1.3°C overall since preindustrial times, Europe is warming more quickly than the rest of the planet, meaning that temperatures on the continent this summer were about 1.5°C to 2.9°C warmer than they would have been without anthropogenic warming.
In a Tuesday press conference, the researchers explained that their estimate of 16,649 climate-related deaths is likely conservative, in part because climate models are known to underestimate warming in Europe. In addition, their estimate includes only deaths in urban centers with populations above 50,000 people—areas that represent only about 30% of Europe’s population. They focused on these urban areas because these locations had greater data availability, but that means the estimate is just a snapshot.
“These numbers represent real people who have lost their lives in the last months due to extreme heat,” said Friederike Otto, a climatologist at ICL’s Centre for Environmental Policy. “Many of these would not have died if it wasn’t for climate change. And if we continue on the path that we are on now, continue burning fossil fuels, these deaths will only increase.”
The Hidden Costs of Heat
The study also notes that northern Europe experienced a higher proportion of heat-related deaths than southern Europe, despite southern Europe enduring higher heat (some cities in the region have warmed by up to 3.6°C) and more excess mortality overall. The reason is that prior to climate change, heat in northern Europe rarely reached levels that affected human health at all. Now, explained Konstantinoudis, “almost all of the heat-related deaths in northern Europe…are due to climate change.”
Courtney Howard, vice-chair of the Global Climate and Health Alliance and an emergency physician in Canada’s Yellowknives Dene Territory, who was not involved in the study, noted that extreme heat can raise the risk of deadly heart attacks and strokes because high heat causes the heart to work harder. It can also fatally worsen respiratory conditions such as asthma because ozone pollution tends to increase during extreme heat events. Thus, many of the deaths that occur during heat waves are not necessarily recorded as heat deaths.
“The result is that heat numbers capture only a small fraction of the real story at the bedside,” she said. “Experts do not believe that we can adapt health systems adequately to cope with the temperatures that we are currently facing. That’s why reducing fossil fuel use is one of the most important public health interventions of our time.”
To estimate heat deaths, researchers turned to an existing dataset that showed relationships between temperature and mortality across the 854 urban areas used in the study. They then estimated the number of daily deaths during the heat wave using historical Eurostat data and information on which days exceeded minimum mortality temperature.
It’s Not Just Europe
Among the countries included in the study, the Baltic nations of Estonia, Latvia, and Lithuania were the only three that did not experience hotter-than-usual summers.
Rome, Athens, and Bucharest saw the highest heat-related death rates per capita among European capital cities, the study found. In general, cities are hotter than surrounding areas because of the urban heat island effect, in which concrete surfaces trap heat and raise city temperatures.
Chris Callahan, a climate scientist at Indiana University Bloomington who was not involved in the study, said that though the study is not peer reviewed, its methods appear to be “standard and based on extensive peer-reviewed research.”
The researchers noted several factors their study did not consider, including cities’ efforts to adapt to climate change and all adverse health effects of heat. It also did not capture changes to baseline populations that occurred post-COVID-19, which might have led to higher numbers for some cities.
“The findings in this study are stark and concerning, as they illustrate that climate change is already the dominant influence on heat-related mortality in Europe,” Callahan told Eos in an email.
Europe faces particularly high risks related to climate change, he added, both because temperatures are rising more quickly in western Europe than in other parts of the world and because Europe’s aging population is highly vulnerable to heat. In fact, this study found that people over 64 made up 85% of the climate-related deaths in European cities this summer.
However, the study authors noted that the growing toll warming is taking on human health is not unique to Europe.
“The specifics will vary wherever you’re looking in the world, but the basic point of these studies will always be the same: that we are warming the world through our fossil fuel emissions and other activities and that this is causing people to die,” said Clair Barnes, a statistician at ICL’s Centre for Environmental Policy.
This article originally appeared in EOS Magazine.
