Climate Change Linked to Thousands of Heatwave Deaths in Europe
An estimated 1,500 people across 12 European cities were killed by human-caused climate change during the latest heatwave, according to a rapid analysis conducted by scientists at Imperial College London and the London School of Hygiene & Tropical Medicine. The study found that burning fossil fuels has made heatwaves up to 4°C hotter in Europe, tripling the number of heat-related deaths that occurred between 23 June and 2 July.
This is the first time a rapid analysis—where researchers assess the influence of climate change on an extreme weather event—has been carried out for a heatwave. While the study focuses on a dozen cities, researchers estimate that the true death toll across Europe could be in the tens of thousands.
Dr Friederike Otto, Professor in Climate Science at the Centre for Environmental Policy, Imperial College London, said: “It shows that climate change is an absolute game changer when it comes to extreme heat, but still very much under-recognised.” She added, “If we continue to follow the wishes of the fossil fuel industry and delay serious mitigation further, more and more people will lose their lives, for the financial benefit of only a tiny, rich, loud, influential minority.”
How Are Heatwave Deaths Estimated?
To estimate how many excess heat deaths were caused by climate change, researchers first analysed historical weather data to determine how intense the temperatures would have been in a world that hadn’t been warmed by 1.3°C. They found that climate change, primarily caused by the burning of oil, coal, and gas, made the heatwave 1–4°C hotter. It’s also making heatwaves strike earlier in June.
Separate research from the EU’s climate change service Copernicus, published today, shows that June 2025 was the fifth hottest June on record in Europe, marked by two significant heatwaves. During the second event between 30 June and 2 July, surface air temperatures exceeded 40°C in several countries, reaching as high as 46°C in Spain and Portugal.
The World Weather Attribution team then used previous research on the relationship between heat and the number of daily deaths, regardless of cause, in the 12 cities. They estimated the number of heat-related deaths in both the recent heatwave and a hypothetical cooler event over ten days.
The study estimates that about 2,300 people died in the extreme temperatures across the cities, from Lisbon to Budapest. If the climate hadn’t been heated up, there would be about 1,500 fewer excess deaths, meaning climate change is behind 65 per cent of these excess deaths.
Where Did the Heatwave Claim the Most Lives?
Climate change was responsible for 317 of the estimated excess heat deaths in Milan, 286 in Barcelona, 235 in Paris, 171 in London, 164 in Rome, 108 in Madrid, 96 in Athens, 47 in Budapest, 31 in Zagreb, 21 in Frankfurt, 21 in Lisbon, and 6 in Sassari, the findings show.
This means the likely death toll was higher than other recent disasters, including last year’s Valencia floods (224 deaths) and the 2021 floods in northwest Europe (243 deaths).
Although the greatest number of excess deaths occurred in Milan, the highest proportion is estimated to be in Madrid: 90 per cent, due to the large increase in heat that pushed temperatures past a threshold where heat deaths increase rapidly.
Who Is Most at Risk?
People aged 65 and over made up 88 per cent of the deaths linked to climate change, highlighting how those with underlying health conditions are most at risk of premature death in heatwaves. In contrast to climate-driven floods and wildfires, heatwaves are regarded as a silent killer.
“Most people who die in heatwaves pass away at home or in hospitals as their bodies become overwhelmed and give in to pre-existing health conditions such as heart disease, diabetes, and respiratory problems,” says Dr Malcolm Mistry, Assistant Professor at the London School of Hygiene & Tropical Medicine.
But people of all ages need to take the threat seriously—contrary to what some media images of people playing on beaches might suggest. “A lot of people might feel they are invincible, but they are not,” says Dr Otto.
European Countries Are Tightening Up Their Heat Action Plans
Good progress has been made in Europe on developing heat action plans, the researchers note. These national plans set out the actions that can be taken before and during dangerous high temperatures, and authorities have got better at spreading the message widely.
However, to protect people from more dangerous heatwaves, long-term strategies to reduce the urban heat island effect are crucial—such as expanding green and blue spaces—as well as short-term measures like cooling centres and support systems for vulnerable citizens, they add.
Ultimately, the best and most efficient measure of all is to drastically cut our greenhouse gas emissions. “The only way to stop European heatwaves from becoming even deadlier is to stop burning fossil fuels,” says Dr Otto.
The Need for Global Action
“A warming climate sure as hell makes heatwaves worse,” comments Richard Allan, Professor of Climate Science at the UK’s University of Reading, who was not involved with the analysis. “Communities need to adapt to an increasingly dangerous world through more resilient infrastructure and improved warning systems, yet it is only with rapid and massive cuts in greenhouse gases through collaboration across all sectors of society that worsening of weather extremes can be reined in.”
Dr Chloe Brimicombe, climate scientist at the Royal Meteorological Society, adds that, “Research like this is important and being used more in climate litigation cases where groups take countries and companies to court over climate change.”
