Study attributes 32,619 European heat deaths to human-caused warming

The estimate excluded May and deaths beyond the 854 studied cities

Record heat across Europe this summer helped kill more than 50,000 people, with nearly two-thirds of that toll blamed on human-caused climate change, a new study by researchers at Imperial College London found. Researchers modeled heat-related deaths for different age groups in 854 European cities during repeated heat waves in June, July and August, and estimated that 50,391 people died from warmer temperatures. Of those deaths, 32,619 were attributed to the extra heat caused by the burning of coal, oil and gas, according to the paper, which is set for an upcoming issue of Nature Health.

The team used an established and accepted scientific method to separate deaths from natural high-summer heat from those associated with changes heat-trapping gases have made to the climate. They ran computer simulations of a world without climate change and compared the modeled deaths with mortality during this summer’s heat waves, treating the difference as the additional toll associated with global warming.

Study co-author Garyfallos Konstantinoudis, a biostatistician at Imperial College London, said the researchers also had to use statistical modeling to come up with the base count of heat deaths because those deaths are underreported and often not listed in death certificates, despite being a major factor. Several outside experts agreed with him that the methods were state of the art.

Barnes said the team then applied a mathematical equation used in several previously peer-reviewed studies. The equation factors in specific ages and temperatures for each of the 854 cities, based on a localized optimal temperature that coincides with the fewest deaths. When conditions are warmer or colder, the equation calculates excess deaths above those lowest-death conditions.

Researchers said this summer’s death figures are underestimates because they do not count a deadly heat wave in May and cover only the 854 cities, which are about 40% of Europe’s population. The estimate of 50,391 deaths is 71% higher than the previous deadliest summer in the studied cities, when the same researchers estimated 29,480 heat-related deaths in 2022. That benchmark came from the team’s study released earlier this month, which tracked yearly summer heat-related deaths in the 854 European cities.

About one-third of the estimated deaths occurred from June 17 to July 1, during an intense heat wave when temperatures were 9.5 degrees Fahrenheit, or 5.3 degrees Celsius, above normal, Konstantinoudis said.

The study identified Italy, France, Spain and Germany as the countries with the highest death tolls. An earlier study from the same team, released earlier this month, found that Rome had the highest heat-death total among European capitals from 2000 through 2025.

More than half of the people who died during Europe’s heat were age 85 or older, Konstantinoudis said. The heat also killed more than 800 people between the ages of 20 and 44.

Barnes said the summer would already have been an abnormal natural hot spell without the additional warming from human activity, on top of a huge amount of climate change. She said Europe is the fastest-warming continent, although the Arctic, which is not a continent, is warming even faster. Europe is 4.5 degrees Fahrenheit, or 2.5 degrees Celsius, hotter than it was during pre-industrial times, she said. Barnes said the additional warming can push temperatures from uncomfortable conditions into dangerous and potentially deadly ones for many people. The underlying warming from human activity, mostly from fossil-fuel burning, is raising temperatures by what can sound like a small amount, she said.

Lead author Clair Barnes, a climate scientist at Imperial College London, said infrastructure in much of Western and Northern Europe was not designed to cope with current temperatures. “Much of Western and Northern Europe, our infrastructure is just not designed to cope with the sort of temperatures that we are seeing now because of the effects of human-caused warming,” she said. Barnes also said some European cities experienced temperatures 21.6 degrees Fahrenheit, or 12 degrees Celsius, above normal this summer.

Barnes said the share of heat deaths attributable to global warming has grown from about 45% in the early 2000s to 65% now. Dr. Howard Frumkin, the former director of the National Center for Environmental Health in the United States and a researcher not involved in the study, said increasing analytical accuracy contributes to higher estimates.

“Summers are getting hotter, and the analytical tools for attributing deaths to heat are getting more accurate,” Frumkin said. “Together, these two trends yield increasingly high and increasingly accurate counts of heat-related deaths.”

Researchers checked their calculations against real-time estimates from government agencies. Konstantinoudis said the results mostly, but not always, matched fairly well. The team’s method calculated 2,700 excess deaths during May and June heat waves in Britain, while the United Kingdom health statistics agency reported 2,800.

Dr. Courtney Howard, a Canadian emergency room physician and president-elect of the Canadian Medical Association who was not part of the research, called for greater heat preparation and reductions in fossil-fuel use. “We need to prepare for the heat we cannot now avoid, with urgent investments in heat early-warning systems, equitable access to low-carbon cooling, and neighborhood buddy systems that check on and support people most at risk — while rapidly reducing the fossil fuel use driving the crisis,” Howard said.

Dr. Jonathan Patz, a University of Wisconsin-Madison professor of health and the environment who was not part of the research but also praised it, said adaptation alone would not address the broader health risk. “We can’t just be mopping up the mess on the floor without thinking about turning the faucet off,” Patz said. He called for better cooling, protection for vulnerable populations from the inevitable increased frequency and extreme heat waves, prevention at multiple levels and absolutely addressing the burning of fossil fuels.