Study estimates 50,391 heat deaths across 854 European cities

Researchers say the estimate excludes a deadly May heat wave and covers about 40% of Europe’s population

Blistering record heat in Europe this summer helped kill more than 50,000 people, according to a study set to appear in an upcoming issue of Nature Health. Researchers modeled heat-related deaths for different age groups in 854 European cities during repeated heat waves in June, July and August and found that 50,391 people died from warmer temperatures, 32,619 of them from the extra heat caused by the burning of coal, oil and gas. The researchers said nearly two-thirds of the modeled toll was attributable to human-caused climate change, but they also said the estimate was an underestimate because it excluded a deadly May heat wave and covered only cities with about 40% of Europe’s population.

The modeled estimate excludes part of the summer’s toll

The same researchers produced an earlier study this month tracking yearly summer heat-related deaths in those 854 cities. Their new findings put this summer’s modeled toll 71% higher than the previous deadliest summer, which recorded 29,480 deaths in 2022.

The researchers said the current figures were underestimates for two reasons: They did not count the deadly heat wave in May, and they included deaths only in the 854 cities, which hold about 40% of Europe’s population.

About one-third of the deaths occurred from June 17 to July 1, during a particularly intense heat wave when temperatures were 9.5 degrees Fahrenheit (5.3 degrees Celsius) above normal, said Garyfallos Konstantinoudis, a biostatistician at Imperial College London and a study co-author.

Barnes cited infrastructure limits in much of Western and Northern Europe

Some European cities recorded temperatures 21.6 F (12 C) warmer than normal this summer, lead author Clair Barnes, a climate scientist at Imperial College London, said.

“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,” Barnes said.

She said Europe is the fastest-warming continent, although the Arctic — which is not a continent — is warming even faster. Europe is 4.5 F (2.5 C) hotter than pre-industrial times, Barnes said.

Without the additional heat from fossil-fuel burning, Barnes said, “This would’ve already been an abnormal natural hot spell on top of a huge amount of climate change.”

“Just the underlying warming from human activity, from mostly the burning of fossil fuels, it’s increasing all of our temperatures by what sounds like quite a small amount,” Barnes said. “For many people, it’s certainly the case that that extra two-and-a-half degrees (Celsius) of warming is what’s going to tip those temperatures from uncomfortable to dangerous and potentially deadly.”

Highest tolls were in four countries; over half of deaths were age 85 or older

Italy, France, Spain and Germany recorded the highest death tolls, the study said. In the team’s earlier study published this month, Rome had the highest heat death total of all the European capitals from 2000 to 2025.

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

Researchers modeled deaths and checked estimates against government data

The team used an established and accepted scientific method to determine how many of the 50,000 heat deaths came from natural high summer heat and how many resulted from heat-trapping gases’ effects on the climate. The researchers ran computer simulations of a world without climate change and compared the results with the deaths that occurred this summer. The difference represented deaths caused by global warming.

The percentage of heat deaths attributable to global warming has grown from about 45% in the early 2000s to 65% now, Barnes said.

The team also used statistical modeling to establish the base count of 50,000 heat deaths because those deaths were underreported and often not listed on death certificates, even though heat was a major factor, Konstantinoudis said. Several outside experts agreed with him and called the methods state-of-the-art.

Barnes said the researchers ran a complex mathematical equation that had been 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 it is warmer or colder, the equation calculates excess deaths above the lowest-death conditions.

The researchers then checked their calculations against real-time estimates from government agencies. Mostly — but not always — the estimates matched fairly well, Konstantinoudis said. The team’s methods for the May and June British heat waves calculated 2,700 excess deaths, while the United Kingdom health statistics agency reported 2,800, he said.

Outside experts urged adaptation and fossil-fuel reductions

“Summers are getting hotter, and the analytical tools for attributing deaths to heat are getting more accurate,” said Dr. Howard Frumkin, former director of the National Center for Environmental Health in the U.S., who was not part of the study. “Together, these two trends yield increasingly high and increasingly accurate counts of heat-related deaths.”

“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,” said Canadian emergency room physician Dr. Courtney Howard, president-elect of the Canadian Medical Association, who was not part of the research.

Adapting is only part of the answer, said Dr. Jonathan Patz of the University of Wisconsin-Madison, who was not part of the research but praised it. “We can’t just be mopping up the mess on the floor without thinking about turning the faucet off,” said Patz, a professor of health and the environment. “So we need prevention at different levels. We need better cooling and protecting vulnerable populations from inevitable increased frequency and extreme heat waves. But we also need to go to the root of the problem and absolutely address the burning of fossil fuels.”