Study Links Two-Thirds of Europe's 50,000 Summer Heat Deaths to Climate Change

The total is 71% higher than the previous deadliest summer, when 29,480 deaths were recorded in 2022, according to the same researchers, who published an earlier study this month tracking yearly summer heat-related deaths in those cities. The authors said the figures are underestimates because they do not count a deadly heat wave in May and cover only the 854 cities, about 40% of Europe's population.

About one-third of the deaths occurred from June 17 to July 1, a particularly intense heat wave when temperatures were 9.5 degrees Fahrenheit, or 5.3 degrees Celsius, above normal, co-author Garyfallos Konstantinoudis, a biostatistician at Imperial College London, said. Lead author Clair Barnes, a climate scientist at the same university, said infrastructure in much of Western and Northern Europe is not designed to cope with temperatures now being seen because of human-caused warming. Some European cities this summer had temperatures 21.6 F, or 12 C, warmer than normal, she said.

Italy, France, Spain and Germany had the highest death tolls, the study said. Among European capitals, Rome had the highest heat death total from 2000 to 2025, according to the team's earlier study this month.

Barnes said Europe would already have experienced an abnormal natural hot spell 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—and is 4.5 F, or 2.5 C, hotter than pre-industrial times. "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."

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.

The team used an established scientific method to determine how many of the 50,000 heat deaths were from natural high summer heat and how many were due to heat-trapping gases. They ran computer simulations of a world without climate change and compared it with the deaths that happened this summer; the difference was attributed to global warming. The share of heat deaths attributable to global warming has grown from about 45% in the early 2000s to 65% now, Barnes said.

"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."

The team also used statistical modeling to arrive at the base count of 50,000 heat deaths because such deaths are underreported and often not listed on death certificates, despite being a major factor, Konstantinoudis said. Several outside experts agreed with him, calling the methods state-of-the-art.

The researchers ran a complex mathematical equation used in several previously peer-reviewed studies, Barnes said. It factors in specific age 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 lowest-death conditions. Researchers checked their calculations against real-time estimates from government agencies; mostly, but not always, they matched fairly well, Konstantinoudis said. The team's methods for May and June British heat waves calculated 2,700 excess deaths, while the United Kingdom health statistics agency said 2,800, he said.