A record toll across European cities
The study, set to appear in an upcoming issue of Nature Health, examined deaths by age during the heat waves of June, July and August. Its estimate exceeds the previous summer record by 71%. In a separate study published earlier this month, the same team estimated 29,480 heat-related deaths in those cities in 2022.
The researchers caution that their estimate does not capture Europe's full toll: The 854 cities account for about 40% of the continent's population, and the summer analysis leaves out the deadly heat wave in May.
Italy, France, Spain and Germany recorded the largest estimated losses. Grist's reporting on the study put Italy's modeled excess deaths at 13,303 and France's at 7,268. The team's earlier analysis also found that Rome had the highest cumulative heat death toll among European capitals from 2000 through 2025.
People 85 and older accounted for more than half of the summer's estimated deaths. The toll also included more than 800 people ages 20 to 44, according to co-author Garyfallos Konstantinoudis, a biostatistician at Imperial College London.
Extreme heat on top of a warming climate
Roughly a third of the estimated deaths occurred during the intense June 17-July 1 heat wave, when temperatures ran 9.5 degrees Fahrenheit (5.3 degrees Celsius) above normal, Konstantinoudis said. Lead author Clair Barnes, a climate scientist at Imperial College London, said some cities experienced temperatures 21.6 F (12 C) above normal during the summer.
The EU's Copernicus Climate Change Service reported that western Europe's summer average reached 21.7°C, exceeding the 1991-2020 average by 2.5°C. That made 2026 the region's warmest summer on record, ahead of 2003. For Europe as a whole, the summer ranked third warmest.
By the season's end, a record 52% of European land had experienced at least "very strong" heat stress, Copernicus reported. That category corresponds to feels-like temperatures of 38°C or higher.
Barnes described the summer as an unusually hot natural spell compounded by substantial human-caused warming. Europe is now 4.5 F (2.5 C) warmer than in preindustrial times and is warming faster than any other continent, she said. The Arctic is warming still faster, but it is not a continent.
That background warming can turn uncomfortable temperatures into dangerous or potentially fatal conditions, Barnes said. She also warned that infrastructure across much of western and northern Europe was not built to handle the temperatures now occurring. The share of heat deaths attributed to global warming has risen from about 45% in the early 2000s to 65% today, she said.
How researchers estimated the deaths
The total is a statistical estimate rather than a count taken from death certificates. Konstantinoudis said heat's contribution to deaths is often unreported or omitted from those records.
To estimate that contribution, the researchers used an equation applied in several earlier peer-reviewed studies. It accounts for age and local temperatures in each city, using the temperature associated with the fewest deaths as a baseline. Temperatures above or below that point yield an estimate of excess deaths.
The team then used an established attribution method to distinguish the effects of natural summer heat from those of human-caused warming. Computer simulations estimated deaths in a world without climate change; the difference between that scenario and this summer's toll was attributed to global warming.
Checks against government agencies' real-time estimates generally showed fairly close agreement, though not in every case, Konstantinoudis said. For British heat waves in May and June, the team's method estimated 2,700 excess deaths, compared with 2,800 reported by the United Kingdom's health statistics agency.
Several independent experts described the methods as state-of-the-art. Dr. Howard Frumkin, a former director of the U.S. National Center for Environmental Health who did not participate in the study, said hotter summers and improving attribution tools were producing higher and more accurate estimates of heat deaths.
Low rivers and extensive wildfires
Copernicus documented other extremes during the summer. European rivers had their lowest summer flows in more than 30 years, with record or near-record lows on the Rhine, Danube, Po, Loire, Rhône and Seine. The low water disrupted cargo shipping, irrigation, cooling for nuclear reactors and hydropower generation.
By September 2, 2026, wildfires had burned almost twice as much land across the European Union as the 2006-2025 average for that point in the year. Spain and France saw particularly extensive fire activity. By the end of summer, European wildfire emissions ranked among the 10 highest totals since 2003, according to Copernicus.
Cooling, protection and prevention
Grist reported that air conditioning is less common in Europe than in the United States, where research by Yale's Kai Chen shows that cooling can reduce heat fatalities by more than half.
Dr. Courtney Howard, an emergency room physician and president-elect of the Canadian Medical Association, urged investment in early-warning systems for heat, equitable access to low-carbon cooling and neighborhood buddy systems to check on people at greatest risk. Howard, who was not involved in the research, also called for rapid reductions in fossil fuel use.
Dr. Jonathan Patz, a University of Wisconsin-Madison professor of health and the environment, praised the research but said adaptation alone was insufficient. He called for better cooling and protection for vulnerable populations alongside action to address fossil fuel burning.
"We can't just be mopping up the mess on the floor without thinking about turning the faucet off," said Patz, who was not involved in the study.
