The most dangerously hot summer that Europe has experienced
Over 50,000 estimated to have died across European cities in summer 2026, with climate crisis responsible for two thirds of these deaths
Heatwaves kill. In the summer of 2026, they are estimated to have killed more than 50,000 people in cities across Europe—the largest such toll this century. What’s more, nearly two thirds of those deaths can be attributed to the effects of human-caused global heating.
These are the key findings from two new research papers being published in the journal Nature Health, from scientists led by teams at Imperial College London and the London School of Hygiene & Tropical Medicine (LSHTM). The release of these sobering numbers comes as Urban Journalism Network and its partners, advised by the LSHTM team, begin a collaboration that aims to put estimates of deaths from extreme heat for individual cities into the hands of journalists across the continent.
As the climate crisis increases its hold, understanding the deadly impact of heatwaves and taking steps to cool cities and protect the elderly and other vulnerable groups will be crucial.
“It will become a problem for almost everyone in Europe,” said Pierre Masselot, a statistician and epidemiologist at LSHTM and one of the leaders of the research. “Even more northern countries. It’s not just a problem for the Mediterranean.”
The new studies depend on epidemiological modeling by Masselot and his colleagues for 854 cities across the European Union, the UK, Norway and Switzerland. The analysis covers only urban areas and accounts for about 40 percent of the population of the 30 countries included.
The team behind the new papers also applied climate models to simulate the temperatures the cities would have experienced in a world that is not in the grip of the climate crisis. This “counterfactual” temperature record allowed them to estimate the proportion of the estimated deaths that can be attributed to human-made climate change—which has grown over the years as the climate crisis has intensified.
How estimates of heat-related deaths are calculated
The new studies depended on complex statistical models that related daily temperature records with patterns of recorded deaths from January 2000 to December 2019 for more than 230 European cities with detailed daily death records, described in an earlier study published in The Lancet Planetary Health.
Because vulnerability to heat varies with age, the researchers trained these models on death records for five different age groups, ranging from 20 to 44 years, to 85 and older. They then built models that accounted for geographic location and a range of characteristics including population density and socioeconomic factors to extend the findings to a wider group of 854 cities.
The result of this statistical modeling was a series of “exposure response functions,” for each city. These make it possible to estimate the number of daily deaths likely to occur at any given temperature. So from daily historical temperature records, the researchers were able to estimate the total number of heat-related deaths in each city for every summer, from June to August, since the turn of the century.
The same methods can also be used to estimate deaths in a hypothetical climate without the influence of global heating. To do this, the researchers applied climate models to simulate daily temperature records for what they call a “counterfactual” climate with no human-caused warming.
While the estimates are the result of statistical modeling based on recorded temperatures, they align well with estimates released by national health authorities, modelled from death records. For example, using similar methods Imperial and LSHTM researchers earlier estimated that 2,700 people died across the UK during heatwaves that hit the nation in May and June 2026. Shortly afterwards the UK Health Security Agency released its own estimate of 2,877, based on an analysis of death records.
However, because they depend on statistical modelling from historical death records, the new estimates cannot account for any measures taken in recent years to mitigate the death toll from heatwaves. So in countries and cities that have aggressively implemented heat action plans, they may overestimate the heat-related death count.
“The results clearly highlight the danger from human-caused global warming,” said Clair Barnes of the Centre for Environmental Policy at Imperial College, who led that part of the work.
Cities are a focus of the analysis for concern not only because of their large populations, but also because of a phenomenon called the urban heat island effect, in which summer temperatures—especially in densely packed, poorer neighborhoods—can be several degrees warmer than surrounding rural areas. This is caused by factors including paved surfaces and buildings absorbing the Sun’s energy, a lack of shade from trees, tall buildings restricting air circulation, plus waste heat from vehicles and other machinery.
Heat took its heaviest absolute toll in southern and western Europe’s big cities this summer. Paris recorded the most estimated heat-related deaths of any city, with more than 2,500 estimated deaths, followed among European capitals by Rome with more than 2,200, then London and Madrid, each with more than 1,000 estimated deaths from heat. Madrid is a striking example, as 91 percent of this high death toll is attributable to the climate crisis.
Italian cities dominate once population is taken into account: Eight out of the ten cities with the highest estimated death rates in the summer of 2026 were in Italy, with Savona, Pavia, Florence and Turin all experiencing more than 1,000 deaths per million people, according to the new estimates.
While northern European cities had many fewer estimated deaths from heat, the proportion attributable to the climate crisis tended to be high. In Stockholm, for instance, 34 of the 43 estimated heat-related deaths—more than 80 percent—were attributed to global heating. By contrast, Valletta in Malta had almost 150 deaths—of which just 31 percent were attributed to human-caused warming.
As the climate crisis places northern regions at higher risk, the researchers say that simple cooling measures used in Southern Europe will become important. “External shades and blinds make a big difference,” said Andrew Hartle, an intensive care consultant at Imperial College Healthcare NHS Trust and a member of the team. “We can learn in Northern European countries the things southern European countries have known for a long time.”
While geographic differences in exposure to high temperatures are the biggest risk factor, explaining why Italy was hit so hard, socioeconomic factors also come into play. Areas with deprived populations, with high density housing, few trees for shade, and where people have limited access to health services, are more vulnerable.
The year 2026 is marked by the deadliest summer in Europe this century, surpassing previous notorious summers of 2003 and 2022. Not only were temperature records set across wide swaths of the continent, but also many cities were hit by repeated heatwaves. In 2003, by contrast, most of the deaths occurred in a single intense heatwave that peaked in early August.
Elderly people were especially hard hit, with people aged 85 and older accounting for almost half of the estimated deaths. Heat typically kills by putting strain on the cardiovascular system and kidneys, as people sweat and pump blood to their skin to lose heat. The elderly and those with preexisting cardiovascular or kidney disease are less able to adapt as temperatures rise.
Estimating the numbers killed by excessive heat is necessary because death certificates rarely record heat as a contributing cause. Many people who die in heatwaves are discovered hours later. By then their body temperature will already have dropped, making it impossible to know whether heat was the main factor involved, especially in cases where they had underlying health problems.
Younger people can also succumb to heat. The researchers estimate more than 830 heat deaths across the 854 cities among people aged 20 to 44 years.
Cities in Italy suffered more than 13,000 estimated heat-related deaths in summer 2026 at a rate of about 775 per million urban residents. There were more than 7,000 estimated deaths in French cities. Other badly hit countries included Austria, Switzerland, Slovenia and Hungary, each estimated to have lost more than 300 people per million city dwellers.
The highest proportion of deaths attributable to human-made climate change occurred in Estonia, Bulgaria and Finland. As the scientists state, those three countries “would have barely reached the mortality threshold in the counterfactual climate, meaning that the small number of modelled deaths are almost entirely due to human-caused warming.”
The researchers say that their findings emphasize the need for authorities to roll out measures to mitigate the deadly effects of extreme heat. In the longer term, that will include changes to urban planning including the planting of trees to provide cooling shade. When heatwaves hit, measures to protect the most vulnerable people—especially the elderly—are also vital. These include providing public buildings that are air conditioned as cooling centers and organizing transport to them.
According to Masselot, priorities should include efforts to reduce car use. “The low-hanging fruit is reducing the amount of cars in cities and the amount of space that car infrastructure takes up, to allow for more green space,” he said.
As the Imperial and LSHTM researchers warn in their paper on the summer of 2026: “Under currently implemented policies, a further 1.4° C of warming is projected by the end of the century; without rapid progress toward net zero emissions to slow the rate of warming, the health burden arising from human-caused warming will continue to increase, placing growing pressure on public health systems.”
Unfortunately, older hospitals are among the infrastructure that has not been designed to handle the heat that European cities are now experiencing, putting already vulnerable patients at further risk. “Hospitals themselves can be quite hot,” Hartle said.