London: Human-driven climate change was responsible for nearly two out of every three heat deaths in Europe during the summer of 2025, according to a new analysis by researchers at Imperial College London.
The early study, which examined mortality data from 854 major cities across the continent, estimated that of the 24,400 heat deaths between June and August, approximately 16,500 fatalities were directly linked to the additional warming caused by greenhouse gas emissions.
The research, based on established epidemiological methods but not yet peer-reviewed, found that climate breakdown made European cities an average of 2.2°C hotter than they would have been without human influence, substantially increasing the number of heat deaths. Scientists compared excess mortality during the hottest months with a hypothetical scenario in which climate change had not occurred, concluding that around 68 percent of Heat deaths were attributable to human-caused warming.
Older people were disproportionately affected: 85 percent of the victims of heat deaths were over 65 years old, and 41 percent were above 85. Most heat deaths occurred indoors, particularly in homes and hospitals, where individuals with pre-existing health conditions were pushed beyond their limits. Despite this, heat is rarely mentioned on death certificates, noted co-author and epidemiologist Garyfallos Konstantinoudis.
Among the few heat deaths publicly reported in local newspapers was Manuel Ariza Serrano, a 77-year-old former councillor from La Rambla, Spain, who collapsed during a walk in August when temperatures hit 45°C in the Córdoba region.
In northern Italy, a 47-year-old father of four, Brahim Ait El Hajjam, who ran a flooring company, died while laying concrete at a school construction site near Bologna in 38°C heat. His heat death came just two days before regional authorities implemented a ban on afternoon outdoor construction work. “He called my mother to tell her he’d be home to prepare lunch by noon,” his 19-year-old son, Salah, told Italian TV channel Antena 3.
Co-author Friederike Otto, a climate scientist at Imperial College London, said the evidence was clear: “The causal chain from fossil fuel burning to rising heat and increased mortality is undeniable. If we had not continued to burn fossil fuels over the last decades, most of the estimated 24,400 people in Europe wouldn’t have suffered heat deaths this summer.”
Despite improvements since the devastating 2003 European heatwave, which claimed 70,000 lives, experts warn that emergency services remain unprepared for the growing health risks associated with extreme heat, particularly in ageing populations.
Doctors and climate specialists are calling for comprehensive local heatwave action plans, greater investment in urban green spaces to mitigate the urban heat island effect, and expanded access to cooling solutions such as air-conditioning, particularly for vulnerable groups like retirement home residents, to prevent more heat deaths.
Madeleine Thomson, a climate adaptation expert at the health non-profit Wellcome, who was not involved in the study, stressed that the findings showed “no city in Europe is immune” to the deadly impacts of rising temperatures.
“If we don’t act now, the toll of heat deaths will rise. We must urgently phase out fossil fuels and implement policies that protect those most at risk from increasingly deadly heatwaves,” Thomson added.
Konstantinoudis warned that dangerous heat is still treated too casually compared with other extreme weather events: “No one would expect someone to risk their life working in torrential rain or hurricane winds. But dangerous heat is still treated too casually, and this underestimation continues to fuel preventable heat deaths.”
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