Rapid analysis report of 854 European cities estimates that climate change responsible for over two-thirds of heat deaths this summer
Climate change intensified Europe's summer heat in 2025 and drove an estimated 16,500 additional deaths across 854 cities, according to a new study led by researchers from the London School of Hygiene & Tropical Medicine (LSHTM) and Imperial College London.
The rapid analysis found that climate change was responsible for around 68% of the 24,400 estimated heat-related deaths this summer. Warmer conditions, amplified by human-driven climate change, increased daily temperatures by an average of 2.2°C, with peaks of up to 3.6°C.
The report highlights how even small increases in temperature can result in thousands of avoidable deaths - with older adults particularly vulnerable. People aged 65 and over made up 85% of the estimated deaths.
The study covered cities representing about 30% of Europe's population, meaning the true death toll is likely to be far higher. Heat-related deaths are often undercounted, as many result from underlying health conditions such as cardiovascular and respiratory disease, with heat rarely recorded as a contributing cause.
Using well-established models, historical data, and peer-review methods, this rapid report builds upon previously published research on temperature-related mortality across Europe. The new report follows another rapid study by the same team earlier in the year, which found that climate change could have tripled the death toll of a July heatwave in Europe.
The study found that climate change contributed to 4,597 heat deaths in Italy, 2,841 in Spain, 1,477 in Germany, 1,444 in France and 1,147 in the UK. In capital cities, Rome, Athens and Paris experienced the highest tolls, each recording hundreds of excess deaths. London was among the highest hit, with 315 excess deaths attributable to climate change, 69% of the total 458 heat-related excess deaths.
Researchers also identified a single week in July when Romania, Bulgaria, Greece and Cyprus experienced exceptionally severe heat, leading to nearly 1,000 deaths in just seven days.
The findings raise urgent questions about protecting Europe's aging population, which is especially vulnerable to extreme heat. The proportion of people aged over 80 in Europe is projected to rise from 6% today to 15% by 2100, placing additional strain on health systems as summers continue to warm.
The researchers warn that unless fossil fuels are rapidly replaced with renewable energy, Europe will face increasingly deadly summers. Urban areas are particularly at risk, with cities typically several degrees hotter than surrounding rural regions due to the urban heat island effect. Expanding green and blue spaces could provide critical lifelines, particularly for low-income communities in denser housing.
Dr Malcolm Mistry, Assistant Professor in the Environment & Health Modelling (EHM) Lab at LSHTM, and co-author of the report said: "Heat-health warning systems and action plans are well developed across most regions of Europe, but the health burden associated with heat has remained consistently high in recent summers. Policies to adapt to heat are important, such as introducing flexible work schedules, adjusting the school calendar, increasing urban greenspace, and sustainable ways for cooling indoor spaces, as well as improving public health infrastructure.
"But the harsh reality is that unless we urgently reduce greenhouse gas emissions, the above interventions are going to have a limited role in mitigating the risks of human-induced global warming."
Dr Garyfallos Konstantinoudis, Lecturer at the Grantham Institute - Climate Change and the Environment, Imperial College London and study co-author, said: "Heatwaves are silent killers. The vast majority of heat deaths happen in homes and hospitals, where people with existing health conditions are pushed to their limit, but heat is rarely mentioned on death certificates.
"Despite being the deadliest type of extreme weather, heat has long been underestimated as a public health risk. No one would expect someone to risk their life working in torrential rain or hurricane winds, but dangerous heat is still treated too casually."
Dr Pierre Masselot, Research Fellow in the EHM Lab at LSHTM and co-author said: "This summer was another stark reminder of the necessity to take climate change seriously. It is important to adapt our cities and societies as a whole to a warming world.
"But ultimately, adaptation will not compensate for extreme heating in Europe. The best way to save thousands of lives from heat remains a drastic cut in greenhouse gas emissions."
The team note that observed death counts were unavailable for all 854 cities, so the study assumed a constant daily death rate, which may underestimate the true burden of heat as deaths typically rise during heatwaves.
The analysis is limited to all-cause mortality, excluding wider health impacts such as hospitalisations or mental health effects. Additionally, as the exposure-response functions (calculations of additional risk of death from exposure to non-optimal temperatures, outlined in previous research in The Lancet Planetary Health) used to estimate heat-related excess deaths were based on city-specific mortality data up to 2019, the results may not reflect recent adaptation measures or demographic changes following COVID-19. Authors also note that temperatures from major cities may not represent conditions across the whole country, and climate models may underestimate warming in Europe, suggesting that the temperature changes attributed to human influence may themselves be conservative.
Publication
Read the full report: Summer heat deaths in 854 European cities more than tripled due to climate change
