A new report from the Grantham Institute and the London School of Hygiene & Tropical Medicine warns that climate change has sharply increased the number of deaths caused by extreme summer heat across Europe.

The analysis, covering 854 European cities, estimates that climate change was responsible for 16,469 additional excess deaths during the summer of 2025. This accounts for almost 70% of the total 24,400 estimated heat deaths in these cities. The researchers used peer-reviewed methods, historical mortality records, and climate modelling to provide early estimates of the season’s fatalities.

Key findings from the report:

• Fourth warmest summer on record: June–August 2025 was 0.9°C warmer than the 1990–2020 average. This heightened risks for vulnerable groups such as older adults, people with pre-existing health conditions, and those in poorly cooled indoor environments.

• Role of climate change: Summer temperatures across Europe were estimated to be 1.5–2.9°C higher than they would have been without human-driven climate change, mainly from burning fossil fuels.

• Cities most affected: Among 30 European capitals, Rome, Athens and Bucharest recorded the highest excess mortality per population. The largest relative proportions of climate-related heat deaths occurred in Stockholm, Madrid and Bratislava, where more than 85% of deaths were attributed to climate change.

• Urban vulnerability: Cities face heightened risks due to the urban heat island effect, where concrete and asphalt trap heat. Expanding green and blue spaces can help provide cooler environments, particularly for lower-income communities less likely to have access to air conditioning.

• Limitations: The study only includes about 30% of Europe’s population, so the true toll is likely higher. Researchers note that climate models often underestimate warming in Europe, and the study’s methods may not capture the most extreme temperature peaks or recent adaptation to heat.

• Global context: Current policies are projected to result in around 2.7°C of warming above pre-industrial levels by 2100, which would drive further increases in heat-related deaths worldwide.

The report underlines that extreme heat is the deadliest type of weather and that official statistics consistently underestimate its impact. The findings highlight the urgent risks of climate change for Europe’s cities, where rising temperatures, ageing populations, and continued urbanisation are converging to increase vulnerability.

To read the full report, please visit: https://www.imperial.ac.uk/grantham/publications/all-publications/summer-heat-deaths-in-854-european-cities-more-than-tripled-due-to-climate-change.php

Citation: Barnes, C., et al. (2025). Summer heat deaths in 854 European cities more than tripled due to climate change. Grantham Institute report. DOI: https://doi.org/10.25560/123873