Mario Guarino, an emergency doctor at Ospedale CTO in Naples, saw emergency room visits rise 15% during the hottest weeks of the summer. Naples was the continent’s hardest-hit city in age-standardised estimates, with 815 heat deaths per million people.
Across European cities, morgues and funeral homes filled with bodies between June and August as heat waves persisted. More than half of the continent experienced “very strong” heat stress, with conditions that felt hotter than 38 degrees Celsius.
Temperatures were especially severe during a heat wave running from 17 June to 1 July. About one-third of the summer’s deaths occurred in that period, when temperatures were 5.3 degrees Celsius (9.5 degrees Fahrenheit) above normal. Some cities recorded temperatures 12 degrees Celsius (21.6 degrees Fahrenheit) warmer than normal.
New peer-reviewed research estimates that heat killed 50,391 people across 854 cities in the European Union, the United Kingdom, Norway and Switzerland during the summer. The cities account for about 40% of the European population in the 30 countries examined.
Italy, France, Spain, Germany and the UK had the highest absolute death tolls. Scientists estimated 4,354 heat deaths in the United Kingdom.
Clair Barnes, the study’s lead author and an extreme weather researcher at Imperial College London, led the work modelling heat deaths across the cities. Malcolm Mistry, a climate and health scientist at the London School of Hygiene & Tropical Medicine, co-authored the research, alongside Garyfallos Konstantinoudis, an assistant professor at Imperial College.
The researchers used historical links between heat and mortality to model the death toll. They estimated that approximately 32,619 deaths, or 65-67% of the total, were attributable to human-caused climate change from greenhouse gas emissions.
The findings, published in two peer-reviewed studies in the academic journal Nature Health, make this the deadliest heat summer this century. The estimated toll was 71% higher than the previous record of 29,480 deaths in 2022.
Older people bore much of the loss. People over 85 accounted for approximately half of the death toll, while more than 800 people aged 20 to 44 also died from the heat.
The researchers’ estimates point to a rising climate contribution to heat deaths. The share attributed to climate change has increased from about 40-45% at the start of the century to 65% this summer.
Europe has warmed approximately twice as fast as the global average and is now 2.5 degrees Celsius (4.5 degrees Fahrenheit) hotter than pre-industrial times. Between 2000 and 2025, European cities recorded approximately 430,000 heat-related deaths, with roughly half caused by climate change.
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