Climate change has intensified the recent heatwave in Europe. A new study shows that the number of heat-related deaths has tripled as a result.

At the end of June and beginning of July, large parts of Europe experienced extreme heat. Temperatures rose above 40 degrees Celsius in several countries. Italy restricted outdoor working hours, and in France, more than 1,300 schools were closed. In Greece, Spain, and Turkey, the dry conditions associated with the heat made it easy for forest fires to spread.

A rapid study led by scientists from Imperial College London and the London School of Hygiene & Tropical Medicine has now concluded that human-induced climate change has intensified the recent heatwave in Europe and tripled the death toll. Of a total of approximately 2,300 heat-related deaths in twelve cities studied, they attribute approximately 1,500 deaths to temperatures being even higher due to climate change. This number is significantly higher than the death toll from other recent disasters, such as the 2024 Valencia floods.

Climate change made heatwave one to four degrees hotter

In their study, the scientists focused on ten days of heat in twelve European cities between June 23 and July 2, 2025. Researchers from the World Weather Attribution (WWA) initiative first analyzed historical weather data to determine what temperatures would have been without global warming. They found that climate change made the past heatwave one to four degrees hotter. Given the current climate, such heatwaves can be expected in most cities every second to fifth summer.

The scientists then determined how heat and the number of deaths, regardless of their cause, are related in cities. This allowed them to estimate the number of heat-related deaths during the recent heatwave and also the number who would have died during a hypothetical heatwave with lower temperatures, i.e., in a Europe without global warming.

According to the scientists' calculations, climate change was responsible for 317 of the estimated additional heat deaths in Milan. In Barcelona, the number was estimated at 286, in Paris 235, 171 in London, and 164 in Rome. In Frankfurt am Main, the scientists blamed global warming for 21 additional heat deaths.

Heat waves as"silent killers"

The study points to why heat waves are also called "silent killers": Most heat-related deaths go unreported. Official government estimates can take months to be released—if they are released at all.

Ben Clarke of Imperial College London, the study's lead author, emphasizes:"Heatwaves don't leave a trail of destruction like wildfires or storms. Their effects are mostly invisible but silently devastating. A change of just two or three degrees Celsius can mean the difference between life and death for thousands of people."

During the recent heatwave, climate change claimed the most victims among people aged 65 and older. According to scientists' calculations, this figure was 88 percent. The causes were mostly pre-existing health problems, such as cardiovascular disease. However, researchers warn that heat can be life-threatening for all age groups.

Probability of early heat waves increases

The June heat arrived unusually early in many parts of Europe. Such high temperatures are typically not expected there until late July or August. Extreme heat that occurs early in the season tends to be more deadly because people are not yet accustomed to summer temperatures. While climate change affects all heatwaves, the intensity of June heatwaves has increased more than those in July. This increases the likelihood of earlier extreme heat events, the authors write in their study.

However, they also note: Europe has already made progress in developing heat action plans. These specify which measures can be taken before and during dangerously high temperatures. To protect against more dangerous heat waves, however, the so-called heat island effect in cities must be reduced in the long term, for example by expanding cooling green spaces and water areas. In the short term, cooling centers could also provide relief from extreme heat for those most at risk.