BRUSSELS — Climate change supercharged last week’s European heat wave and tripled the death toll, a group of scientists said Wednesday.
Extreme temperatures baked large swaths of the continent in late June and early July, exposing millions of Europeans to dangerous levels of heat.
Looking at 12 European cities, the researchers found that in 11 of them, heat waves of the type that peaked last week would have been significantly less intense — between 2 to 4 degrees Celsius cooler — in a world without man-made global warming.
This climate-induced change in temperatures, the scientists said, led to a surge in excess deaths in those cities. Of the 2,300 additional fatalities linked to high temperatures, around 1,500 of them can be attributed to global warming, they estimated.
“Climate change is an absolute game changer when it comes to extreme heat,” said Friederike Otto, a climate scientist at Imperial College London, which co-led the research.
A construction worker in Italy and a street cleaner in Spain were among those thought to have died of heat stroke last week. But most heat-related deaths, particularly among the elderly, go unreported. The scientists said the vast majority of deaths they analyzed occurred among Europeans aged 65 or older.
As a result, heat is often dubbed a “silent killer,” though it’s no less deadly than other climate-related disasters. The scientists noted that last week’s heat wave killed more people than devastating flood events in recent years, which resulted in several hundred deaths.
“Our study is only a snapshot of the true death toll linked to climate change-driven temperatures across Europe, which may have reached into the tens of thousands,” said Garyfallos Konstantinoudis, also a climate specialist at Imperial College London.
Global warming, driven by burning fossil fuels such as coal, oil and natural gas, is increasing the severity and frequency of heat waves in Europe and worldwide. An aging population also makes Europe more vulnerable to the health effects of extreme temperatures.
The European Environment Agency has warned that heat-related deaths are expected to increase tenfold if the planet warms 1.5 C, and thirtyfold at 3 C. The planet is already 1.3 C hotter than in preindustrial times and on track to warm 2.7 C this century.
The toll of extreme heat
The rapid analysis published Wednesday — which uses methods considered scientifically reliable but has not undergone peer review — was led by researchers at Imperial College London and the London School of Hygiene & Tropical Medicine.
The scientists looked at deaths in Milan (where they estimated 317 fatalities were due to changes in the climate), Barcelona (286), Paris (235), London (171), Rome (164), Madrid (108), Athens (96), Budapest (47), Zagreb (31), Frankfurt (21), Lisbon (also 21) and the Sardinian city of Sassari (six) between June 23 and July 2.
“These numbers represent real people that have lost their lives in the last days due to the extreme heat. Two-thirds of these would not have died were it not for climate change,” said Otto.
Last week’s heat also drove up wildfire risk across Europe, with fires still raging in many parts of the continent. The analysis does not include deaths linked to fire or smoke. In Spain, for example, two farmers were killed trying to flee encroaching flames last week.
The Spanish government separately monitors heat-related excess deaths and found that between June 21 and July 2, more than 450 people died due to extreme temperatures — 73 percent more than in the same period in 2022, which saw record numbers of deaths.
Western Europe’s hottest June
The EU’s Copernicus climate monitoring service, meanwhile, said Wednesday morning that last month was the third-hottest June on record worldwide.
For Europe, it was the fifth-warmest June, though the western part of the continent saw its hottest June on record, the scientists said — just above the 2003 record, which was followed by a summer marked by deadly heat.
The temperatures in Europe are further amplified by what Copernicus terms an “exceptional” marine heat wave in the Mediterranean Sea. The water surface temperatures have hit their highest level on record, not just for June but for any month.
“June 2025 saw an exceptional heat wave impact large parts of western Europe, with much of the region experiencing very strong heat stress. This heatwave was made more intense by record sea surface temperatures in the western Mediterranean,” said Samantha Burgess, strategic climate lead at the European Centre for Medium-Range Weather Forecasts.
“In a warming world, heat waves are likely to become more frequent, more intense and impact more people across Europe,” she added.
Cory Bennett contributed to this report.
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