Recent extreme heat across Europe was made significantly more intense by human-driven climate change, with temperatures rising up to 4°C higher in numerous cities and pushing conditions into deadly territory for vulnerable populations, according to a new scientific analysis.
An assessment conducted by more than a dozen researchers from five European institutions concluded that the extreme heat likely resulted in more fatalities than would have occurred without the influence of global warming.
From late June to early July, temperatures surged past 40°C in several European countries. The first major heatwave of the summer shattered records and prompted widespread public health alerts. ALSO READ: Authorities issue warnings, as Spain & southern Europe hit by summer’s first major heatwave.
The EU’s Copernicus climate monitoring service reported on Wednesday that June 2025 was the hottest June ever recorded in western Europe. As temperatures soared, schools and popular tourist attractions were forced to close in some areas.
To determine the extent to which climate change influenced the heatwave, scientists used historical climate data to simulate how severe the event would have been in a world unaffected by large-scale fossil fuel combustion.
Their findings showed that, in 11 of the 12 cities analysed, the heatwave would have been 2°C to 4°C cooler without human-caused climate change.
This additional heat significantly increased health risks for the combined population of more than 30 million people in these urban areas, which include major cities such as Madrid, Barcelona, Paris and London.
‘What that does is it brings certain groups of people into more dangerous territory,’ said Ben Clarke, a researcher at Imperial College London. Imperial co-led the study with the London School of Hygiene and Tropical Medicine.
‘For some people it’s still warm, fine weather. But for now a huge sector of the population, it’s more dangerous.’
For the first time, the researchers also tried to estimate how many deaths occurred due to the heatwave across the dozen cities – and how many of those deaths could be attributed specifically to climate change.
Using peer-reviewed methods and existing scientific research on heat-related mortality, the study estimated that around 2,300 people died between 23 June and 2 July in the cities studied.
Of those, approximately 1,500 deaths – about two-thirds – would likely not have happened if the climate had not warmed to such extremes, the researchers said.
The team, which included experts from the UK, the Netherlands, Denmark and Switzerland, stressed that this figure is only a partial estimate, as official data on excess deaths is not yet available.
Heatwaves are especially hazardous for older adults, people with pre-existing conditions, children, those working outdoors, and anyone exposed to high temperatures without adequate cooling.
Urban environments are particularly affected because buildings and paved surfaces retain heat, making cities significantly warmer than surrounding areas.
During this latest heatwave, Copernicus noted that large regions of southern Europe experienced ‘tropical nights’, during which temperatures remain high overnight, preventing the body from cooling down.
‘An increase in heatwave temperature of just two or four degrees can mean the difference between life and death for thousands of people,’ said Garyfallos Konstantinoudis, a lecturer at Imperial College London.
‘This is why heatwaves are known as silent killers. Most heat-related deaths occur in homes and hospitals out of public view and are rarely reported,’ he told journalists. ALSO READ: Unions demand review of safety rules after death of cleaner in Barcelona during heatwave.
Authorities caution that it may take several weeks before a clearer picture of the heatwave’s death toll emerges. Similar extreme heat events have caused tens of thousands of deaths in Europe in past years.
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Climate change tripled the expected death toll of last week’s European heatwave, according to Imperial and @LSHTM experts.
A 2 to 4°C rise can cause thousands more heat-related deaths, highlighting why heatwaves are called “silent killers.”https://t.co/jadtdZw6bA
— Imperial College London (@imperialcollege) July 9, 2025
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