A recent heatwave that swept across Europe between June and July 2025 is estimated to have caused significantly more deaths than last year’s Valencia floods, with new research blaming human-induced climate change for much of the devastation.

A rapid study by scientists from Imperial College London and the London School of Hygiene & Tropical Medicine estimates that around 1,500 of the 2,300 heat-related deaths across 12 European cities during the 10-day period from 23 June to 2 July can be directly attributed to climate change. The research suggests that burning fossil fuels made the heatwave up to 4°C hotter, tripling the number of excess deaths.

This marks the first time a rapid attribution analysis which measures the influence of climate change on specific weather events has been conducted for a heatwave. Though the study focused on just a dozen cities, researchers believe the true death toll across Europe could be in the tens of thousands.

“Climate change is an absolute game changer when it comes to extreme heat, but it remains under-recognised,” said Dr. Friederike Otto, Professor in Climate Science at Imperial College London. “If we continue to delay serious climate action, more lives will be lost — all for the benefit of a wealthy, influential few.”

To determine the number of deaths linked to global warming, researchers analysed historical climate data to estimate how hot it would have been without the 1.3°C of warming caused by greenhouse gas emissions. The analysis found that climate change was responsible for 65 per cent of the heat-related excess deaths recorded during the heatwave.

According to the World Weather Attribution team, the impact was felt most in Milan (317 deaths), Barcelona (286), Paris (235), London (171), Rome (164), Madrid (108), Athens (96), Budapest (47), Zagreb (31), Frankfurt (21), Lisbon (21), and Sassari (6). Notably, Madrid had the highest proportion of climate-related heat deaths — a staggering 90 per cent — due to the severity of the temperature increase pushing past critical health thresholds.

Dr. Garyfallos Konstantinoudis, lecturer at the Grantham Institute for Climate Change and the Environment, stressed the urgency of climate action: “This study shows that every fraction of a degree matters. Even seemingly small increases, like from 1.4°C to 1.6°C, result in deadlier heatwaves and more loss of life.”

Elderly people were especially vulnerable, with those aged 65 and above accounting for 88 per cent of climate-related heat deaths. The study warns that heatwaves are a “silent killer”, often claiming lives quietly at home or in hospitals as pre-existing conditions like heart disease and respiratory issues worsen in extreme heat.

“Unlike floods or wildfires, heat doesn’t make headlines the same way, but it is just as deadly,” said Dr. Malcolm Mistry, Assistant Professor at the London School of Hygiene & Tropical Medicine. “The elderly are most at risk, but the threat extends to all age groups.”

Separate data from Copernicus, the EU’s climate change service, confirmed that June 2025 was the fifth hottest June on record in Europe, with parts of Spain and Portugal recording temperatures as high as 46°C.

Dr. Otto added a sobering warning: “Many people think they are invincible in the face of heat, but they’re not. These are not just statistics — they represent real people who have lost their lives.”