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Human-induced climate change may have intensified the European heat wave between 23 June and 2 July 2025, and increased the number of heat-related deaths, according to a new .

Extreme heat swept across Europe in late June and early July, with temperatures above 40°C recorded in several countries. Research suggests that this heat wave has been intensified by human-induced climate change, which has already led to a rise in the average global surface air temperature of about 1.3°C above pre-industrial level.

The rapid study, led by researchers from the London School of Hygiene & Tropical Medicine (LSHTM) and Imperial College London, analyzed historical weather data from across 12 European cities to estimate how intense the temperatures may have been over the 10-day heat wave period, if the climate had not already warmed.

When compared to the temperatures actually recorded, their estimates suggest the impacts of climate change to date made the heat wave between 1°C and 4°C hotter.

Using well-established models, on temperature-related mortality across Europe, and a recently developed for near-real-time analysis, the researchers then calculated the number of heat-related deaths that may be attributed to the recent heat wave for each city. They then compared this to expected heat-related deaths if the climate had been cooler.

They found that around 2,300 people may have died as a result of the extreme temperatures recorded over the 10-day period across the 12 cities analyzed. This is about three times higher than the number of deaths without human-induced climate change (800 deaths). It equates to about 65% deaths in the heat wave due to global warming, from practices including the burning of fossil fuels.

The full report, which includes data for each of the 12 cities, can be found .

Dr. Pierre Masselot, Assistant Professor at LSHTM and a co-author of the study, said, "We wouldn't be able to do rapid analyses like this if we had not spent years developing our underlying methodology and collating data across Europe's cities.

"At the rate the world is warming, heat waves are not going away and we have to prepare for their public health impacts. Cities can adapt by planting trees, reducing the space given to cars and caring for the most vulnerable. But ultimately, the best way to avoid dire consequences is to aggressively reduce greenhouse gas emissions."

Dr. Malcolm Mistry, Assistant Professor in Climate and Geo-spatial Modeling at LSHTM, who also worked on the analysis, said, "Our study demonstrates why heat waves are known as silent killers. While a handful of deaths have already been reported in Spain, France and Italy, thousands more people across Europe are expected to have died as a result of the blistering temperatures recorded at the end of June this year.

"It can often take around six months for public health officials to publish mortality data from heat waves and even then, heat as a possible factor is rarely recorded when a person dies.

"Given the important early heat-health advisories issued by various meteorological and health authorities across Europe, we sincerely hope that our findings will be an overestimate to the actual toll, but these figures will still only be estimates by the authorities themselves. However, we believe it's important to issue these warnings now to reach as many people as possible and encourage them to take further precautions, so they are better prepared for further heat waves expected across Europe this season."

Dr. Garyfallos Konstantinoudis, Lecturer at the Grantham Institute, Climate Change and the Environment, Imperial College London, and co-author of the study, said, "Climate change kills. It's intensifying heat waves and pushing vulnerable people to their limit. This study shows that every fraction of a degree of warming makes a huge difference, whether it is 1.4°C, 1.5°C or 1.6°C.

"These seemingly small changes will result in hotter heat waves and huge surges in heat deaths."

The team say that their estimates for expected deaths from the recent heat wave are irrespective of underlying health conditions, but did not take into account climate interventions already in place at the local level, such as cool roofs painted green or white. Early warning systems and heat-health action plans across Europe, designed to educate and protect people on the risks of extreme heat, are also improving and may reduce the expected mortality.