Scientists have confirmed that human-caused climate change significantly worsened the recent heatwave that swept across Europe between late June and early July 2025. According to a new scientific study, the extreme temperatures were up to 4°C hotter in many cities due to global warming, pushing conditions into life-threatening territory for millions of vulnerable people.
The research, conducted by more than a dozen experts from five European institutions—including Imperial College London and the London School of Hygiene and Tropical Medicine—analyzed how the heatwave would have played out in a world without climate change. The study concluded that nearly all 12 major cities assessed, including Paris, London, and Madrid, would have experienced temperatures that were 2 to 4 degrees cooler without the impact of fossil fuel-driven climate change.
Over 30 Million People Affected in Major Urban Areas
The cities studied have a combined population of over 30 million people. Researchers warned that the added heat significantly raised health risks, particularly for the elderly, children, outdoor workers, and individuals with pre-existing health conditions.
Ben Clarke, a researcher from Imperial College London, explained that while some may view the heat as pleasant summer weather, for many others, the elevated temperatures crossed into dangerous territory. He noted that this shift has severe implications for public health, especially for those unable to find relief from the heat.
Europe Records Its Hottest June Ever
The European Union’s climate monitoring service, Copernicus, reported that June 2025 was the hottest June on record in western Europe. Countries across the continent saw temperatures soar well above 40°C (104°F), leading to widespread health alerts. In response, several schools and tourist attractions were forced to close as authorities scrambled to protect public health.
During this period, southern Europe experienced “tropical nights,” where overnight temperatures remained too high for the human body to recover from the day’s heat. This made the heatwave even more dangerous, especially in densely populated urban centers where concrete and asphalt trap heat, a phenomenon known as the urban heat island effect.
Study Estimates 2,300 Deaths from the Heatwave
For the first time, researchers also estimated the number of deaths directly linked to the heatwave and how many were influenced by climate change. Based on peer-reviewed scientific methods and heat-related mortality data, the study concluded that about 2,300 people died in the 12 cities between June 23 and July 2, 2025.
Out of these, approximately 1,500 deaths—nearly two-thirds—were attributed to climate change, meaning they would likely not have occurred without the higher temperatures driven by global warming.
Dr. Garyfallos Konstantinoudis of Imperial College London emphasized that even a two- or four-degree temperature rise can mean the difference between life and death for thousands. He called heatwaves “silent killers” because most heat-related deaths happen behind closed doors in homes and hospitals and often go unreported until much later.
Vulnerable Populations Hit Hardest
The study pointed out that the most vulnerable populations include elderly residents, very young children, those with existing health issues, and people working long hours outdoors. Many of these individuals lack access to cooling options such as air conditioning, putting them at even greater risk.
In urban environments, the risks are amplified. Heat absorbed by buildings and roads makes cities hotter than surrounding areas, and without cooler nights, there is little chance for recovery. This relentless exposure to high temperatures can be fatal, especially for those already in poor health.
A Call for Urgent Climate Action
This study highlights the urgent need for both climate adaptation and mitigation strategies. With global temperatures rising and extreme weather events becoming more frequent, cities must invest in better infrastructure, early warning systems, and public health measures to protect at-risk populations.
The findings are a stark reminder of the real-world consequences of fossil fuel consumption and greenhouse gas emissions. As similar heatwaves become increasingly common, experts warn that without bold climate action, more lives will be at risk.
