Climate Change Fuelling Heat Deaths in Europe, Study Reveals

The summer of 2025 began with an intense heat wave in Europe in late June and early July, following an exceptionally warm June that set multiple temperature records across the continent. This episode triggered widespread health alerts including a red alert in Paris and an amber alert in London and caused significant social disruptions such as school closures in parts of France and a ban on outdoor work during the hottest hours of the day in Italy.

Following this episode, the Grantham Institute Climate Change and Environment at Imperial College London conducted a rapid attribution study and found that climate change directly drove a substantial portion of heat-related deaths over this 10-day period, effectively tripling the expected mortality.

The study attributes the persistent heat mainly to a high-pressure system known as a “heat dome” that trapped warm and dry air over Western Europe. As it moved eastward, the system intensified the heat by drawing warm air from North Africa. Its severity was reflected in alerts warning of a “heightened risk of death for vulnerable people,” according to the authors.

Beyond direct heat exposure, the wave increased the demand for health services and electricity, straining critical infrastructure and potentially compromising medical care in the region. Extreme conditions also increase the risk of wildfires, especially in Eastern Europe, the Balkans, and Turkey. In Sardinia, fires affected hospitals and airports, and major blazes in Crete and İzmir sent smoke across the region, exacerbating health impacts.

Across 12 major European cities, the study estimated 2305 excess deaths due to heat (95% empirical CI, 2022-2576) during those 10 days, of which 1504 (95% CI, 1262-1709) were linked directly to climate change.

This suggests that a 1.3 °C rise in the global temperature does not produce a linear increase in heat-related mortality. Instead, it raises the baseline risk, making extreme events far more likely and pushing mortality along a steeper, nonlinear curve. Small additional temperature increases could trigger exponential increases in health impact.

Older populations were the most affected; more than 80% of excess heat deaths occurred in people over 65 years, with those aged over 85 years accounting for 1028 deaths, 684 of which were linked to climate change. The early timing of the wave also proved more deadly, as physiologically unacclimatised populations and limited public preparedness amplified these risks.

The study noted that June heat waves have intensified more sharply than those in July, raising the likelihood of deadly early-season events. Disaggregated data revealed wide variability between cities: Milan recorded 499 heat deaths in 10 days, 317 (95% CI, 258-370) of which were attributed to climate change. Madrid saw over 90% of its 118 excess deaths tied to warming, whereas Lisbon’s Atlantic influence accounted for only 23% of its 92 excess deaths linked to climate change.

The report highlights urban heat island effects, where built environments absorb and re-emit more heat than rural areas, identifying cities as critical risk hotspots. Although “heat-action plans and early warning systems to reduce heat deaths are increasingly implemented,” the authors warned of an “urgent need to accelerate new adaptation measures” in response to the converging trends of climate change, population aging, and urbanisation.

The study used established epidemiological models and the World Weather Attribution framework to integrate factual and counterfactual temperature data with published exposure-response functions. 

One limitation of this study is the assumption of a constant daily mortality rate based on previous years, which likely underestimated the total number of excess heat deaths. However, relative metrics such as the climate-attributable proportion remain robust under this assumption. Exposure response functions derived from mortality data up to 2019 may not capture recent adaptation efforts, and evidence for widespread, highly effective adaptations remains limited.

Although adaptation is vital for immediate protection, safeguarding long-term public health requires accelerated global mitigation. As long as fossil fuels remain dominant, pressure on health systems will rise, and society’s risk will exceed its adaptive capacity. 

This is not only an environmental challenge but also a defining public health crisis demanding urgent, decisive action across all sectors to build climate-resilient communities and health systems and ensure that physicians are prepared to care for patients affected by future heat waves.

This story was translated from Medscape’s Spanish edition.