Every time a new study is published on the increase of heat-related mortality under climate change, those with opposing views stress that at the same time cold-related mortality decreases. Critics say that cold-related mortality currently exceeds heat-related mortality by far. The impact of climate change would be a reduction of cold-related mortality exceeding the projected increase of heat-related mortality, with a net positive effect of climate change on public health. So why worry?

Well, this line of reasoning is a bit too simple. Yes, cold-related mortality exceeds heat-related mortality. According to previous studies there are roughly ten cold-related deaths for each heat-related death. However, the increase of heat-related mortality as temperature rises follows a steeper curve than the decrease of cold-related mortality. As a result, net mortality will increase this century even under the mildest climate change scenario. This is the conclusion of a new study, based on a comprehensive assessment of 854 European cities from north to south and east to west.

In their study, the researchers used temperature projections for mid-century and the end of this century from several climate models. They focused on three scenarios of socio-economic developments and related impacts on climate change: one including a substantial action toward both mitigation and adaptation, one with slow progresses, and one with little to no mitigation and adaptation efforts.

No adaptation

Across all considered scenarios, the increase in heat-related deaths would consistently exceed any decrease in cold-related deaths in Europe, if Europeans would not adapt to the increasing heat. This increase would be a peak of almost 8% in 2060, decreasing slightly afterward, for the low-end scenario of climate change. Under the high-end scenario, the net effect would be a strong increase over this century to reach 45% by 2100.

In numbers, these percentages agree with almost 8,000 climate change-related annual excess deaths by 2100 under the low-end scenario of climate change, if Europeans were not to adapt to the increasing heat. Under the high-end scenario of climate change, this number would be 80,000. However, the range of uncertainty surrounding these figures is large.

The projected increase of temperature-related mortality is strongest for Southern Europe, with Malta being the most affected country. For Eastern and Western Europe, the projected net effects are close to the European average. Only in Northern Europe the decrease in cold-related deaths slightly offsets the increase in heat-related deaths.

Adaptation

The authors of this study also looked whether adaptation to the increasing heat could reverse this increase. The answer is no. Even under high adaptation scenarios, the number of climate change-related annual excess deaths is projected to increase this century. A slight net decrease of death rates is projected for Northern Europe, but vulnerability remains high in the Mediterranean region and in Eastern Europe.

Both strong reductions in greenhouse gas emissions and adaptation measures are needed to avoid an increase of temperature-related mortality burden in most European cities.

Source: Masselot et al., 2025. Nature Medicine. DOI: 10.1038/s41591-024-03452-2.