The Lancet Planetary Health, July 2025

Too hot to handle?

Extreme temperature is perhaps the aspect of climate change that has the most direct effects on our health. Non-optimal temperatures are estimated to contribute to about 5 million deaths a year (or around 9% of all deaths).

Due to the shape of the temperature-mortality exposure–response relationship there are generally more deaths related to cold (below optimum temperatures, which occur more frequently); however, the relative risk of death is much higher on a given exceptionally hot day compared with an exceptionally cold one. The sensitivity of people’s health to extreme heat combined with the trend towards more frequent and more extreme hot weather events due to ongoing climate change, makes them an important target for research.