Estimation of the mortality attributable to heat in France between 2014 and 2023: an indicator to document the health effects of climate change

Abstract Developing indicators to monitor spatial and temporal trends in the health effects of climate change is crucial to encouraging adaptation. Heat is one of the most studied climate-related health issues, but its impact is still little known to decision-makers. We propose an approach for producing annual estimates of heat-related mortality, as an indicator to support adaptation policies. A first step was to develop temperature-mortality relationships for each of the 96 metropolitan French departments, for summers (June- September) 2014-2022. Several approaches were tested to control for a possible influence of the COVID-19 pandemic since 2020. Those models were then used to compute the annual mortality attributable to heat for 2014-2023. Heat-related risks tended to be slighly higher after the pandemic ; an increase from 19.8°C to 28.5°C was associated with a relative risk of 1.25 [CI 95% 1.21 :1.30] in 2004-2019, and 1.31 [1.24 :1.38] in 2020-2022. Between 2014 and 2023, 37,825 deaths [IC95% 34,273 : 40,483] were attributable to heat. The largest impacts are observed in 2022 (6,969 [6,277 : 7,445]), 2023 (5 167 [4 587 ; 5 551]), and 2019 (4,441 [4,086 : 4,717]). The 2014-2022 temperature-mortality relationships will be used to compute the heat-related mortality for the coming year. A regular update of the relationships is planned. This indicator documents the mortality impact of heat during the summer and during extreme heat waves. It shows that the impact is increasing, despite major prevention efforts. This call for a more ambitious, transformative adaptation to climate change.