Future burden of humid-heat related mortality in Europe aggravated by compound day-night warming and aging

Abstract Summer heatwaves are shifting from typical dry-heat to more humid conditions, with more frequent day-night compound heat extremes. As the fastest warming and aging continent, understanding the roles of climate and population dynamics is crucial for Europe to avoid underestimation of future heat-related health risks. Here we use a distributed lag nonlinear model that accounts for humid heat and day-night compound hot extremes to quantify future heat-related excess mortality in Europe due to changes in climate, population size, and age structure. We find humid heat can reduce the root mean square error of the model by 26 deaths compared to dry-bulb tempreature alone. Day-night compound hot extremes posing a 1.5 times higher risk of death than daytime only heat when lasting over 3 days. We project that total annual heat-induced mortality in Europe will increase by 24,670–69,827 deaths per degree of global warming under different Shared Socio-economic Pathways (SSPs), with western and northern Europe suffering the most. The increase in the future burden of heat-related mortality burden in Europe is dominanted by increased warming levels (accounting for 51.2–89.1% of the increase heat-related deaths) and an aging population structure (explaining 37.9–72.2% of the increase in the attributable heat-related mortality), although population decline under certain SSPs, such as SSP3 (a pathway of increased nationalism, regional rivalry, and decreased globalization), offsets over 34,000 heat-related deaths. Our analysis thus highlights the essential roles of mitigating and adapting to climate changes and increasing the resilience of older adults in reducing heat-related health risks in Europe.