Rising cause-specific mortality risk and burden of compound heatwaves amid climate change

Global warming shifts daytime-only heatwaves to nighttime-only and day–night compound heatwaves. However, evidence on the cause-specific burdens of these heatwaves in a changing climate and ageing population is limited. Here, by analysing 1,088,742 non-accidental deaths from 272 Chinese cities, we found that compound heatwaves posed significantly higher cardiopulmonary mortality risks and burdens than daytime-only and nighttime-only heatwaves, particularly for ischaemic stroke, chronic obstructive pulmonary disease and regions with high summer temperature variation. Projections suggested substantial increases in compound heatwave-related mortality (4.0–7.6-fold) by the 2090s relative to the 2010s under medium and high greenhouse gas emission scenarios, outpacing nighttime-only heatwaves (0.7–1.9-fold) and contrasting with decreasing daytime heatwave-related mortality (0.3–0.8-fold). A strict emission control scenario (Shared Socioeconomic Pathway 1-1.9) may reverse most heatwave-related mortality increases. The confluence of global warming and ageing amplifies heatwave-related burdens, outstripping the sum of their individual impacts. Our findings underscore the importance of addressing compound heatwaves amid global warming. The authors analyse data from 272 Chinese cities, projecting that compound heatwaves will cause higher burdens for all major cardiopulmonary diseases than daytime or nighttime heatwaves, especially under scenarios with higher emissions and ageing and in areas with high summer temperature variability.