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.