Anthropogenic aerosol changes disproportionately impact the evolution of global heatwave hazard and exposure

Abstract Understanding and predicting heatwave risk is a societal imperative in the face of climate change. Anthropogenic aerosol emissions impact heat extremes more strongly per unit of mean warming than do greenhouse gases, but the influence of aerosols’ evolving spatial pattern on time-varying heatwave hazard and resulting population exposure has been largely ignored. Aerosols’ spatially heterogeneous forcing is often co-located with population centers due to aerosols’ industrial sources and short atmospheric lifetime, potentially resulting in amplified exposure to aerosol-driven climate effects. Here, we quantify the influence of historical and projected future changes in aerosol emissions through 2100 on global patterns of heatwave hazard (i.e. the frequency of heatwave days) and exposure (i.e. population-weighted hazard) using the NCAR Community Earth System Model v1 single forcing large ensemble (LE). Our results show that increased aerosol emissions since 1920 have suppressed heatwave frequency (HWF) over populated regions by roughly half through present-day—a trend that is now reversing with shifting emission patterns and net global declining emissions. This may already be leading to an aerosol-driven acceleration in HWF, a signal that is amplified in populated regions. Aerosols’ influence on heatwaves is strongly co-located with population, creating out-sized exposure, which evolves through time with aerosols’ evolving emissions pattern within this LE. Our results suggest that near-term changes in aerosol emissions will be a disproportionate driver of trends in heatwave exposure, meriting dedicated future study, and that aerosols’ evolving spatial pattern should be considered in attempts to attribute recent heatwave trends to human activity.