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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. 

Abstract With continued fossil‐fuel dependence, anthropogenic aerosols over South Asia are projected to increase until the mid‐21st century along with greenhouse gases (GHGs). Using the Community Earth System Model (CESM1) Large Ensemble, we quantify the influence of aerosols and GHGs on South Asian seasonal precipitation patterns over the 21st century under a very high‐emissions (RCP 8.5) trajectory. We find that increasing local aerosol concentrations could continue to suppress precipitation over South Asia in the near‐term, delaying the emergence of precipitation increases in response to GHGs by several decades in the monsoon season and a decade in the post‐monsoon season. Emergence of this wetting signal is expected in both seasons by the mid‐21st century. Our results demonstrate that the trajectory of local aerosols together with GHGs will shape near‐future precipitation patterns over South Asia. Therefore, constraining precipitation response to different trajectories of both forcers is critical for informing near‐term adaptation efforts.