Black carbon aerosols intensified India’s 2015 mega heatwave and expanded heat stress exposure

Large-scale climatic drivers are known to amplify heatwave temperatures, whereas aerosols have complex regional temperature responses depending upon aerosol composition. With the help of recent observations and chemistry-coupled regional climate model simulations, we show that coincident aerosols—black carbon in particular—elevated the heatwave intensity of India’s deadly 2015 heatwave event. During the heatwave period in 2015, aerosols increased daily temperature maxima by 0.2–1.5 °C, which was spatially averaged over the heatwave-affected region. Further, increased surface humidity from aerosol-induced dynamic changes in moisture transport activated a moist heat stress episode, increasing daily wet-bulb temperature maxima by 0.25–1.8 °C. Overall, the aerosol effects additionally exposed about 30 million persons and 0.2 million km² of land area to extremely dry and moist heat stress. This highlights the need for a coordinated clean air and climate strategy, addressing the emission sources of black carbon for efficient air quality and heat stress management.