Air pollution amplifies the humid heat anomalies in India

Abstract India is confronting intensifying humid heat coupled with severe air pollution. While air pollution is known to reduce near-surface temperatures, its non-linear impact on humid heat remains insufficiently understood, limiting our comprehension of current warming conditions and future projections for India. Here, using observations, reanalysis data, and model simulations, we demonstrate how air pollution affects humid heat and project its future evolution under climate change. Our results indicate that air pollution generally mitigates dry heat conditions, however, it exacerbates humid heat anomalies on approximately one-fifth of days. Absorbing aerosols warm the atmosphere, induce a heat dome effect, elevate surface sensible heat flux, and reduce soil moisture. This process strengthens soil moisture-atmosphere coupling, ultimately amplifying humid heat anomalies. Projections under different future scenarios indicate a prospective increase in humid heat over India, with the most prominent changes expected in the densely populated Ganges Plain. A moderate development pathway can constrain humid heat rise to its historical average rate, but more stringent climate policies and greenhouse gas mitigation measures are urgently required. Our findings demonstrate that implementing synergistic climate and air quality policies is crucial for curbing the escalating risk of humid heat in India and similar regions.