Absorbing aerosols and rising dry–moist heat extremes over India: Evidence of a strengthening air pollution–climate nexus

India has witnessed a significant rise in surface temperature during the pre-monsoon season, driving more intense, frequent, and prolonged heatwaves, particularly over the northwest and central regions of the country. While there is a clear consensus on the role of greenhouse gases driving global warming, the role of anthropogenic aerosols, particularly absorbing ones such as black carbon, brown carbon, and dust, on regional warming remains uncertain and is less understood. While scattering aerosols dominate in many regions, India exhibits a high loading of absorbing aerosols, mainly mineral dust and black carbon from natural transport and combustion sources. These absorbing aerosols can offset aerosol-induced cooling and amplify regional near-surface warming. These absorbing aerosols trap solar radiation, heat the atmosphere, and stabilize the atmospheric boundary layer, further amplifying the heatwave conditions by offsetting surface cooling. Studies through observations and model simulations have linked the possible links between the elevated absorbing aerosols and heat extremes through strong radiative forcing and an increase in shortwave energy to the surface layer. However, long-term observational evidence quantifying the relationships between absorbing aerosols and temperature extremes (for both dry and moist heat) over India is yet to be established, motivating this study.

For this, we obtained the pre-monsoon season (March–June; MAMJ) absorbing aerosol and extreme heat data over India (66.5°- 100.5°E; 6.5°-36.5°N) for 1980-2024. The Absorbing Aerosol Index (AAI) is used as a qualitative measure of UV‐absorbing aerosols, obtained from the TOMS satellite record (1980–2004) and the OMI instrument (2005–2024). For extreme heat, we used daily maximum temperature (Tmax) obtained from the Indian Meteorological Department (IMD) to characterize dry heat, while we calculated wet bulb temperature (WBT) by combining Tmax from IMD and relative humidity from ERA5 datasets to define moist heat. We further computed the temporal season mean trends of variables along with their statistical significance at a 95% confidence level. We selected 3 boxes based on significant trends and reported heatwave-prone regions over northwest, eastern, and southern India to analyze the co-evolution of AAI and extreme heat variables.

We found substantial positive trends in season mean AAI and temperature variables across India, with an approximate rate of 0.25 units per decade, ~0.20°C per decade (dry heat), and ~0.2-0.4°C per decade (moist heat), respectively. The increase is highly significant in north-central India in the case of Tmax and AAI, while Central and eastern India show significance for moist heat. The consistent elevated summer temperatures in north-central India are in agreement with scientifically recognized meteorological conditions such as North Atlantic blocking creating high-pressure systems aiding the role of absorbing aerosols in amplifying heat stress. Meanwhile, moist heat increases are linked to rises in pre-monsoon humidity, which are associated with increases in irrigation and sea-surface temperature across India. The current findings have significant implications for coordinated climate and air-quality action to reduce aerosol-driven climate risks associated with extreme heat at regional scales.