Near-Future Anthropogenic Aerosol Emission Scenarios and Their Direct Radiative Effects on the Present-Day Characteristics of the Indian Summer Monsoon

Various air pollution mitigation scenarios have been proposed to improve the existing severe air quality problem over South Asia. Here we use a regional climate model to examine the response of the Indian summer monsoon (ISM) to two projected anthropogenic aerosol emission scenarios (a) short-lived climate pollutant "mitigation" scenario (2020-2030) and (b) current legislation "baseline" scenario (2005-2015). In the mitigation scenario, carbonaceous aerosol (black carbon and organic carbon) emissions are projected to decrease while sulfate emissions are projected to increase. This is expected to result in a marginal increase in anthropogenic aerosol optical depth over India (by 0.04-0.08). The dominating effect of scattering aerosols over absorbing aerosols in the mitigation scenario is expected to enhance atmospheric cooling over the Indian landmass, which in turn dampens the latitudinal thermal gradient and leads to a weakening of the ISM. This effect also reduces dust emissions over the Arabian Peninsula and transport across the Arabian Sea, decreasing the influence of the dust radiative feedback on the ISM. In addition, the increased amounts of sulfate and decreased amounts of carbonaceous aerosols are expected to result in drier conditions over the central parts of India. We also show that changes in emissions of different types of anthropogenic aerosols induce a chain of feedbacks, which can modulate the space-time variability of dust, thereby affecting the magnitude of dust radiative effects on the ISM dynamics. We conclude that it is critical from the policy point of view to implement strategies to cut the currently increasing sulfate emissions.