Impact of Asian aerosols on the summer monsoon strongly modulated by regional precipitation biases

Attributing variations in the Asian summer monsoon to aerosol forcing is crucial for reducing uncertainties in future regional water availability projections. This is essential for effective risk management and adaptation planning in this densely populated region. However, accurately simulating the monsoon remains a significant challenge for climate models due to persistent biases, which compromise their reliability in attributing anthropogenic influences. In this study, we analyze a set of climate model experiments to uncover the connection between these biases and the monsoon’s response to Asian aerosols, focusing on the underlying physical mechanisms, including large-scale circulation changes. The impact of aerosols on monsoon precipitation and circulation is strongly shaped by a model's ability to represent the spatio-temporal variability in climatological monsoon winds, clouds, and precipitation across Asia. This variability modulates the magnitude and efficacy of aerosol–cloud–precipitation interactions, a key component of the total aerosol response. Our findings reveal a strong interplay between South Asia and East Asia monsoon precipitation biases, with their relative dominance significantly influencing the overall monsoon response. Notably, there is a sharp contrast between aerosol-driven changes during early and late summer, which can be attributed to the opposing signs and seasonal evolution of biases in these two regions. Realistically simulating the progression of large-scale atmospheric circulation is essential to fully capture the aerosol impact across Asia. These insights have significant implications for improving the understanding and reducing inconsistencies in model responses to aerosol changes over Asia, both in historical simulations and future projections.