Issue South Asian aerosol loading threatening the monsoon

Summary

The global aerosol indicator lies within the safe space, but aerosol effects on climate vary strongly by region, so no single global threshold can capture local risks. The report therefore proposes a regional boundary of 0.25 for aerosol optical depth over South Asia, based on impacts on the summer monsoon, with an uncertainty zone reaching 0.5. In the 2026 assessment the value is about 0.32, beyond that boundary, and the latest trend points further outside the safe space. Recent climate model work shows that raising optical depth to 0.25 cuts South Asian monsoon rainfall by about 10 percent, producing drought conditions, while 0.5 cuts it by 15 to 20 percent. Heavy aerosol loading raises the risk of prolonged drought and lower crop yields and is tied to harmful fine particulate pollution that increases respiratory illness. The report names sulfur dioxide and black carbon from industry, power generation and transport, along with biomass burning such as crop residue fires, as key sources.