Decreased Interhemispheric Asymmetries Of Global Land Monsoon Precipitation Toward the Carbon Neutrality Goal

Global land monsoon precipitation (GLMP) is highly sensitive to changes in interhemispheric thermal contrast (ITC). Amplified interhemispheric asymmetries of GLMP due to enhanced ITC driven by high-level anthropogenic emissions are expected to simultaneously increase the probability of regional floods and droughts, threatening ecosystems within global terrestrial monsoon regions and the freshwater supply for billions of residents in these areas. In this study, the responses of GLMP to the evolution of ITC toward the carbon neutrality goal are assessed using multi-model outputs from a new model intercomparison project (CovidMIP). The results show that the Northern Hemisphere-Southern Hemisphere (NH-SH) asymmetry of GLMP in boreal summer weakens during the 2040s, as a persistent reduction in well-mixed greenhouse gases (WMGHGs) emissions leads to a downward trend in the ITC after 2040.At the same time,reduction in WMGHGs emissions dampens the Eastern Hemisphere-Western Hemisphere (EH-WH) asymmetry of GLMP by inducing La Niña-like cooling and enhancing moisture transport to Inner America. The resulting increases in land monsoon precipitation (LMP) may alleviate drought under the global warming scenario by about 19-25% and 7-9% in the WH and SH monsoon regions, respectively. However, persistent reduction in aerosol emissions in Asia will dominate the increases in LMP in this region until the mid-21st century, and these increases may be approximately 23-60% of the growth under the global warming scenario. Our results highlight the different rates of response of aerosol and WMGHG concentrations to the carbon neutrality goal, leading to various changes in LMP at global and regional scales.