Amplified Interhemispheric Rainfall Contrast in Boreal Summer Due To Reduction in Anthropogenic Emissions Under COVID-MIP Green Economic-Recovery Scenarios

Our study looks at the precipitation responses to two possible future emission-mitigation pathways, pushed by the Coronavirus Disease 2019 pandemic (COVID-19) and achieving carbon neutrality in the mid-21st century. We find that a simultaneous-reduction in well-mixed greenhouse gases (WMGHGs) and anthropogenic aerosol emissions results in an enhanced interhemispheric precipitation contrast in the 2040s by amplifying the interhemispheric thermal contrast and strengthening the meridional overturning circulation in the tropics. Reduced aerosol emissions induce generally-increased precipitation in the Northern Hemisphere (NH) and an amplified intertropical rainfall contrast, while reduced WMGHG emissions dominate decrease in precipitation in the areas away from aerosol emission sources. Further, the above precipitation contrast will be enhanced under stronger emission-mitigation pathways, mainly attributed to larger precipitation increases in the NH caused by reduced aerosols. More aggressive WMGHGs mitigation policies are necessary to counteract the aerosol-induced warming in the NH, thereby mitigating the risk of regional drying or wetting due to the asymmetry in interhemispheric energy budgets. Under the background that most countries around the world have made carbon-neutral commitments to pursue the 1.5 degrees C warming limit and mitigate climate change, the emergence and persistence of the Coronavirus Disease 2019 (COVID-19) pandemic has provided a unique opportunity to investigate the impacts of anthropogenic emissions mitigation on climate. In this study we estimated the changes in boreal summer rainfall due to reductions in emissions of anthropogenic forcing agents, such as WMGHGs and aerosols, under the latest COVID-19 green economic-recovery scenarios using an aerosol-climate coupled model. We find that reductions in aerosol emissions induce generally increased precipitation in the Northern Hemisphere (NH) and decreased precipitation at low latitudes of the Southern Hemisphere (SH), while reduced WMGHG emissions dominate decreases in precipitation over the SH middle latitudes. The comprehensive effect of simultaneous decreases in anthropogenic emissions may lead to more abundant summer rainfall in the NH, while drier winters in the SH. Urgent mitigation actions of WMGHGs and aerosols are of course needed to limit widespread climate impacts and improve air quality. In pursuing such pathways, we need to factor their specific climate response into adaptation plans to build climate resilience and pathway-appropriate adaptation policies. Reduced anthropogenic aerosol emissions lead to a global-scale increase in boreal summer rainfall in the mid-21st centuryDecreased greenhouse gas emissions under green scenario induce reduction in boreal summer rainfall around the world in the mid-21st centurySimultaneous reductions in aerosol and greenhouse gas emissions induce amplified interhemispheric rainfall contrast in the mid-21st century

Automated summary

Our study examines the effect of emission reductions on precipitation and finds that reducing aerosol emissions increases precipitation in the Northern Hemisphere, while reducing greenhouse gas emissions decreases precipitation in the Southern Hemisphere. Simultaneous emissions reductions lead to an enhanced precipitation contrast between hemispheres, and more aggressive greenhouse gas mitigation policies are necessary to counteract aerosol-induced warming. This study is important for understanding climate change and informing adaptation policies.