Total ozone content, total cloud cover, and aerosol optical depth in CMIP6: simulations performance and projected changes

This study is focused on the evaluation of the projected changes in total ozone content (TOC), total cloud cover (TCC), and aerosol optical depth at 550 nm (AOD550) over the twenty-first century. For that, we first evaluated current climate (1980–2014) simulations provided by six Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) by contrasting them with the fifth generation of European Reanalysis (ERA5) and the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). We have considered the ESMs projections forced under the Shared Socioeconomic Pathways (SSPs) scenarios for future time slices. As expected, the mean of the multi-model ensemble showed biases and root-mean-square errors (RMSE) close to the reanalysis data. For TOC, pronounced increases are projected at mid and high latitudes, towards the end of the century, and under higher radiative forcing scenarios (SSP3-7.0 and SSP5-8.5). Over Antarctica, increases of up to 30.0% projected for 2081–2100 indicate ozone recovery. On the other hand, greenhouse gas (GHG) emissions impact the signal of change in the tropical region, with decreases (up to − 4.0%) under SSP1-2.6 and increases (up to 7.0%) under SSP3-7.0. Regarding TCC, increases over the Eastern Tropical Pacific Ocean in all SSPs, with maximum values ~ 27.0% (in the long-term; 2081–2100), are related to the Intertropical Convergence Zone (ITCZ). By contrast, TCC decline in South Africa (up to − 21.0%) and South America (up to − 16.0%) are consistent with the reduction of cloudiness due to the intensification of subtropical anticyclones. For AOD550, increases of up to 28.0% (SSP3-7.0) and 99.0% (SSP5-8.5) are projected in India, Central, and East Africa in 2081–2100. On the other hand, decreases in AOD550 in North America, Europe, and China over the century may be due to the air quality policies and pollutant emissions control, mainly under the SSP1-2.6 scenario.