Comment on egusphere-2022-919

Abstract

The potential future trend in African aerosol emissions is uncertain, with a large range found in future scenarios used to drive climate projections. The future climate impact of these emissions is therefore uncertain. Using the Shared Socioeconomic Pathway (SSP) scenarios, transient future experiments were performed with the UK Earth System Model UKESM1, investigating the effect of African emissions following the high emission SSP370 scenario as the rest of the world follows the more sustainable SSP119, relative to a global SSP119 control. This isolates the effect of Africa following a relatively more polluted future emissions pathway. SSP370 sees higher direct anthropogenic aerosol emissions, but lower biomass burning emissions, over Africa. Increased aerosol reduces the local incident surface radiation, causing a local cooling, but the dominance of the black carbon absorption effect remotely from Africa leads to a global warming. The local cooling persists even when including the higher African CO2 emissions under SSP370 than SSP119. Precipitation also exhibits complex changes, with large-scale shifts in the Inter-Tropical Convergence Zone (ITCZ) due to hemispheric asymmetries in the applied forcing, and enhanced local rainfall due to mid-tropospheric instability from BC absorption. These results highlight the importance of future African aerosol emissions for regional and global climate, and the spatial complexity of this climate influence.