The Local and Remote Atmospheric Impacts of Africas 21st Century Aerosol Emissions Trajectory

Using the Shared Socioeconomic Pathway scenarios (SSPs), transient future experiments were performed in UKESM1, investigating the effect of African emissions following a weak mitigation scenario (SSP3-RCP7.0) scenario whilst the rest of the world follows a strong mitigation scenario (SSP1-RCP1.9), relative to a global strong mitigation (SSP1-RCP1.9) control. SSP3 sees higher direct anthropogenic aerosol emissions, but lower biomass burning (BB) emissions, over Africa. Experiments were performed using SSP3-RCP7.0 for several sets of species: BB aerosol and precursor emissions (except CH4), nonBB aerosol and precursor emissions, both of these together, CO2 concentrations (with and without changing aerosols and precursors), and additionally changing CH4. Impacts on radiation fluxes, temperature, circulation and precipitation are investigated, both over the emission region (Africa), where microphysical effects dominate, and remotely, where dynamical influences become more relevant. The aerosol differences are driven by carbonaceous aerosol, with the temperature in turn driven by the BC absorption response, leading to a general warming effect under increased emissions; locally, reduced surface radiation generates a relative cooling, which persists even when including CO2 and CH4 warming. These mean changes are reflected in shifts in extreme daily temperatures. Shifts in the ITCZ are seen due to the hemispherically asymmetric forcings, with local precipitation increases due to enhanced mid-level convection under BC absorption too.