An uncertain future for the climate and health impacts of anthropogenic aerosols in Africa

Abstract. Limited data availability and distinct regional characteristics of sources lead to a wide range of future aerosol emissions projections for Africa. Here we quantify and explore the implications of this spread for climate and health impact assessments. Using the Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants (ECLIPSE), the Shared Socioeconomic Pathways (SSPs), and the United Nations Environment Programme (UNEP) emission projections, we find high scenario diversity and regional heterogeneity in projected air pollution emissions across sub-Saharan Africa. Using 10 different emissions pathways as input to the Oslo chemical transport model version 3 (OsloCTM3), we find that regionally-averaged annual-mean population-weighted PM_2.5 concentrations exhibit divergent trends depending on scenario stringency, with Eastern Africa PM_2.5 concentrations increasing by up to 6 µg m^-3 (37 %) by 2050 under the UNEP Baseline, SSP370, and ECLIPSE current legislation scenarios. In almost all cases, there is a substantial increase in the number of excess deaths, with increases of up to more than 2.5 times compared to the baseline. We also find a net positive aerosol-induced radiative forcing across sub-Saharan Africa in all scenarios by 2050 except two high-sulfur emission UNEP scenarios, with values ranging from 0.03 W m^-2 in SSP119 to 0.27 W m^-2 in SSP585. The wide spread in projected emissions and differences in sectoral distributions across scenarios highlights the critical need for accurate activity data and harmonization efforts in preparation for upcoming assessments such as the 7th Assessment Report of the Intergovernmental Panel on Climate Change.