An uncertain future for anthropogenic aerosols in Africa, and their climate and health impacts

We explore the wide spread in projections of African mid-century anthropogenic air pollution levels, and associated health impacts, resulting from the large diversity in available future emission pathways for the region. While emissions of aerosols and their precursors have declined in some regions, first in North America and Europe, more recently in China, many low- and middle-income countries, including much of Africa, are increasing their emissions and are projected to continue to do so with future industrialization, although the evolution depends in socioeconomic and technological factors. This is likely to drive changes in climate hazards as well as deterioration of air quality, increasing risks for under-resourced, vulnerable populations. The impacts of African aerosols on regional temperature, hydroclimate, and extreme events are, however, less well studied and quantified than for other historical emission hotspots. Moreover, very limited data availability and distinct regional characteristics of sources result in high uncertainties in estimates of African emissions. This uncertainty translates into future projections, which exhibit a striking spread in magnitudes and trends. For instance, available estimates for emissions of sulfur dioxide and black carbon in 2050 differ by up to 70% and 90% between the Shared Socioeconomic Pathways (SSPs) and scenarios developed for the UN Environmental Programmes (UNEP) Integrated Assessment of Air Pollution and Climate Change in Africa. Here we explore implications of this spread for downstream modeled quantities of relevance for climate and health impact assessments. We use emissions from 10 different pathways as input to the chemical transport model OsloCTM3 and simulate the distribution of anthropogenic aerosols across the African continent in 2050. The associated impact on premature mortality is calculated. Preliminary results show surface PM2.5 concentrations differing by up to a factor 2 between the highest and lowest scenario when averaged over the African continents, with markedly higher local spread. Sub-continental differences are substantial, pointing to the need to consider Africa in more geographical detail than often done.