Abstract
Abstract Past changes in global industrial aerosol emissions have played a significant role in historical shifts in African rainfall, and yet assessment of the impact on African rainfall of near-term (10–40 yr) potential aerosol emission pathways remains largely unexplored. While existing literature links future aerosol declines to a northward shift of Sahel rainfall, existing climate projections rely on RCP scenarios that do not explore the range of air quality drivers. Here we present projections from two emission scenarios that better envelop the range of potential aerosol emissions. More aggressive emission cuts result in northward shifts of the tropical rainbands whose signal can emerge from expected internal variability on short, 10–20-yr time horizons. We also show for the first time that this northward shift also impacts East Africa, with evidence of delays to both onset and withdrawal of the short rains. However, comparisons of rainfall impacts across models suggest that only certain aspects of both the West and East African model responses may be robust, given model uncertainties. This work motivates the need for wider exploration of air quality scenarios in the climate science community to assess the robustness of these projected changes and to provide evidence to underpin climate adaptation in Africa. In particular, revised estimates of emission impacts of legislated measures every 5–10 years would have a value in providing near-term climate adaptation information for African stakeholders.
Highlights
Sub-Saharan and East Africa have experienced both prolonged periods of drought and increased flooding over the last 50 years (Dai et al 2004; Held et al 2005; Dai 2012; Nicholson 2016, 2017), with devastating consequences on society
The two scenarios differ in their aerosol emissions, with their either emissions following those under current legalization (CLE) air quality measures only or exploring what emissions would look like were maximum technological feasible reduction (MTFR) to take place (Stohl et al 2015)
Projected future aerosol declines have been shown to drive a northward shift in the tropical monsoon systems (Allen 2015; Rotstayn et al 2015)
Summary
SCANNELL ET AL. CLAIRE SCANNELL,a BEN B. B. BOOTH,a NICK J. DUNSTONE,a DAVID P. ROWELL,a DAN J. BERNIE,a MATTHEW KASOAR,b,c APOSTOLOS VOULGARAKIS,b LAURA J. WILCOX,d,e JUAN C. ACOSTA NAVARRO,f,g,h ØYVIND SELAND,i AND DAVID J. PAYNTERj a Met Office Hadley Centre, Exeter, United Kingdom b Department of Physics, Imperial College London, London, United Kingdom c Grantham Institute-Climate Change and the Environment, Imperial College London, London, United Kingdom d National Centre for Atmospheric Science, Leeds, United Kingdom e Department of Meteorology, University of Reading, Reading, United Kingdom f Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden g Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden h Earth Sciences Department, Barcelona Supercomputing Center, Barcelona, Spain i Norwegian Meteorological Institute, Oslo, Norway j NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey (Manuscript received 25 October 2018, in final form 16 August 2019)
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