Anthropogenic Aerosols Modulated 20th‐Century Sahel Rainfall Variability Via Their Impacts on North Atlantic Sea Surface Temperature. Issue 1 (28th December 2021)

• Record Type: Journal Article
• Authors: Zhang, Shipeng; Stier, Philip; Dagan, Guy; Wang, Minghuai
• Is Part Of: Geophysical research letters. Volume 49:Issue 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-28
• Subjects: aerosols -- Sahel rainfall -- North Atlantic variability -- aerosol‐cloud‐interactions; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL095629
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The Sahel rainfall has a close teleconnection with North Atlantic sea surface temperature (NASST) variability, which has separately been shown to be affected by aerosols. Therefore, changes in regional aerosols emission could potentially drive multidecadal Sahel rainfall variability. Here we combine ensembles of state‐of‐the‐art global climate models (the CESM and CanESM large ensemble simulations and CMIP6 models) with observational data sets to demonstrate that anthropogenic aerosols have significantly impacted 20th‐century detrended Sahel rainfall multidecadal variability through modifying NASST. We show that aerosol‐induced multidecadal variations of downward solar radiative fluxes over the North Atlantic cause NASST variability during the 20th century, altering the ITCZ position and dynamically linking aerosol effects to Sahel rainfall variability. This process chain is caused by aerosol‐induced changes in radiative surface fluxes rather than changes in ocean circulations. CMIP6 models further suggest that aerosol‐cloud interactions modulate the inter‐model uncertainty of simulated NASST and potentially the Sahel rainfall variability. Plain Language Summary: Sahel rainfall experienced significant multidecadal variability over the 20th century, with large societal implications. However, the drivers of this variability remain debated. Here we show that anthropogenic aerosols largely contributed to the Sahel rainfall variability. We propose a process chain, from changing sulfate emissions from Europe and North America, to changes in North Atlantic surface net radiative fluxes, via North Atlantic sea surface temperature variability to a shift of ITCZ and changes in West African monsoon, and finally Sahel rainfall variability. This process chain is consistently evidenced by ensembles of state‐of‐the‐art global climate models as well as observational data sets. We show that aerosol‐radiation interactions and aerosol‐cloud interactions are both important processes in this chain. These findings highlight the importance of accurate representation of regional aerosol‐cloud‐radiation interactions for the simulation of Sahel rainfall variability. Key Points: A process chain from anthropogenic aerosol emissions to the Sahel rainfall is proposed Large ensemble and CMIP6 simulations suggest that this link is mediated by aerosol impacts on North Atlantic SST Both aerosol‐cloud interactions and aerosol‐radiation interactions are important in this chain process