Assessing the Response of Surface Cloud Radiative Effects to Stratospheric Aerosol Injections Over West and Central Africa

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025JD043576

Authors: Atanas Dommo, Francis Nkrumah, Kwesi A. Quagraine, Nana Ama Browne Klutse, Gandome Mayeul Léger Davy Quenum, Hubert A. Koffi

First published: 17 October 2025

https://doi.org/10.1029/2025JD043576

Abstract

This study investigates the response of surface cloud radiative effects (CREs) to Assessing Responses and Impacts of Solar Climate Intervention on the Earth system with Stratospheric Aerosol Injection (ARISE-SAI) relative to Shared Socio-Economic Pathways (SSP2-4.5) across three regions: Southern West Africa (SWA), Central Africa (CA), and Sahara (SAH). We utilize 10 members of the simulations from the Community Earth System Model version 2 (CESM2) with the Whole Atmosphere Community Climate Model version 6 (WACCM6) under the ARISE-SAI-1.5 scenario, comparing the outputs to those from the SSP2.4-5 scenario. Compared to SSP2-4.5, the findings indicate that ARISE-SAI-1.5 has the potential to mitigate the decreasing trend of shortwave cloud cooling by −0.35, −0.99, and −0.20 W/m2, while significantly enhancing the longwave warming by +1.06, +0.62, and +0.23 W/m2, over CA, SWA, and SAH, respectively, during the period 2035–2069. However, the changes in shortwave cloud cooling are not robust and may be attributable to natural variability rather than the direct effects of ARISE-SAI. The changes in cloud radiative effects underpin high sensitivity to changes in liquid water path, while the increased fractional cloud cover contributes to enhancing longwave cloud warming at the surface. Results also reveal strengthened precipitation associated with increased shortwave cloud cooling effect outweighing its longwave counterpart on the one hand or increased shortwave cloud cooling and reduced longwave cloud warming on the other hand. It is noteworthy that our results, although based solely on ARISE-SAI-1.5 simulations, pave the way to comprehensive comparisons between model results for a better assessment of the impacts of SAI deployment.

Plain Language Summary

Stratospheric Aerosol Injection is a technique for introducing sulfur dioxide into the atmosphere to form sulfate aerosols that would cool the Earth's surface, thereby mitigating the adverse effects of anthropogenic global warming. Simulations termed Assessing Responses and Impacts of Solar Climate Intervention on the Earth system with Stratospheric Aerosol Injection are utilized in this study to examine to what extent cloud may cool or warm the surface in order to evaluate the impact of the aforementioned technique over Central Africa, Southern West Africa, and the Sahara. Investigating the response of cloud radiative effects to Stratospheric Aerosol Injection is of paramount importance in assessing the broad impacts of that technique. The findings indicate that Stratospheric Aerosol Injection could mitigate the decreasing trend of longwave cloud radiative effects induced by global warming over Central Africa, Southern West Africa, and the Sahara region compared to moderate scenarios. One of the possible implications of this technology after deployment could be the strengthened precipitation as a response to increased shortwave cloud cooling driven by enhanced liquid water in the atmospheric column over southern West Africa, the Sahara, and Central Africa.

Key Points

Stratospheric Aerosol Injection could mitigate the decreasing trend of longwave cloud warming under rising greenhouse gases

Strengthened precipitation could be associated with increased shortwave cloud cooling outweighing longwave cloud warming effect changes

The changes in cloud radiative effects are highly sensitive with changes in liquid water path

Source: AGU