Stratospheric aerosol geoengineering (SAG) is suggested as a potential way to reduce the climate impacts of global warming. Using simulations from the Geoengineering Large Ensemble project that employed stratospheric sulfate aerosols injection to keep global mean surface temperature and also the interhemispheric and equator‐to‐pole temperature gradients at their 2020 values (present‐day climate) under Representative Concentration Pathway 8.5 scenario, we investigate the potential impact of SAG on the West African Summer Monsoon (WASM) precipitation and the involved physical processes. Results indicate that under Representative Concentration Pathway 8.5, during the monsoon period, precipitation increases by 44.76%, 19.74%, and 5.14% compared to the present‐day climate in the Northern Sahel, Southern Sahel, and Western Africa region, respectively. Under SAG, relative to the present‐day climate, the WASM rainfall is practically unchanged in the Northern Sahel region but in Southern Sahel and Western Africa regions, rainfall is reduced by 4.06% (0.19 ± 0.22 mm) and 10.87% (0.72 ± 0.27 mm), respectively. This suggests that SAG deployed to offset all warming would be effective at offsetting the effects of climate change on rainfall in the Sahel regions but that it would be overeffective in Western Africa, turning a modest positive trend into a negative trend twice as large. By applying the decomposition method, we quantified the relative contribution of different physical mechanisms responsible for precipitation changes under SAG. Results reveal that changes in the WASM precipitation are mainly driven by the reduction of the low‐level land‐sea thermal contrast that leads to weakened monsoon circulation and a northward shift of the monsoon precipitation.

This study assesses changes in extremes precipitation and temperature in West Africa under a high greenhouse gas scenario, that is, a representative concentration pathway 8.5, and under a scenario of stratospheric aerosol geoengineering (SAG) deployment using the NCAR Community Earth System Model version 1. We use results from the Geoengineering Large Ensemble simulations (GLENS), where SAG is deployed to keep global surface temperatures at present day values. This impact study evaluates changes in some of the extreme climate indices recommended by the Expert Team Monitoring on Climate Change Detection and Indices. The results indicate that SAG would effectively keep surface temperatures at present day‐conditions across a range of indices compared to the control (CRTL) period, including Cold days, Cold nights and Cold Spell Duration Indicator which show no significant increase compared to the CRTL period. Regarding the extremes precipitation, GLENS shows mostly a statistically significant increase in annual precipitation and statistically significant decrease in the number of heavy and very heavy precipitation events relative to the CRTL period in some regions of Gulf of Guinea. In the Sahel, we notice a mix of statistically significant increase and decrease in Max 1‐day and Max 5‐days precipitation amount relative to the CRTL period at the end of the 21st century when large amounts of SAG has been applied. The changes in extreme precipitation indices are linked to changes in Atlantic Multidecadal Oscillation, NINO3.4 and Indian Ocean Dipole and these changes in extreme precipitation are driven by change in near surface specific humidty and atmospheric circulation.

By increasing Earth-atmosphere system albedo, Stratospheric Aerosol Geoengineering (SAG) using sulfur dioxide is an artificial potential means, with the goal to mitigate the global warming effects. In this study, we used the simulations from Geoengineering Large Ensemble project realized under the climate change scenario of Representative Concentration Pathway 8.5 (RCP8.5), to investigate the potential impact of SAG on the Sea Surface Temperature (SST) in Equatorial Atlantic Cold Tongue (EACT) and the physical processes driving these changes. Results reveal that in the EACT region, under RCP8.5, SST warms significantly (compared to present‐day climate) with a maximum of 1.7 °C in July, and this increase in SST is mainly due to the local processes related to the weakening of vertical mixing at the base of the mixed layer. This reduction of the vertical mixing is associated to the diminution of the vertical shear from July to April and to the increase of ocean stratification from May to June. However, under SAG, SST decreases significantly throughout the year (compared to present‐day climate) with a maximum cooling of − 0.4 °C in the cold tongue period (May–June). This SST cooling is mainly associated with the non-local processes related to intensification of the westerly equatorial Atlantic wind stress. Finally, results show that the use of SAG to offset all global warming under RCP8.5 results in a slight over compensation of SST in the EACT region.