Changes in West African Summer Monsoon Precipitation Under Stratospheric Aerosol Geoengineering. Issue 7 (16th July 2020)

• Record Type: Journal Article
• Authors: Da‐Allada, C. Y.; Baloïtcha, E.; Alamou, E. A.; Awo, F. M.; Bonou, F.; Pomalegni, Y.; Biao, E. I.; Obada, E.; Zandagba, J. E.; Tilmes, S.; Irvine, P. J.
• Is Part Of: Earth's future. Volume 8:Issue 7(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-16
• Subjects: SAG -- impact -- WASM -- precipitation -- climate model -- monsoon circulation; Environmental sciences -- Periodicals; Environmental sciences; Periodicals; 550
• DOI: 10.1029/2020EF001595
• Languages: English
• ISSNs: 2328-4277

Abstract

Abstract: 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. Plain Language Summary: Stratospheric aerosol geoengineering is one of methods that could artificially reduce the amount of sunlight that reaches the Earth's surface in order to cool the planet. This method is identified as a possible means to reduce the climate impacts of global warming. One of the key variables affected by climate change is precipitation which is of great importance in monsoon regions such as West Africa. Here the potential impact of the stratospheric aerosol geoengineering on the West African Summer Monsoon precipitation and the associated mechanisms are investigated, using climate model simulations from the Geoengineering Large Ensemble project that used stratospheric sulfate aerosols injection to stabilize global mean surface temperature and, also, the interhemispheric and equator‐to‐pole temperature gradients at their 2020 values under RCP8.5 scenario. Results reveal that using stratospheric aerosol geoengineering, summer monsoon precipitation is nearly unchanged in the northern and southern Sahel regions compared to present day, whereas significantly decrease in monsoonal precipitation is noted in the Western Africa region. The relative contribution of the different mechanisms controlling changes in precipitation under stratospheric aerosol geoengineering is examined using the method of decomposition and results show that changes in precipitation are largely related to changes in the dynamic processes (monsoon circulation). Key Points: We explore the potential impact of stratospheric aerosol geoengineering on the West African Summer Monsoon precipitation and the associated driving mechanisms Use of stratospheric aerosol geoengineering is effective for rainfall in the northern and southern Sahel whereas it is overeffective in Western Africa region Under stratospheric aerosol geoengineering, changes in the monsoon precipitation are mainly caused by changes in the dynamic processes (monsoon circulation)