Response of the Equatorial Atlantic Cold Tongue to Stratospheric Aerosol Geoengineering

Y W Pomalegni,F Bonou,E Baloïtcha,F M Awo,P J Irvine,J E Zandagba,I Biao,Z Sohou,E A Alamou,S Tilmes,E Obada,C Y Da-Allada

doi:10.1007/s41810-021-00127-0

Abstract

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.

Highlights

Among diverse theoretical approaches to limit the effects of the increase of global warming, solar radiation modification (SRM) aims to reduce some amount of incoming solar short-wave radiation reaching Earth’s surface and has been indicated as a suplementary approach for counteracting the effects of global warming (e.g., Crutzen 2006; Kravitz et al 2013; Visioni et al 2020)
This comparison shows that the seasonal cycle of the vertical ocean temperature profile in the historical simulation (HIST) simulation and in the PIRATA buoys observations are in good agreement
The model again has a slight warm bias that extends through the ocean column, meaning that the D20 is slightly deeper compared to PIRATA

Summary

Introduction

Among diverse theoretical approaches to limit the effects of the increase of global warming, solar radiation modification (SRM) aims to reduce some amount of incoming solar short-wave radiation reaching Earth’s surface and has been indicated as a suplementary approach for counteracting the effects of global warming (e.g., Crutzen 2006; Kravitz et al 2013; Visioni et al 2020). While SAG is generally effective in reducing the effects of global warming (climate change), it can be over effective in offsetting hydrological change, meaning that if deployed to offset all warming it can produce a net weakening of the hydrological cycle (Tilmes et al 2013; Irvine et al 2019; Kravitz et al 2018). This applies at the regional scale, for example, Da-Allada et al 2020 showed that under global warming, there is an increase (relatively to the present-day climate) in the monsoonal precipitation in the western African region,. By modifying the trade winds, the use of SAG could affect the tropical Atlantic Ocean circulation and sea surface temperature (SST) in the region

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