[Preprint] Stratospheric Sulfate Aerosols impacts on West African monsoon precipitation using GeoMIP Models

[Geoeng Info]

https://www.essoar.org/doi/10.1002/essoar.10507841.1

Stratospheric Sulfate Aerosols impacts on West African monsoon precipitation using GeoMIP Models

Frederic Bonou, Casimir Yelognisse Da-Allada, Ezinvi Baloïtcha, Eric Alamou, Eliezer Iboukoun Biao, Josué Zandagba, Ezéchiel Obada, Yves Kpomalegni, Peter J. Irvine, Olivier Boucher, Simone Tilmes

Abstract

Stratospheric Aerosol Geoengineering (SAG) is proposed to offset global warming; the use of this approach can impact the hydrological cycle. We use simulations from Coupled Model Intercomparison Project (CMIP5) and Geoengineering Model Intercomparison Project (G3 simulation) to analyze the impacts of SAG on precipitation (P) and to determine its responsible causes in West Africa and Sahel region. CMIP5 Historical data are firstly validated, the results obtained are consistent with those of observations data (CMAP and GPCP). Under the Representative Concentration Pathway (RCP) scenario RCP4.5, a slight increase is found in West Africa Region (WAR) relative to present-day climate. The dynamic processes especially the monsoon shifts are responsible for this change of precipitation. Under RCP4.5, during the monsoon period, reductions in P are 0.86%, 0.80% related to the present-day climate in the Northern Sahel (NSA), Southern Sahel (SSA) respectively while P is increased by 1.04% in WAR. Under SAG, 3.71% of P change (decrease) was associated with a -3.51 value of efficacy in the West African Region (AR). Under G3, a significant decrease of P is found in the West African region. This decrease in monsoon precipitation is mainly explained by changes in dynamics, which leads to weakened monsoon circulation and a shift in the distribution of monsoon precipitation. This result suggests that SAG deployment to balancing all warming can be harmful to rainfall in WAR if the amount of SO₂ to be injected in this tropical area is not taken into consideration.

[SALTER Stephen]

Hi All

The Bonou et al. results below for stratospheric aerosol should be compared with those for tropospheric sea salt from Stjern et al 2018 for a gentle treatment of a 50% increase of nuclei concentration in cloudy ocean regions shown in the attached file.  I am sure that with help from the Cicero labs we get an even more beneficial result from a more sophisticated tactical spray plan but we should remember that a 10% increase in almost nothing is almost almost nothing. 

I recall a study claiming that if an increase in the West African monsoon could produce vegetation up to 18 degrees North latitude it would then spread all the way to the Mediterranean. This is supported by cave paintings and bones of crocodiles and hippos in the Sahara.

Stephen

 

 

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