Author: ["Jim M. Haywood","Andy Jones","Nicolas Bellouin","David Stephenson"]
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Abstract
Sahelian drought is investigated by analysing de-trended observations between 1900 and 2010, which show that substantial Northern Hemisphere volcanic eruptions preceded three of the four driest summers. Modelling both episodic volcanic eruptions and geoengineering by continuous deliberate stratospheric injection shows that large asymmetric aerosol loadings in the Northern Hemisphere are a precursor of Sahelian drought, whereas if the aerosol loadings are concentrated in the Southern Hemisphere greening of the Sahel is induced. The Sahelian drought of the 1970s–1990s was one of the largest humanitarian disasters of the past 50 years, causing up to 250,000 deaths and creating 10 million refugees1. It has been attributed to natural variability2,3,4,5, over-grazing6 and the impact of industrial emissions of sulphur dioxide7,8. Each mechanism can influence the Atlantic sea surface temperature gradient, which is strongly coupled to Sahelian precipitation2,3. We suggest that sporadic volcanic eruptions in the Northern Hemisphere also strongly influence this gradient and cause Sahelian drought. Using de-trended observations from 1900 to 2010, we show that three of the four driest Sahelian summers were preceded by substantial Northern Hemisphere volcanic eruptions. We use a state-of-the-art coupled global atmosphere–ocean model to simulate both episodic volcanic eruptions and geoengineering by continuous deliberate injection into the stratosphere. In either case, large asymmetric stratospheric aerosol loadings concentrated in the Northern Hemisphere are a harbinger of Sahelian drought whereas those concentrated in the Southern Hemisphere induce a greening of the Sahel. Further studies of the detailed regional impacts on the Sahel and other vulnerable areas are required to inform policymakers in developing careful consensual global governance before any practical solar radiation management geoengineering scheme is implemented.Cite this article
Haywood, J., Jones, A., Bellouin, N. et al. Asymmetric forcing from stratospheric aerosols impacts Sahelian rainfall. Nature Clim Change 3, 660–665 (2013). https://doi.org/10.1038/nclimate1857 