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Dominant role of greenhouse-gas forcing in the recovery of Sahel rainfall

Nature Climate Change volume 5, pages 757–760 (2015)Cite this article

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Abstract

Sahelian summer rainfall, controlled by the West African monsoon, exhibited large-amplitude multidecadal variability during the twentieth century. Particularly important was the severe drought of the 1970s and 1980s, which had widespread impacts1,2,3,4,5,6. Research into the causes of this drought has identified anthropogenic aerosol forcing3,4,7 and changes in sea surface temperatures (SSTs; refs 1, 2, 6, 8, 9, 10, 11) as the most important drivers. Since the 1980s, there has been some recovery of Sahel rainfall amounts2,3,4,5,6,11,12,13,14, although not to the pre-drought levels of the 1940s and 1950s. Here we report on experiments with the atmospheric component of a state-of-the-art global climate model to identify the causes of this recovery. Our results suggest that the direct influence of higher levels of greenhouse gases in the atmosphere was the main cause, with an additional role for changes in anthropogenic aerosol precursor emissions. We find that recent changes in SSTs, although substantial, did not have a significant impact on the recovery. The simulated response to anthropogenic greenhouse-gas and aerosol forcing is consistent with a multivariate fingerprint of the observed recovery, raising confidence in our findings. Although robust predictions are not yet possible, our results suggest that the recent recovery in Sahel rainfall amounts is most likely to be sustained or amplified in the near term.

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Figure 1: The recent recovery in Sahel rainfall: observed changes and model-simulated responses.
Figure 2: Observed and model-simulated seasonal mean (July–September) changes in Sahel rainfall and related variables.
Figure 3: Spatial patterns of model-simulated seasonal mean (July–September) changes in response to different forcings.

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Acknowledgements

This work was supported by the PAGODA project of the Changing Water Cycle programme of the UK Natural Environment Research Council (NERC) under grant NE/I006672/1 and the European Union’s Seventh Framework Programme [FP7/2007-2013] under grant agreement no 607085. B.D. and R.S. are also supported by the UK National Centre for Atmospheric Science, funded by the Natural Environment Research Council. The authors would like to thank A. Giannini for helpful comments.

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  1. Department of Meteorology, National Centre for Atmospheric Science, University of Reading, Reading, RG6 6BB, UK

    Buwen Dong & Rowan Sutton

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  1. Buwen Dong
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B.D. and R.S. designed the research. B.D. carried out experiments and analyses. B.D. and R.S. worked together on the interpretation of results and wrote the paper.

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Correspondence to Buwen Dong or Rowan Sutton.

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Dong, B., Sutton, R. Dominant role of greenhouse-gas forcing in the recovery of Sahel rainfall. Nature Clim Change 5, 757–760 (2015). https://doi.org/10.1038/nclimate2664

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