Letter | Published:

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

Nature Climate Change volume 5, pages 757760 (2015) | Download Citation

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.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1.

    , & Sahel rainfall and worldwide sea temperatures, 1901–85. Nature 320, 602–607 (1986).

  2. 2.

    , & Oceanic forcing of Sahel rainfall on interannual to interdecadal time scales. Science 302, 1027–1030 (2003).

  3. 3.

    , , , & Simulation of Sahel drought in the 20th and 21st centuries. Proc. Natl Acad. Sci. USA 102, 17891–17896 (2005).

  4. 4.

    & Robust Sahel drying in response to late 20th century forcings. Geophys. Res. Lett. 33, L11706 (2006).

  5. 5.

    Forced Sahel rainfall trends in the CMIP5 archive. J. Geophys. Res. 118, 1613–1623 (2013).

  6. 6.

    et al. A unifying view of climate change in the Sahel linking intra-seasonal, interannual and longer time scales. Environ. Res. Lett. 8, 024010 (2013).

  7. 7.

    et al. Sensitivity of twentieth-century Sahel rainfall to sulphate aerosol and CO2 forcing. J. Clim. 24, 4999–5014 (2011).

  8. 8.

    & Impact of Atlantic multidecadal oscillations on India/Sahel rainfall and Atlantic hurricanes. Geophys. Res. Lett. 33, L17712 (2006).

  9. 9.

    , & The Multidecadal Atlantic SST—Sahel rainfall teleconnection in CMIP5 simulations. J. Clim. 27, 784–806 (2014).

  10. 10.

    & The impact of decadal-scale Indian Ocean sea surface temperature anomalies on Sahelian rainfall and the North Atlantic Oscillation. Geophys. Res. Lett. 30, 2169 (2003).

  11. 11.

    & Ocean warming and late-twentieth-century Sahel drought and recovery. J. Clim. 21, 3797–3814 (2008).

  12. 12.

    , , & Sahel rainfall variability and response to greenhouse warming. Geophys. Res. Lett. 32, L17702 (2005).

  13. 13.

    , , & Recent changes in precipitations, ITCZ convection and northern tropical circulation over North Africa (1979–2007). Int. J. Climatol. 31, 633–648 (2011).

  14. 14.

    et al. Water vapor–forced greenhouse warming over the Sahara Desert and the recent recovery from the Sahelian drought. J. Clim. 28, 108–123 (2015).

  15. 15.

    Dynamics of deserts and drought in Sahel. Quart. J. R. Meteorol. Soc. 101, 193–202 (1975).

  16. 16.

    , & Influence of twenty-first-century atmospheric and sea surface temperature forcing on west African climate. J. Clim. 25, 527–542 (2012).

  17. 17.

    Mechanisms of climate change in the semiarid African Sahel: The local view. J. Clim. 23, 743–756 (2010).

  18. 18.

    & Projected changes in African easterly wave intensity and track in response to greenhouse forcing. Proc. Natl Acad. Sci. USA 111, 6882–6887 (2014).

  19. 19.

    et al. The present and future of the West African monsoon: A process-oriented assessment of CMIP5 simulations along the AMMA transect. J. Clim. 26, 1–88 (2013).

  20. 20.

    & The central west Saharan dust hot spot and its relation to African easterly waves and extratropical disturbances. J. Geophys. Res. 115, D12117 (2010).

  21. 21.

    , & Analysis of African easterly wave structures and their role in influencing tropical cyclogenesis. Mon. Weath. Rev. 138, 1399–1419 (2010).

  22. 22.

    , , & Updated high-resolution grids of monthly climatic observations—the CRU TS3.10 Dataset. Int. J. Climatol. 34, 623–642 (2014).

  23. 23.

    et al. The version 2 Global Precipitation Climatology Project (GPCP) monthly precipitation analysis (1979–present). J. Hydrometeor. 4, 1147–1167 (2003).

  24. 24.

    , , & Global surface temperature change. Rev. Geophys. 48, RG4004 (2010).

  25. 25.

    et al. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. 108, 4407 (2003).

  26. 26.

    et al. NCEP–DOE AMIP-II Reanalysis (R-2). Bull. Am. Meteorol. Soc. 83, 1631–1643 (2002).

  27. 27.

    et al. The Twentieth Century Reanalysis Project. Q. J. R. Meteorol. Soc. 137, 1–28 (2011).

  28. 28.

    et al. Historical (1850–2000) gridded anthropogenic and biomass burning emissions of reactive gases and aerosols: Methodology and application. Atmos. Chem. Phys. 10, 7017–7039 (2010).

  29. 29.

    et al. Design and implementation of the infrastructure of HadGEM3: The next-generation Met Office climate modelling system. Geosci. Model Dev. 4, 223–253 (2011).

  30. 30.

    et al. A seamless assessment of the role of convection in the water cycle of the West African monsoon. J. Geophys. Res. 119, 2890–2912 (2014).

Download references

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.

Author information

Affiliations

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

    • Buwen Dong
    •  & Rowan Sutton

Authors

  1. Search for Buwen Dong in:

  2. Search for Rowan Sutton in:

Contributions

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.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Buwen Dong or Rowan Sutton.

Supplementary information

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/nclimate2664

Further reading