Letter | Published:

Asymmetric forcing from stratospheric aerosols impacts Sahelian rainfall

Nature Climate Change volume 3, pages 660665 (2013) | Download Citation

Abstract

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.

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.

    .

  2. 2.

    Drought in the Sahel. Science 302, 999–1000 (2003).

  3. 3.

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

  4. 4.

    et al. Oceanic link between abrupt changes in the North Atlantic Ocean and the African monsoon. Nature Geosci. 1, 444–448 (2008).

  5. 5.

    et al. Atlantic forcing of persistent drought in West Africa. Science 324, 377–380 (2009).

  6. 6.

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

  7. 7.

    , , , & Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability. Nature 484, 228–232 (2012).

  8. 8.

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

  9. 9.

    , & Aerosol forcing, climate response and climate sensitivity in the Hadley Centre climate model HadGEM2-AML. J. Geophys. Res. 112, D20211 (2007).

  10. 10.

    An investigation of interannual rainfall variability in Africa. J. Clim. 1, 240–255 (1988).

  11. 11.

    .

  12. 12.

    Robust locally weighted regression and smoothing scatterplots. J. Am. Stat. Assoc. 74, 829–836 (1979).

  13. 13.

    , , & Stratospheric aerosol optical depth, 1850–1990. J. Geophys. Res. 98, 22987–22994 (1993).

  14. 14.

    See .

  15. 15.

    & The volcanic signal in Goddard Institute for Space Studies three-dimensional model simulations. J. Clim. 7, 44–55 (1994).

  16. 16.

    , , & High-latitude eruptions cast shadow over the African monsoon and the flow of the Nile. Geophys. Res. Lett. 33, L18711 (2006).

  17. 17.

    & The relationship of the El Niño-Southern Oscillation to African rainfall. Int. J. Climatol. 17, 117–135 (1997).

  18. 18.

    20 reasons why geoengineering may be a bad idea. Bull. Atom. Scient. 64, 14–18 (2008).

  19. 19.

    & The radiative forcing potential of different climate geoengineering options. Atmos. Chem. Phys. 9, 5539–5561.

  20. 20.

    , & Research on global sun block needed now. Nature 463, 426–427 (2010).

  21. 21.

    , , , & Geoengineering by stratospheric SO2 injection: Results from the Met Office HadGEM2 climate model and comparison with the Goddard Institute for Space Studies ModelE. Atmos. Chem. Phys. 10, 5999–6006 (2010).

  22. 22.

    , & Regional climate responses to geoengineering with tropical and Arctic SO2 injection. J. Geophys. Res. 113, D16101 (2008).

  23. 23.

    et al. The Geoengineering Model Intercomparison Project (GeoMIP). Atmos. Sci. Lett. 12, 162–167 (2011).

  24. 24.

    et al. Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: Climate responses simulated by four Earth system models. Earth Syst. Dynam. 3, 63–78 (2012).

  25. 25.

    & Global and Arctic climate engineering: Numerical model studies. Phil. Trans. R. Soc. A 366, 4039–4056 (2008).

  26. 26.

    , , & Climate response to imposed solar radiation reductions in high latitudes. Earth Syst. Dynam. Discuss. 3, 715–757 (2012).

  27. 27.

    et al. Arctic oscillation response to volcanic eruptions in the IPCC AR4 climate models. J. Geophys. Res. 111, D07107 (2006).

  28. 28.

    et al. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. 108, D14, 4407 (2003).

  29. 29.

    et al. Development and evaluation of an Earth-system model—HadGEM2. Geosci. Model Dev. 4, 1051–1075 (2011).

  30. 30.

    , , , , & Aerosol forcing in the CMIP5 simulations by HadGEM2-ES and the role of ammonium nitrate. J. Geophys. Res. 116, D20206 (2011).

  31. 31.

    et al. The next generation of scenarios for climate change research and assessment. Nature 463, 747–756 (2010).

  32. 32.

    et al. Observations of the eruption of the Sarychev volcano and simulations using the HadGEM2 climate model. J. Geophys. Res. 115, D21212 (2010).

Download references

Acknowledgements

N. Rayner is thanked for providing the HadISST SSTA data. T. Mitchell is thanked for maintaining the JISAO SPA records. P. Cox and T. Lenton are thanked for their encouragement. O. Morton and J. Knight are thanked for comments regarding the content, style and presentation of the work. This work was supported by the SPICE programme (http://www2.eng.cam.ac.uk/~hemh/climate/Geoengineering_RoySoc.htm), the IAGP programme (http://www.iagp.ac.uk/) and the Joint DECC/Defra Met Office Hadley Centre Climate Programme.

Author information

Author notes

    • Nicolas Bellouin

    Present address: Department of Meteorology, University of Reading, Reading RG6 6BB, UK

Affiliations

  1. Met Office Hadley Centre, FitzRoy Road, Exeter EX1 3PB, UK

    • Jim M. Haywood
    • , Andy Jones
    •  & Nicolas Bellouin
  2. CEMPS, University of Exeter, Exeter EX4 4QF, UK

    • Jim M. Haywood
    •  & David Stephenson

Authors

  1. Search for Jim M. Haywood in:

  2. Search for Andy Jones in:

  3. Search for Nicolas Bellouin in:

  4. Search for David Stephenson in:

Contributions

J.M.H. came up with the idea for the experiments, analysed the experimental and model data, and wrote the paper. A.J. set up and ran the experiments, and analysed the model and observational data. N.B. performed analysis of the model and observational data. D.S. performed statistical analysis of the observational data.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Jim M. Haywood.

Supplementary information

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/nclimate1857

Further reading