Asymmetric forcing from stratospheric aerosols impacts Sahelian rainfall - Jim M. Haywood<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#auth-1> , - Andy Jones<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#auth-2> , - Nicolas Bellouin<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#auth-3> - & David Stephenson<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#auth-4>
Nature Climate Change (2013) doi:10.1038/nclimate1857Received 23 October 2012 Accepted 22 February 2013 Published online 31 March 2013 Article tools 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<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref1>. It has been attributed to natural variability2<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref2> , 3<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref3> , 4<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref4> , 5<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref5>, over-grazing6<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref6> and the impact of industrial emissions of sulphur dioxide7<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref7> , 8<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref8>. Each mechanism can influence the Atlantic sea surface temperature gradient, which is strongly coupled to Sahelian precipitation2<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref2> , 3<http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html#ref3>. 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. Full article at http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1857.html Blogpost by me at http://heliophage.wordpress.com/2013/03/31/climate-geoengineering-for-natural-disasters/ Extract: One implication is that climate geoengineering deployed in just the northern hemisphere looks like a very bad idea. Programmes in just the north have been considered and studied, in part because of the worries people have about something suddenly going wrong in the Arctic, something that needs “fixing” quickly. This research makes such approaches look dangerous. More interesting, and more novel, is the implication that geoengineering might be used to avert a Sahelian drought caused by a volcano. If the stratospheric sulphates released in a major northern eruption were promptly countered by a deliberate release of sulphates into the southern hemisphere, both hemispheres would cool. The ITCZ would stay put, and a drought might well be averted. For a major drought, that would be a big win. The drought in the 1980s, which followed on the 1982 eruption of El Chichon in Mexico, killed about a quarter of a million people and turned millions more into refugees. ... And if the Earth is left to its own devices, such droughts will happen again. Last century there were two eruptions that cooled the north and were followed by drought in the Sahel. The north is better endowed with volcanoes than the south, since the Pacific “ring of fire” is more a horseshoe of fire, with a gap in the south but a continuous arc in the north. The odds of at least one eruption in the Pinatubo-to-Krakatoa range somewhere of the Earth in this century are better than even. The chances of one happening in the north are obviously lower; but the odds are hardly long. If humans had had the technological wherewithal to stop the 1980s Sahel drought in its tracks, would people have wanted to use it? It seems likely that there would have been a constituency for it, not least in the Sahel. And many of the reasons people have for objecting to geoengineering as an inappropriate “technical fix” to man-made climate change might apply with rather less force if the technology was being used to forestall a natural disaster on a continental scale. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
