'Sunshade' for global warming could cause drought

09 August 2007

NewScientist.com news service
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MIMICKING volcanoes has been proposed as a last-ditch solution to climate change. The idea is that pumping sulphur particles into the atmosphere would reproduce the cooling effect of a large eruption. All very well - except it now seems it could also cause catastrophic drought.

Kevin Trenberth and Aiguo Dai of the National Center for Atmospheric Research in Colorado have shown that a "sulphur sunshade" could have a deleterious effect on the environment by reducing rainfall. Sulphur sunshades are inspired by the climatic effects of large volcanic eruptions, which blast sulphate particles into the stratosphere. The particles reflect some of the sun's radiation back into space, reducing the amount of heat that reaches the Earth.

To study the effect on rainfall, Trenberth and Dai analysed precipitation and continental run-off after the 1991 eruption of Mount Pinatubo in the Philippines, which pumped vast amounts of sulphates into the atmosphere, cooling Earth by a few tenths of a degree for several years.

Following the eruption there was a marked decrease in rainfall and run-off (Geophysical Research Letters, DOI: 10.1029/2007GL030524). Dai and Trenberth say this suggests that artificially injecting large amounts of sulphate particles into the atmosphere could have catastrophic effects on the planet's water cycle.