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Declining aerosol pollution could make severe drought in the Amazon rainforest more common in the twenty-first century, report scientists in Nature today (8 May).

British and Brazilian researchers used mathematical models to simulate the effect of climate change on rainfall variation in the Amazon. They used the severe drought in the western Amazon in 2005 — one of the most severe in the last 100 years — as a reference point.

The 2005 drought (see Amazon drought 'could worsen climate change') was associated with sea surface temperatures in the North Atlantic being unusually warm compared with the South Atlantic, which led to decreased rainfall.

The scientists' simulations of projected climate change, which included factors such as carbon dioxide concentrations and atmospheric aerosols, found that such Atlantic temperature gradients are likely to become more common.

This is because a decline in coal burning in the Northern Hemisphere has reduced emissions of sulphur dioxide aerosols. These have a cooling effect on the climate, and removing this effect will increase the sea surface temperature in the North Atlantic relative to the South Atlantic.

According to the model, the conditions surrounding the 2005 drought were approximately a 1-in-20-year event, but will become a 1-in-2-year event by 2025, and a 9-in-10-year event by 2060.

Lead author Peter Cox holds the Met Office chair in Climate System Dynamics at the University of Exeter, UK. He told SciDev.Net, "Aerosol pollution can lead to acid rain, and low-level aerosol particles are generally bad for air quality — and therefore human-health. So reducing them is the right thing to do." 

"However, as we clean-up air quality, we face a bigger challenge — to slow-down and halt climate change — because sulphate aerosols have also offset a large-part of the global warming from greenhouse gases."

Previous studies have shown how falling aerosol pollution will affect the rate of global climate change. The new study explains why this is especially an issue for the Amazon rainforest.

"Our study confirms that Amazonian droughts can be more and more frequent. It's very important to reaffirm the need for reducing carbon dioxide emissions," adds co-author José Marengo, of the Brazilian National Institute for Space Studies.

Link to full paper in Nature


Nature 453 212 (2008)