Friday, June 19, 2009

How aerosols mask climate change

BBC: A Norwegian scientist says he has shown how much aerosols influence climate. Aerosol particles scatter and reflect the Sun's rays - an effect that "masks" global warming. This study aimed to bring together models and observations of this "direct aerosol effect", to accurately estimate the magnitude of this cooling.

Reporting in the journal Science, climate scientist Gunnar Myhre has found that the effect is weaker than previous studies have estimated. Dr Myhre, from the Center for International Climate and Environmental Research in Oslo, said this clarifies just how much humans have changed the climate so far.

The pollution particles he studied include industrial aerosols such as sulphates, nitrates found in smoke from burning agricultural waste and black carbon (soot) from diesel engines and other forms of combustion.

"Global models of the emission of these aerosols suggest the cooling effect they have cancels out approximately 10% of the global warming caused by greenhouse gases," explained Jim Haywood, an aerosol researcher from the UK Met Office, who was not involved in this study. "But satellite methods that detect the amount of aerosols in the atmosphere suggest a cooling effect that cancels out about 20%."

By identifying the source of this discrepancy, Dr Myhre was able to reconcile the two approaches and come up with a more precise estimate - closer to 10%. This suggests the effect is weaker than the Intergovernmental Panel on Climate Change (IPCC) has estimated.

…Dr Haywood praised the research. "Until the publication of this paper, us aerosol researchers have been scratching our heads trying to understand the difference between model-based and observational-based assessments," he said. "This will have an impact on future climate predictions."

Severe haze over Kuala Lumpur, shot by Saperaud, Wikimedia Commons, under the Creative Commons Attribution-ShareAlike 3.0 license.

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