Asian haze impacts on Australian rainfall

Asian haze impacts onAustralian rainfall

12 December 2006

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Asia/Australia — Elevated particle emissions resulting from increased economicactivity in Asia may have increased Australia’s tropical rainfall, according tonew research on the way pollution influences our climate.

“Until now, there has been ample evidence that these particles haveimportant effects on climate in the Northern Hemisphere but little such evidencein the Southern Hemisphere,” says Commonwealth Scientific and IndustrialResearch Organization (CSIRO) Marine and Atmospheric Research scientist, Dr LeonRotstayn.
“What we have seen in our latest climate simulations is that the ‘Asianhaze’ is having an effect on the Australian hydrological cycle and generatedincreasing rainfall and cloudiness since 1950, especially over northwest andcentral Australia. The effect occurs because the haze cools the Asian continentand nearby oceans, and thereby alters the delicate balance of temperature andwinds between Asia and Australia. It has nothing to do with Asian pollutionbeing transported directly over Australia.”
Dr Rotstayn says this implies that decreasing pollution in Asia later thiscentury could reverse this effect and lead to an increase in Australian dryingtrends.
 “We are really at the beginning of understanding the trends butsooner or later these emissions will be cleaned up and then a trend ofincreasing rainfall in the northwest and centre could be reversed. This ispotentially serious, because the northwest and centre are the only parts ofAustralia where rainfall has been increasing in recent decades.”
Dr Rotstayn stresses that climate modelling is a valuable tool for teasing outwhat is actually causing weather trends, rather than simply assuming that thesetrends are all related to greenhouse gases.
At a time when Australian science agencies are investing in new climateforecasting capabilities, the research – to be published early in 2007 in theJournal of Geophysical Research – increases confidence in the accuracy of futureclimate simulations for Australia.
An aerosol is a haze of particles in the atmosphere. Dr Rotstayn saysrepresenting aerosols in climate models and understanding their influence oncloud formation and rainfall is one of the biggest challenges facing climatescientists.
“Because the cooling effect of aerosol pollution is possibly comparable tothe warming effect of increased levels of carbon dioxide, the message from thisresearch is that aerosols are an essential inclusion if we are to accuratelydescribe present and future Australian climate,” he says.
The new research is based on simulations performed with a new low-resolutionversion of CSIRO’s global climate model – including a treatment of aerosols fromboth natural and human-induced sources.
Dr Rotstayn was lead author of the paper with contributing scientists from: theCooperative Research Centre for Greenhouse Accounting; the University ofMichigan’s Department of Atmospheric, Oceanic and Space Sciences; and, the U.S.National Oceanic and Atmospheric Administration’s Geophysical Fluid DynamicsLaboratory in Princeton.

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