Clearer Asian skies may worsen drought

Clearer Asian skies may worsen drought

13 December 2006

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Australia — More of Australia could become affected by drought if itsnearest neighbours start reducing air pollution, a study suggests.

Dr Leon Rotstayn of CSIROMarine and Atmospheric Research says a new computer climate model showsaerosol pollution in Asia is having a long-distance effect on weather inAustralia.

He says the modelling shows that the airborne haze made up of tiny particlesfrom industrial and domestic pollution is cooling the land and oceans aroundAsia.

The haze isn’t travelling to Australia. But it’s been changing the balance ofwind and temperature between Asia and Australia, causing heavier rainfalls incentral and northwest parts of Australia.

“What has been observed in the last 50 years is that it has been gettingdrier in the south and east of Australia and wetter in the northwest and centre,”he says.

“Our pilot modelling results suggest that the Asian haze may be drivingthat trend towards more rain.”

Getting rid of the haze could reverse that pattern, he says.

The research, which will be published in the Journal of Geophysical Researchearly next year, is the first time researchers have tried to demonstrate theeffect of aerosols on Australia’s climate.


The pollution factored into the CSIRO model includes industrial and domesticemissions of particles such as black carbon, from burning diesel, and sulfideparticles from coal.

Rotstayn says this aerosol pollution has a cooling effect because it forms ablanket that keeps the Sun’s radiation from reaching the surface of the Earth.

The particles also cause thicker and more persistent clouds, which reflect heatback into space.

“The cooling effect of aerosols is a combination of the direct effect ofstopping sunlight getting through and the indirect effect whereby the aerosolsmake clouds more effective,” he says.

“The aerosol haze is cooling Asia and the oceans around [it] and that’saffecting the monsoonal winds which bring the summer-time rainfall to thenorthern parts of Australia.”

He says the trend could be reversed, with serious implications for Australia, ifAsian emissions are reduced.

“Sooner or later those emissions will be cleaned up and a trend ofincreasing rainfall in the northwest and centre could be reversed,” he says.

“This is potentially serious, because the northwest and centre are the onlyparts of Australia where rainfall has been increasing.”

Not just a greenhouse problem

The study shows that we shouldn’t underestimate the impact of aerosols onAustralia’s climate, Rotstayn says.

“We don’t really have much aerosol pollution in Australia most of the timeso there’s been an assumption that aerosols are not very important to Australianclimate.

“But when we did these simulations … without the aerosols we got acompletely different rainfall response over Australia.

“That’s suggesting [aerosols are] something we have to take very seriouslyif we’re going to be able to predict climate change and not simply treat it assolely a greenhouse gas problem, because it clearly is not.”

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