August 16, 2009 – Original Source: The Sydney Morning Herald
DROUGHT experts have for the first time proven a link between rising levels of greenhouse gases and a decline in rainfall.
A three-year collaboration between the Bureau of Meteorology and CSIRO has confirmed that the drought is not just a natural dry stretch but a shift related to climate change.
Scientists working on the $7 million South Eastern Australian Climate Initiative said the rain had dropped away because the subtropical ridge – a band of high pressure systems that sits over the country’s south – had strengthened over the past 13 years.
Last year, using sophisticated computer climate models in the United States, the scientists ran simulations with only the ”natural” influences on temperature, such as differing levels of solar activity.
The model results showed no intensification of the subtropical ridge and no decline in rainfall.
But when human influences on the atmosphere were added to the simulations – such as greenhouse gases, aerosols and ozone depletion – the models mimicked what has been observed in south-east Australia: strengthening high pressure systems and the significant loss of rain.
”It’s reasonable to say that a lot of the current drought of the last 12 to 13 years is due to ongoing global warming,” said the bureau’s Bertrand Timbal.
”In the minds of a lot of people the rainfall we had in the 1950s, ’60s and ’70s was a benchmark. A lot of our [water and agriculture] planning was done during that time. But we are just not going to have that sort of good rain again as long as the system is warming up.”
Dr Timbal said that 80 per cent of the rain loss in south-east Australia could be attributed to the intensification of the subtropical ridge. The research program covers the Murray-Darling Basin, including parts of NSW, all of Victoria and parts of South Australia.
Monash University’s Neville Nicholls, a lead author on the Intergovernmental Panel on Climate Change who has also published work on the subtropical ridge, said he believed the research program’s results were right.
“We did think that the loss of rain was simply due to the [rain-bearing] storms shifting south, off the continent,” Professor Nicholls said. “Now we know the reason they have slipped south is that the subtropical ridge has become more intense. It is getting bigger and stronger and that is pushing the rain storms further south.”
The scientific results have implications for many State Government water programs and drought funding, some of which factor in climate change and some of which do not. Projections for the water coming to Melbourne in the north-south pipe, for instance, are based on the assumption that Victoria will return to rainfall levels of last century.
The Victorian Farmers Federation new president, Andrew Broad, said he would not speculate about whether there was a connection between drought and climate change.
“I have a healthy scepticism for scientists,” he said. “But I will say that the doomsday people in climate change are robbing people of hope at a time when that’s all they’ve got left.”
Melbourne’s dams get roughly a third less water than they did before the drought began in October 1996.