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Climate Change Spreads Drought Across Australia

PERTH, Australia, March 14, 2002 (ENS) - The southwestern part of Australia has been bone dry for 27 years, and Australian government scientists say the lengthy drought could be a foretaste of future experiences across the nation due to the greenhouse effect.

The burning of fossil fuels and emission of industrial gases has shrouded the Earth in a blanket of gases that is trapping the Sun's rays close to the planet, raising its surface temperature in a greenhouse effect, most climate scientists around the world agree.

Scientists with the Commonwealth Scientific, Industrial and Research Organization (CSIRO) are investigating the possibility that a climate shift has brought a long term decline in rainfall over the southwestern region of Western Australia.

"Measurements indicate a slow decline in rainfall since the 1940s to 1950s, leading to the present drier regime," says Dr. Bryson Bates of CSIRO Land and Water.

In some parts of the southwestern region, average rainfall appears to have settled into a pattern about 20 percent lower than the norm for the first half of the 20th century.

desert

Dryland on the road from Darwin to Perth (Photo courtesy Galen Frysinger)
But, researchers have observed, as the thirsty landscape soaks up more moisture, this has led to a 40 percent reduction in water flowing into Perth's dams. At the start of this summer, the dams were less than a third of capacity.

The main change lies in the absence of wet winters, which once recharged the dams. Since 1975 there has been only one winter of above average inflow to the dams, compared with 13 in the period from 1950 to 1975.

The immediate cause, says Dr. Bates, is a clearly discernible climate shift that took place in the mid 1970s.

"At that time the tropical Pacific warmed abruptly and stayed warm, and there was a sudden warming in sea surface temperatures in the Indian Ocean. Since then there have been unusually frequent, persistent and intense El Niņos, and fewer La Niņas," he said.

El Niņos are a warming pattern of the eastern tropical Pacific Ocean that occur every two to seven years, while La Niņas are a corresponding cooling pattern in the same ocean region. Both weather patterns affect climate conditions around the world, bringing droughts and floods.

Working from global atmospheric data, the CSIRO researchers have been trying to work out what their observations mean for local climate and rainfall across the southern part of Western Australia.

As to what is causing the new climate pattern, the team is exploring apparent links with changes in the behavior of El Niņo and the Antarctic Oscillation Index, a large-scale mode of climate variability that also occurs in the Arctic.

Before the 1970s, when times were wetter, the Antarctic Oscillation Index was negative. But since the mid-1970s, it has swung into the positive, with zones of higher than usual air pressure forming over the southern Indian and Pacific Oceans.

Bates

CSIRO climate scientist Dr. Bryson Bates (Photo courtesy CSIRO)
"To be frank, we don't know really what's behind it yet. To begin with, says Dr. Bates, "we blamed it all on changes in the Indian Ocean, but now we've realized we may be dealing with something that affects the entire Southern Hemisphere."

"So we've started to explore this idea that shifts in pressure patterns off the Antarctic can have an influence across southern, and particular southwestern Australia," he said.

Dr. Bates says such a prolonged dry spell is fairly rare, and that it is likely to be due to the earth's natural climatic fluctuations, rather than human induced changes to the atmosphere.

"However, the present experience matches what climate projections are indicating may happen over the next 100 years. So the experience of southwestern WA may foreshadow the sorts of impacts we will start to see in southern Australia under greenhouse induced climate change," he said.

When funds are available, the team hopes to extend the implications of this climate work to other states, such as South Australia and Victoria.



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