IOD News 5 Oct 2007! Three-headed dog cruels spring hopes
Three-headed dog cruels spring hopes
News from The Sydney Morning Herald
Deborah Smith Science EditorOctober 5, 2007
DROUGHT-STRICKEN farmers could face spring rainfall that is up to 40 per cent below average because of a rare weather pattern last seen 40 years ago.
A CSIRO scientist, Wenju Cai, told the Greenhouse 2007 conference in Sydney yesterday that Australia was experiencing an unusual combination of two events: a La Nina phenomenon in the Pacific Ocean in the east, and an Indian Ocean Dipole phenomenon in the west.
"The only time in [recorded] history we had this kind of combination was in 1967," he said.
In that year, spring was extremely dry in the south and east of the country, and this could provide an indication of what was ahead in the next few months, he said.
Although La Nina usually brings more rainfall to eastern Australia, it appeared to have been overwhelmed in 1967 by the positive Indian Ocean Dipole, which reduces rainfall across Australia, including in the south-east.
Dr Cai said that, overall, the projection in coming decades was for reduced rainfall in winter and spring in southern Australia, with a decline of up to 15 per cent by 2070.
"There is no longer any doubt that climate change caused by increases in greenhouse gases is influencing seasonal shifts in rainfall patterns," he said.
Global warming would also lead to greater evaporation that would magnify water shortages. "Our results provide strong evidence that rising temperatures impact on Australia's water resources, in addition to any reduction in rainfall."
Dr Cai said that three major phenomena, which he likened to a "three-headed dog", influenced Australia's rainfall: El Nino events, the Indian Ocean Dipole, and the Southern Annular Mode, a weather pattern in the Southern Ocean that promotes airflow towards south east Australia.
Last year, each had had only a small effect on rainfall decline. "But in sequence they gave us a very big dry, on top of the impact of the very high temperatures," he said.
The good news was that the dog had "a tail", which may be able to partially offset some drying. This was rapidly heating waters in the Tasman Sea, which research suggested could lead to an increase in rainfall in the south-east during summers.
Dr Cai said that greenhouse gas emissions accounted for about half the rainfall reduction in the south west of the country, where there has been a 10 per cent decline since the early 1970s.
Separate research on an Antarctic ice core suggests this drying may represent a very unusual event.
Tas van Ommen, of the Australian Antarctic Division, told the conference his team had identified a link between rainfall in the south-west and snowfall at a site called Law Dome in East Antarctica.
Their study of an ice core from Law Dome that covers the past 750 years suggests that the last 30 years in south-west Australia has been the driest period, and longest period of reduced rainfall, since the year 1250.
"So media suggestions that the drought in Australia is a 1-in-1000-year event is not unreasonable, at least for the south-west," Dr van Ommen said.
News from The Sydney Morning Herald
Deborah Smith Science EditorOctober 5, 2007
DROUGHT-STRICKEN farmers could face spring rainfall that is up to 40 per cent below average because of a rare weather pattern last seen 40 years ago.
A CSIRO scientist, Wenju Cai, told the Greenhouse 2007 conference in Sydney yesterday that Australia was experiencing an unusual combination of two events: a La Nina phenomenon in the Pacific Ocean in the east, and an Indian Ocean Dipole phenomenon in the west.
"The only time in [recorded] history we had this kind of combination was in 1967," he said.
In that year, spring was extremely dry in the south and east of the country, and this could provide an indication of what was ahead in the next few months, he said.
Although La Nina usually brings more rainfall to eastern Australia, it appeared to have been overwhelmed in 1967 by the positive Indian Ocean Dipole, which reduces rainfall across Australia, including in the south-east.
Dr Cai said that, overall, the projection in coming decades was for reduced rainfall in winter and spring in southern Australia, with a decline of up to 15 per cent by 2070.
"There is no longer any doubt that climate change caused by increases in greenhouse gases is influencing seasonal shifts in rainfall patterns," he said.
Global warming would also lead to greater evaporation that would magnify water shortages. "Our results provide strong evidence that rising temperatures impact on Australia's water resources, in addition to any reduction in rainfall."
Dr Cai said that three major phenomena, which he likened to a "three-headed dog", influenced Australia's rainfall: El Nino events, the Indian Ocean Dipole, and the Southern Annular Mode, a weather pattern in the Southern Ocean that promotes airflow towards south east Australia.
Last year, each had had only a small effect on rainfall decline. "But in sequence they gave us a very big dry, on top of the impact of the very high temperatures," he said.
The good news was that the dog had "a tail", which may be able to partially offset some drying. This was rapidly heating waters in the Tasman Sea, which research suggested could lead to an increase in rainfall in the south-east during summers.
Dr Cai said that greenhouse gas emissions accounted for about half the rainfall reduction in the south west of the country, where there has been a 10 per cent decline since the early 1970s.
Separate research on an Antarctic ice core suggests this drying may represent a very unusual event.
Tas van Ommen, of the Australian Antarctic Division, told the conference his team had identified a link between rainfall in the south-west and snowfall at a site called Law Dome in East Antarctica.
Their study of an ice core from Law Dome that covers the past 750 years suggests that the last 30 years in south-west Australia has been the driest period, and longest period of reduced rainfall, since the year 1250.
"So media suggestions that the drought in Australia is a 1-in-1000-year event is not unreasonable, at least for the south-west," Dr van Ommen said.
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