Thanks to Luke Walker for blog post title and The Sydney Mornig Herald article:
Three-headed dog cruels spring hopes
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…………..
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.
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.
El Niño returns: Southern Africa droughts in 2007
afrol News 6 October – Satellite photos of the Pacific reveal the return of a world-wide weather phenomenon, the so-called “El Niño”. For Southern Africa, the phenomenon always has spelled severe drought and famine. Scientists expect the Niño to strike already in 2007. The 1991-92 El Niño brought the worst drought in southern Africa during the 20th century.
The US space agency NASA today reported that it has detected a “weak El Niño” returning to the Pacific Ocean, the first since the dramatic climatic season of 1997-98. NASA’s Aqua and Jason satellites have measured increasing ocean surface temperatures in belts across the middle and eastern Pacific, which are signs of a major transformation of global weather systems.
Every few years, such unusually warm currents flow off the western coast of South America. Its appearance after Christmas lead sailors in Peru to christen it El Niño, the Christ-child in Spanish. Like a child, it is sometimes unpredictable, and sometimes creates havoc. In El Niño’s case, it brings natural disasters such as storms, floods and droughts and famine in far-flung parts of the world.
El Niño events occur irregularly, about every 2-7 years and they last from 12 to 18 months, according to the World Health Organisations (WHO), which is very conscious about its many health risks around the world.
Southern Africa is known to be one of the regions world-wide to be most strongly impacted by an El Niño period, together with parts of South America and South-East Asia. In Southern Africa, it is followed by severe droughts almost every time it occurs. “The 1991-92 El Niño brought the worst drought in southern Africa [the 20th] century, which affected nearly 100 million people,” according to WHO.
The 1997-8 El Niño – the last until now – also caused drought in Southern Africa. Its effects were however strongest in Australia – which experienced its worst drought in decades – and in South-East Asia. Throughout the Americas, devastating floods caused great material damage……..
Jennifer Marohasy BSc PhD has worked in industry and government. She is currently researching a novel technique for long-range weather forecasting funded by the B. Macfie Family Foundation.