SYDNEY, Oct 9 (Reuters) Interactions between major oceans, triggered by climate change, will produce increasingly dry conditions in southern parts of Australia for decades to come, projections by the country's main science organisation show.
Further projected decreases in rainfall in southwest and southeast Australia could be arrested if carbon dioxide emission increases were halted, but a full recovery would take around 600 years, Dr Wenju Cai, a leading scientist with the government-backed Commonwealth Scientific and Industrial Research Organisation (CSIRO) said.
''The recovery takes a long, long time.... Not in our lifetime,'' Cai said.
As it stands, the CSIRO is confidently forecasting a further 10-15 per cent decline in rainfall in southeast Australia and a decline of over 20 per cent in southwest Australia by 2050.
This takes in Australia's capital cities, almost all of the national population of around 20 million and farmlands which produce one of the biggest exportable surpluses of agricultural produce in the world.
As crops wilt and die for lack of rain, this year's spring rainfall could be as much as 40 per cent below average because of an unusual weather pattern last seen in 1967 - but which is now more likely to recur because of climate change, Cai said.
Cai, a senior CSIRO scientist who specialises in marine and atmospheric research, said in an interview that Australia was presently being affected by the conflicting influences of a ''wet weather'' La Nina event in the Pacific and a ''dry weather'' Indian Ocean Dipole effect in the west.
The Indian Ocean effect was showing itself to be the stronger, replicating results in 1967 when a weak Pacific La Nina was overwhelmed by the Indian Ocean and Australian rainfall dried up to 40 per cent less than average.
This explained the puzzling lack of rain which has accompanied the formation of a La Nina this year, dashing hopes after last year's El Nino produced one of the worst droughts on record.
La Nina events typically produce wet weather in eastern Australia and Southeast Asia from warming Pacific sea temperatures.
El Ninos produce opposite effects.
Cai said greenhouse gases were now likely to create such conditions more often as they warmed the dry Australian landmass faster than the ocean.
In southwest Western Australia, the drying-out is being intensified by westerly wind jets shifting towards the Antarctic in response to ozone depletion over the last 30 years. This is now being intensified by increased carbon dioxide emissions.
The overall effect is reduced rainfall for southern Australia in winter and spring -- exactly when it is needed to grow the country's main crops of wheat, barley and canola.
Cai calls the overall effect a ''three-headed dog'', made up by the Indian Ocean Dipole, the Southern Annular Mode shifting westerlies southward, and increasingly powerful El Nino events.
Together the three effects are threatening permanent closure for many southern farmlands, already on the brink in the driest inhabited continent in the world.
Cai sees no relief from the present dry spell until November - too late for wheat, with at least 40 percent of the crop now lost.
Talk is beginning to emerge of a long-term solution in moving farms to the high-rainfall belt in the far north.
Howver, Cai's studies urge caution, saying more work needs to be done to see if this pattern will last.
REUTERS ARB KP0846