El Nino odds rising with warming Pacific

Michael Perry, Reuters 28 May 09;

SYDNEY (Reuters) - The chances of a 2009 El Nino, a warming of eastern Pacific waters that often brings drought to Australia's farmlands, has risen and is above a 20 percent probability, the Australian Bureau of Meteorology said on Thursday.

International climate models are now predicting a warming of the Pacific Ocean," said the bureau.

"The average of the forecasts from each of these five models predict El Nino conditions being established by the southern spring, and by mid-winter in four of them," said the bureau in its latest report.

"With this higher predictability and better agreement between the forecasts, the probability of the development of an El Nino event in 2009 is now much higher than one month ago and it is significantly higher than the climatological probability of about 20 percent."

The possibility of a drier spring could reduce estimates of Australia's 2009/10 wheat crop, now being planted.

Current estimates range from 21 million to 23 million tonnes, little changed from the 21.4 million tonnes harvested in 2008/09, which was the best crop in four years following drought-breaking rains in some parts of eastern Australia.

Australia, the world's fourth largest wheat exporter, has been battling its worst drought in 100 years, but rains in 2008 and early 2009 along the northeast coast have eased conditions in parts of the country.

The bureau said the Southern Oscillation Index was neutral but in a "rapidly warming phase." The index measures atmospheric pressure differences between Darwin in northern Australia and Tahiti in the central Pacific.

Sea surface temperatures continued to warm right across the Pacific Ocean and were now about half a degree warmer than average, it said.

"Below the surface, equatorial Pacific Ocean temperatures are warmer than average by 2-3 degree Celsius across much of the basin," said the bureau.

Scientists have linked El Nino events in the Pacific Ocean with Australian droughts. El Nino occurs when the eastern Pacific Ocean heats up, with warmer, moist weather moving toward the east, leaving drier weather in the western Pacific and Australia.

La Nina occurs when the eastern Pacific Ocean cools, leaving the western Pacific warmer and increasing the chance of wetter conditions over Australia.

(Editing by Alex Richardson)