Experts have warned the central and eastern Pacific Ocean has shown signs of the La Nina phenomenon, which may threaten winter harvests.

A report released by the China National Climate Center (CNCC) said the sea-surface temperature in the Equatorial Pacific is cooler than normal, based on satellite monitoring and analysis.

"The temperature has been 0.5 C lower for two consecutive months over the same period in average years," CNCC's Guo Yanjun said.

"If it keeps cooling for over six months we call it a La Nina event," Guo said.

La Nina is defined as cooler than normal sea-surface temperatures in the central and eastern Pacific that impact on global weather patterns. It recurs every few years and can persist for as long as two years.

It usually has a negative impact on the crops growing in winter in South China and can cause freezing temperatures elsewhere in the country, China News Service reported.

Experts, however, said the impact of a minor La Nina would not be that serious.

"The area where La Nina events occur is far from China. It is along the coasts in South America," Guo said.

Lin Erda, a retired researcher studying the interaction between climate change and agriculture said this year's La Nina would not have a direct impact on agricultural yield.

"What I know for sure is it will have an impact in terms of uneven rainfall distribution next year," Lin said.

"Weather forecasting is not fortune-telling Seeking to interpret direct or sensational results is unscientific," he said.

La Nina and El Nino (higher than normal water surface temperatures) are both naturally generated and refer to large-scale changes in sea surface temperatures across the Tropical Pacific.

Last year El Nino affected this year's rainfall distribution, with large areas in South China suffering floods, while central and northern parts had droughts.

"That's the visible and predictable result of El Nino," Lin said.

(China Daily September 14, 2007)