The El Ni�o phenomenon, which is capable of disrupting climate and weather patterns across much of the globe, will return next year, United Nations scientists have warned.

However, speaking at the headquarters of the World Meteorological Organisation (WMO) in Geneva, the researchers forecast a much weaker El Ni�o than the one that took hold during 1997 and 1998.

"This coming event is nowhere near on that scale," said Michael Coughlan, director of the WMO's climate programme.

El Ni�o occurs when the warm ocean conditions normally confined to the western tropical Pacific begin to appear along the coast of Ecuador and Peru. This prompts an often dramatic switch in weather patterns, with the wet conditions normally seen in the western Pacific moving to the east, and the arid conditions common in the east appearing in the west.

The last El Ni�o triggered many extreme events. Severe drought affected Indonesia, Papua New Guinea and northern Brazil, while floods hit Ecuador and northern Peru; Chile and California were rocked by severe winter storms.

The WMO researchers "have seen some indication of El Ni�o" in recent weeks, Michael Coughlan said.

As yet they could only predict climate trends until early 2002 and could not say whether El Ni�o would strengthen or decline next year, he added.

The El Ni�o events that began in 1982 and in 1997 were the most severe of the 20th Century. The property damaged during the last event was valued at $32bn.

Michael Coughlan told the BBC: "At the beginning of the 1997/8 event, we started to show some skill in prediction. It wasn't perfect but at least we were forewarning of an El Ni�o event. And, of course, different countries took this on board to different degrees.

"But I think the 1997/8 event has sensitised those countries most likely to be affected by a severe event to be prepared for the next one."