"Clearly for the past 25 or 26 years, the warming is accelerating...The rate of increase is unprecedented in the last 1,000 years," Kenneth Davidson, director of WMO's world climate programme told a news briefing.

A moderate El Nino system warming the tropical Pacific since mid-year was expected to last through April, according to WMO.

While El Nino is smaller in magnitude than the 1997-98 event, which caused $34 billion in damage, it has coincided with "climate anomalies" including droughts in Australia and southern Africa, as well as warmer conditions across Asia, it added.

WMO scientists were presenting a report on the status of the global climate in 2002, based on observations through November from a network of land-based weather stations, ships and buoys.

Global surface temperatures have risen six-tenths of a degree Celsius since 1900, according to the Geneva-based body.

Scientists say the world needs to slash emissions of carbon dioxide (CO2) and other greenhouse gases which trap heat in the atmosphere if it is to avoid disastrous floods, droughts and a rise in sea levels in coming decades.

Davidson called greenhouses gases "the major influence affecting the climate".

Hong Yan, WMO assistant secretary-general, went further: "If no very effective measures are taken for preventing further release of greenhouse gases, then the trend will continue."

The United States, the largest producer of greenhouse gases, has rejected the Kyoto treaty which aims to cut emissions from developed countries by 2012 to 5.2 percent below 1990 levels.

The El Nino phenomenon, from the Spanish term for a boy child, is the warming of the central and eastern tropical Pacific, the world's largest ocean basin, every few years.

It can wreak havoc on weather patterns, but no two El Nino events are identical, scientists say.

"The drought in Southern Africa appears very strongly linked to El Nino. The drought in Ethiopia appears not to be," said Paul Llanso, head of WMO's climate data and monitoring division.