"Failure to recognise the urgency of this message and to act on it would be nothing less than criminally irresponsible," said de Boer.

Scientists and government officials from the 130-state Intergovernmental Panel on Climate Change (IPCC) are meeting in this Spanish port city until Nov. 17.

They aim to condense the findings of three reports they have issued this year on the causes, consequences and possible remedies for climate change into a brief summary that policy-makers can use to take decisions.

A draft circulated ahead of the conference blames human activities for rising temperatures and says cuts in greenhouse gas emissions, mainly from burning fossil fuels, are needed to avert more heat waves, melting glaciers and rising seas.

Global warming is already under way and its effects will be negative overall.

"Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level," it says.

POORER COUNTRIES SUFFER MOST

The world's poorest communities in Africa and Asia could suffer the most from climate change, the draft adds.

Such is the importance of the Valencia meeting that a previously scheduled conference of world environment ministers, now set to start in Bali, Indonesia, on Dec. 10, was delayed 10 days to give the climate panel time to finish its work.

Ministers will try to approve a two-year timetable to work out a successor to the UN's Kyoto Protocol, the main UN plan to curb warming until 2012.

The treaty obliges 36 industrial nations to cut emissions by at least 5 percent below 1990 levels by 2008-12.

A new deal would aim to involve outsiders led by the United States and China, the world's top two emitters which have no Kyoto goals.

There is still time to slow warming, the IPCC draft says, and it need not cost too much. Even the toughest targets for curbing emissions would cost less than 0.12 percent per year of world economic output.

De Boer said that earlier work of the nearly 20-year-old IPCC had been vital in preparing the way for the Kyoto treaty and now it needed to come up with a "Bali roadmap".

Politically, the signs seemed promising, with the European Union and the G8 group calling for progress and several leading developing countries announcing ambitious national plans to cut greenhouse gas emissions. "The lights seem to be on green ... inertia is disappearing," de Boer said.