"There is a plan to seek the support of the secretary general for a special climate summit involving heads of state," UNEP spokesman Nick Nuttall told AFP in Nairobi, where Ban was to meet UNEP chief Achim Steiner.

The summit plan was launched earlier this month by Yvo de Boer, executive secretary of the UN Framework Convention on Climate Change (UNFCCC), amid deepening concern for the Kyoto Protocol after its present commitment period runs out in 2012.

Kyoto -- the only international treaty to set targets for limiting the fossil fuel pollution that causes the greenhouse effect -- has been in a bad way since it was abandoned in 2001 by the United States, which accounts for nearly a quarter of all global carbon emissions.

Even if its pledges are met, Kyoto will deliver just a tiny fraction of the reductions needed to stave off climate damage, so the post-2012 curbs must deliver swingeing cuts.

This means negotiators must coax the United States back into some global deal and also encourage China, India and Brazil -- now big polluters in their own right -- to rein in their own emissions.

But in a sign of shifting attitudes US lawmakers called Tuesday for an end to American complacency over global warming as the new Democratic-controlled Congress weighed measures to reduce greenhouse gases.

"We must act now to address global warming," said the Senate Environment Committee's new chairwoman, liberal Democrat Barbara Boxer.

At a committee hearing Democratic Senator Hillary Clinton said that after years of delay, global warming was "an issue whose time has come."

"If we look at where we are ... we are not making progress. In fact, emissions are still going up," she said.

"I'm hoping that we can get beyond the usual rhetoric and try to find some common ground," said Clinton, who currently leads the field of Democratic contenders for her party's 2008 presidential nomination.

After years of relegating climate change to the bottom of the legislative agenda, Democrats who wrested control of the House and the Senate from the Republicans in November elections, have vowed to make it a priority.

"The US comprises only four percent of the world's population, yet emits 20 percent of the world's carbon dioxide," said Republican Senator Olympia Snowe.

"It's time our response to this crisis become proportional to our nation's contribution to the problem."

In Paris, meanwhile, a report drafted for the UN's top climate scientists said there was now a 90-percent probability that man-made greenhouse gases had driven up Earth's surface temperature over the past half century.

Eleven of the last 12 years rank among the warmest years for which there are reliable records, according to the draft, which is being discussed line by line at the four-day meeting of the Intergovernmental Panel on Climate Change (IPCC).

According to the draft "summary for policymakers", a copy of which was obtained by AFP, the temperature has already risen by 0.74 degrees Celsius (1.33 degrees Fahrenheit) over the last century.

The average temperature of the global seas has increased to depths of at least 3,000 metres (10,500 feet), showing that the warming of the atmosphere is now spreading to the deep ocean.

Among other things, the document declares it "very likely" that heatwaves and pounding rain will become more frequent, snow cover is projected to contract and typhoons and hurricanes will become less frequent but more powerful.

And it says that CO2 pollution spewed out this century will stoke global warming and sea-level rise "for more than a millennium", given the time it takes for fossil fuel pollution to degrade.

The Paris document, on the scientific basis for global warming, will be issued on Friday. It is one of three that the IPCC will issue this year, the others being on the effects of climate change and how to cope with them.

The international Red Cross said on Tuesday its budget for 2007 will rise by 80 percent to 220 million euros (285 million dollars) as it seeks to tackle the twin threats of climate change and AIDS.

The International Federation of Red Cross and Red Crescent Societies said the budget hike "highlights the need for more money to be spent on disaster preparedness and risk reduction in response to the increasing frequency and intensity of natural disasters linked to climate change."

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