Environment ministers are meeting in the Kenyan capital for talks on how to accelerate pollution-cutting action under the UN's Kyoto Protocol when the landmark accord runs out at the end of 2012.

In its present format, Kyoto will not even dent global emissions of carbon gases -- the by-product of burning fossil fuels that capture heat from the Sun and drive dangerous climate change.

One of Kyoto's flaws is that it does not include the world's biggest polluter, the United States, which by itself accounts for a quarter of global output of man-made emissions.

After signing up to Kyoto as a framework treaty and then largely determining its complex machinery, the United States walked away from the accord in 2001.

President George W. Bush declared he would not submit the draft treaty for Senate ratification, arguing the pledges were too costly and also unfair, as big developing countries were not obliged to make targeted emissions cuts.

Delegates at the Nairobi talks say negotiations for Kyoto's second commitment period, running from 2013 to 2017, will start in earnest next year.

While some countries want the deal to be wrapped by the end of 2008, there is a widespread expectation that the conclusion will be at the end of 2009 at a venue that is likely to be Copenhagen, they said.

The haggle will be so long because of the challenge of securing far deeper cuts from industrialised countries and of coaxing Brazil, China, India and other fast-growing developing countries into tackling their own surging levels of carbon pollution.

This has major implications for any US return into the Kyoto fold, said Greenpeace campaigner Steve Sawyer.

"If we accept the premise that Bush is not going to change his stripes, then we are waiting for a new president" for any such a move, he said.

Bush leaves office in January 2009.

As every new president takes at least half a year to settle in, make new appointments and take the measure of Congress, it would no doubt be impossible for the United States to ratify Kyoto in time to join the negotiations for 2013-2017 round, said Sawyer.

"The timing works just about right for the US to come in for the formal negotiations on (...) the third commitment period, covering 2018 to 2022," Sawyer said.

The negotiations on the 2013-2017 pledges cannot be postponed beyond the end of 2009 because the draft treaty has to be ratified and governments have to implement laws and policies in line with their pledges.

Some experts indeed are calling for the negotiations to wrap by the end of 2008 to reassure the fledgling Kyoto carbon market that business will continue smoothly after 2012.

"We have been arguing for a 2008 end-date, precisely because it took so long to get the (first commitment period) of the Kyoto Protocol to be ratified," Hans Verolme, director of WWF's climate-change programme, told AFP.

The putative timetable means that -- assuming domestic politics encourage a return to the Kyoto fold -- the United States will lose enormous clout in shaping treaty provisions that touch on emissions caps and on trade and investment worth potentially tens of billions of dollars.

But, said Verolme and Sawyer, not everything was lost for US environmentalists or for American corporations keen to use Kyoto's market mechanisms.

During the long interim, the United States could set a national emissions target and a cap-and-trade scheme that could then be linked with Kyoto's own market in carbon emissions trading.

In addition, the United States retains the right to observer status in Kyoto talks and is a full member of the UN Framework Convention on Climate Change (UNFCCC), Kyoto's parent treaty.

"I don't think the Americans will miss out entirely on the second commitment period," said Verolme. "There are different legal views on what could happen."

On Wednesday, three leading Democratic senators said that next year they would push for laws setting mandatory limits on greenhouse gases and urged Bush to work with the international community to forge an "equitable" global agreement on climate change.

Senators Barbara Boxer, Jeff Bingaman and Joseph Lieberman are set to head key committees on global warming when Democrats take over Congress in January, following last week's crushing electoral defeat for Bush's Republicans.

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