Senators Barbara Boxer, Jeff Bingaman and Joseph Lieberman, all set to head key committees on global warming when Democrats take over Congress in January, called on Bush to work with the incoming majority to pass "meaningful" climate change legislation next year.

"The US must move quickly to adopt economy-wide constraints on domestic GHG (greenhouse gas) emissions and then work with the international community to forge an effective and equitable global agreement," the senators said in a letter sent to Bush Wednesday.

Bush has refused to ratify the Kyoto Protocol, saying it would hurt the US economy, and is strongly opposed to its approach of binding cuts, also called caps, in emissions.

Instead, he has promoted voluntary action, backed by some incentives for cleaner energy sources and gains in energy efficiency.

Kyoto commits industrialized countries that have signed and ratified it to trim greenhouse gases by 2012, as compared with a 1990 benchmark. It does not require big developing countries to make these pledges, an approach that Bush says is unfair.

The senators said the Democratic victory over Bush's Republicans in last week's elections, which ended their 12-year majority in Congress, has "signaled a need to change direction in many areas, including global warming."

"If we are to leave our children a world that resembles the Earth we inherited, we must act now to address GHG emissions," they wrote.

"When the 110th Congress begins in January, we pledge to work to pass an effective system of mandatory limits on greenhouse gases," the senators said.

"We urge you to work with us to reach this result and to signal to the world that global warming legislation is on the way."

The letter coincided with a meeting in Nairobi of the UN Framework Convention on Climate Change (UNFCCC), parent treaty of the Kyoto Protocol.

Green activists at the talks were jubilant over the senators' move, claiming it was a devastating federal setback for Bush's climate policies, which in the past year have been under attack at US state and city level.

Jeremy Symons of the US National Wildlife Federation hailed it as "an important turning point in US politics on global warming."

"For senators to unite behind such a clear call for climate action so soon after the elections is a strong signal that climate change is going to be at the top of the Democrats' agenda in the new Congress," he said.

"This leadership is a welcome breath of fresh air after years of hot air from the Bush administration on global warming."

Greenpeace campaigner Steve Sawyer admitted "we are not anticipating that George Bush will have an epiphany" on global warming.

Even so, "this means that there will in fact be mounting pressure, political, public and every other variety, so that the Bush administration's position will very, very soon become a relic of history," said Sawyer.

He predicted the United States would eventually set up a cap-and-trade system in carbon emissions that could link up with Kyoto's own model, which was launched in January 2005.

The senators' letter added: "Unfortunately, we have not been satisfied with the level of US participation in the international negotiations or in reducing our own domestic greenhouse gas (GHG) emissions," they wrote.

"Therefore, as incoming Chairs of three important Senate Committees on global warming, we seek your commitment to work with the new Congress to pass meaningful climate change legislation in 2007," the senators said.

Boxer will chair the environment and public works committee, Bingaman will lead the energy and natural resources committee and Lieberman will head the homeland security and governmental affairs committee.

The United States is the world's biggest single contributor to man-made global warming, accounting by itself for a quarter of global emissions of greenhouse gases, although China is fast catching up.

The top US representative in Nairobi, Paula Dobriansky, on Wednesday offered no sign of any shift in the US position and contended Bush's climate policy would be backed by Congress.

"This administration is continued to (be committed to) action and I know that that action will in fact be supported by our Congress in terms of how we go forward," Dobriansky, who is undersecretary of state for democracy and global affairs, told reporters.

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