"My very strong belief is that we need to reorient our investments toward this transition to a clean energy economy, and it will be the engine of growth for getting us out of the doldrums that we've gotten in right now," Zoi told the Reuters Global Environment Summit this week.

The reorientation must include US limits on emissions of climate-warming carbon in the United States, she said: "Unless we take action at home, we're not going to be able to have much influence in the international arena about what gets done."

The Bush administration accepts that human-spurred climate change is a reality but rejects mandatory across-the-board caps on carbon as a disadvantage when competing with fast-growing, big-emitting countries like China and India.

The United States is alone among the major developed countries in staying out of the carbon-capping Kyoto Protocol, but is part of international discussions on new targets to fight climate change by the end of 2009 at a meeting in Copenhagen.

Both major US presidential candidates -- Democrat Barack Obama and Republican John McCain -- favor requiring reductions in greenhouse emissions, and environmental activists have said whoever won the White House in the Nov. 4 elections would be an improvement over President George W. Bush.

"EARLY SIGNAL" NEEDED FROM NEXT US PRESIDENT

"There is an urgent need for whichever party wins the US election to give an early signal (of an intent to do more to combat global warming) or there cannot be a credible reason for 190 nations to come together in Copenhagen," said Achim Steiner, head of the UN Development Programme.

Rajendra Pachauri, who shared the 2007 Nobel Peace Price with Gore and who chairs the UN Intergovernmental Panel on Climate Change, said an Obama presidency would probably be more favorable to the fight against climate change.

But he added: "Even if McCain wins, he has been very committed."

There is little chance of passing a US law to mandate a program to cap and trade carbon emissions before Bush leaves office in January.

However, the first draft of a cap-and-trade bill was released this week by US Democratic Representatives John Dingell of Michigan -- home of the Big Three automakers -- and Rick Boucher of Virginia -- coal-mining country -- that is likely to frame debate next year.

The draft legislation drew measured applause from environmental activists, who noted it contains options that could substantially weaken controls on greenhouse emissions from some sectors.

But the fact that these two lawmakers are crafting legislation aimed at curbing climate change indicates a possible change in tone in Washington.

Despite comments from Sarah Palin, the Alaska governor who is McCain's running-mate, questioning the human causes of global warming, most officials in US government -- including Bush -- acknowledge that people contribute to the problem.

The anthropogenic roots of global warming are clear to Prince Albert of Monaco, who told the Reuters summit he didn't "adhere" to Palin's skeptical view.

"There are obviously cycles, but how can you not consider the graphs that have been shown to us?," Prince Albert said. "Those who can't see the correlation between man-made activities and greenhouse gas emissions, it's going to be hard to convince them; but somehow we will have to do so." (For summit blog: http://summitnotebook.reuters.com/) (Reporting by Deborah Zabarenko and Alister Doyle, editing by Gerald E. McCormick)