In the halls of the Palais de Congres, where international talks are under way on next steps to combat global warming, all eyes are turning to the challenge of bringing developing countries on board.
Many of these nations have ratified the Kyoto Protocol, but as yet have no obligations to reduce emissions under the pact, which targets rich countries through 2012.
Delegates hope to lure developing nations with emissions-control ideas that are flexible and acknowledge their need for economic development.
But a key hurdle may be emerging. The United States is refusing to take part in discussions that could be seen as prodding Washington toward mandatory targets and timetables. The battleground: the 1992 Framework Convention on Climate Change, which the US has ratified and which outlines broad but voluntary climate goals. Some industrial countries say that the framework could provide the basis for some of these more-flexible approaches that nonetheless are binding.
As the first half of the two-week conference draws to a close, the 190 participants can point to some accomplishments. They formally adopted the rules under Kyoto for reducing greenhouse gases - everything from investment in developing countries to trading carbon credits that allow larger polluters to meet their goals by buying credits from those who beat their targets.
A sense of urgency is growing, many here say. They point to recent research that appears to bear out projections of global warming's direct and indirect effects -- from shrinking Arctic ice packs to a slowing of deep-ocean circulation in the North Atlantic.
Kyoto binds its signatories to begin talks this year about what follows after the protocol's first commitment period expires in 2012. A key concern is that the US stance outside the Kyoto pact, and its current position on talks under the Framework Convention, may block discussions central to drawing in developing countries further down the road.
"I don't expect a lot of debate about the necessity to do more," says Canada's environment minister, Stéphane Dion, who is presiding over the talks. "I do expect debates about what to do and who needs to do what."
At a briefing earlier this week, Harlan Watson, who heads the US team, acknowledged signatories' obligations to start talks about the emissions-reduction regime for 2012 and beyond, but made it clear that the US would not join in if binding commitments came into play.
"We respect that obligation and expect that they will meet their commitment to do so," he said. "However, the United States is opposed to any such discussions under the Framework Convention."
In many ways, the hoped-for outcome of these two-week talks is, essentially, an agreement to keep talking. Many developing countries are interested in seeing the Kyoto process move beyond 2012, notes Jennifer Morgan, who heads the climate change program of the World Wildlife Fund International. Particularly in the months since Kyoto took effect, leaders in developing nations such as South Africa are saying, she says, that "we need to do our fair share."
Yet taking even first steps toward commitments are a hard sell back home when the US is seen as failing to act as a full partner in reducing emissions.
One fear is that if Kyoto-related discussions are the only forum for emissions discussions, the US lack of involvement in Kyoto could trigger a stampede away from future tighter targets.
"The Bush administration is playing a big game of chicken," says Alden Meyer, director of strategy and policy for the Union of Concerned Scientists. "It's saying: If you want to go ahead, fine. But you can't do it here." Since all actions are taken by consensus, he and others note, US opposition amounts to a veto.
One tack Mr. Alden and others are taking is to try to convince developing countries that US policy may change after the Bush administration.
More Kyoto-like policies are emerging at the state and local levels in the US, and environmental lobbyists here say that they see a friendlier climate in the Senate for greater action - something they hope will convince delegates from developing nations to stay the course.
They argue that enough flexibility can be instilled in the Kyoto process to overcome developing-country concerns.
Seasoned diplomats here are quick to point out that the first week of talks traditionally sees participants hewing to their hardest line. Things start to shift in the final week, when ministers arrive.
"Developing countries ratified the Kyoto Protocol, and they are eager for the benefits" of the financial tools it has set up to help Kyoto countries meet their reduction goals, says Artur Runge-Metzger, who heads the European Commission's delegation.