It is no coincidence that as the treaty takes effect, a slew of bipartisan legislative proposals to control greenhouse gases are being introduced in Congress. And some states are taking matters into their own hands. California is demanding steep reductions in vehicle emissions. Several northeastern states are banding together to limit greenhouse emissions and set up the kind of trading system that could easily blend into the Kyoto model.
"Arizona is moving forward because they see droughts, wildfires," said Pew's Claussen. "North Carolina is considering a comprehensive policy because they are concerned about the barrier islands."
No one expects the Bush administration to change course, but dealing with a hodgepodge system might eventually prove more expensive to American industry than outright participation in a global system, said Robert W. Fri, a board member at American Electric Power Co., which burns more coal than any other utility in the United States.
The treaty's activation this week will intensify a debate in corporate boardrooms over the cost of doing nothing vs. the cost of doing something, said Fri, who formerly headed the environmental advocacy group Resources for the Future. He and Claussen said most American companies acknowledge -- at least in private -- that global controls on greenhouse gas emissions are inevitable. Farsighted companies, they said, want a seat at the bargaining table and are investing in cleaner technologies.
Both sides agree on one thing: The most contentious battles over controlling greenhouse emissions lie ahead.
Under the treaty, the European Union committed to reducing its emissions 8 percent below 1990 levels; Japan and Canada committed to a 6 percent cut; and Russia, whose entry three months ago provided the quorum needed to put the treaty into effect, committed to limit emissions right at 1990 levels. The United States would have had to limit emissions at 7 percent below 1990 levels, Petsonk said.
That would have been a prescription for disaster, said the White House's Connaughton, adding that it would have cost 5 million jobs and $400 billion annually. "The problem with Kyoto is it tried to reverse before we had put the brakes on and come to a stop," he said.
Connaughton and Frank Maisano, an energy lobbyist and former spokesman for a defunct industry coalition on climate change, said that rather than limit emissions, the United States should help spread clean technology in the developing world.
By 2010, said William O'Keefe, a former oil industry executive who now works at the Marshall Institute, an advocacy organization, developing countries will account for the bulk of greenhouse emissions. Maisano endorsed a recent proposal by Sen. Chuck Hagel (R-Neb.) to develop and spread clean technology. Rather than set limits on emissions, the proposal seeks to set efficiency standards.
Environmentalists dispute Connaughton's estimate of the costs and say the administration is ignoring a fundamental reality: Improving efficiency, while necessary, will never suffice to lower greenhouse gas levels.
"You can't solve global warming by increasing emissions," said Jeremy Symons, manager of the global warming program at the National Wildlife Federation, an advocacy group. "That is what we are doing now. That is what President Bush is doing. You can't stop an environmental problem by increasing pollution."
The countries that ratified Kyoto believe that wealthy countries need to demonstrate a commitment to reducing emission levels in the first phase of the treaty, from 2008 to 2012, before the developing world can be asked to make cuts.
"You can't expect developing countries to waive their right to grow because the industrialized countries for the last 100 years have eaten all the cake," said Donkers of the European Union delegation in Washington.
Many environmentalists are getting behind a proposal by Sens. John McCain (R-Ariz.) and Joseph I. Lieberman (D-Conn.) that would impose modest emission limits in the United States and establish a trading system analogous to Kyoto to give American companies a financial incentive to develop technologies that lower emissions.
McCain said Thursday that it is time to end the wrangling over global warming. If scientists are wrong about the catastrophic consequences of greenhouse gases, efforts to limit emissions would still result in cleaner air and a more competitive industrial base, he said.
"Given the high stakes involved -- the future of our children and our grandchildren, not to mention the future of the planet as we inherited it -- which approach are you willing to bet on?" he asked.