WASHINGTON -- With Democrats controlling the environmental agenda in Congress, a panel of international scientists saying there's a greater-than-90 percent chance that humans contribute to global warming, and former vice president Al Gore calling climate change a moral issue, many besieged global warming skeptics are starting to tone down their rhetoric.
Some, though, are sticking to aggressive tactics, even contending they are gaining momentum. And they have influential allies: some scientists, conservative think-tank pundits, a minority of Republicans in Congress, and a sympathetic White House that has rejected attempts to force companies to curb carbon dioxide emissions -- even though the vast majority of scientists say those emissions are heating up the earth.
Still, both sides acknowledge that the global warming debate has changed significantly in recent weeks. The biggest factor is the Feb. 2 report by the Intergovernmental Panel on Climate Change, or IPCC -- a review of scientific literature by hundreds of scientists who determined that it is more than 90 percent certain humans contribute to global warming.
That seemingly irrefutable conclusion helped shift the position of ExxonMobil, which had taken the strongest stance among oil companies against global warming policy.
Last week, Rex W. Tillerson , ExxonMobil's chief executive, acknowledged that greenhouse gases from car and industrial exhausts are factors in global warming, a stark reversal in the company's long-held position. For years, ExxonMobil has funded several Washington think tanks that have questioned the science -- and whether national policies would be effective.
Scott Barrett , a global warming believer and director of the International Policy Program at Johns Hopkins' School of Advanced International Studies , said ExxonMobil's about-face is significant. "They accepted the responsibility to do something, and that could change the debate" from uncertainty about climate change to finding solutions to a fast-approaching crisis, he said.
Other oil giants, including BP and Shell, had made the shift much earlier; both are aggressively promoting fossil-fuel alternatives such as solar and wind power.
"A lot of the focus is going to shift into how much effort you should put into reducing emissions versus adapting to climate change," Barrett said. Adapting to a warmer global climate, he said, could include anything from building farther inland to guard against rises in sea level to investing in a malaria vaccine, anticipating that disease-carrying mosquitoes could spread northward from the tropics.
The debate shift has been felt elsewhere as well. The American Enterprise Institute, a conservative Washington think tank that had offered $10,000 last year to scientists to challenge the IPCC report, is rethinking the project, said Kenneth Green , who is overseeing the effort.
"There is a backlash growing against skeptics, a kind of climate inquisition," said Green. "What do people do if they have alternative ideas and they don't have independent institutions to back them up? They will be attacked."
Global warming skeptics say they believe the media and Congress aren't interested in hearing their side of the debate.
"The size of the megaphones for the other side is very large," said Myron Ebell , director of energy and global warming policy at Competitive Enterprise Institute, one of the leading doubters of the issue. "On our side we are using bare voices without amplification."
But those who don't believe humans contribute to global warming have some scientists, and an influential lawmaker, on their side.
Senator James M. Inhofe , the Oklahoma Republican who famously declared global warming a "hoax," said this week that the skeptics were gaining momentum. He said President Vaclav Klaus of the Czech Republic and scientists from France and Israel, among others, are now among the doubters.
Writing in the Sunday Times of London this week, Nigel Calder, former editor of New Scientist magazine, suggested that the IPCC's main conclusion -- that there is more than a 90 percent certainty humans are contributing to global warming -- means there's a 10 percent chance that man is blameless, "a wide-open breach for any latter-day Galileo or Einstein to storm through with a better idea. That is how science really works."
Dr. Willie Soon , a scientist at the Harvard-Smithsonian Center for Astrophysics who believes that variations in the sun's energy might be the chief reason for a warming planet, agrees. Speaking for himself and not the center, Soon accused mainstream scientists of "attacking me. But as a scientist, you just ignore them."
Meanwhile, Christopher C. Horner , published a book this week called "The Politically Incorrect Guide to Global Warming and Environmentalism," a primer for doubters that yesterday was ranked 33 d on Amazon.com's best-sellers' list. Horner, a fellow at Competitive Enterprise Institute, has denounced Democrats in Congress, alleging that they are delaying action on global warming to preserve it as a presidential campaign issue in 2008.
But Representative Henry A. Waxman , a California Democrat, has said he doubts any comprehensive global warming legislation will emerge until 2009 for a different reason: Though Democrats control Congress, they don't have the votes to override a likely veto by President Bush.
Bill McKibben , the author of "The End of Nature," which in 1989 warned about global warming, said skeptics "at best are taking pot shots around the edges" of the debate. Still, McKibben sees a great irony as he listens to their arguments: "There is nothing I would rather see than these guys be right."