"I despise the man," responds Singer, reached at SEPP’s headquarters in Arlington, Virginia. "He lies, he says things about me that aren’t true. He uses ad hominem attacks." But strangely, when asked for an example, he cites Gelbspan’s claim about the ExxonMobil money — because, he explains, he has not personally received any oil money. "We have received some donations. So what?" Singer demands. "We have never asked for it. There are no strings attached." Singer then uncorks a high hard one of his own: he claims that Gelbspan has falsely claimed to have won a Pulitzer Prize, an accusation that, on close inspection, falls apart. Gelbspan, a retired Boston Globe staffer, was an editor on "Boston: The Race Factor," a series that won the Globe the 1984 Pulitzer for local reporting. The Pulitzer board, which does not officially recognize the contributions of editors, does not name Gelbspan as a recipient. But the Globe has always recognized Gelbspan; both his name and his photo are on the Globe’s online list of Pulitzer winners.

Bottom line: there’s no reason to think Singer’s scientific conclusions are anything other than his honest opinion, regardless of where SEPP gets its money; and Gelbspan, technicalities aside, is a legitimate Pulitzer winner.

If the theories cited by global-warming skeptics such as Singer are uncertain, their effect is anything but. The effect is not necessarily direct; after the National Academy of Sciences report was issued, George Bush himself felt compelled to give a short Rose Garden address in which he acknowledged its findings. "We will act, learn, and act again, adjusting our approaches as science advances and technology evolves," he said. Indirectly, though, the skeptics succeed by sowing doubt, by sapping the will to act, by holding out hope that the enormous sacrifices necessary to reduce greenhouse-gas emissions need not be made at all.

Conservative journalist and author James Glassman, a resident fellow at the American Enterprise Institute and the host of a Web site called TechCentralStation.com, has become a leading debunker of global warming. He’s written in conservative publications such as the Weekly Standard, the American Spectator, and the Wall Street Journal editorial page — often in collaboration with Sallie Baliunas, who has the scientific credentials he lacks — contending that the global-warming theorists are wrong, and that they’re leading us down a road that will ruin our economy.

When asked what influence he thinks he’s had on Bush-administration policy, he replies, "I think it’s really hard to tell whether we’ve had a direct effect. I have no evidence. I’m not plugged in to the administration. I hope we’ve had a direct effect." As for his own beliefs, he says, "There are huge gaps in the knowledge. I realize that we have to proceed with public-policy decisions before we have 100 percent certainty on anything. But in this case, the only logical public-policy position is to wait until we know more."

By the way, Glassman is the co-author of a book titled Dow 36,000 (Times Books) — a case for why the Dow Jones Industrial Average will reach 36,000. It’s a case that looked stronger in 1999, when the book was published, than it does today. "The thesis of the book is just as sound as it’s ever been," Glassman insists. Still, you can’t help but think the reality of global warming will be proven long before the Dow hits 36,000.

TO SUSANNE Moser, a climate-change staff scientist at the Union of Concerned Scientists, the case for human-caused, potentially catastrophic global warming has long been proven. Never mind the computer models and the surface-temperature readings that the skeptics are so fond of citing, she says; consider, instead, the evidence that glaciers are melting, and that plant and animal species are moving from warmer to cooler latitudes, and from lower to higher altitudes. And it is an established fact that there is more carbon dioxide in the atmosphere today than there has been at any time over the past 450,000 years.

"All these physical and biological reactions don’t happen for no reason," she says. "For me it’s getting harder and harder to understand why the skeptics maintain that there is no evidence. I can only conclude that they must be driven by some personal desire to influence the debate in a certain way, or are too stubborn to admit they made a mistake."

Bob Reiss, the author of The Coming Storm: Extreme Weather and Our Terrifying Future (Hyperion, September 2001), says, "Scientists who don’t believe in global warming have been around since the debate started, and scientists who don’t believe in global warming will be around in 50 years."

The potential consequences of global warming are truly terrifying, ranging from the spread of tropical diseases to a new ice age, a counterintuitive possibility that might come to pass if rising temperatures disrupt ocean currents.

Who knows? Maybe the business interests that are driving Bush’s environmental policies, and the conservative media and naysaying scientists who provide them with political and intellectual support, will someday be proven right.

But it bears repeating that theirs is a minority view, and that the mainstream scientific consensus is that we need to take drastic action — the sooner the better.

The skeptics will have much to answer for if it turns out that they’re wrong.

Dan Kennedy can be reached at dkennedy[a]phx.com