WITH HIS BEARD and tweedy jacket, Richard Lindzen looks like a cheerful physics professor from the fifties, inspiring nostalgia for the age of space exploration and other grand, forward-looking American endeavors. On a cold March evening in New London, Connecticut, the 67-year-old atmospheric scientist from MIT is trying to serve up a little optimism about the gloomiest topic of our time: global warming.

Optimism? Yeah, as in: Don't worry about a thing. Just now, Lindzen is scoffing at the widely accepted view that CO2 buildup is to blame for the heat waves, prolonged droughts, and intense hurricanes that the U.S. and other countries have experienced in recent years. At a time when much of the nation's political, intellectual, and business leadership accepts the idea that people are the cause of global warming, Lindzen loudly disagrees.

"All scientific issues—and this is no different—are difficult to understand," he tells a group of cadets and locals assembled in an auditorium at the U.S. Coast Guard Academy. "Extreme weather events are always present. There's no evidence it's getting better, or worse, or changing."

Lindzen's relaxed delivery gives the audience a comfortable sense that they, like him, are smart enough to question the pronouncements of nervous scientists and high-octane advocates like Al Gore. Skepticism is a good idea, he says, since so many people who sound off about global warming don't bother to read the documents that supposedly forecast climate apocalypse. "The Intergovernmental Panel on Climate Change report, if you read it—and no one does ..." he says, and that phrase alone prompts laughter.

This ability to put people at ease helps explain why, after nearly two decades of effort, Lindzen has achieved exalted status among the current crop of global-warming doubters. He has personally briefed President Bush's top science adviser on climate change and is very popular with senior GOP lawmakers on Capitol Hill. He publishes opinion pieces in The Wall Street Journal and speaks publicly several times a month, both in the U.S. and abroad. With so many Americans searching for answers on climate change, an endowed MIT professor with pithy quotes offers a level of assurance that few can rival.

In doing so, however, Lindzen is challenging the scientific establishment, which tends to sing in scary harmony about this issue. The UN's Intergovernmental Panel on Climate Change (IPCC) is an international scientific body, 2,500 researchers strong, that weighs in on the planet's climate health every five years or so. Earlier this year, the IPCC rolled out a series of three massive documents asserting that global warming is an established fact and outlining where it all will lead.

The reports maintain that there's more than a 90 percent chance that human activity—primarily the burning of fossil fuels, resulting in increased levels of atmospheric CO2—is responsible for the earth's recent warming, which amounts to a 1.2-degree-Fahrenheit rise in global mean temperature over the past 100 years. Noting that the current atmospheric concentration of CO2 is higher than it's been in the past 650,000 years, the IPCC predicts that human-induced climate change could spell extinction for 20 to 30 percent of the world's species by the end of this century, cause increasingly destructive weather patterns, and flood coastal cities.

Lindzen doesn't dispute that the planet has warmed up in the past three decades, but he argues that human-generated CO2 accounts for no more than 30 percent of this temperature rise. Much of the warming, he says, stems from fluctuations in temperature that have occurred for millions of years—explained by complicated natural changes in equilibrium between the oceans and the atmosphere—and the latest period of warming will not result in catastrophe.

Whether such arguments are true, false, or nuts, they seem to make an impression on the Coast Guard crowd. Edward Hug, a Massachusetts retiree who came to hear Lindzen speak, is exactly the kind of person the professor wants to sway. Hug, who used to work in underwater acoustics for the Naval Undersea Warfare Center, says he's been diligently trying to educate himself about global warming.

"I've seen Al Gore's film twice, but I've also read Michael Crichton's State of Fear, which makes a compelling case on the other side," says Hug, referring to the controversial 2004 novel in which Crichton—using scientific arguments that were hotly challenged by critics—ridiculed the global-warming consensus as the work of conspiratorial alarmists.

Hug sees the IPCC as "the closest thing to a gold standard when it comes to science," but he still wants to know whether Americans have to change their lifestyles radically in order to save the planet. "The question is," he said earlier as he settled in to hear Lindzen, "is it worth making the sacrifice?"

By evening's end, he decides to join the skeptical camp. "I find him very convincing," Hug says of Lindzen, recalling how he invoked scientific data and theories to buttress his points. "He's just as good as Michael Crichton."