SOUTHBORO, Mass.

LAST MONTH, Prof. Richard Lindzen of the Massachusetts Institute of Technology spoke to the 350 students at St. Marks School on the science of global warming.

With his large glasses and unruly hair, he could have been a professor from central casting. While he was being introduced by the headmaster, he leaned casually against the wall of the wood-paneled, three-level auditorium — a little shocking at a prep school, where not long ago bad posture could get the odd fifth-quintilian the boot.

The students had been called together because last year, they had viewed Al Gore’s movie An Inconvenient Truth. The movie — which won an Oscar and helped lead to Gore’s being awarded the Nobel Peace Prize — has been praised for describing in dramatic terms the consequences of the unchecked accumulation of greenhouse gases in the atmosphere, chiefly carbon dioxide from the burning of coal and oil by the world’s industrialized economies. The movie predicts the melting of the Greenland ice sheet and the rise of sea levels by as much as 20 feet, increasingly violent weather patterns and droughts that will kill millions.

To the school’s credit, it asked Professor Lindzen, a critic of some of the extreme claims of global warming apostles, to give his views. Lindzen has been a minor affliction to those, like Gore, who maintain that the science on global warming is settled and the debate is over. Mr. Lindzen, the Alfred P. Sloan Professor of Meteorology in MIT’s Department of Earth, Atmosphere and Planetary Sciences, has been pilloried as a mouthpiece for oil companies who has somehow infiltrated one of the country’s leading science institutions.

Science is not knowledge, he told his audience. It is a method for determining what is true, based on observation and theory. Given the sorry state of science education in America, that may have been a revelation to students even at this fine private school.

In numerous papers and in other media Lindzen has cast doubt specifically on the impact of humans in global warming and climate change. As he told the students, the earth’s climate is always changing: At present it seems to be warming, and greenhouse gases that we produce are probably contributing to it, but, for all our wasteful ways, the amounts aren’t enough to make a difference. Beyond that, he doubted that the effects of warming are necessarily bad. Gore’s dire forecasts of the amount of warming we can expect, as well as the severity of storms and droughts, are exaggerated.

If the debate surrounding global warming has become polarized and bitter, Lindzen said, it is because politics and science are not well suited to each other. Science is about description; politics is about authority and control. Science is disinterested, politics is partisan. Politics distorts science.

An Inconvenient Truth, starting with the title, is a good example, Lindzen said. Even the 2,000-member Intergovernmental Panel on Climate Change, which shared the Nobel with Gore, has shied away from his most politically incendiary charges, such as the amount of sea-level rise, which would sink many of the world’s cities. At the IPCC’s extreme end, the estimates are in the range of three feet by year 2100, which is manageable, but most estimates are much lower than that.

Lindzen has likened the global-warming controversy to other pseudo-science movements that have been taken up in the political sphere, such as eugenics a century ago. Lindzen, whose parents survived the Holocaust, finds Gore’s assertion that his argument should be clear to any kindergarten child particularly repugnant. Nothing in the assessment of climate change, which requires a rigorous analysis of vast quantities of often contradictory information, is simple.

A lot is not as it appears in Gore’s movie and book of the same name. For example, Lindzen displayed a chart from the book tracking the correlation of temperature and CO{-2} over hundreds of thousands of years, derived from samples of ice cores in the Antarctic, pointing out that it actually showed a pattern of temperature rise preceding rises in atmospheric CO{-2}. Gore presents it as showing the opposite. But Lindzen’s larger point was that the whole exercise is suspect, because the dating of ice cores is too complex and uncertain to be used dogmatically, as Gore uses the data — unless, of course, one is trying to sway children.

Another chart showed the celebrated “hockey stick,” depicting the purported rapid rise in global temperature in recent decades, after holding steady for hundreds of years. In its latest report, the IPCC has withdrawn this particular graphic, because the global record shows no such rise, or steadiness. Temperatures 800 years ago were warmer than now. The Medieval Warm Period, well documented by such sources as the detailed records maintained by monasteries of crop plantings, and the settlement of Greenland by the Norse, has been a persistent note of discord for the global-warming choir.

And finally, there is the matter of the computer models that Gore and others rely on to plot the bleak future of the earth. Lindzen explained the “compounding of error,” the tendency of elaborate hypotheses to collapse because they depend on too many factors behaving in exactly the prescribed way. In fact, especially in a matter such as this, in which many elements of climate are poorly understood, particularly the role of ocean currents in distributing heat, these models cannot be considered reliable.

To conclude, he took his students through an exercise. The Kyoto Accords aim to remove some hundreds of thousands of megatons of carbon from the atmosphere, which sounds like a lot. Starting from the fact that the atmosphere weighs about 15 pounds per square inch, multiplied by the square inches of the earth’s surface, the St. Mark’s students, at least those who had brought calculators, came up with a number for the megaton mass of the atmosphere that had some 18 zeros, or to the 18th power, as physicists put it. Against that number, the half-dozen zeros of Kyoto — even if they could be realized, even if the treaty were to include China and India — were pretty puny.

Lindzen’s point was that the earth is huge, and a still mysterious place in many ways. Much of the problem assessing these questions comes from the difficulty of conceptualizing the scale of the entities involved — chiefly the atmosphere and the oceans.

There were some questions following the talk, and Lindzen was asked if it wouldn’t be better to sign Kyoto and follow-on agreements just to be on the safe side. Lindzen said no. Combating a hypothetical problem would waste resources, human more than material, which could be much better devoted to other ends, such as improving public health.

But the further problem with making global warming the object of a huge and highly political international project may be that every action has an equal and opposite reaction; that when the theory is inevitably discredited and dismissed, possibly after a few bad snowstorms, the whole package of environmentalism will be discredited too, along with all the worthy parts involving the reduction of harmful pollutants and preservation of wildlife habitat.

We’ll have squandered much by chasing a will-o’-the-wisp — a term in folklore for a floating ball of light. Most people believe a will-o’-the-wisp is — fittingly, in this case — a phenomenon related to methane, a greenhouse gas.

Irving C. Sheldon Jr. is a member of The Journal’s editorial board.