With the virtual apotheosis of Al Gore, talk of global warming has become pervasive”and pervasively one-sided. Churches of all varieties have signed on as a moral cause. Corporations, including former doubters, have adopted anti-warming language, either from new conviction or convenient public image. Politicians, with few exceptions, dare not openly deny that there is a problem, though their responses may vary.

Through it all, one would never know there are dissenters of distinguished credentials in the scientific community. Even where their existence is admitted, they are thoroughly marginalized, accused of being in the pay of the oil companies (Gore slyly and meanly implies this in his movie, An Inconvenient Truth ), or dismissed as over-the-hill retirees out of touch and perhaps a bit senile. Their articles are denied publication in Science and Nature , those two so-called flagship science journals of high reputation despite some embarrassing lapses.

When dissenters do speak and publish, the majority who embrace the prevailing theory that humans are causing global warming try to silence them on the grounds that, because they are in error, they must not be allowed to be heard. Newspapers who seek balance in their reporting are told that they are doing a disservice to the public, to truth, and to the survival of the human race. The Weather Channel, a full-bore promoter of global-warming alarm (which feeds its appetite for newsworthy disaster), has, through its chief climate expert Heidi Cullen, even said that weather reporters who don’t accept the reigning thesis should be decertified by the American Meteorological Society”in other words, believe our way or lose your job. When British television producer Martin Durkin made a counter-movie to Gore’s, the head of the Royal Society declared that he should not be allowed to show it.

The result is that anyone who finds the dissenters persuasive”including me”is suspected of being a right-wing extremist, making politics determine science. In vain do we point out that dissenters from established scientific consensus have often been dramatically vindicated. Undeterred, some of our critics have even compared us to Holocaust deniers or urged that dissenters be tried as war criminals. Or maybe burned at the stake for heresy”for our religious critics do think of us as heretics and sinners.

This dismal state of affairs is made possible by an astonishing historical amnesia. It is indisputable that climate swings are a regular feature of our planet’s life. Short-term changes lie within our personal memories: The current warming trend dates from only about 1975. Before that, a pronounced cooling period starting about 1940 led the scientific consensus of the 1970s to proclaim global cooling and perhaps the first signs of an ice age. Note that these swings do not correspond to the amount of CO2 released into the atmosphere; 60 percent of global warming since 1850 occurred before 1940, while 80 percent of CO2 was emitted after that date”and temperatures fell from 1940 until the turnaround in the late 1970s.

Going further back, we find the “little ice age” of the sixteenth and seventeenth centuries, when the Hudson and the Thames froze, crops failed, and disease was rampant, so that millions died. Before that, we come upon the “medieval climate optimum,” when a prevailing warmth made life pleasant, grape vines grew in England, and the Vikings established settlements in Greenland and Newfoundland (which they called Vinland; the names are revealing)”settlements that lasted until the little ice age froze them out.

That period was, in turn, preceded by an unfavorable climate in the Dark Ages, and that by another warm stretch in Roman times. Using proxy records (tree rings, ice-core samples, ocean-bottom sediment), geologists have determined that such climate swings stretch back into prehistory. Fred Singer (who has impeccable credentials and experience as a climate scientist) and Dennis Avery have calculated that this swing-and-return pattern occurs roughly but regularly every 1,500 years. Obviously, the pattern has nothing to do with human activity. Nor does it correspond to the levels of CO2 in the atmosphere. If anything, climate change appears to precede , not follow, increases in CO2.

So what’s going on? There is a significant body of scientific opinion that finds the sun to be the principal climate driver. The sun’s output is variable and complex, more and less intense at different periods. A German team has shown an almost perfect correlation between air temperatures and solar cycles for the past 150 years. A Danish team likewise has constructed a multi-era match of solar activity (measured by sunspots) to global temperatures. Nigel Weiss of Cambridge University, a mathematical astrophysicist and past president of the Royal Astronomical Society, also correlates sunspot activity with changes in the earth’s climate. Because solar activity is cyclical, he expects that a downturn is coming and will usher in a cooling climate for earth in, maybe, three decades. Actually, global average temperature seems to have plateaued since 2000, though it is probably too soon to expect the downturn to have begun. Still, Richard Lindzen, a distinguished atmospheric physicist at MIT and a leading doubter that human activity is driving warming, thinks the odds are about 50 percent that the earth will be cooler in twenty years”due to natural cycles.

It may or may not be significant, but it is suggestive, that NASA’s instruments calculate that Mars, Jupiter, Pluto, and the Titan moon of Neptune are warming, suggesting a solar-system-wide phenomenon. To be sure, this is not hard evidence; other factors (axis tilt and wobble on Mars, for instance) may be a cause. Still, it may be a clue to what is happening here on our planet.

Some caveats are in order. Human activity may add something to the natural cycle, though how much is hard to tell. I have seen a paper that estimates the human contribution at 3 percent and another that gives it at 0.28 percent, for an almost undetectable effect on climate. The principal greenhouse gas, some 97 percent of the total, is water vapor, which leaves little for CO2 and other trace gasses. Scott McIntosh, of the Southwest Research Institute in Boulder, says that warming caused by CO2 compared to the effect of solar magnetic fields is like a flea’s contribution to the weight of an elephant.

We do know, however, that atmospheric emissions can affect climate”for example, the serious consequences of the ash cloud thrown up by volcanic eruptions; so perhaps there is something to the greenhouse-gas theory. People can also argue about the historical record and try to modify the data that shows natural climate cycles. There may be problems with the sun theory; climate is also affected by ocean currents, meteor impact, the tilt of the earth’s axis, cosmic rays, precipitation systems, and other factors. And so on. Those of us who are doubters will not complain when we in turn are doubted. Debate is healthy and must not be choked off.

Nevertheless, the large, rough historical record should be enough to awaken the critical instincts and make anyone take a long second look at the claims of the global-warming alarmists”and alarmists they certainly are, deliberately and unabashedly so.

They’ve claimed, for example, that the glaciers will melt in Greenland and Antarctica and raise the oceans so much that low-lying cities and countries will be submerged and the Gulf Stream will shut down and plunge Europe into an ice age.

As it happens, while there is edge-melting in Greenland and along the peninsula of Antarctica that stretches toward South America, snow is accumulating in the interior of Greenland and in most of Antarctica. The warming peninsula there is just 2 percent of the continent; the other 98 percent is cooling. The Larson B ice shelf, which collapsed, was 1/246 the size of the West Antarctic ice shelf, which has been retreating slowly anyway for thousands of years. As for the Gulf Stream threat, oceanographers debunk it. Even the Intergovernmental Panel on Climate Change (IPCC), the U.N. body that puts out huge periodic reports warning of climate disaster, has backed down from its earlier estimates of sea rise, from three feet for the next century to seventeen inches”and many scientists think even that is too high.

Speaking of glaciers, the alarmists point out that they are melting everywhere. Kilimanjaro will be bare in a few years, and the Alpine glaciers will be but pale shadows of themselves, and so on around the globe. But Claude Allègre, a distinguished French climate scientist, has recanted his earlier support for the IPCC’s conclusions, and says of Kilimanjaro specifically that its snow cap is retreating from natural causes having to do with moisture from the Indian Ocean. Alpine glaciers, like most everywhere, grow and retreat often through their lives. In 2003, as the Schnidenjoch glacier in Switzerland was retreating, a 4,700-year-old archer’s quiver was exposed; that pass has been open to human travel many times since the last ice age.

On and on, the alarms go. Perhaps you’ve seen the claim that the Arctic sea ice is disappearing and that polar bears are threatened with extinction because they can’t hunt from ice floes any more. But Arctic sea ice, like the glaciers, grows and retreats in natural cycles. Gore’s computer simulation of the drowning polar bear may look sad, but, of course, it’s fake. Canadian wildlife biologists say most populations of the bears are actually increasing.

Or perhaps you’ve heard that storms on land and sea will increase in number and intensity, and we can expect more Katrinas. In fact, there has actually been a downward trend in the number of the bigger, detectable tornadoes since 1950; we detect more because better reporting picks up more small ones. New evidence shows that hurricane intensity does not correlate with ocean temperature.

Maybe you’ve read that tropical diseases such as malaria will spread into now-temperate zones, higher latitudes, and higher altitudes”Nairobi, for example. But Nairobi was built when malaria was already endemic there. It was repelled with better insecticide, especially, in Africa, DDT. The current resurgence of malaria comes not from global warming but from the ban on DDT spraying, growing resistance to drugs, and poverty.

You’ve also been told that failing to curb our greenhouse-gas emissions will cause irreparable economic damage to the poorer nations, as the Stern Report insisted. But the report was savaged by economists. William Nordhaus of Yale is among those who fault Stern for using a near-zero social-discount rate, which would charge current generations for problems not likely to occur for two or three centuries hence.

In fact, one can make the opposite case from Stern’s with greater plausibility: Economies would be wrecked by adoption of the Kyoto targets. Even a moderate stabilization of greenhouse-gas emissions would require something like a 60 to 80 percent reduction in fossil-fuel use, and standards of living would drop through the floor. Poor countries would have a nearly impossible time rising out of their poverty. Is it any wonder that China and India and other developing nations will have none of Kyoto-style proposals, and are loudly and clearly telling the developed nations to proceed without their participation? Naturally, they are much more interested in Bush’s proposal to bypass the useless Kyoto framework and substitute technological changes and voluntary goals for the binding targets championed by the Europeans.

One of the goofiest ways of raising consciousness about global warming has been the lectures we’ve received about purchasing carbon offsets. As it happens, the purchase of carbon offsets allows the buyer to continue his merry energy-guzzling ways, his sins having been forgiven for a cash payment. The process has the ring of a medieval indulgence sale, as many critics have gleefully noted. Gore buys carbon offsets so he can justify living in a mansion with huge electricity use. And he can certainly afford that, as his $100,000 lecture fees and his relations with Internet companies and environmental businesses have made him extraordinarily wealthy.

Everywhere you go, you hear the news that we have only a few years to save the planet before we reach the point of no return, the tipping point, irreversible catastrophic climate change, and the end of civilization. Hyperbolic statements like these are meant mainly to scare people into acting and accepting the enormous sums required for the proposed reduction program. Sir John Houghton, the first chair of the IPCC, wrote in a 1994 book, “Unless we announce disasters, no one will listen.”

A backlash against such exaggeration is growing, not least among scientists concerned for their own professional integrity. In any case, we need cooler heads to go with a warmer climate. Lindzen and Israeli astrophysicist Nir Shaviv calculate that a doubling of CO2 in the atmosphere by 2100 would cause a temperature rise of 1 degree Celsius, which is only a little more than the rise from the late nineteenth century to the present has been. A 50 percent rise would yield a 0.5-degree-C. increase. There are, of course, good reasons for controlling many emissions and finding alternative sources to fossil fuels: pollution control, for instance, and freedom from economic fealty to some rather nasty oil-producing regimes. But stopping global warming is not one of them.

It almost seems as if the issue is not in science but in ideology and social psychology. Environmental alarmism is part of a systematic rejection of industrial civilization, of technology, consumerism, globalization, and what most of us think of as growth and progress, in favor of a return to local, simpler, largely agricultural societies”and, of course, fewer children, since humans are the ultimate pollution. Climate reversal has grown to become the latest focus of this way of thinking.

It is an issue that has acquired popular traction, even among people who do not share the radical goals of the larger movement, thanks to deliberate alarmism; and it is now firmly entrenched in our public discourse, especially in our politics. I suspect that it will stay there until the temperature starts to decline again, at which point, as in the 1970s, we’ll hear more about the inevitable return of an ice age.

Thomas Sieger Derr is professor emeritus of religion and ethics at Smith College and the author of Environmental Ethics and Christian Humanism.