Among its fevered champions, the campaign against global warming has come to resemble a religious crusade. Militant activists present the fate of a warming world as a sort of secular “end of days,” and cast their own efforts in correspondingly messianic terms. Al Gore, declaring that he is fighting to ensure “the survival of our civilization and the habitability of the Earth,” congratulates himself and his followers on the “compelling moral purpose” of their “generational mission.” As for the heretics who oppose this new religion, woe be unto them. The top scientist at the UN’s International Panel on Climate Change (IPCC) has likened some critics of the Kyoto Protocol, the main international agreement for limiting greenhouse-gas emissions, to Adolf Hitler.

The Danish social scientist Bjorn Lomborg believes that such shrill rhetoric and emotionalism have made it impossible to have any kind of sensible dialogue about the issue. In Cool It: The Skeptical Environmentalist’s Guide to Global Warming, he attempts to bring the debate back to the cost-benefit analysis typically used to tackle environmental problems. Applying the calm utilitarian approach that was the hallmark of his groundbreaking 2001 book, The Skeptical Environmentalist, Lomborg systematically catalogues the economic and humanitarian risks of global warming, and then sets them against the costs of carbon abatement. Global warming, he concedes, is a real and serious problem; but, he asks heretically, might there not be better ways to spend the trillions of dollars being earmarked to fight it?

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The central premise of Cool It is that keeping the earth’s temperature from rising should not be regarded as an end in itself, but rather as a means toward bettering humanity’s lot. Chapter by chapter, Lomborg evaluates the available options for tackling climate change—from doing nothing, to instituting the restrictions called for by Kyoto, to cutting greenhouse-gas emissions in the industrialized countries by 96 percent over the next quarter-century (as in one British proposal).

A professional contrarian, Lomborg delights in showing all the ways in which the available scientific data contradict received political wisdom. He demonstrates, for instance, that in most parts of the world, the number of deaths attributable to the effects of excessively hot weather is typically an order of magnitude lower than that for excessively cold weather. In Athens, about 7,900 people die each year from cold, compared to only about 1,400 who die from heat. In Europe as a whole, the figures are 1.5 million versus 200,000. Overall, experts predict that by 2050 a warmer planet will save a total of 1.4 million lives a year.

As Lomborg emphasizes, this does not mean that higher temperatures will provide a net benefit to the world. Poorer, hotter regions such as South Asia and Africa will suffer greater hardships from rising sea levels, crop failures, epidemics, and extreme weather events. But very little of this damage, Lomborg shows, can be abated through the measures now being considered.

Reducing the emission of greenhouse gases turns out to be a spectacularly expensive enterprise, even when done in moderation. The global compliance costs of Kyoto alone amount to about $180 billion a year. Yet, according to the best available projections, these enormous sums would delay the globe’s expected rate of heating over the next century by just 5 percent. Assuming that Kyoto is allowed to expire in 2012, its total effect will have been to delay the pace of global warming by an estimated one week.

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In making his case, Lomborg relies on the rich body of peer-reviewed studies that have attempted to assess the likely overall effects of climate change by measuring its impact on farming, forestry, fisheries, water availability, human infrastructure, natural disasters, land erosion, pollution, and human migration. His bottom line is that, if Kyoto were to be fully implemented by all its signatories—including the United States—the environmental benefits accruing to the world over the next century would amount in dollar terms to slightly less than $2 trillion. As against this, the cost of implementing the agreement, even assuming that governments employed the most efficient carbon-limiting measures available, would be more than $5 trillion.

In other words, fighting climate change according to the requirements of Kyoto would earn the world about 34 cents on the dollar. An even more ambitious carbon-abatement plan now being floated by the European Union makes even less economic sense, offering to deliver just 13 cents on the dollar.

Some advocates argue that, not-withstanding such low rates of return, Kyoto is a morally necessary means to protect the developing world from the effects of the West’s accumulated carbon-dioxide emissions. As Lomborg demonstrates, however, much more relief could be provided to poorer nations if even a small fraction of the trillions that would be spent on Kyoto were redirected toward alleviating more pressing problems.

As the organizer of the Copenhagen Consensus (a global think tank that assigns priorities to the world’s health emergencies), Lomborg has developed an expertise in the economics of foreign aid. In 2004, the group ranked the world’s health problems according to how much humanitarian benefit could be achieved per dollar invested in fighting them. The Kyoto Protocol appeared near the bottom of the list, trailing far behind HIV/AIDS prevention, the provision of micro-nutrients, trade liberalization, malaria control, water purification, and basic local health services.

In the case of AIDS, each dollar spent on prevention programs yields about $40 worth of social good in the form of saved lives and less societal disruption. In the case of malaria, whose spread is often cited prominently as a by-product of global warming, the implementation of Kyoto would prevent an estimated 140,000 people from being killed by the disease in coming decades, while for a tiny fraction of the overall cost of Kyoto the West could save 85 million lives with straightforward anti-malarial measures. That is, the same money that, invested in Kyoto, would save one life from malaria could save 36,000 lives if invested in medication, mosquito netting, and the like. Lomborg makes similar arguments with respect to starvation, land erosion, hurricane protection, and even the much-touted threat to the world’s polar bears.

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Not surprisingly, most environmentalists have little use for Lomborg’s analysis. According to George Monbiot, a left-wing British activist who writes a weekly column for the Guardian (and who proposed the 96-percent reduction in emissions mentioned above), an insistence on comparing costs and benefits is the mark of one who has “spent too much time with [his] calculator and not enough with human beings.” To which Lomborg replies: “If this approach means you end up helping five thousand Ethiopians each time Monbiot helps one, it certainly seems like you care more about humans, too.”

Cool It is a book that should be read by citizens and politicians alike. At a time when exacting cost-benefit analysis is used to evaluate even the smallest capital project in the private or public sector, it is extraordinary that decision-making on climate-change policies, which could cost trillions of dollars over the course of generations, seems to be guided by little more than emotion, slogans, vacuous appeals to “the will of the international community,” and a quasi-religious desire to embark on a “generational mission.”

Global warming is a complex problem with potentially dramatic consequences, not all of which are within man’s power to control. But, as Lomborg argues, this does not mean we should discard our rational faculties in dealing with it. If we treat climate change as something more mystical than it is, we will waste money and lives alike. Environmentalists may distrust Lomborg for turning their crusade into an accounting exercise, but when the stakes are so high, numbers are a far better guide than blind faith.