For three decades, I have been debating alternative solutions for sustainable development with thousands of fellow scientists and policy analysts--exchanges carried out in myriad articles and formal meetings. Despite all that, I readily confess a lingering frustration: uncertainties so infuse the issue of climate change that it is still impossible to rule out either mild or catastrophic outcomes, let alone provide confident probabilities for all the claims and counterclaims made about environmental problems.

Even the most credible international assessment body, the Intergovernmental Panel on Climate Change (IPCC), has refused to attempt subjective probabilistic estimates of future temperatures. This has forced politicians to make their own guesses about the likelihood of various degrees of global warming. Will temperatures in 2100 increase by 1.4 degrees Celsius or by 5.8? The difference means relatively adaptable changes or very damaging ones.

Against this background of frustration, I began increasingly to hear that a young Danish statistician in a political science department, Bjorn Lomborg, had applied his skills in statistics to better determine how serious environmental problems are, Of course, I was anxious to see this highly publicized contribution--The Skeptical Environmentalist: Measuring the Real State of the World. A "skeptical environmentalist" is certainly the best kind, I mused, because uncertainties are so endemic in these complex problems that suffer from missing data, incomplete theory and nonlinear interactions. But the "real state of the world"--that is a high bar to set, given the large range of plausible outcomes.

And who is Lomborg, I wondered, and why haven't I come across him at any of the meetings where the usual suspects debate costs, benefits, extinction rates, carrying capacity or cloud feedback? I couldn't recall reading any scientific or policy contributions from him either. But there was this massive 515-page tome with a whopping 2,930 endnotes to wade through. On page xx of his preface, Lomborg admits, "I am not myself an expert as regards environmental problems"--truer words are not found in the rest of the book, as I'll soon illustrate. I will report primarily on the thick global warming chapter and its 600-plus endnotes. That kind of deadweight of detail alone conjures at least the trappings of comprehensive and careful scholarship. So how does the reality of the text hold up to the pretense? I'm sure you can already guess, but let me give some examples to make clear what I learned by reading.

The climate chapter makes four basic arguments:

Climate science is very uncertain, but nonetheless the real state of the science is that the sensitivity of the climate to carbon dioxide will turn out to be at the low end of the IPCC uncertainty range--which is for a warming of 1.5 to 4.5 degrees C if carbon dioxide were to double and be held fixed over time.

Emissions scenarios, according to the IPCC, fall into six "equally sound" alternative paths. These paths span a doubling in carbon dioxide concentrations in 2100 up to more than tripling and well beyond tripling in the 22nd century. Lomborg, however, dismisses all but the lowest of the scenarios: "Temperatures will increase much less than the maximum estimates from IPCC--it is likely that the temperature will be at or below the B1 estimate [the lowest emissions scenario] (less than 2° C in 2100) and the temperature will certainly not increase even further into the twenty-second century."

Cost-benefit calculations show that although the benefits of avoiding climate change could be substantial ($5 trillion is the single figure Lomborg cites), this is not worth the cost to the economy of trying to constrain fossil-fuel emissions (a $3-trillion to $33-trillion range he pulls from the economics literature). Asymmetrically, no range is given for the climate damages.

The Kyoto Protocol, which caps industrialized countries' output of greenhouse gases, is too expensive. It would reduce warming in 2100 by only a few tenths of a degree--"putting off the temperature increase just six years." This number, though, is based on a strawman policy that nobody has seriously proposed: Lomborg extrapolates the Kyoto Protocol, which is applicable only up to 2012, as the world's sole climate policy for another nine decades.

Before providing specifics of why I believe each of these assertions is fatally flawed, I should say something about Lomborg's methods. First, most of his nearly 3,000 citations are to secondary literature and media articles. Moreover, even when cited, the peer-reviewed articles come elliptically from those studies that support his rosy view that only the low end of the uncertainty ranges will be plausible. IPCC authors, in contrast, were subjected to three rounds of review by hundreds of outside experts. They didn't have the luxury of reporting primarily from the part of the community that agrees with their individual views.

Second, it is ironic that in a popular book by a statistician one can't find a clear discussion of the distinction among different types of probabilities, such as frequentist and Bayesian (that is, "objective'' and "subjective"). He uses the word "plausible" often, but, curiously for a statistician, he never attaches any probability to what is "plausible." The Third Assessment Report of the IPCC, on the other hand, explicitly confronted the need to quantify all confidence terms. Working Group I, for example, gave the term "likely" a 66 to 90 percent chance of occurring. Although the IPCC gives a wide range for most of its projections, Lomborg generally dismisses these ranges, focusing on the least serious outcomes. Not so much as one probability is offered for the chance of a dangerous outcome, yet he makes a firm assertion that climate "will certainly" not go beyond 2 degrees C warming in the 22nd century--a conclusion at variance with the IPCC, other national climate assessments and most recent studies in the field of climate science.

Now let us look in more detail at the four major arguments he makes in this chapter.

Climate science. A typical example of Lomborg's method is his paraphrase of a secondary source in reporting a 1989 Hadley Center paper in the journal Nature in which the researchers make modifications to their climate model: "The programmers then improved the cloud parameterizations in two places, and the model reacted by reducing its temperature estimate from 5.2°C to 1.9° C." Had this been first-rate scholarship, Lomborg would have consulted the original article, in which the concluding sentence of the first paragraph presents the authors' caveat: "Note that although the revised cloud scheme is more detailed it is not necessarily more accurate than the less sophisticated scheme."

In a similar vein, he cites Richard S. Lindzen's controversial stabilizing feedback, or "iris effect," as evidence that the IPCC climate sensitivity range should be reduced by a factor of almost three. He fails either to understand this mechanism or to tell us that it is based on only a few years of data in a small part of one ocean. Extrapolating this small sample of data to the entire globe is like extrapolating the strong destabilizing feedback over midcontinental landmasses as snow melts during the spring--such an inappropriate projection would likely increase estimates of climate sensitivity by a factor of several.

As a final example, he quotes a controversial hypothesis from Danish cloud physicists that solar magnetic events modulate cosmic rays and produce "a clear connection between global low-level cloud cover and incoming cosmic radiation." The Danish researchers use this hypothesis to support an alternative to carbon dioxide for explaining recent climate change. Lomborg fails to discuss--and I haven't seen it treated by the authors of that speculative theory either--what such purported changes to this cloud cover have done to the radiative balance of the earth. Increasing clouds, it has been well known since papers by Syukuro Manabe and Richard T. Wetherald in 1967 and myself in 1972, can warm or cool the atmosphere depending on the height of the cloud tops, the reflectivity of the underlying surface, the season and the latitude. The reason the IPCC discounts this theory is that its advocates have not demonstrated any radiative forcing sufficient to match that of much more parsimonious theories, such as anthropogenic forcing.

Emissions scenarios. Lomborg asserts that over the next several decades new, improved solar machines and other renewable technologies will crowd fossil fuels off the market. This will be done so efficiently that the IPCC scenarios vastly overestimate the chance for major increases in carbon dioxide. How I wish this would turn out to be true! But wishes aren't analysis. One study is cited; ignored is the huge body of economics work he later accepts to estimate a range of costs if we were to implement emissions controls. In fact, most of these economists strongly believe high emissions are quite likely: they usually project carbon dioxide doubling to tripling (or more) as "optimal" economic policy. I have attacked this literature for failing to point out that climate policies that raise the price of conventional fuels spur investments in alternative energy systems. But such incentives need policies first--and Lomborg opposes those very policies. No credible analyst can just assert that a fossil-fuel-intensive scenario is not plausible--and, typically, he gives no probability that it might occur.

Cost-benefit calculations. Lomborg's most egregious distortions and poorest analyses are his citations of cost-benefit calculations. First, he chides the governments that modified the penultimate draft of the report from IPCC's Working Group II. These modifications downgraded the significance of economic studies that aggregate climate change damages. Lomborg says: "A political decision stopped IPCC from looking at the total cost-benefit of global warming." (As an aside, I should mention that it is strange he chose to cite the penultimate and preapproval draft report in this case but didn't mention the very first item in the approved summary--that recent temperature trends have caused a discernible effect on plants and animals. Even more puzzling is his failure to discuss ecological impacts in general, focusing instead on health and agriculture, sectors he thinks won't be much harmed by climate change of the minuscule amount he predicts.)

The government representatives downgraded aggregate cost-benefit studies for a reason: these studies fail to consider so many categories of damages held to be important by political leaders as to render them just a guideline on market-sector transactions, not the "total cost-benefit" analysis Lomborg wants. A total analysis would have to include the value of species lost, crucial ecosystem services degraded, inequity created by the poor being hurt more than the rich (which Lomborg does acknowledge), quality of life reduced (for example, a rise in sea level driving small-island inhabitants from traditional homelands), and likely changes to climatic extremes and variability. Then again, Lomborg cites only one value for climate damages--$5 trillion--even though the same economics papers he refers to for costs of climate policy generally acknowledge that climate damages can vary from benefits up to catastrophic losses.

It is precisely because the responsible scientific community cannot rule out such catastrophic outcomes at a high level of confidence that climate mitigation polices are seriously proposed. And to give one number--rather than a broad range--for avoided climate damages defies explanation, especially when he does give a range for climate policy costs. This range, however, is based on the economics literature but ignores the findings of engineers. Engineers dispute the economists' typical estimates because the economists fail to take into account preexisting market imperfections such as energy-inefficient machines, houses and processes. These engineering studies, including a famous one by five U.S. Department of Energy laboratories-hardly environmental radicals--suggest that climate policies that provide incentives to replace inefficient equipment with more efficient state-of-the-art products could actually reduce some emissions at below-zero costs.

The Kyoto Protocol. Lomborg's creation of a 100-year regime for a decade-long protocol is a distortion of the climate policy process. Every IPCC report has noted that carbon dioxide emissions need to be cut by more than 50 percent below most baseline projections to avoid large increases in concentration in the late 21st and 22nd centuries. Most analysts know "Kyoto extended'' can't make such large cuts and that both developed and developing nations will have to fashion cooperative and cost-effective solutions over time. This will take a great deal of learning-by-doing: international cooperation is not a common experience. Kyoto is a starting point. And yet Lomborg, with his creation of a straw-man 100-year projection, would squash even this first step.

So what then is "the real state of the world"? Clearly, it isn't knowable in traditional statistical terms, even though subjective estimates can be responsibly offered. The ranges presented by the IPCC in its peer-reviewed reports give the best snapshot of the real state of climate change: we could be lucky and see a mild effect or unlucky and get the catastrophic outcomes. The IPCC frames the issue as a risk-management decision about hedging. It is not the everything-will-turn-out-fine affair that Lomborg would have us believe.

For such an interdisciplinary topic, the publisher would have been wise to ask natural scientists as well as social scientists to review the manuscript, which was published by the social science side of the house. It's not surprising that the reviewers failed to spot Lomborg's unbalanced presentation of the natural science, given the complexity of the many intertwining fields. But that the natural scientists weren't asked is a serious omission for a respectable publisher such as Cambridge University Press.

Unfortunately, angry reviews such as this one will be the result. Worse still, many laypeople and policymakers won't see the reviews and could well be tricked into thinking thousands of citations and hundreds of pages constitute balanced scholarship. A better rule of thumb is to see who talks in ranges and subjective probabilities and to beware of the myth busters and "truth tellers."

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By Stephen Schneider

Stephen Schneider, professor in the department of biological sciences and senior fellow at the Institute for International Studies at Stanford University, is editor of Climatic Change and the Encyclopedia of Climate and Weather and lead author of several IPCC chapters and the IPCC guidance paper on uncertainties.