Though the fear of man-made global warming has come to dominate our cultural discourse, the science behind the scare is looking increasingly uncertain. David Evans is representative of scientists who have become disillusioned with the theory that industrial carbon dioxide emissions are the root cause of global warming: as he points out, the computer models don’t seem to fit the data, while at the same time evidence is mounting in favor of alternative hypotheses, like the idea that climate change may be caused in large part by fluctuations in solar radiation. A series of articles by Lawrence Solomon, who has profiled prominent climate-change dissenters, demonstrates that Evans is hardly alone—and calls into question the often-parroted assertion that there is some sort of scientific “consensus” on the issue (whatever that might mean).

One of Evans’s interesting asides is that “the integrity of the scientific community will win out in the end, following the evidence wherever it leads.” Although this is true in the long run, it’s a bit simplistic. Once a theory gains ascendancy, it may take years or even decades before its adherents are willing to abandon it, even in the face of contradictory data. (See Thomas Kuhn’s landmark book The Structure of Scientific Revolutions for a picture of this phenomenon.) At the most basic level, scientists have their jobs and reputations to think about; it’s only natural to resist the suggestion that one has spent one’s career trying to prove, or solve, a nonexistent problem. No doubt this would be true even in the absence of external pressure. But with the political stakes now so high, scientific integrity is at a decided disadvantage.

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Max Boot’s insistence that only climatologists should be allowed to comment on global warming is bizarre, and actually anti-scientific, if you think about it. As I’ve pointed out before, science is not some kind of cabal, or a secret society open only to initiates; the beauty of science is that the evidence is there for everyone to look at and interpret. (This is why Al Gore, an ex-politician who earned a D in a college course called “Man’s Place in Nature,” feels qualified to disagree with Richard Lindzen, the Sloan Professor of Atmospheric Science at MIT.) The “consensus” offered in the IPCC Summary for Policymakers is not evidence, but the interpretation of evidence that’s been sanctioned by a particular body of scientists. But that doesn’t mean it’s the right one—especially if that body has been engineered to exclude or put pressure on scientists with other views.

The cancer analogy Mr. Boot offers doesn’t make much sense. When an oncologist tells you that you have cancer, you’re dealing with something that can be proven beyond a doubt—usually by looking at a biopsy sample. By contrast, the worry about global warming involves changes that are merely predicted to occur with more or less likelihood. In most cases, the predictions are based on trends whose existence can’t even be established with certainty. There’s no gold standard here; there’s only a set of assumptions and the statistical models built around them. You don’t have to be a climatologist to understand the potential pitfalls of making predictions this way.

A better analogy would be asking twenty oncologists about the odds that you’ll develop cancer at some point in the near future. It’s almost impossible to imagine that you’d get the same answer from all of them, and some of their guesses might be no better than a meteorologist’s—especially if the meteorologist has read the literature on cancer risk factors, as anyone with a basic understanding of statistics and experimental design can easily do. In fact, such a meteorologist might be able to tell you that the “consensus” of medical professionals on cancer detection and prevention often has no basis in fact. Of course, it’s cheap and easy to eat more fiber, or to do a breast self-exam (neither has been proven to reduce cancer mortality), so one might as well do these things. Cutting carbon dioxide emissions in half, by contrast, is neither cheap nor easy.

One might ask, moreover, why Mr. Boot feels that the “policy implications” of global warming are something that can be discussed without any scientific literacy. Consider his recommendation that we end sugar subsidies to make sugar-derived ethanol cheaper. What makes Mr. Boot think that burning ethanol would contribute less to climate change than burning fossil fuels? Isn’t this also a scientific question?

I certainly agree with Mr. Boot that it would be desirable for us to reduce our dependence on foreign oil, but the argument for this doesn’t have to invoke the bogeyman of climate change.

I thought that Max Boot’s analogy between the conventional wisdom on climate change and the pre-war intelligence on Iraq’s WMD’s was an apt one. But I’m not sure why he concluded from this that conservatives should abandon their skepticism about efforts to “fight” climate change by curtailing CO₂ emissions. It seems to me that one should logically draw the opposite conclusion—namely, that we ought to be wary of the “consensus” of “experts” on matters where the uncertainty is large, the stakes are high, and political pressures are at work.

In this respect, the latest IPCC Summary for Policymakers doesn’t really do much to change the picture. (These summaries have tended to offer a rather skewed representation of the actual reports they purport to summarize, as the Wall Street Journal reminds us.) The latest summary hardly even qualifies as news: it merely reiterates the “consensus” that human activity has contributed to an increase in the atmospheric levels of various greenhouse gases, and that such increases are correlated with climate change. Whereas previous IPCC reports told us that a causal relationship was simply likely, now we are told that it is almost certain. The question is, precisely what kind of causation is almost certain?

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