When is a scientific debate finished? When should naysayers just be ignored? And in cases where the topic involves science-based public policy, deeply relevant to the well-being of the citizenry, when should doubters be denied the public forum of government funding and media attention?

These are interesting questions, made more complicated by the many times in the history of science when the evidence turned out to be misinterpreted or misleading. Evidence is often dependent on its observers and their techniques. Scientific observation seeks to be pure, free of influence, but it is rarely so, from the subatomic to the sociological.

For that matter, settled science is frequently disrupted, from the idea of the indivisible atom (still a fact in the living memory of those who learned all their science before 1942) to the idea that causality cannot be violated (except where it is, in the bizarre domain of quantum physics). Widely held scientific theories have later been shown to be fads or just bunk, from phrenology to the odious eugenics (the latter broadly accepted as settled science by an embarrassingly wide array of scientists and intellectuals).

Youd have to be in a deep coma not to know that global warming, more specifically the idea of imminent catastrophic human-induced global warming, is anchored in this complicated issue of settled-versus-unsettled science. The universe of books on global warming is now overwhelming in its extent, if not its opacity. Yet another entrant to this pantheon is the recently published Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming, (Bloomsbury press) by Naomi Oreskes and Erik M. Conway.

Merchants of Doubts authors take sides entirely with the contention that the science is indeed a settled fact of contemporary reality. Rather than focus on the evidence for human-induced catastrophic global warming, the book instead slogs through the entire canon of signature issues of similar science-tinged public policy challenges which have regularly created ideological divides. It gives short shrift to the substance of these issues, in favor of speculations about personalities and motives of various players who (the authors contend) successfully counter the (lefts) argument.

In the end, Merchants of Doubt is the kind of book that will persuade only those already sympathetic to its worldview. It is nonetheless instructive, although not necessarily in the ways the authors intended. That is why Merchants of Doubt is important. Fundamentally, it matters little whether or not you believe that catastrophic global warming is a valid theory, because this is not the first, nor will it be the last science-centric public policy issue we will have to deal with. Nor is global warming the primary science-centered issue the book deals with. What really matters about these kinds of debates is the paradigm of the debate itself: how we explore, engage, resolve and treat the various players in these kinds of science-centered debates.

Oreskes and Conway treat evidence as the sacrosanct foundation on which science is builtthough, in fact, much of what scientists do is try to determine what constitutes relevant or valid evidence in the first place. Consider this line from Merchants of Doubt: Research produces evidence. . . . After that point, there are no sides. There is simply accepted scientific knowledge. Or this line: While the idea of equal time makes sense in a two-party political system, it does not work for science, because science is not about opinion. It is about evidence.

Well, yes, it is about evidence, but evidence itself is the question. To explore one relevant example from the books primary concern, global warming, one must consider that there were no weather stations available to document the thousand years necessary to assemble a consistent data series of planetary temperatures. Scientists are forced to make adjustments to whatever secondary or tertiary data are available, interpreting indirect indicators such as tree rings. This is far from precise, pure, or perfect. Some of these data are decently indicative, some not.

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To muddy the waters even more, some of the recordings of temperatureand many of the interpretive adjustmentshave been demonstrably shoddy or inexplicably selective, as we learned in recent months though the widely publicized emails leaked from the East Anglia Climate Research unit (one of the few keepers of data on planetary historical temperatures). Even the most fundamental scientific evidence in the global-warming debate is far from immutably settled.

Merchants of Doubt cannot bring itself to address these aspects of global warming or, indeed, any of the other issues the authors use. What theyre interested in is influence, the process of debate about contentious issues of high import and how, they insist, it is used to subvert true science for personal and political reasons.