Moviegoers should be aware that "Merchants of Doubt," a documentary about spin doctors and opinion pushers, has an agenda of its own. It isn't hidden, exactly, but it surfaces fully only near the film's end. The movie presents a forceful and compelling argument, but a little more honesty upfront would have been nice.

Inspired by a book by science historians Naomi Oreskes of Harvard and Erik M. Conway of the California Institute of Technology, "Merchants of Doubt" presents a parade of well-dressed talk-show guests and pseudo-experts who are, in fact, paid by corporations with vested interests. This is something many of us suspected, but it's still a little shocking to be proven right. What's more, director Robert Kenner makes a convincing case that it was the tobacco industry, threatened by damning medical studies during the 1950s, that wrote the modern bible of black-op public relations.

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The film is framed by magician Jamy Ian Swiss, who introduces us to trade terminology like misdirection and distraction; Kenner then presents us with the real-world analogues. For example: As concerns grew over house fires caused by cigarettes, the tobacco industry shifted the blame to furniture makers. As a result, an entirely different industry -- flame-retardant producers -- began pushing to make its products mandatory in couches, cribs and pajamas. Speaking before legislators, Dr. David Heimbach, a surgeon representing Citizens for Fire Safety, told harrowing stories about the badly burned babies he had treated. It turned out that his advocacy group consisted of the world's largest retardant-producing manufacturers. And the babies described by Heimbach never even existed.

"Merchants of Doubt" shows that similar tactics are used to discredit scientific studies on man-made climate change. The George C. Marshall Institute, a think tank with a history of ties to the oil industry, comes off looking bad, as does the Cato Institute, whose book attacking climate change is mocked up to look virtually indistinguishable from the official U.S. government report.

Right about here, "Merchants of Doubt" lays out its cards. This compelling and detailed history of disinformation is also a direct plea to join the climate-change believers, and it even closes with a song from a U2 sound-alike. Misdirection can come from anywhere.