Back around 2003, three years before An Inconvenient Truth, Harvard geoscientist and historian of science Naomi Oreskes asked a question about climate change. Whenever it was publicly discussed, some politician or “expert” invariably materialized, claiming there was no “scientific consensus” on the subject—was that true? After reviewing 928 abstracts published in peer-reviewed journals between 1993 and 2003 with the keywords “climate change,” she got her answer. Not only was there a consensus, but it was unanimous.

Her next question: Who are these “experts” claiming otherwise? That investigation led Oreskes and her colleague Erik M. Conway (a historian with NASA) to their 2010 book Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming. That, in turn, became the basis for this ruckus of a documentary about a handful of ideologically driven scientists (particularly two Cold War-era bomb and rocket experts) and professional dissemblers who have made lucrative careers from sowing doubt about truths that are not just inconvenient but fatal—and could cost a very small number of people a great deal of wealth.

Merchants of Doubt is a chilling but enthralling anatomy lesson in uncertainty campaigns that have been waged since the 1950s to battle bad news—about tobacco, pesticides, pharmaceuticals, toxic flame retardants that don’t really work—with the same tactics: deflect, manufacture confusion, create false controversy, attack the messenger, appeal to people’s sense of “freedom.” Uncertainty campaigns can stall change for decades: It took 50 years for the facts to catch up with the tobacco industry, which made its famous payout in 1998. But when it comes to climate change, Oreskes points out, we don’t have 50 years to spare.

Director Robert Kenner introduces us to a legion of rich characters: scientists, journalists, popular magician and debunker Jamay Ian Swiss. But his best scores are interviews with the doubt peddlers, who range from shamelessly unctuous to stubbornly belligerent. The most heartrending portraits are of former climate-change skeptics who changed their minds after studying the research, but couldn’t convince their friends and colleagues. Congressman Bob Inglis (R-South Carolina), for example, lost his seat after trying to explain what he’d learned on the House Committee on Science. “The reason we need the science to be wrong is that otherwise we see that we need to change,” he says toward the close of Merchants. "That’s a really hard pill to swallow.” People, he says, will do almost anything to repel the notion that the most basic notions about the way they live their lives are wrong.

But Inglis—along with Kenner, Oreskes, and Conway—is trying to convince us that there’s a real battle going on for the public’s attention. On one side, we have scientists; on the other, we have advertising agencies. Who, the film asks, are you going to believe?