Directed by Robert Kenner and based on the book by Naomi Oreskes and Erik M. Conway, the film exposes how individuals purporting to express informed opinion are often financially tied to companies seeking to instill doubt about scientific evidence, such doubt meant to thwart regulation of harmful practices.

The film is visually clever, starting with demonstrations of sleight-of-hand card tricks to emphasize the deceptiveness with which the so-called merchants of doubt operate. We see how long a time representatives of cigarette manufacturers insisted that smoking did not cause cancer.

The more recent issue is global warming. Responsible scientific opinion overwhelmingly points to danger to our planet. The professional doubt-manufacturers attack on two fronts. First, they create doubt about the scientific findings. They also attack the concept that whatever danger there may be is man-made and not just forces of nature.

There are clips revealing the messengers and the tactics, as well as counter-attacks by those who believe the methods need to be exposed and the public mobilized against them. One key figure is Bob Inglis, a conservative who lost is red state South Carolina congressional seat in an election after he began taking a position against global warming. He is a very articulate spokesman for the need to help preserve the environment.