It’s hard to think of a documentary that was more effective in getting viewers to at least think about altering their behavior than Robert Kenner’s Food, Inc. If you walked out and didn’t change your grocery-shopping habits or scan a food label, then you must have fallen asleep during the movie. But Kenner’s follow-up, Merchants of Doubt, would seem to face a challenge in the “call to action” department. Here, Kenner deals with climate change, an urgent issue that requires not simply single actions but massive social and economic change to conquer. Climate change, however, is the film’s broad focus. […]