Every year, Al Gore pauses from his overscheduled itinerary of making a fool of himself at climate change speeches around the world to pause at the South by Southwest festival in Austin, Texas, where he drops by to make a fool of himself in front of hipsters, activists and a sizable jumble of uninterested partiers. This year, the rhetoric got harsh — as in “punish-the-deniers” harsh. While Gore was talking specifically about politicians who reject the idea that government should divert public funds to combat the effects of a changing climate, his tone toward anyone who thinks the jury’s still...