You can read the 2018 IPCC report or you can watch Leonardo DiCaprio’s dry, portentous narration of “Ice on Fire,” superbly scripted and unfolded by Leila Conners. Or you should do both. The formal report encapsulates the most formidable, global scientific enterprise the world has ever known, iterated over thirty years. The documentary puts flesh onto the horrifying downsides and the obstacles ahead, while offering encouragement through stories of technologies and ventures that can, right now, reduce carbon emissions or mitigate consequences of climate change. Cycling round dozens of persuasive scientists and commentators, focusing (per the title) on ice melt and water rise, and including brilliant cinematography, “Ice on Fire” treads a fine line between frightening and reassuring, and it does it so well. Go see this.