Given Oliver Stone’s track record of diving into political controversies with his work (“Platoon,” “JFK,” “Snowden”), it is perhaps surprising how staid his approach is to his new documentary, “Nuclear Now.” All the more surprising is that the film’s measured tone is what lends it its visceral power. With his straightforward proposal — that nuclear energy has been the solution to climate change all along — Stone looks past politics, providing an antidote to the climate domerism that many viewers have probably felt over the last several years. The film, a vital rejoiner to the 2006 documentary “An Inconvenient Truth,” considers both the past and future of nuclear power and, by laying out the simple facts of the ever-worsening state of climate change, makes a compelling case for it as the energy source that can most reasonably and realistically help us face the crisis. Stone, who wrote the film with Joshua Goldstein and narrates it, knows the perceptions he’s up against. The documentary’s first half wrestles with the enduring fear that nuclear boosters have struggled to debunk — the result of a few snowballing factors, the film argues, including the association of nuclear power with nuclear warfare and the exceptional disasters that occurred in 1986 at the Chernobyl Nuclear Power Plant, and in 20 11 at the Fukushima Daiichi Nuclear Power Station. The latter sections, concerning the innovations and obstacles to future applications of nuclear power, veer somewhat into the weeds. But the film’s aversion to formal or rhetorical bombast as it discusses scientists’ hopes for a better future is its own balm . We’re staring down catastrophe, Stone explains matter-of-factly, but our greatest tool is already in our grasp. Nuclear NowNot rated. Running time: 1 hour 45 minutes. In theaters.