Years uses celebrities differently, as proxies for the viewer—they’re educated about climate change along with the audience. Shows like Vice, which airs on HBO, have built a brand out of choosing correspondents with public appeal rather than subject-matter expertise. As have other climate-change documentaries, like the Leonardo DiCaprio-narrated film, The 11th Hour, which, despite its splashy headliner, received critical acclaim but a middling audience. Unlike DiCaprio, who acted as a climate-change expert in the film—at one point professing, literally, from a mountaintop—Olivia Munn’s growing knowledge on the subject in theory makes her more relatable, a hidden journalist for a generation wary of reporters. But inserting celebrities into Years also fundamentally changes the mechanism of storytelling. When Ian Somerhalder, the actor from The Vampire Diaries, shot a scene at a North Carolina coal rally, half the picketers were young girls who’d shown up to see the tween star. Indonesia’s forestry minister told the press that Harrison Ford should be deported, after a particularly challenging interview where the actor went at him “tougher than any journalist would’ve had the nerve to,” said Solly Granatstein, the co-executive producer who filmed the shoot.

The hope is that the celebrities on Years will make the subject of climate change more interesting by their interest in it, so the producers have made a habit of courting celebrities whose fan bases might not otherwise watch a film on global warming. (“Do you know who Ian Somerhalder is?” Gelber asked me over lunch. “He’s very popular with young people.” When I shook my head no, he looked crushed.) Gelber believes that applying the 60 Minutes model of storytelling—compelling characters with uncertain outcomes—is enough to make the subject take root. He also believes covering it is an ethical imperative, comparing the situation to Peter Jennings’ insistence on covering Bosnia at CBS ABC, though the story placed low on viewer surveys. “If there’s a genocide happening in the world, how can you not cover it?” Gelber said. “It’s a self-fulfilling assumption; if you don’t tell the story, you signal that it’s unimportant. I’ve always felt that climate change is where the civil rights movement was in 1957. We’re really just starting to pick up steam.”

But there are limits to the reach of any one film. By the fall of 2008, when the film had been released on DVD, 17 percent of the American public had seen An Inconvenient Truth, mostly high-income liberals, which Yale’s Anthony Leiserowitz called “stunning for a documentary.” Still, that means 83 percent of the population didn’t see the movie. Leiserowitz said the most influential movie about climate change is the 2004 doomsday thriller, The Day After Tomorrow. “The movie took some artistic license with the science, but the public reaction was gigantic compared to An Inconvenient Truth,” he said. According to surveys after the film, “the 30 million people who saw it were overwhelmingly influenced; they were convinced that climate change was happening and that humans were causing it.”

When I asked Leiserowitz if he thought Years could influence public perception of climate change, he was skeptical. “It will play an important role in that if it’s told well and told accurately it will reach the people it reaches,” he said. “But that’s certainly not going to be the majority of the American public. It’s gotta be the right movie, told really well, at the right moment when the culture is ready to hear it. An Inconvenient Truth just got really lucky.”

In late September, 100 people gathered at Thalassa, a lavish Indian restaurant in Manhattan, where Gelber was scheduled to screen a rough cut from the documentary during a dinner hosted by the Environmental Defense Fund, whose board had provided some of the documentary’s funders. The night before, Gelber had been up late tinkering with the segment he was scheduled to screen, but mingling over baklava and bite-sized brownies he was avuncular and pleasantly self-deprecating. “I haven’t worn a tie since my bar mitzvah,” he joked to a group of Climate Corps fellows who were profiled in the segment, “I think it’s the same one.” He told the joke four more times throughout the evening.

While attendees puttered around dessert, Gelber screened his trailer. There was a round of applause, punctuated by whispers of approval. “Why isn’t this on HBO?” muttered Nick Nicholas, the former chairman of HBO.

When Gelber asked for questions, Nicholas had one. “David, on Showtime, you get maybe 15 million households—so 90 percent of the households in the US do not have access to Showtime. You’re a CBS veteran; they have access to all of the households. Do you have the right to take this national?”

Alexis Sobel Fitts is a senior writer at CJR. Follow her on Twitter at @fittsofalexis.