In Toronto, Leonardo DiCaprio delivers ‘Before the Flood,’ a documentary rallying cry about climate change

About six years ago, Leonardo DiCaprio and the actor-director Fisher Stevens found themselves on a TED-sponsored trip to the Galapagos Islands.

The two had known each other from L.A. pickup basketball games, but they soon were down to more serious matters: the dangers facing the environment. And then, shortly after, to graver affairs still: What if they made a movie about those dangers?

“I thought, ‘Oh great. Now Leo is all excited and we have to make this movie,’” said Stevens, a producer on the environmental documentary “The Cove” and a generally wry presence. “But it was clear this guy has been feeling it in his gut for a long time. I was blown away with how much he knew. I thought, ‘We really could have something here.’”

This past weekend at the Toronto International Film Festival, those conversations amid the marine iguanas and sea snakes reached their culmination. “Before the Flood” (directed by Stevens and starring DiCaprio) is a documentary that offers a look, via some of the world’s most famous names, at the threats posed by climate change — a more modern, globetrotting “An Inconvenient Truth.” The film played to a hooting audience more befitting a “Titanic” premiere than an exploration of the dangers of greenhouse gas emissions.

“The origins of wanting to do this movie is to give the scientific community out there a voice,” DiCaprio said before the screening, to more cheers in the packed house, at the city’s giant and august Princess of Wales Theater. “Because we have ignored the predictions of the scientific community for way too long.”

“Flood” follows the Oscar winner, in various stages of facial growth, on a kind of tour of global environmental hot spots. He goes from the Canadian Arctic to Indonesian forests to melting portions of Greenland to the homes of American scientists and economists and back to the Canadian tundra. So called climate change deniers, including Sen. James Inhofe (R.-Okla. are given air time, then debunked. On-set scenes of “The Revenant” figure in too; that movie’s themes about harsh natural conditions, shot in Alberta, Canada, fit in easily with the ideas in this film.

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(“Flood,” incidentally, also benefited from the guidance of Martin Scorsese, who executive produced and offered some key notes, including adding more of the deniers and opening on a more swelling note involving a painting that hung over DiCaprio’s crib as a child.)

Though much of the science explained in the film will be well known to the many who follow such issues, telling details are nestled within: the destructive effect of raising cows for beef given the methane they release, for instance, or the way that fully 99% of the Sumatran forest has been destroyed in the bid to harvest cheap palm oil for processed snack foods.

What could seem lecture-y or ponderous becomes a lighter, more watchable affair thanks to DiCaprio. In addition to the many scientists he interviews — he serves as a kind of audience surrogate--”Flood” also features scenes of the “Wolf of Wall Street” star talking to the likes of Secretary of State John F. Kerry, President Obama and Pope Francis (even if the film is hampered by the crew receiving only a small percentage of the video shot by the Vatican during the meeting).

“There have been a lot of great climate docs, but they’ve been heady,” said Stevens, also a well-known character actor in a host of TV series and films. (See if you can spot him in “The Night Of.”) . “We wanted to do something different — something palatable and entertaining. Not anti-intellectual, just accessible.”

Financed by the documentary division of Brett Ratner’s Ratpac, “Flood” will air on TV’s National Geographic Channel in the U.S. and around the world at the end of October. The timing is not accidental: With the U.S. election approaching, filmmakers want to motivate votes for green candidates up and down the ticket. (There will be a small theatrical run as well.)

Like many such films, “Flood” aims to start a movement as much as attract an audience, and the end-credits are preceded by calls to action on such issues as a carbon tax.

“I know it’s not the most exciting thing to see in a movie — get out, make a difference, that kind of thing” Stevens said. “But if you infuse it with emotion — that if we don’t change, then the world as we know it will become a much darker place — I think people begin to understand.”

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The director admitted that prevailing on DiCaprio to focus on prospects for change as much as current bleakness was a challenge. “I’m more optimistic, and Leo’s more pessimistic,” he said. “But I think that combination worked well.”

One model for all this, of course, is “Inconvenient Truth,” which more than a decade ago was widely seen and, in the process, altered popular perception. Then again, Davis Guggenheim’s Al Gore-centric film came at much earlier moment in our understanding of climate change — audiences informed or jaded now were still learning then. And it came at a much earlier point in the development of environmental films; the last decade has seen dozens.

Still, filmmakers see reasons why this movie is different.

“You have the most global issue in the world with one of the most famous movie stars in the world and one of the biggest networks in the world,” Ratner said in an interview. “I think it’s all lined up nicely.” Indeed, National Geographic has local channels in more than 170 countries and a massive social media presence. DiCaprio, meanwhile, will help test the notion of whether a star’s fan base is so devoted it will follow him even to places it normally wouldn’t go.

“Flood” was set to end with a street speech DiCaprio was to give at a rally outside talks on the Paris Agreement on climate change late last year. However, that event was canceled in the wake of terrorist attacks in Paris. The filmmakers then pivoted and arranged a speech at the United Nations, where DiCaprio talked about the grave threats before a bevy of world diplomats, offering a kind of rallying-cry end to the film. The moment epitomizes the hybrid quality — Hollywood meets wonkiness — of “Flood” itself.

“It’s almost this insane science fiction film playing out before our very eyes, and we’re the root cause,” DiCaprio said in Toronto. “I don’t want to look back in 20 or 30 years and say I didn’t do anything.”

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