Toward the end of what NASA has determined the hottest year on record, a new climate change movie, “Before the Flood,” hits screens across the country, starring none other than Leonardo DiCaprio, who was named United Nations Messenger of Peace on climate change just a year before he went on to star in one of the most violent (and beautiful) films of 2015.

Leo has taken some heat of his own of late over his alleged connections to a Malaysian embezzlement scandal, but in “Before the Flood,” directed by Fisher Stevens, he plays an earnest John Doe whose beard seems to vary with the whims of the atmosphere.

Those familiar with Stevens know that the veteran character actor (of “Early Edition” and “Grand Budapest Hotel,” among dozens of others) has moved past the sidelines of the stage and screen to the center of documentary filmmaking, earning for “The Cove” an Oscar for Best Documentary Feature in 2010. In the years since, he has directed or produced three more films focused on the degradation of the environment: “Mission Blue” (2011), “Racing Extinction” (2015) and “Before the Flood” (which premiered at the Toronto International Film Festival in September).

Salon spoke with Fisher about the impetus for this latest film, DiCaprio’s pivotal role as both producer and protagonist, along with the choice to release “Before the Flood” less than two weeks before the presidential election. The conversation was edited for length.

Ten years have passed since Davis Guggenheim’s “Inconvenient Truth,” which put climate change (then “global warming”) on the mainstream map for millions of people. What has happened since to catalyze the making of “Before the Flood,” which covers similar ground?

“Inconvenient Truth” put climate change on the map in a great way.

Leo and I had both been following this issue for a while — Leo certainly longer than I, as you can see in the film — and we both were pretty frustrated in how slow things were going and why many people still just didn’t seem to take climate change seriously. With “Before the Flood,” we wanted to a) examine why this was, and b) debunk any skeptics.

Six years ago, Leo and I went deep-sea diving on a trip together to the Galapagos for my film “Mission Blue” on Dr. Sylvia Earl. Leo already had a climate change film on his mind — to be in one, rather than just narrate. At the time, I was already directing another climate change film, “Racing Extinction,” so it wasn’t really on my mind to do another documentary on this topic. It’s not an easy topic to cover; it’s depressing. But I still felt like I was banging my head against the wall to get people to understand this issue.

When Leo knew he was going to be tapped by the United Nations to be a messenger of peace on climate change, everything came together at one time. We thought, “Let’s go for it. Let’s try to make something that is really accessible to everyone, that really gets the youth energized around this issue as they’re the ones who are going to be feeling its effects more than anyone.” The time was now, so to speak.

In previous docs you produced or directed — “The Cove” and “Mission Blue,” for instance — the film tends to orbit around a heroic expert who has devoted his or her vocational life to a cause. What led you to stray from that pattern in this film?

There are so many amazing climate change documentaries, but no one sees them. A lot of people saw “Inconvenient Truth” because 2006 was a very good time for Al Gore. He had basically won the presidency, then had it snatched away from him, and no one had heard from him for several years. In that sense, we learned that a documentary needs someone for people to hold onto.

The key to making people understand this issue is making it accessible but also as entertaining as possible. I’ve filmed so many scientists all my life — I can’t even tell you how many — and it’s nice to film someone like Leo who has the quality of charisma. We wanted Leo to meet the experts and make the experts more palatable, so that everyone could understand them.

I was admittedly reticent at first to embrace Leo as the protagonist, as opposed to someone like Indian environmentalist Sunita Narain, who also shows up in your film. But Leo seems to become a kind of stand-in for the average American citizen. Unlike Al Gore, who plays the resident expert in “Inconvenient Truth,” Leo asks a lot of questions and doesn’t pretend to know everything. He’s easier to relate to, even though he’s a movie star.

Yes, that’s what we wanted. We wanted Leo to be Everyman. Obviously, he lives a very rarefied life, but in this film he plays a kind of Everyman in terms of this issue. He actually has a good effect on the experts during interviews; they want him to understand, to make it clear. And that was what ultimately most important to us — that people understand exactly why climate change exists but also why climate change denial exists. I thought he was the perfect guy, which is why I agreed to make another climate change film. Of course, once you learn about the issue, you can keep going and going and going. [Laughs]

I’ve written before about a shift in Leo’s public persona. In your film he seems to mature in his understanding of climate change at the same rate that the American population is intended to mature in terms of our own responsibility, how we each play a part in it. He seemed humbler than I’ve seen him before. My favorite part is when he meets the pope; he seems visibly nervous!

He was! Very nervous. It was important to humanize Leo, to make him seem vulnerable. And he was vulnerable; we all were. When you’re walking on ice in the Arctic you have trust people to tell you where to walk or you’re gone. When you’re in Greenland, you take a wrong step and you shoot down the rapids. When you’re in a helicopter flying over bushfires in Sumatra, it can be pretty terrifying. The fact that Leo is willing to go there and do all this — none of us made any money on this film, and certainly he didn’t — it shows that he really cares.

I found the footage on climate change from the ’50s and ’60s really entertaining, but cringeworthy as well. So many think this phenomenon is a relatively new discovery.

Yes, the oil and gas companies have really suppressed this information. The attorney general of New York is currently suing ExxonMobil for misleading its stockholders. The company knew as early as 1948 that burning fossil fuels could have a negative effect on the earth and the atmosphere and suppressed the information. The oil and gas industries have been actively trying to suppress this information forever.

The National Geographic Channel is airing the film on Oct. 30, just days before the presidential election. That it will be available to those who don’t live in big cities seem really important. Donald Trump has called climate change “bullshit” and a hoax. Is the film meant as a wake-up call right before the election?

One of our main objectives was to release this film before the election and not only did Nat Geo say they would do it, they organized over 220 university screenings before the election and are giving it away free on other platforms. Nat Geo takes climate change really seriously. I’m deeply indebted to them.

While we were making the film, it became clear that it was going to be Donald Trump, Ted Cruz or Marco Rubio for the Republican candidate and that we had to get this out. Leo and I both thought it would be Cruz or Rubio — not in our wildest dreams did we think it would be Donald Trump! [Laughs]

But in a lot of ways, Cruz and Rubio are equally as bad. But it isn’t just about the presidential election but also about the Senate and the Congress. If the Senate changes the way it looks like it might, that could really help tackle this issue. But the truth is, if a Republican is president, that person could dismantle all the good of the Paris climate accord and the EPA restrictions that President Obama has put into place.

Most importantly, if a Republican appoints another Scalia for next Supreme Court judge, there is a good chance that all of Obama’s EPA regulations would be in danger. There’s a bill now to say that the president was unconstitutional in even making carbon emission standards — which is insane. I could go on and on.

All the beauty of what has been accomplished at the Paris climate summit — which is still isn’t enough — could be dismantled if things don’t go the right way. After Obama finally in the last three years has made climate change part of his agenda, it could all go away. It could all be dismantled if Trump gets in and the Supreme Court goes back to how it was. It’s very scary.

Justice Scalia was a Roman Catholic judge, and yet his policies toward the environment and climate change didn’t jibe with what seems to be the current direction of a huge sect of Christianity on the global level. How did you determine that Leo should meet with Pope Francis, a very new symbol of environmental awareness?

Pope Francis has probably turned more of the world on to understanding climate change than anyone because he has such a huge following. We were really lucky to get him included in the film. I don’t know how many people have read his mostrecent encyclical on poverty and the environment, but it’s a beautiful piece of writing — a plea to humanity to take care of Mother Earth, to get us to understand that the poor will be affected the worst and the poor had nothing to do with it.

What’s crazy is that when the pope came to speak in front of Congress and mentioned climate change in his speech, these senators and congressmen said, “The pope should stick to what he knows. He knows nothing about climate change. He’s not a scientist. He should shut up about this.” And a lot of them were Roman Catholics, too.

Exactly. It befuddles me.

What it shows is that the guys who are voting on laws that affect the climate should also stick to what they know — and they don’t know anything and they don’t actually listen to the scientists like Pope Francis has. And 97 to 98 percent of scientists have all said the same thing. That’s the kind of stuff that makes Leo and I go crazy, and it’s another reason we had to make this film.

I was moved by a verse in “A Minute to Breathe,” sung by Trent Reznor at the end of the film: “We will all be judged by what we leave behind.” It seems this credo has been a force in your own work since you started producing and directing documentaries — a desire to reconcile the human ability to destroy the natural world with the human ability to creatively represent and restore it. As a creative person, do you feel a responsibility to not only entertain but to inform and move to action?

I was raised to believe that I do have that kind of responsibility. I always thought, if I ever become really famous, I’m going to use my fame to vocalize causes I believe in. But what it turned out to be is I’m going to make films — with or without famous people — to use what voice I have to highlight what I think is important, the unconscionable things that humans are doing to each other.

And to the planet.

Yes, when you think about the year 2050 — when my young kids will only be like 35 or 40 — there could be between 9 1/2 and 10 billion people on the planet. And then you think about how right now in China the middle class alone is almost the size of the United States. And they’re going to be another 250 to 300 million people who are trying to get to the middle class. And then you have 300 million people in India who are still without power now and are trying to get it. If we have another 3 or 4 billion people using electricity, using cars, there’s no way the planet can sustain it. We’re in a lot of trouble.

One of the most disquieting moments of your film is when Sunita Narain says, “American consumption is going to put a hole in the planet.” Leo responds by saying that he doesn’t think it’s realistic to expect American citizens to change their lifestyles. Do you agree?

Well, I agree with Sunita. [Laughs]

Leo’s playing Everyman. I like that he says that and that she shakes her head in disagreement. It’s a great moment.

I try to live a pretty low-carbon life in terms of diet. I try not to use plastic bags or take long showers. I turn off lights. But it’s not even the plastic bag itself that necessarily makes a difference; it’s the fact that I’m living with this in mind. The only thing that I do a lot of that’s bad for the planet — until they develop solar-powered planes, that is — is fly all over the world to do these movies and to get people to see these movies. But my wife and I — we do our best. I am very aware of it. If everyone was more aware of it, we can make an impact.

What’s good about what Leo said to Sunita is that, well, we try not to preach or lecture to anyone in this film. But if you look at the end credits of this film . . . you can go to carbontax.org and fill out the questionnaire and pay a voluntary carbon tax that will go to reforesting one of the rain forests in the Congo, Indonesia or the Amazon.

And everyone is encouraged to write their congressperson or senator and say, “I want a carbon tax.” What Leo and I found making the film is that the quickest way to reduce carbon emissions, the quickest way to get out of this mess, is to institute a carbon tax.

Ironically, in the Wikileaks just released, it turns out that Hillary Clinton is actually for a carbon tax, but didn’t want it to come out. I have to say, I was really psyched. It made me love Hillary even more.

“Before the Flood” opened in theaters nationwide Oct. 21.