On a spring day in New York, Before the Flood director Fisher Stevens stands outside in the 90-degree heat, perturbed about the ever-worsening state of the environment and America’s contribution to the problem. Stevens doesn’t know that within two weeks, President Donald Trump will withdraw the United States from the Paris climate accord, though listening to the director speak, it seems this development would not surprise him.

Teaming with Leonardo DiCaprio on the climate change doc from NatGeo—which premiered at the Toronto Film Festival last fall—Stevens saw environmental devastation firsthand, leveraging DiCaprio’s movie star status to gain access to subjects including Former POTUS Barack Obama and Pope Francis, influential players in the fight for climate change awareness. Below, the documentarian discusses the origins of his environmental consciousness and the way in which DiCaprio’s film The Revenant came into the fold of the documentary.

You’ve had a long, successful career as an actor. Stepping outside of that, your directorial efforts have mostly come in documentary form. What drives you, as an artist, to participate in this arena?

I’ve always been trying to do social activism since I was a kid. I remember my mother taking me to pass out anti-Vietnam War flyers when I was four years old, so I was raised in that kind of world.

There was something about working on documentaries, where you could mix activism and filmmaking, that I got really excited about. One of the reasons I love to act is I love to become other people and learn about other worlds. When you play a character, one of the things you get to do, which is cool, is hang out with people in a whole different walk of life, and learn about their life.

What’s cool about documentaries is you get to do that on hyper-speed. It just opened all these worlds for me. The first time I got involved in the documentary, even though it wasn’t activism, I just thought, “Wow, I love this form.”

Being an actor helped me because I would try to get into everybody I’m interviewing. When I would edit a film as a producer or director, I would always think about a performance as you interview. There’s a performance, and your characters are characters, like in a feature. I think that’s why I love it, and that’s kind of how I approach making docs.

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How long has climate change been a major point of concern for you? Was there an inciting incident that spurred you to take the issue on in documentary form?

I’ve always been about protecting the planet, but I didn’t understand what was happening until I met this guy named Jim Clark. Jim Clark was one of the creators of Netscape, and there was a book by Michael Lewis about him called The New New Thing. He was a professor before he was a billionaire, and he’s a brilliant guy.

I got to be friends with him through scuba diving, and he basically explained to me what CO2 was, and coral bleaching, and how we’re putting too much of this stuff into the air. This is back in like 2006, and he would explain to me how we have to take care of the planet.

He also got me involved in The Cove—he was financing the movie, and I got involved very heavily with [director] Louie Psihoyos. Ironically, I had also had mercury poisoning due to the amount of seafood I was eating.

All this got me very involved, and when I worked on The Cove, I started learning more and more about what was going on. Once you know, you want to try and do something about it. The Cove was more to me than dolphin slaughter; it was about protecting animals and protecting ourselves.

When I got involved in The Cove, there was a whole section on mercury poisoning, which was just a tiny moment in the movie, but we ended up doing a whole 30-minute DVD extra just about that.

I love scuba diving, and anyone who loves diving knows how incredible it is down there. But also, you can really see the degradation pretty clearly in many places.

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Then, Leo [DiCaprio] and I were on this trip together to the Galápagos in 2010. I was filming Dr. Sylvia Earle, a great marine biologist, and making a film about her. Leo and I scuba dived together, and we knew each other through acting a little bit. I’d never worked with him, but we’d see each other around a little bit. But that trip, I was kind of blown away by his knowledge of the environment, and climate change, and species.

We stayed in touched, and then he saw the finished film called Mission Blue, that I did for Netflix. He called me up and asked me if I wanted to work with him on another climate change doc. I had been at that time working on yet another climate change doc, called Racing Extinction.

So it was really the last thing I wanted to do, to be honest with you, to do another one. But I also had a feeling that if Leo was going to be in a film about this subject, that would get the biggest audience possible. We made a deal that if I worked on it, he would be in it. He told me that he was going to be named Messenger of Peace for climate change from the UN, and I said, “Well let’s make that the beginning of the film.”

So we had the beginning, but we still didn’t know exactly what we were going to do. We knew there were certain issues we wanted to tackle, and we knew we wanted to make a film, not for the converted, not for people who go and watch climate change movies, but for people that ordinarily wouldn’t give a s—t about climate change, or even think about it. That was our dream.

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Was Leonardo’s status as a global movie star instrumental in securing access to figures like President Obama and the Pope?

Yeah, for sure. We wanted President Obama because we knew that he was going to really push the Paris Climate Agreement, and we knew that in the last three years of his administration, he had really pushed climate change, and made it part of his agenda.

It was kind of funny because we don’t have any talking heads in this film. It’s all vérité and Leo.

When we called the White House, I basically said, “Guys, we don’t want to do a sit-down interview. We want to do a walk and talk.” And they were like, “What?” I had to come in a day early and walk it through.

It was pretty fun. It was cool, but at the same time, because of who he was, yes, we did have amazing access. Very few people turned us down. The Koch brothers, we tried to get them, but we were pretty lucky.

But we also shot a lot of people that we couldn’t fit it in [to the doc]. Creating a storyline about such a big subject is never easy. It took a long time to craft it, and it’s a huge subject.

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Can you expand on the nature of your collaboration with DiCaprio?

We really were collaborators on the film, and we had amazing editors. Mark Monroe wrote it with us, and [producer] Trevor Davidoski helped. It was a great team, but I would say that Leo definitely trusted us and me because he is a very private person, and I don’t think he’s ever said lines in any film that weren’t written for him, where he wasn’t playing some other character.

He really dove in. We went to some crazy places together, and he came into the editing room quite a bit. We definitely debated what to keep, and what not to keep at times. It was a really healthy working relationship. We pushed each other, and he was all in.

In one fascinating segment of the doc, you go to the set of The Revenant—the film that won DiCaprio his first Oscar—which played perfectly into the subject at hand. As we see in the doc, director Alejandro González Iñárritu had to move production to Argentina at one point to chase the snow.

Yeah, he was shooting The Revenant for over a year. Originally, the tie-in was more that [the film covered] the beginning of the Industrial Revolution, when we started to put carbon into the air. I thought also it was cool to see Leo doing two things at once because that was the real deal. He really was working on both films. So we followed him.

There were more scenes we shot on location with him, but then when they had to shut down and move to Argentina, that was just like, “Oh my god”. It was unlucky for their film, but it worked for us. Alejandro was great—he’s really into the environment, and it was great to have him involved. He was totally open with it, even though he was stressing out at that time, obviously. He had to move halfway around the world.

I think Leo was very hesitant at first to let us do that, but then he got into it. Like I said, he was very trustworthy, and I’m grateful. I think it’s one of the reasons that the film worked, is because we had each other’s back and looked out for each other. It was just a weird coincidence.

I mean, I’m in New York today. It’s 90 degrees on May 18th. So it’s going down. It’s really bizarre what’s happening. Why we’re even having debates about this is just crazy to both of us.

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What would you say to those leaders in government who continue to deny the reality of climate change?

It’s so devastating, what’s happened, and it’s not just Trump. You can say Trump, you can say Jeff [Sessions], the Attorney General, you could say [EPA Administrator] Scott Pruitt. It is the people that Trump put into place. It’s all of them.

Our Secretary of State has had one job prior, and that’s to work for ExxonMobil. Our Attorney General tried to dismantle the EPA, our Secretary of Energy [Rick Perry] ran for president, couldn’t even remember the name of the Energy Department, and wanted to get rid of it.

It’s like the cast of Batman‘s villains in power right now, in terms of the environment. All I can say is it seems like the house of cards is tumbling, and I feel like people are waking up and going, “Oh my god, this guy wants to deregulate what goes into the air, and what goes into the water? Are you kidding me? What my kids are drinking, the air my kids are breathing?”

Thank god [Senators] John McCain and Lindsey Graham and Susan Collins voted to keep the methane laws as they are, and not deregulate. Thank god for those three sensible Republicans—I applaud them going against the rest of their party. We need more patriots like that to stand up.

All I can tell you is it’s tragic. You see the movie now, and it’s dark—it’s a dark movie because of where we’re at. The Koch brothers control the Congress, and the Koch brothers control one of the largest energy companies in the world, and it’s a tragedy.

We’ll see. I just hope that the American people keep standing up. We can’t let this madness occur, but everyday the environment’s taking a backseat to this other madness.

When we made this movie, I would have never, ever thought we’d be in this situation. It’s crazy, what’s going on right now.

You see, we can green the energy and grow the economy—it’s been proven. Look at the jobs green energy has created in the state of California. We can do that everywhere. Coal kills: that’s the bottom line, and we don’t need it anymore.