When New York–based filmmaker Fisher Stevens came down with mercury poisoning in 2006 he was baffled. “My doctor said I had incredibly high counts of mercury, and it was all from the pollution in fish,” the 36-year-old filmmaker says of the incident that prompted him to produce his award-winning film, The Cove in 2008, which chronicles the unlawful capture and slaughter of dolphins. Since then, Fisher has devoted his career to humanitarian-minded films, his most recent one being Before the Flood, a call-to-action documentary that follows Leonardo DiCaprio as he visits over 10 different countries to explore the catastrophic ramifications of global warming. (The film's original working title: Are We Fucked?)

Shot over a course of three years, Before the Flood, which opens today, features DiCaprio in his alternate career as a United Nations Messenger of Peace, a position that has come under fire lately. From deforested palm oil plantations in Indonesia to crumbling glaciers in Greenland, the actor confronts the realities of global warming. “Unless you see it and experience it, you don’t really feel it, and nothing gets done,” Stevens explains. “I tried to make a movie where people would feel like they’re experiencing something, and see the devastation we’ve already done.”

The film features interviews with an impressive array of personalities, from President Obama, to Pope Francis, to Elon Musk, and concludes with an interview with NASA scientist Peter Sellers, who admits that despite the damage, our planet is in fact fixable if we act now. Here, the director talks about his most shocking realizations, and near death experiences he and DiCaprio had while filming.

There’s this terrifying scene when you’re in the helicopter with Leo flying over the fracking fields. We see the massive deforestation and depleting ice sheets. Leo says that we’re past the point where changing to a halogen light bulb or taking shorter showers make a difference. It’s now so much bigger than that.Yes, it was mind-blowingly bad to see tar sands, palm oil plantations and melting glaciers. to see what we’re doing to that part of the world. It’s definitely intense and puts a weight on your shoulders when you’re filming, but what’s interesting is that climate change is all done by man. We created it so we can get ourselves out of it. That was my only saving grace, that is what kept me going.

The end of the film was very clear about that, when NASA's Peter Sellers explained that the situation is in fact salvageable.He gives us hope. Leo was pessimistic and I was much more optimistic, which I think was the ying and yang to the film. He came at it with such a negative and dark side. At the end it leveled out a bit: I got a little beaten down and he got more optimistic after securing Obama, the Pope, and Elon Musk, who spoke about all the technologies that could help repair the earth. So it was a great balance, I think.

The cast of characters you interviewed was truly incredible.You should see who’s on the cutting room floor... I want to do something more with it. We have great interviews with people. I certainly had nothing to do with securing the interviewing. The beauty of Leonardo is he has amazing access. He’s got that kind of power which made my life easier as a director. And there were so many more people. We had to get this film out before this presidential election. If there wasn’t the election we probably would have been shooting another year or two. Also, the climate is changing so fast, we had to get it out.

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There’s definitely an urgency. The footage was so harrowing.That was the idea. We were very ambitious and we really wanted to cover everything. The main goal was to make it basic and make young people understand the urgency of this issue — make it clear, entertaining, and something you want to pay attention to. We made an effort not to preach, but let people discover through Leo’s eyes what’s going on.

How did you end up connecting with Leo for this project?Six years ago I was filming Dr. Silvia Earl as she took a hundred people to the Galapagos Islands on a boat to teach them about the oceans. I was filming her and Leo was on the trip. We had been in touch since The Cove, but we reconnected and dove together. He actually started filming for me at one point. We were on a dive and he took one of my cameras down with him, and he ended up following a school of sting rays with Silvia and Edward Norton. He ran out of air and Edward Norton actually had to save him and give him oxygen. It was a great trip.

He saw my other film, Mission Blue, and called me up and said, “I want to make a climate change doc I’d be in.” If anyone could bring attention to this issue it’s Leo. He’s been doing this for 20 years, he knows so much. So we set off three years ago to do this and it’s been a trip. We finished a month ago. The subject is so big and broad, it’s daunting.

What were the most harrowing experiences?We had a couple of incidents in helicopters. A bad one was when we were in Indonesia flying over the palm oil planation, and the combination between the smog and clouds. We got into the middle of a mountain range and you could barely see anything; Leo was freaking out, I thought for sure we were screwed. The arctic was also crazy. There were moments that if we stepped in the wrong spot the water would go up to your crotch and it was freezing cold. And a lot of times if you took one foot this way or that, it was good night.

What was the craziest site to see in terms of realizing the amount of pollution?India was intense. In New Delhi, the pollution was unbelievably shocking. It’s normal for people there, but when you arrive… Wow. Also, when we were in Greenland on the glaciers, and Leo asks “What’s this hose?” and the researcher says this 30 foot rubber cord was underground, buried in ice just five years ago, which means they’ve had at least 30 feet of melt. That freaked us out.

You’ve done plays, acting, what prompted you to get into humanitarian work?I got mercury poisoning. I was eating fish and I started feeling strange. I went to the doctor, and he said I had incredible high counts of Mercury, and it was all from the pollution in fish. Then I met Louie Psihoyos [the director of The Cove], who had mercury poisoning, too. Once I started The Cove it was over. I started filming for the UN. The more you know the more you feel you have to do something. I’m sure it will continue since we’re still so far from being done.

So it all started with mercury poising?And scuba diving. I’m a scuba diver. And I went back 20 years later to the same reef, and they were totally dead. I was like, "We have to do something about this." That’s the problem with climate change, unless you experience it, you don’t really feel it and nothing gets done. I tried to make a movie where people would feel like they’re experiencing something. I see the devastation we’ve already done.

Lastly, I need to know who’s on your cutting room floor.Let’s just say there’s going to be a sequel of some sort.