Leonardo DiCaprio says it was years ago when then-Vice President Al Gore took the time to explain to him the phenomenon of global warming and what it means for Earth.
"I was terrified, "DiCaprio said. "I think I was terrified, like anyone would be. And I didn't quite understand the connection that we had as human beings and the fact that we could literally alter our climate in that way."
Now the 32-year-old actor, whose career skyrocketed even as the on-screen Titanic sunk, is a passionate advocate for the environment and saving the planet. His documentary "The 11th Hour," set for release this week, presents an argument that says, in a nutshell, "Time is running out. You need to listen and believe it."
Like his mentor Gore in "An Inconvenient Truth," DiCaprio acts as an investigator presenting the ideas of 54 scientists and analysts.
One of them says, "Not only is it the 11th hour, it's 11:59 and 59 seconds."
Another, Kenny Ausubel, founder of the Bioneers Network, says in the documentary, "No civilization that has exceeded its ecological limits has ever recovered from that."
"What is it, over 90 percent of the scientific community has a consensus that mankind does have an impact on our climate? I tend to side with them," DiCaprio said.
His narration follows the development of civilization from mere subsistence to a crowded world upon which humans burn millions of years' worth of stored coal and oil, changing the environment that sustains life. The documentary tracks how human beings have dramatically altered nature, leading to the extinction of thousands of species while changing patterns of weather and heating Earth's atmosphere.
DiCaprio is careful not to present himself as an environmental expert. "There's a certain stigma with people in Hollywood trying to become experts on the subject," he said.
He tries to lead by example. He drives a hybrid car and has built a house with all the bells and whistles of green technology. "Solar panels and everything," he said. "It's insulated in the proper ways. I've got clean air, clean water. It's very complicated stuff, but it's green."
Paper or plastic? "Paper, of course," he said.
Before the interview with DiCaprio, "Nightline" solicited viewer questions for ask the movie star. Outside of marriage proposals, they narrowed down to a few themes.
One man from Los Angeles asked, "How do poorer families and households that don't have much money — how do they go green?"
"Well, of course, buying energy-efficient appliances is one thing," DiCaprio replied. "Changing your light bulbs to energy-efficient light bulbs, trying to get a car that gets better gas mileage, keeping your tires properly inflated.There's a million different things you could do."
Several viewers asked about the use of private jets in the entertainment industry and how DiCaprio can consider himself environmentally responsible flying solo in private. He's been asked the question before and said in response, "There are situations within my industry where I have to get to someplace during a time frame where it's impossible to fly commercial. Otherwise, I demand that I do fly commercial. Not to mention the fact that if there were a hybrid private plane, I would be on it."