After Al Gore lost his bid for president in 2000, he returned home to chart a new course for his life. A longtime advocate for the environment, Gore developed a slide show about the threat posed by global warming, and took it on the road. Over the last six years, he has presented the show more than 1,000 times around the world.

In hopes of reaching a wider audience, Gore joined filmmakers to turn the lecture into a documentary film that opened in New York and Los Angeles May 24 and will be shown in theaters across the United States in early June.

The movie is called An Inconvenient Truth  and -- like the slide show, it opens with Al Gore at center stage. "I am Al Gore. I used to be the next president of the United States of America."  It doesn't take long for him to get serious. Over scenes of crumbling glaciers and rising water he says global warming exists and is putting the planet in grave danger.  "The arctic is experiencing faster melting. If this were to go, sea level worldwide would go up 20 feet (6 meters)."

Then there is a close up of Shanghai, Calcutta and the World Trade Center Memorial in New York. "That would be under water he says. Think of the impact of a couple hundred thousand refugees and then imagine 100 million."

Al Gore knows his stuff. Decades ago, he wrote a best-selling book about the effects of global warming, and as Vice President, he helped negotiate the Kyoto Protocol on Climate Change, the global treaty that the U.S. signed but never ratified.

An Inconvenient Truth deploys computer simulations, graphics, charts, facts and predictions to tell its story. "It's all about the truth of the situation we are facing now," he says. "We have quadrupled the population of the planet in less than a century. Our technologies are a thousand times more powerful. And, now all of a sudden, we are capable of doing damage to our only home, and we have to quickly grasp the danger that this creates."

The movie makes the case for reducing heat-trapping carbon dioxide emissions that have been linked to severe storms, melting ice caps, rising sea levels and the spread of infectious disease.

But Fred Smith does not buy the message. He heads the Competitive Enterprise Institute, a policy forum that opposes mandatory curbs on CO2 emissions, and favors a free market approach to environmental issues. Smith says Gore's views -- and the movie that represents them -- are alarmist. "It's a sales attempt. It is not an attempt to be an objective science, explaining on the one hand this and on the other hand that. Gore is saying that everything is going to hell in a hand basket. Listen to me or else the world you live in will cease to exist." Smith calls the movie a fear-mongering lecture. "Is it effective? To me it wasn't effective."

The Competitive Enterprise Institute broadcast television ads timed to coincide with the release of An Inconvenient Truth. They question the impact of global warming and the politics of dealing with it. "Why are they trying to scare us?" one asks.

Al Gore says the images in An Inconvenient Truth are a wake up call. The movie, he says, strips away politics and ideology to direct the audience to face a planetary emergency. "This is a moral issue, an ethical issue and in the highest sense it really is a spiritual issue," he says. "We have to tear the mask away. Labeling this a political issue is just another way of saying that it is insignificant. This is the most crucial challenge that any of us have ever faced, and it's happening in our lifetimes."

Getting that message out is why Davis Guggenheim signed on to direct the film. He hopes An Inconvenient Truth becomes a catalyst for change. "I would love people at the end of this movie to say, 'Controversy over. This is real. We are causing it and it's urgent. And if we don't do something right now, we will change things forever.'"

Guggenheim says in An Inconvenient Truth, Al Gore is not asking for a vote for political office, he is asking for a vote for the planet.