A Green "Truth"

For the past 20 years, former Vice President Al Gore has been traveling the world speaking about global warming, a passion of his since college. In 2006, his lecture was made into the documentary An Inconvenient Truth. Now available on DVD, this is the third-highest-grossing documentary of all time.

In his lectures, book and documentary, Gore explains that if we continue to ignore what we are doing to our planet, we risk destroying the very future of our civilization. And the former vice president says that we must act before it's too late.

"Some of the leading scientists are now saying we may have as little as 10 years before we cross a kind of point of no return, beyond which it's much more difficult to save the habitability of the planet in the future," Gore says.

"I believe that everybody should see [An Inconvenient Truth]," Oprah says.