I have just watched An Inconvenient Truth, dunno if that can be considered a movie, anyway, I thought it was really good. The only other movie on global warming I remember was The Day After Tomorrow, and it was really bad. This one, though, actually included a lot of scientific stuff which I, so far, had only read in books (I'm a bit of a global warming junkie). So if you are into that kind of stuff, I really recommend watching An Inconvenient Truth. I have pretty much read a lot on what was said in there, just brought to the screen.
I didn't exactly understand who this Al Gore guy was, though, a former president or something or what? I'm really not into politics, the only political event that I have ever noticed is the Ukrainian Orange "Revolution"...