Inconvenient, but how true?

National Geographic News has a good article on Al Gore's film "An Inconvenient Truth." The earth scientist who reviews it, Eric Steig, is a believer in human-caused global warming. He thinks the science is mostly correct but finds the film guilty of some exaggerations and questionable cause-and-effect claims. It does harp on worst-case scenarios, although most of those, according to Steig, are at least possible.