I believe that he is right, although there are many good arguments against him.
Scientists have however, found that some of the units in the book were wrong, and over exaggerated to add to the whole 'fear factor' of the movie. I thought that it was great that Gore was trying to get Global Warming out and all, but he needs to tone down the whole theme of horror.
A common argument for non-believers is that humans occupy less than 1% of the land on Earth, and that we couldn't cause that much damage to the atmosphere.
Another common argument is that we're just part of a natural cycle.
Really, I think there's solid evidence on both sides, though I'm going to have to side against the nonbelievers on this one.
By the way, Donut, I like the new G-Man icon