I think it's great that he received it and his work regarding global warming is something I respect. I don't mean science fiction as works of bad literature and worse internal consistency.
Still, as I understand it, he received the Prize for educating people about global warming so the world's people can do something about. This will reduce water scarcity in the future. More water available to more people will reduce wars fought over this resource.
Al Gore has won the Peace Prize for reducing conflict in the future - how cool is that?
Partial text of the award can be found at the Panda's Thumb.