The Earth's climate is a very complex issue, and the way Al Gore sells his message is that we are all going to die in 50 years because the earth is about to destroy itself. It is an alarmist message, he is an alarmist, and there are some big glaring errors in his film and message. As a filmmaker, I wonder why Gore didn't have his filmmaking team go out and shoot real footage of polar bears falling into the water? Instead he uses a nice animation to show his point, but research shows polar bears are doing ok. Documentaries are hardly close to true. With editing anyone can make any point seem true and valid.
Are humans having an effect on the environment? Oh sure we are, but the climate is much bigger than us and has been changing for thousands of years. Remember the Ice Age before melted without any humans driving cars? I guess that's proof that the climate will change with or without men running around.