Really, I can't be more clear than saying you should go to
http://www.climatecrisis.net, which is the website for Al Gore's presentation. He's got all his facts straight, and he's far more eloquent on the subject than I'll ever be. He'd better be after studying it for forty years.
Yes, there's a natural fluctuation in avg temperature. Yes, there are natural processes that can cause these same changes OVER HUNDREDS OF THOUSANDS OF YEARS. We went from a little warming and cooling here and there to the sharpest spike in a million years over just the last hundred and some odd years in direct correlation with our physical effect on the world. There is no debate over this in the scientific community. The public at large only thinks there's a debate because a small minority of non-scientists with a political or economic agenda have been given equal airtime in a misguided attempt at "balance". Facts are facts. You don't give equal air time to the antithesis of a fact and call it BALANCE! (Yes, this makes me angry. I was a journalist once and all things considered I'm often ashamed to be associated with what passes for journalism now).
You can think of it like a tetherball. It swings around a little bit without you touching it, because of wind or other natural reasons. If you hit it, it makes the same motion but more quickly, violently and so much farther than the natural process ever did. Would you debate why the tetherball swung so much farther now than it was when you weren't hitting it? No.
