Al Gore's self contradiction

I recently watched "An Inconvenient Truth". Overall, I thought it was well done. I could see what Al Gore intended to accomplish with it, and I think he did an excellent job.

The main thing that made me wince was his use of Mark Twain's quote,

"It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so"

And then he immediately proceeds show everyone what he knows for sure.

I'm not a Global Warming denier. I believe that the best scientific evidence available to us today is quite alarming.

However, I do not see how these facts predict the future climate with any accuracy whatsoever. All they show is that the current conditions are unprecedented in recent earth history. The fact that it's unprecedented is exactly what makes it so difficult to predict what is going to happen. It could very well turn out that balancing forces will come into play that we haven't thought of yet. For instance, vast forests spring up near the poles (where few plants could live before), inhaling vast amounts of C02 and putting the brakes on Global Warming. That's just off the top of my head.

I am not saying that I'm going to drive a Hummer in circles just for fun, because all this Global Warming stuff is bunk. All of us have known that our cars waste energy and pollute, regardless of Global Warming. And there's plenty of other ways we waste energy and pollute. Why not clean up our act for those reasons, and just throw in the possibility of disastrous climate change to seal the deal?