This is like an extention of my hurried previous comment:
The planet changes, plain and simple. It's a dynamic system. Humans have trouble seeing that. We're ego-centric for one, and our lifespans are too short to really comprehend the magnitude of things.
I think what is hardest to get around is that we are releasing CO2 that has been pent up for millions of years, stored out of the system. Now it's back in the system. The question is: does that mean anything? I'm not saying that we should assume that means we're affecting the climate. But that's the question that needs to (and hasn't been in my mind) definatively answered. I think the general opinion is, "It certainly seems like it would have
some effect." But no one knows. This whole issue is being discussed A LOT in academia, but it's already been decided in the media.
Gaia is always a very interesting theory about the planet, and I've met some professors who actually believe this:
http://en.wikipedia.org/wiki/Gaia_theory_%28science%29