Personally, I had always thought of the Global Warming phenomenon as a "myth created by environmentalists." But, recently, my fiance had me watch the new movie "An Inconvenient Truth." Though I don't like how most of it is presented, the facts and research is there. The only thing that is lacks is the "opposing point of view." If you haven't seen it, I strongly recommend it, just to add to your understanding of the issue.
On that note, the question remains, just how much of the problem is man made and how much can we influence it at this point. Even if we did cause it, what can we do to fix it. I still place some weight on the cyclic climate theory though. To me, the earth is a big place and I know that we can influence it...but just how much? It has survived far worse challenges than humans and I am sure that it will survive us as well.
With that said, we need to take care of it, because the Earth can survive, but humans require a very specific and strict set of criteria to live....those can change quickly....and how knows just how much change we can survive.