I've found that this site is pretty good for addressing the scientific debate surrounding global warming (or "climate change," as it is now called).
I found it particularly helpful in addressing a recent column by George Will that cited articles from the 1970s claiming that we were in the grip of global cooling. Also, I found a debunking of the claim that there were computational errors in the "hockey stick" model of global temperature change.
There is no doubt that the site is of the opinion that there is sufficient scientific data to support the theory that human activity is contributing to an increase in the temperature of the earth. While that typically implies a certain political stance, the site restricts itself to references to the current scientific literature and generally avoids politically charged descriptions of human behavior.
Worth spending some time there, especially if you have some skepticism about global warming and would like a view of the current scientific thinking.