Here are rather exhaustive lists of the skeptics' arguments on science grounds, along with brief analyses and links to underlying publications: Coby Beck: How to talk to Global Warming Skeptic Brian Angliss A Thorough Debunking New Scientist: Climate Change: A guide for the perplexed RealClimate...
[Snark Alert!] A recent article in Nature Geoscience that shows that measurable climate change - this time the expansion of the tropics - is outpacing predictions. The actual article is abstracted here: http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo.2007.38.html Amazing how the strong belief...