Can I please please please link everybody here to something that I believe should be considered the most valuable source in this debate.
http://www.aaas.org/news/press_room/climate_change/media/4th_spm2feb07.pdf
Its a summary of a report from the IPCC and states with no political bias that it is likely that there has been significant anthropogenic warming over the last 50 years. In other words they think that there is a more than 66% chance that the human contribution to the warming climate has been significant. And they believe that there is at least a 90% chance that humans have contributed in some way to the warming.
Seriously, just read it. Its only 21 pages long and its very interesting what they think as these guys are basically a huge heap of experts in the field.
http://en.wikipedia.org/wiki/IPCC
