Misinformation. Since those making a ton of money from the status quo don't want things to change, they finance the FUDdites to sow seeds of doubt and deception so folks can feel justified in ignoring the writing on the wall. The eagerness of folks to ignore reality is what Jared Diamond wrote about in his book Collapse, and it appears that our culture is headed down that path because of our lack of motivation/ability to take the time to learn how our planet works.
Most folks don't have a clue how the carbon cycle works, for instance, and yet feel perfectly comfortable in concluding that humans can't impact the climate. For those folks (and anyone else, for that matter), I think NASA's Earth Observatory has an excellent overview of the carbon cycle that puts everything in the context that we need to have in order to have a decent dialogue on the topic:
http://earthobservatory.nasa.gov/Features/CarbonCycle/page1.php 
