Why is there still vagueness regarding anthropogenic global warming?

All students should view samples of the following videos and other website sources of information about global warming. Students are assigned to write 1 page critiques (summarize and critically evaluate the argument) on specific websites as detailed below. Everyone should view atleast 3 to 4 of the Youtube videos on global warming found at:

http://www.youtube.com/watch?v=-zeGY8zbzc8&feature=related

Students should randomly select one of the videos that portrays global warming as a scam, hoax, lie, conspiracy, or otherwise challenges the science related to global warming; view it, write a 1 -1.5 page critique and be prepared to discuss it for the rest of the class.