We find that 66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming. Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming. source
Urban legend: http://www.snopes.com/critters/gnus/litter.asp
Although the Glee version is a very close reproduction, I don't think it's done by channel phase inverting trick because that technique results in a mono backing track, and their backing track is clearly stereo. Plus if you listen closely on headphones you can hear they're using different drum samples and the instruments sound a bit different.
However, it's worth noting that the only thing used in Jonathan Coulton's cover from the original is the lyrics. The cover has completely new chord progression and vocal melody that doesn't exist in the original rap at all. Essentially in this case the "cover" is a completely different song with the lyrics from "Baby got back", so I think it's still a clear copyright violation regardless of how they reproduced Coulton's music.