The federal government has gotten more interested in greenhouse gases, and as a result there has been a lot of tough talk concerning raised CAFE numbers. Much less time has been devoted to reducing CO2, which is the single largest contributor to global warming. Now that the spotlight is shining squarely on emissions, the 9th U.S. Circuit Court of Appeals panel has thrown out the 2008-2011 CAFE rating for light trucks. The 2008-2011 changes represented the largest jump in fuel economy in the history of CAFE, with MPG going from 22.2 to 24, but with the growing problem of greenhouse gases, that obviously didn't go far enough for the courts.
[Source: Automotive News - Sub. Req.]