US Congress ordered in the 2007 energy bill, which required a quadrupling of annual ethanol production to 36 billion gallons by 2022. In practical terms, this meant more traditional corn ethanol, until other more advanced forms of ethanol could make their way out of the labs. Congress stipulated that ethanol from any source be cleaner than conventional gasoline. It handed the job of measuring emissions to the E.P.A., and told it to consider the fuel’s entire life cycle. This included counting the greenhouse gases released when forests or grasslands are plowed under and planted to make up for the crops used to make ethanol. When the E.P.A.’s scientists counted these indirect effects, corn ethanol emitted more greenhouse gases than gasoline over a 30-year period.
http://www.nytimes.com/2009/05/24/opinion/24sun2.html?_r=1&ref=opinion