Two studies recently published in the journal Science claim that biofuels, as they are currently created and used, are not as green as the public believes.  One study projects the impacts of a ramp-up of biofuel production over this century.  As biofuel production increases, both cropland currently used for food and pastureland would potentially be put into biofuel production.  This could drastically impact global food supplies.  There would also be an increase in carbon emissions due to the amount of fertilizer needed to grow crops for biofuel.  Increased fertilizer use would in turn increase emissions of nitrous oxide, a potent greenhouse gas.

The second study found a flaw in the method used to calculate carbon emissions from bioenergy.  Currently, government calculations treat biofuels as if they are carbon neutral, which they clearly are not.  When biofuels are burned they do release CO2 into the atmosphere.  Also, if biofuel production decreases plant growth, which would decrease the removal of CO2 from the atmosphere, CO2 levels would increase.  For more information on these studies, see Reuters.