A study revealed in the Feb. 8 issue of the journal Science concludes that much more carbon is lost when natural ecosystems are converted to cropland for use in making biofuels.
Many natural ecosystems store enormous amounts of carbon. Scientists found that converting land for biofuels can release as much as 420 times the amound of CO2 that the fuels are supposed to offset or prevent in the first place.
There's an interesting article from a research institute funded by BP that calls into question the validity of the Science study. Check it out at http://media.cleantech.com/2427/biofuel-industries-call-studies-naive-nature-conservancy-princeton.