FARGIONE, Joseph. "Converting rainforests, peatlands, savannas, or grasslands to produce food crop–based biofuels... creates a “biofuel carbon debt” by releasing 17 to 420 times more CO2 than the annual greenhouse gas (GHG) reductions that these biofuels would provide by displacing fossil fuels "

Dr Joseph Fargione et al. on biofuel Carbon Debt (2008): “Increasing energy use, climate change, and carbon dioxide (CO₂) emissions from fossil fuels make switching to low-carbon fuels a high priority. Biofuels are a potential low-carbon energy source, but whether biofuels offer carbon savings depends on how they are produced. Converting rainforests, peatlands, savannas, or grasslands to produce food crop–based biofuels in Brazil, Southeast Asia, and the United States creates a “biofuel carbon debt” by releasing 17 to 420 times more CO₂ than the annual greenhouse gas (GHG) reductions that these biofuels would provide by displacing fossil fuels. In contrast, biofuels made from waste biomass or from biomass grown on degraded and abandoned agricultural lands planted with perennials incur little or no carbon debt and can offer immediate and sustained GHG advantages” (Joseph Fargione, Jason Hill, David Tilman, Stephen Polasky, Peter Hawthorne, “Land clearing and the biofuel carbon debt”, Science 29 February 2008, Vol. 319, Issue 5867, pp. 1235-1238: http://science.sciencemag.org/content/319/5867/1235 ).