Several comments on my Yale e360 piece on alt fuels policy take the common view that biofuels are "essentially carbon neutral" and "inherently sustainable," as Mr. Lloyd puts it. However, nothing is inherently sustainable, and the carbon balance of any system is something that must be verified. My piece asks "Where's the climate benefit?" and for biofuels at market scale, it is not possible to answer to that question in an verifiable manner.
Simply substituting biomass carbon for fossil carbon does not suffice to ensure a net CO2 reduction, as shown by the example my article gives for corn ethanol. It may leave more fossil carbon in the ground, but that doesn't mean less carbon overall went into the air. A formal analysis of this issue is given in my new paper on "Biofuels Carbon Balance."