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."
For many years, modeling studies have built in an assumption of carbon neutrality without ever validating it against what is actually occurring on the ground. An additionality test is not just "clever"; it is required to scientifically assess the extent to which any biofuel system actually reduces the net CO2 flux to the atmosphere. Wariness over policies that promote biofuels without such an evaluation is consistent with the principle of "above all, do no harm" when treating an environmental ill (in this case, the CO2 emissions from fuel use). This cautious view allows for biofuel systems that benefit climate, but implies a need to carefully identify the location and magnitude of that benefit as a starting point.
Other than a few facilities producing fuel products in the fraction of a percent range volumetrically, all commercial biofuel production relies on established industrial agriculture. That's true for corn-based ethanol in the United States (the world's dominant biofuel), cane-based ethanol in Brazil and the smaller but still significant volumes of commercial biodiesel on several continents. These production systems are far from sustainable and certainly not carbon neutral.
The technical analysis on which my article is based works from current data about real-world conditions. It doesn't invoke the hypothetical systems and modeling studies that conclude that, under certain idealized conditions, biofuels might be "beneficial," as wistfully envisioned in the Science article that Mr. Mazza cites. Sadly, most of those paper studies still use a simplistic assumption of carbon neutrality, embedded at the core of complex lifecycle analysis (LCA) models, and fail to empirically address the question of "Where's the climate benefit?"
A commenter asks if everything that CARB and EPA have done on lifecycle analysis of biofuels is wrong. The short answer is yes, in terms of the key issue of carbon balance, and in spite of much respectable and heroic analysis. And yes, Mr. Kaplan, unfortunately the LCFS and other so-called "clean fuel" standards that pretend to address GHG emissions are also ill-grounded and should indeed be "swept away." (That's in contrast to vehicle efficiency and emissions standards that are based on directly verifiable benefits of reduced fuel use and tailpipe emissions.) My critique of the use of LCA to specify policy and other citations to related literature are given in the journal article "Biofuels and Carbon Management" and a substantively similar working paper is available for free download.
Those questioning my scientific literacy may be amused to know that I've been looking at these issues for so long that my current work repudiates some of my earlier work. I was the lead author of the first two papers to call for the use of LCA in fuels policy, a book chapter in 1997 and a journal article in 1998. Back then my views were similar to those that are commonplace today. However, more in-depth study of the issues has led me to the much more cautious stance summarized in my e360 article and recent papers on the topic.
A few comments highlight the octane benefits of ethanol, which can enable more fuel-efficient engine designs. But that's not the only way to raise engine efficiency. Diesel engines can be even more fuel efficient and in general there's a long list of technologies for improving vehicle efficiency. Moreover, ethanol is not the only way to boost octane, for which refiners have processing options other than ethanol and other additives such as lead or MTBE. Raising fuel octane levels may well be a good idea, but again, that's no reason to give special policy favor to ethanol.