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The basic point of these studies is correct: the development of biofuels can cause changes in land use that lead to relatively large emissions of carbon from soils and biomass. Indeed, this basic finding has been known, and quantified, for almost 20 years. The Searchinger et al. paper does do something relatively new: it uses an agricultural model to estimate global changes in production and consumption, the first step in estimating emissions due to land use change. (It also has a detailed treatment of changes in land use by type of ecosystem.) However, both papers suffer three serious general deficiencies, apart from whatever legitimate questions one might have about details of the modeling.

First, the studies do not have a complete conceptual treatment of what happens over time. Most importantly, they ignore the carbon sequestration that will tend to happen when the biofuel programs end and the land-use changes that occurred at the start of the program are reversed. Related to this, the explicit or implicit treatment of the timing of impacts in the studies – namely, that there is no distinction to be made between climate impacts that occur today and climate impacts that occur many decades from now – is not economically realistic.

Second, changes in land use affect much more than just carbon stocks in soils and biomass: they also affect albedo, hydrodynamics, the nitrogen cycle, dust emissions, and more. All of these omitted factors can have significant effects on climate, and not all of these effects are “bad” (i.e., warming). Without doing a comprehensive analysis of all of the climate-relevant effects of land-use change, it is not possible to make general statements about the effects of land-use change on climate.

Third, both studies add emissions from land-use change to emissions from the rest of the lifecycle of biofuels, and then make general statements about how considering land-use change affects total emissions from and the overall desirability of biofuels. However, there is as yet no remotely good model of emissions from the “rest” of the life cycle of biofuels, and as a result it is not possible to make any definitive statements about the overall impact of considering land-use change emissions in lifecycle analysis.

In sum, these studies highlight an important (and generally well known) effect of the development of biofuels, but leave out a great many important factors, and do not tell us anything definitive about the overall impact of biofuels on climate.

Mark Delucchi
Institute of Transportation Studies
University of California, Davis
www.its.ucdavis.edu/people/faculty/delucchi

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I also feel like this begs the question of why are people growing corn for use as a biofuel? Brazil is certainly the leader in biofuel use and they use the byproducts of their sugarcane industry, which growing sugarcane for biofuel alone would not be a good idea, but it does highlight that corn is not the only answer. Corn takes a tremendous amount of resources to grow, because it is a woody plant and tends to suck nutrients from the soil. If biofuels were being derived from legumes or algae the impact would be much less.

Furthermore it seems silly that people would want to grow food grade crops for use as a biofuel, it seems like you could grow a fallow orchard of low grade fruits (which has more sugars than corn) and harvest the fruit to make bioethanol or biobutane with a much lower impact than growing corn. I really feel like agribusiness has pushed bioethanol and corn together for their own ends and environmentalist need to split them up post haste!

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