As the Environmental Protection Agency fulfills its requirement to determine how direct and indirect land use change is impacted by crops produced to make biofuels, it needs to assure that good science is used to create good policy.
It would be easy - and wrong - to rely on a much-publicized study that connects U.S. corn ethanol production to greenhouse gas release via indirect land use change. Indirect land use change refers to bringing new lands into agricultural production, and thereby creating a "carbon debt," because of market forces.
This study, first publicized in ScienceExpress online in February 2008 and widely quoted in a Time magazine cover story in March, cast a pall over all biofuels and has chilled investment in advanced non-grain-based biofuels such as cellulosic ethanol. My evaluation is that the study meets neither the standards for scientific significance nor life cycle analysis as required in the Energy Independence and Security Act (EISA) of 2007.
No actual data exist that connect U.S. domestic ethanol production with, to cite a widely quoted example, the clearing of the Amazon rain forest. Instead, the paper's conclusions depend entirely on economic modeling and assumptions. The validity of these assumptions and the reliability of the models are now being explored by other scientists.
Thus far, the paper is not holding up well to scrutiny. For example, other analyses predict that hypothetical land use change will occur primarily in U.S. grasslands and commercial forests, not in tropical forests. The "carbon debt" resulting from grassland conversion is much less than what would result from tropical forest conversion.
The study considers only the worst case for land management following land use change. My own research group has shown appropriate land management strategies following land use change can eliminate or greatly reduce the "carbon debt." Until its conclusions are supported by independent analyses using a variety of tools and assumptions, the paper is not scientifically significant.
The International Standards Organization (ISO) established parameters for life cycle analysis. These include: (1) using the most recent data, (2) making appropriate comparisons, (3) determining the sensitivity of results to changes in major assumptions and data, and (4) allocating environmental impacts among all system products.
The study does not meet these standards. For example, the paper infers all land use change is driven by agricultural expansion. Land use change, in fact, is due to multiple factors, including infrastructure development, such as road construction; timber harvest as well as agricultural expansion. In more than 150 cases of observed land use change, mostly in the tropics, simple agricultural expansion could explain only 4 percent of the observed cases. However, for more than 90 percent of the observed cases of land use clearing, a cluster of three factors: infrastructure development (roads, etc.), timber harvest and agricultural expansion were all present together. Agricultural expansion alone is seldom the reason for land use change.
In another incongruity, the paper compares future ethanol production with past gasoline production. But the new, or incremental, gallon of ethanol should be compared with the incremental gallon of gasoline. Most new gasoline today is coming from the Athabasca tar sands of Canada. Processing Canadian tar sands into liquid fuels generates about 3 times more greenhouse gases per gallon than gasoline from conventional oil. Including just this one factor in the analysis reduces the hypothetical land use change carbon debt by three fold.
Indirect land use change makes U.S. farmers and biofuel producers potentially responsible for the greenhouse gas emissions of their competitors around the world, a burden no other domestic industry bears. Congress can revisit the EISA and alter what may be an unintended consequence of the law or otherwise clarify its meaning. Regulatory agencies, including the EPA, that are charged with implementing energy policy need to recognize that this study should not be used to formulate policy. Sound science must come before sound policy.
Bruce Dale, University Distinguished Professor, Department of Chemical Engineering, Michigan State University and the Great Lakes Bioenergy Research Center. The Great Lakes Bioenergy Research Center is one of three Energy Department-sponsored biofuel research centers.