Greenhouse Gas Impacts of Ethanol from Iowa Corn: Life Cycle Analysis versus System-wide Accounting

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2008-02-01
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Babcock, Bruce
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Feng, Hongli
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Center for Agricultural and Rural Development

The Center for Agricultural and Rural Development (CARD) conducts innovative public policy and economic research on agricultural, environmental, and food issues. CARD uniquely combines academic excellence with engagement and anticipatory thinking to inform and benefit society.

CARD researchers develop and apply economic theory, quantitative methods, and interdisciplinary approaches to create relevant knowledge. Communication efforts target state and federal policymakers; the research community; agricultural, food, and environmental groups; individual decision-makers; and international audiences.

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Life cycle analysis (LCA) is the standard approach used to evaluate the greenhouse gas (GHG) benefits of biofuels. However, it is increasingly recognized that LCA results do not account for some impacts—including land use changes—that have important implications on GHGs. Thus, an alternative accounting system that goes beyond LCA is needed. In this paper, we contribute to the literature by laying out the basics of a system-wide accounting (SWA) method that takes into account all potential changes in GHGs resulting from biofuel expansion. We applied both LCA and SWA to assess the GHG impacts of ethanol based on Iowa corn.

Growing corn in rotation with soybeans generated 35% less GHG emissions than growing corn after corn. Based on average corn production, ethanol's GHG benefits were lower in 2007 than in 2006 because of an increase in continuous corn in 2007. When only additional corn was considered, ethanol emitted about 22% less GHGs than gasoline. Results from SWA varied with the choice of baseline and the definition of geographical boundaries. Using 2006 as a baseline and 2007 as a scenario, corn ethanol's benefits were about 20% of the emissions of gasoline. If we expand geographical limits beyond Iowa, but assume the same emission rates for soybean production and land use changes as those in Iowa, then corn ethanol generated more GHG emissions than gasoline. These results highlight the importance of boundary definition for both LCA and SWA.

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