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Published online on July 12, 2006, 10.1073/pnas.0604600103
PNAS | July 25, 2006 | vol. 103 | no. 30 | 11206-11210


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From the Cover
BIOLOGICAL SCIENCES / SOCIAL SCIENCES / ECOLOGY / SUSTAINABILITY SCIENCE-SS
Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels

Jason Hill*,{dagger},{ddagger},§, Erik Nelson{dagger}, David Tilman*,§, Stephen Polasky*,{dagger}, and Douglas Tiffany{dagger}

Departments of *Ecology, Evolution, and Behavior and {dagger}Applied Economics, University of Minnesota, St. Paul, MN 55108; and {ddagger}Department of Biology, St. Olaf College, Northfield, MN 55057

Contributed by David Tilman, June 2, 2006

Negative environmental consequences of fossil fuels and concerns about petroleum supplies have spurred the search for renewable transportation biofuels. To be a viable alternative, a biofuel should provide a net energy gain, have environmental benefits, be economically competitive, and be producible in large quantities without reducing food supplies. We use these criteria to evaluate, through life-cycle accounting, ethanol from corn grain and biodiesel from soybeans. Ethanol yields 25% more energy than the energy invested in its production, whereas biodiesel yields 93% more. Compared with ethanol, biodiesel releases just 1.0%, 8.3%, and 13% of the agricultural nitrogen, phosphorus, and pesticide pollutants, respectively, per net energy gain. Relative to the fossil fuels they displace, greenhouse gas emissions are reduced 12% by the production and combustion of ethanol and 41% by biodiesel. Biodiesel also releases less air pollutants per net energy gain than ethanol. These advantages of biodiesel over ethanol come from lower agricultural inputs and more efficient conversion of feedstocks to fuel. Neither biofuel can replace much petroleum without impacting food supplies. Even dedicating all U.S. corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand. Until recent increases in petroleum prices, high production costs made biofuels unprofitable without subsidies. Biodiesel provides sufficient environmental advantages to merit subsidy. Transportation biofuels such as synfuel hydrocarbons or cellulosic ethanol, if produced from low-input biomass grown on agriculturally marginal land or from waste biomass, could provide much greater supplies and environmental benefits than food-based biofuels.

corn | soybean | life-cycle accounting | agriculture | fossil fuel

Author contributions: J.H., D. Tilman, and S.P. designed research; J.H., E.N., D. Tilman, S.P., and D. Tiffany performed research; J.H., E.N., D. Tilman, S.P., and D. Tiffany analyzed data; and J.H., D. Tilman, and S.P. wrote the paper.

Conflict of interest statement: No conflicts declared.

§To whom correspondence may be addressed at: Department of Ecology, Evolution, and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108. E-mail: hill0408{at}umn.edu or tilman{at}umn.edu

© 2006 by The National Academy of Sciences of the USA


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