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HillEtAl2006 - Environmental economic and energetic costs...

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Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels Jason Hill* †‡§ , Erik Nelson , David Tilman* § , Stephen Polasky* , and Douglas Tiffany Departments of *Ecology, Evolution, and Behavior and Applied Economics, University of Minnesota, St. Paul, MN 55108; and 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 eco- nomically competitive, and be producible in large quantities with- out reducing food supplies. We use these criteria to evaluate, through life-cycle accounting, ethanol from corn grain and biodie- sel 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 feed- stocks 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 hydro- carbons 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 H igh energy prices, increasing energy imports, concerns about petroleum supplies, and greater recognition of the environmental consequences of fossil fuels have driven interest in transportation biofuels. Determining whether alternative fuels provide benefits over the fossil fuels they displace requires thorough accounting of the direct and indirect inputs and outputs for their full production and use life cycles. Here we determine the net societal benefits of corn grain ( Zea mays ssp. mays ) ethanol and soybean ( Glycine max ) biodiesel, the two predominant U.S. alternative transportation fuels, relative to gasoline and diesel, the fossil fuels they displace in the market.
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