TAMU BICH 407 - PNAScostbenefit (5 pages)

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PNAScostbenefit



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PNAScostbenefit

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Pages:
5
School:
Texas A&M University
Course:
Bich 407 - Horizons Biol Chem Ii

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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 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



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