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.<\/b> <\/p>\n
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. <\/p>\n
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. <\/p>\n
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. <\/p>\n
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. <\/p>\n
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.<\/p>\n
Download study<\/a> (PDF-File)<\/p>\n 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.<\/p>\n To whom correspondence may be addressed at:<\/b> <\/p>\n Department of Ecology, Evolution, and Behavior
University of Minnesota<\/a>
1987 Upper Buford Circle
St. Paul, MN 55108.
Jason Hill, E-mail: hill0408@umn.edu<\/a>
David Tilman, E-mail: tilman@umn.edu<\/a><\/p>\n