RESEARCH AND ANALYS I S Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol

biofuel corn-ethanol greenhouse gas (GHG) emissions industrial ecology life cycle assessment (LCA) net energy Supplementary material is available on the JIE Web site Summary Corn-ethanol production is expanding rapidly with the adop-tion of improved technologies to increase energy efficiency and profitability in crop production, ethanol conversion, and coproduct use. Life cycle assessment can evaluate the im-pact of these changes on environmental performance met-rics. To this end, we analyzed the life cycles of corn-ethanol systems accounting for the majority of U.S. capacity to esti-mate greenhouse gas (GHG) emissions and energy efficien-cies on the basis of updated values for crop management and yields, biorefinery operation, and coproduct utilization. Direct-effect GHG emissions were estimated to be equivalent to a 48 % to 59 % reduction compared to gasoline, a twofold to threefold greater reduction than reported in previous studies. Ethanol-to-petroleum output/input ratios ranged from 10:1 to 13:1 but could be increased to 19:1 if farmers adopted high-yield progressive crop and soil management practices. An advanced closed-loop biorefinery with anaerobic diges-tion reduced GHG emissions by 67 % and increased the net energy ratio to 2.2, from 1.5 to 1.8 for the most common systems. Such improved technologies have the potential to move corn-ethanol closer to the hypothetical performance of cellulosic biofuels. Likewise, the larger GHG reductions es-timated in this study allow a greater buffer for inclusion of indirect-effect land-use change emissions while still meeting regulatory GHG reduction targets. These results suggest that corn-ethanol systems have substantially greater potential to mitigate GHG emissions and reduce dependence on imported petroleum for transportation fuels than reported previously. Address correspondence to