Life-cycle GHG emissions for gasoline and corn ethanol by scenario and source category. RIA: Regulatory Impact Analysis; BAU: Business as Usual Scenario; HEHC: High Efficiency High Conservation Scenario; N2O: Nitrous Oxide. Source: Lewandrowski et al.

U.S. greenhouse gas (GHG) emissions associated with corn-based ethanol are about 39% lower than gasoline-related emissions. According to U.S. Department of Agriculture (USDA) researchers, refining the ethanol at natural gas-fueled refineries further lowers the emissions to 43% below gasoline.

The study, published in Biofuels, attributes these air quality benefits to revised estimates of the impacts of land-use change as a result of demand for ethanol. Previous estimates anticipated farmers bringing additional land into production as a result of increased corn prices, but recent analysis finds only modest increases in crop acreage. Additional improvements at ethanol refineries, combined with reduced tillage and other on-farm conservation practices that reduce greenhouse gas emissions, have further decreased emissions associated with corn ethanol.

The analysis considered a business-as-usual scenario based on a continuation through 2022 of trends that have been reducing corn ethanol’s GHG profile over time, such as refineries switching from coal to natural gas as a process fuel. Life-cycle GHG emissions for corn ethanol are projected to total 54,588 g carbon dioxide equivalents (CO2e)/MMBtu in 2022. Even if the ethanol industry does not act to reduce emissions, the GHG profile of corn ethanol will continue to improve and will be, on average, 44.3% lower than the emissions associated with producing and combusting gasoline.

A high efficiency high conservation scenario was also prepared and assumes a proactive approach by refineries to lower the GHG profile of ethanol. Projected emissions for corn ethanol in 2022 are 27,852 g CO2e/MMBtu, which is a 71.6% reduction in GHG emissions relative to gasoline.