USDA study finds GHG from corn-based ethanol ~39% to 43% lower than from gasoline; reduction of >70% possible by 2022
A new study released by the US Department of Agriculture (USDA) finds greenhouse gas emissions from corn-based ethanol are about 39% lower than gasoline. The study also states that when ethanol is refined at natural gas-powered refineries, the greenhouse gas emissions are even lower—around 43% below gasoline.
The study, led by Dr. Jan Lewandrowski of USDA’s Office of the Chief Economist, and published in the journal Biofuels, supports findings of other research that ethanol has a significantly better greenhouse gas profile than previously estimated.
The study attributes much of these additional benefits to revised estimates of the impacts of land-use change as a result of demand for ethanol.
Where previous estimates anticipated farmers bringing additional land into production as a result of increased corn prices, recent analysis finds only modest increases in crop acreage.
Additional improvements at ethanol refineries, combined with on-farm conservation practices that reduce greenhouse gas emissions, such as reduced tillage and cover crops, have further decreased emissions associated with corn ethanol.
The study projects that with added improvements in refineries and on farms, a reduction of more 70% in lifecycle emissions is possible by 2022.
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. Lewandrowski et al.
Background. Quantifying the GHG profile of corn ethanol has been contentious since Searchinger et al. concluded in a 2008 paper published in Science that the emissions associated with ethanol production and combustion exceeded the emissions associated with producing and combusting an energy-equivalent quantity of gasoline.
The authors argued that using billions of kilograms of US corn to produce ethanol reduces supplies of, and increases prices for, corn and other commodities in domestic and world food and feed markets. Farmers in the United States and elsewhere respond by bringing new land into production. These land-use changes (LUC) are related to ethanol production because the new land is used to grow more corn and to replace some of the decreased production of other commodities that occurs when US farmers allocate more existing cropland to corn.
Searchinger et al. argued that including LUC emissions results in corn ethanol having a higher GHG profile than gasoline.
RFS2 directed the US Environmental Protection Agency (EPA) to do a full GHG life-cycle analysis (LCA) for corn ethanol, including both direct and significant indirect sources of emissions. The EPA concluded that in 2022, the emissions profile of a unit of corn ethanol from a new natural gas-powered refinery would be 21% lower than the emissions profile of an energy-equivalent quantity of ‘average’ gasoline in 2005.
Since 2010, the RIA [Regulatory Impact Analysis] LCA for corn ethanol has dominated policy discussions and federal regulations related to ethanol as a renewable fuel and a GHG mitigation option. During this time, a large body of new data, scientific studies, technical reports, and other information has become available collectively showing that the emissions pathway corn ethanol has followed since 2010 is much lower than that projected in the RIA. Our objective is to assess corn ethanol’s current GHG profile in light of this new information. This work is timely as many countries (e.g. Colombia, Japan, Brazil, Canada and the European Union) are developing renewable energy policies that require biofuel substitutes for gasoline to reduce GHG emissions by more than 21%. Our results could help position US corn ethanol to compete in these new and growing markets.—Lewandrowski et al.
In the new USDA study the researchers reviewed the RIA projection, described relevant new information that has become available since 2010, and quantified a new emissions value—where needed—based on the new information.
Most of the new data, emission factors (EFs), and global warming potentials used in this analysis have become available from 2010 to 2015. Most of the studies the team used have publication dates between 2013 and 2015.
Jan Lewandrowski, Jeffrey Rosenfeld, Diana Pape, Tommy Hendrickson, Kirsten Jaglo & Katrin Moffroid (2019) “The greenhouse gas benefits of corn ethanol – assessing recent evidence,” Biofuels doi: 10.1080/17597269.2018.1546488