Publication DetailsTitle : Comments on Ethanol's Broken Promise by the Environmental Working Group (May 2014)
Publication Date : June 11, 2014
Authors : Michael Wang, Jennifer B. Dunn, Steffen Mueller, Zhangcai Qin, Wally Tyner, and Barry Goodwin
Abstract : In their recent report, the Environmental Working Group (EWG) posited that the life-cycle emissions of corn ethanol are greater than those of gasoline. EWG concluded that lowering the ethanol mandate under the Renewable Fuel Standard (RFS) by the United States Environmental Protection Agency (EPA) would reduce greenhouse gas (GHG) emissions by 3 million tons of CO2 equivalents (CO2e) in 2014. The EWG report was organized into three sections. First, EWG maintained that a significant amount of grasslands and wetlands were converted to corn farming between 2008 and 2012. This conclusion was based on two EWG earlier reports that used U.S. Department of Agriculture's (USDA's) Cropland Data Layer (CDL) and satellite data. EWG then applied the emission factors of land conversions from earlier work by Plevin et al. to estimate total emissions associated with conversion of grasslands and wetlands to corn farms. The land areas EWG estimated to have been converted to wetlands and grasslands are high compared to earlier detailed studies and modeling results. Further, the emission factors they applied are high compared to those in other reports and studies that take into account important variations in initial and final land states. Most importantly, the emission factor EWG applied to wetland-to-corn agriculture transitions reflects emissions from conversion of peat- and carbon-rich tropical wetlands rather than from conversion of temperate wetlands found in the United States. Conversion of U.S. temperate wetlands should be less carbon-intensive. Second, EWG used EPA's land-use change (LUC) GHG emissions results for corn ethanol for year 2012 to calculate high life-cycle GHG emissions for corn ethanol. EPA's intent for including corn ethanol LUC GHG emissions results for 2012 and 2017, however, seems to have been mostly for sensitivity analyses because these emissions were not discussed in the RFS final rule or its Regulatory Impact Analysis (RIA). Further, 2012 emissions were not calculated for all biofuel pathways included in RFS. In their report, EWG picked the EPA 2012 GHG emissions for corn ethanol and applied them to the EPA-proposed reduced volume for corn ethanol in 2014 to make the erroneous conclusion that the proposal resulted in 3 million tonnes of CO2 reduction in 2014. Finally, EWG stated that Argonne National Laboratory's Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREETTM) model uses unrealistic assumptions in estimating LUC associated with increased corn ethanol production. EWG confused parameters in GREET with those in an economic model, the Global Trade Analysis Project (GTAP). The particular parameter EWG discussed, the yield-price elasticity, in the GTAP model is supported by a recent analysis. In the discussion below, we address in detail each of these three areas and several other issues in the EWG report.