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RFA to EPA: Use Current Data and GREET Model to Update Corn Ethanol GHG Analysis

April 4, 2022

Environment, EPA


In response to the U.S. Environmental Protection Agency’s recent workshop on biofuel greenhouse gas modeling, the Renewable Fuels Association submitted comments Friday stressing the importance of using updated and transparent data,  a level analytical playing field, and state-of-the-art modeling tools when conducting lifecycle analysis.


“RFA commends the EPA for holding the recent workshop and soliciting related comments,” wrote RFA President and CEO Geoff Cooper in a cover letter. “The Agency’s last analysis of the GHG emissions associated with corn ethanol was conducted in 2010, as part of the rulemaking process for the RFS after it was revised by the Energy Independence and Security Act of 2007. Over the ensuing 12 years, the RFA has consistently urged the EPA to update its analysis to reflect the efficiencies that have been gained in ethanol production and the advances that have been made in lifecycle analysis.”


Calling it the “gold standard” of lifecycle models, RFA strongly recommended that EPA use the Argonne National Laboratory GREET model to update the agency’s corn ethanol GHG analysis. In addition, EPA must consider significant indirect GHG effects for all fuels, including petroleum, which is consistent with the Energy Independence and Security Act of 2007.


Rebuttal to Lark et al.


Importantly, RFA used this comment opportunity to provide a thorough rebuttal to a recent paper by the University of Wisconsin’s Tyler Lark and others in the Proceedings of the National Academy of Sciences, titled “Environmental Outcomes of the U.S. Renewable Fuel Standard.”


“There are a number of fundamental flaws and serious questions associated with the methods used by Lark et al.,” RFA notes. “Their paper overtly contrasts their findings to those of Argonne and the California Air Resources Board. However, those mainstream analyses have been refined over a decade or more, and it is the work by Lark et al. that does not stand up once it is subjected to scrutiny.”


Among the problems cited:


  • The analysis covers the period 2008-2016, but the proper starting year would have been 2007. For renewable fuel to qualify toward RFS2, the feedstock from which it is produced must be grown on land cleared or cultivated prior to Dec. 2007, when the Energy Independence and Security Act of 2007 was enacted.
  • Lark et al. claim that the RFS has caused cropland to expand. However, this is inconsistent with EPA’s annual estimates of U.S. agricultural land, which in recent years have been 20-25 mil. ac. (5-6%) lower than the 2007 level.
  • Lark et al. claim that “native” grassland with high carbon storage has been converted to corn production, but they use satellite imagery to attempt to determine what types of land were converted, an approach that has been shown to be fundamentally flawed.
  • Lark et al. overestimate the GHG emissions that would be associated with hypothesized land-use change.