Comment on ‘Carbon intensity of corn ethanol in the United States: state of the science’

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Seth Spawn-Lee, Tyler J. Lark, Holly Gibbs, Richard A. Houghton, Christopher J Kucharik, Chris Malins, Rylie Pelton, G. Philip Robertson


Scully et al [1] in their recent contribution review and revise past life cycle assessments (LCAs) of corn-grain ethanol’s carbon (C) intensity to suggest that a current ‘central best estimate’ is considerably less than all prior estimates. Their conclusion emerges from selection and recombination of sector-specific greenhouse gas emission predictions from disparate studies in a way that disproportionately favors small values and optimistic assumptions without rigorous justification nor empirical support. Their revisions most profoundly reduce predicted land use change (LUC) emissions, for which they propose a central estimate that is roughly half the smallest comparable value they review (Figure 1). This LUC estimate represents the midpoint of (i) values retained after filtering the predictions of past studies based on a set of unfounded criteria; and (ii) a new estimate they generate for domestic (i.e. U.S.) LUC emissions. The filter the authors apply endorses a singular means of LUC assessment which they assert as the ‘best practice’ despite a recent unacknowledged review [2] that shows this method almost certainly underestimates LUC. Moreover, their domestic C intensity estimate surprisingly suggests that cropland expansion newly sequesters soil C, counter to ecological theory and empirical evidence. These issues, among others, prove to grossly underestimate the C intensity of corn-grain ethanol and mischaracterize the state of our science at the risk of affecting perverse policy outcomes.



Agricultural and Resource Economics, Agricultural Economics, Agricultural Science, Agriculture, Agronomy and Crop Sciences Life Sciences, Biogeochemistry, Earth Sciences, Ecology and Evolutionary Biology, Energy Policy, Environmental Indicators and Impact Assessment, Environmental Policy, Environmental Sciences, Environmental Studies, Geography, Life Sciences, Oil, Gas, and Energy, Physical and Environmental Geography, Physical Sciences and Mathematics, Plant Sciences, Public Affairs, Public Policy and Public Administration, Social and Behavioral Sciences, Soil Science, Sustainability


CCLUB, co-products, corn ethanol life cycle assessment, GREET, land intensification, land use change, soil carbon, yield price elasticity


Published: 2021-05-06 21:00

Last Updated: 2021-05-16 20:23

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