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

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

doi:10.1088/1748-9326/ac2e35

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

Journal Article · Tue Nov 02 00:00:00 EDT 2021 · Environmental Research Letters

DOI:https://doi.org/10.1088/1748-9326/ac2e35· OSTI ID:1828996

; ; ; ; Kucharik, Christopher J.; ; ; Robertson, G. Philip

Abstract

In their recent contribution, Scully et al (2021 Environ. Res. Lett. 16 043001) review and revise past life cycle assessments 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 (a) values retained after filtering the predictions of past studies based on a set of unfounded criteria; and (b) 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 (Malins et al 2020 J. Clean. Prod. 258 120716) 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 perversely affecting policy outcomes.

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Sponsoring Organization:: USDOE

Grant/Contract Number:: SC0018409

OSTI ID:: 1828996

Journal Information:: Environmental Research Letters, Journal Name: Environmental Research Letters Journal Issue: 11 Vol. 16; ISSN 1748-9326

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United Kingdom

Language:: English

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