Response to Plevin: Implications for Life Cycle Emissions Regulations

A robust dialogue concerning appropriate parameter values for life cycle assessment (LCA) models is necessary because regulation of life cycle greenhouse gas (GHG) emissions from biofuel systems will determine market access and government subsidies for biofuel producers.1 Such a dialogue is also critical for creating more accurate LCA methods that will be accepted by scientists, industry, and the public. Plevin (2009) has identified multiple concerns with the life cycle emissions methodology employed in our previous analysis using the Biofuel Energy Systems Simulator (BESS) model (Liska et al. 2009), but only four alter our estimates substantially: (1) denaturant addition (+6.5 gCO2e MJ–1), (2) lime application rate and emission factor (+3.8), (3) upstream fossil fuel emissions (+2.3), and (4) electricity emission factor (+1.5), which sum to a +14.1 gCO2e MJ–1 upward adjustment to our original estimate of 45.1 gCO2e MJ–1 (Plevin 2009, Table 1). Plevin’s other concerns total 1.5 gCO2e MJ–1 in additional emissions, which does not substantially alter the GHG reduction estimates in BESS. Therefore, we address these four key issues 2 and show that, after correction for the relevant errors, life cycle GHG emissions from Midwest corn-ethanol are 47% less compared to gasoline, which is similar to the original BESS estimate of a 51% reduction (these estimates do not include indirect emissions, e.g., from land use change [Liska and Perrin 20091). This small reduction in the BESS estimate does not change the findings reported in our article (Liska et al. 2009)