Michael O'Hare¹, Richard Plevin², Jeremy Martin³, Andy Jones², Alissa Kendall⁴, and Eli Hopson³.

¹ Goldman School for Public Policy, UC Berkeley
² Energy and Resources Group, UC Berkeley
³ Union of Concerned Scientists, Cambridge, MA
⁴ Department of Civil and Environmental Engineering, UC Davis

Download the paper:

• O'Hare, M., Plevin, R. J., Martin, J., Hopson, E., Jones, A. D., & Kendall, A. (2009), Proper accounting for time in LCA increases crop-competitive GHG deficit relative to petroleum. Environ. Res. Lett. 4(024001).

Download the BTIME model (version 1.1, released 27 Jan 2009)

• XLS format (516 KB)
• XLS format (zipped) (172 KB)
• XLSX format (248 KB)

Requires Microsoft Excel or work-alike.

Abstract
The global warming intensities of crop-based biofuels and fossil fuels differ not only in amount but also in their discharge patterns over time. Early discharges, for example, from market-mediated land use change, will have created more global warming by any time in the future than later discharges, owing to the slow decay of atmospheric CO₂. A spreadsheet model of this process, BTIME, captures this important time pattern effect using the Bern CO₂ decay model to allow fuels to be compared for policy decisions on the basis of their real warming effects with a variety of user-supplied parameter values. The model also allows economic discounting of climate effects extended far into the future. Compared to approaches that simply sum greenhouse gas emissions over time, recognizing the physics of atmospheric CO₂ decay significantly increases the deficit relative to fossil fuel of any biofuel causing land use change.

CO₂ emissions and resulting atmospheric abundance for gasoline (25 years at 94 g CO₂e MJ^-1) and maize ethanol (25 years at 60 g CO₂e MJ^-1 plus iLUC discharge of 776 g CO₂ MJ^-1 and foregone sequestration totaling 102 g CO₂ MJ^-1; post-cultivation recovery of 50% of the lost biomass carbon over 30 years). (Click on figure to enlarge.)