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Life cycle assessment is the most relevant framework to evaluate biofuel greenhouse gas burdens


Life cycle assessment (LCA) is used extensively to assess the greenhouse gas (GHG) implications of biofuels. Some argue that the common treatment of biogenic carbon emissions as being carbon neutral in LCA is flawed. From this divergent perspective, biofuels have potential benefits only if additional atmospheric CO2 is captured or feedstocks that would otherwise quickly decompose (e.g. agricultural residues) are utilized. An alternative method, Annual Basis Carbon (ABC) accounting, has recently been demonstrated for a single ethanol facility comparing the year-over-year GHG impacts of the cropland supplying the facility, the fuel production processes (gasoline prior to construction and ethanol after), and vehicle tailpipe emissions. Our review of the ABC method identifies inconsistencies in the treatment of the non-fuel products: corn, soybeans, and distiller's dried grain solubles (DDGS). While these products are also consumed annually, the GHG emissions were not considered in evaluating the system performance. Furthermore, GHG impacts, both in terms of burdens from inputs and crop CO2 uptake, were not allocated to the products leaving the system. Thus in the initial state, the petroleum-fueled system received a substantial benefit from crop CO2 uptake, but none of the subsequent emission burdens associated with the consumption of non-fuel (i.e., food/feed) ‘exports’. In the final state, conversely, most biomass was combusted as ethanol and captured within the considered system. A system expansion is needed to better account for impacts. While concerns about the degree of carbon additionality have some merit, consequential LCA methods provide for more consistent and comprehensive approaches for evaluating biofuel GHG performance. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd