The benefit to the climate of using biofuels as a substitute for fossil fuels has been sharply contested for years; much of the disagreement is based on the assumptions underlying the carbon accounting in the lifecycle analysis. The argument essentially boils down to whether or not biofuels are inherently carbon neutral because the CO2 released when they are burned is derived from CO2 uptake during feedstock growth.
A paper and subsequent formal comments and responses in the journal Climatic Change highlights the conceptual differences and the impact on policy. Professor John DeCicco at the University of Michigan Energy Institute has grown increasingly critical of the lifecycle analysis methods used to justify and administer biofuel policies. In a 2016 open-access paper in Climatic Change, he and his colleagues argued that once estimates for process emissions and displacement effects including land-use change are considered, US biofuel use to date is associated with a net increase rather than a net decrease in CO2 emissions. (earlier post)
That paper has now drawn a rebuttal from a team at Ford’s Research & Advanced Engineering Group in Dearborn. In a Commentary published in Climatic Change , Robert De Kleine and his colleagues argue that the assumptions used by DeCicco and his colleagues are invalid.
The analysis presented by DeCicco et al. relies on three key assertions. First, that if biofuel carbon combustion emissions are not completely offset by additional net ecosystem production (NEP), then the biofuel should not receive full biogenic carbon credit. Second, that changes in agricultural NEP related to biofuel production can be accurately estimated from national-level agricultural production statistics. Third, that agricultural NEP is a pertinent measure of biofuel global warming impacts.
We show that following the conventional definition of NEP the combustion of biofuel by definition leads to an exactly equal increase in NEP; therefore, the first assertion is not meaningful. Regarding the second assertion, we show that estimation of biofuel-related NEP changes from agricultural production statistics is not a robust methodology. Finally, we argue that agricultural NEP is an important parameter for estimating land-use change effects, but in isolation is an irrelevant GHG metric for current biofuels. We find that the conclusions above from DeCicco et al. are unfounded and do not invalidate the application of biogenic carbon offsets in life cycle assessments of biofuels currently used in national and international regulations.—De Kleine et. al
NEP is defined as the difference between the amount of carbon fixed by photosynthesis (characterized as gross primary production, GPP) and the total ecosystem carbon respiration (Re). Total ecosystem respiration is the sum of autotrophic (Ra) and heterotrophic respiration (Rh).
DeCicco and co-authors argue that the biogenic carbon captured from the atmosphere and converted into biofuel would have been otherwise captured by plants and that biofuels therefore should not necessarily receive full biogenic uptake “credit.” DeCicco and co-authors claim that NEP is the critical metric to consider and that if biofuel production does not increase NEP by at least as much as the embodied biogenic carbon, then the biofuel should not receive the full biogenic carbon credit. We argue that the logic applied and the argument developed by DeDicco and co-authors is false because it does not recognize the fact that biogenic carbon produced for food or animal feed in cropland ecosystems will be returned to the atmosphere via heterotrophic respiration in the non- cropland ecosystems to which the food/feed is exported.—De Kleine et al. (2017)
In response, Professor DeCicco argues that the logic used by De Kleine and colleagues—as well as by the majority of biofuel researchers and government officials who apply lifecycle analysis for policy—is faulty.
Assuming that biogenic carbon flows are always in balance over a biomass product’s lifecycle—i.e., that flows of CO2 between the atmosphere and biosphere —leads to the belief that lifecycle analysis, which treats carbon flows as being steady (not varying over time) is suitable for evaluating biofuels, DeCicco argues.
In reality, however, carbon flows are dynamic (vary over time). The atmosphere and biosphere are not in balance because mankind is consuming ever more biogenic carbon for food and other economic uses. It is therefore necessary to examine the dynamics of biofuel use and determine the extent to which biogenic CO2 emissions are balanced by CO2 uptake on a case-by-case basis.—John DeCicco
Attempting to refute our work by recourse to the faulty lifecycle logic that our method was designed to avoid is itself but a form of circular reasoning. Our critics seem unable to let go of the assumption of a stylized circular carbon flow for biofuels, as embodied by construction in the LCA methods they espouse and in their recourse to a tautology of global carbon accounting. De Kleine et al. fail to raise any scientifically substantive objections to our paper, displaying the power of a false paradigm to blind researchers to seeing the world for what it really is.—DeCicco (2017)
DeCicco, J.M., D.Y. Liu, J. Heo, R. Krishnan, A. Kurthen and L. Wang (2016) “Carbon balance effects of U.S. biofuel production and use.” Climatic Change 138(3): 667-80 doi: 10.1007/s10584-016-1764-4
De Kleine R., T.J. Wallington, J.E. Anderson and H.C. Kim (2017) “Commentary on ‘Carbon balance effects of U.S. biofuel production and use’ by DeCicco et al. (2016)” Climatic Change doi: 10.1007/s10584-017-2032-y
DeCicco, J.M. (2017) “Author’s response to commentary on ‘Carbon balance effects of U.S. biofuel production and use.’” Climatic Change doi: 10.1007/s10584-017-2026-9