The liquid carbon challenge:evolving views on transportation fuels and climate

摘要

Carbon-based liquid fuels are highly valued for transportation; they are theworld’srnlargest form of commercial energy and second largest source of anthropogenicrncarbon dioxide (CO_2) emissions. Strategies to address their CO_2 emissions havernbeen shaped by fuel cycle analysis (FCA), a version of lifecycle assessmentrnthat examines fuel products and their supply chains. FCA studies have diversernfindings and large uncertainties. Disagreements are particularly sharp for biofuels,rnwhich are seen as key replacements for petroleum fuels. A critical reading ofrnthe evolving literature reveals problems of model structure, including systemrnboundary misspecification, flawed carbon cycle representation, and use of a staticrnframework to analyze dynamic systems. New analytic paradigms are needed forrnliquid fuels, given their tradability, the realities of the carbon cycle, and thernimplausibility of capturing carbon from mobile sources. Logical decomposition ofrnoptions shows that, beyond measures to limit fuel demand, CO_2 emissions fromrnliquid fuels must be balanced by increasing the rate of net carbon fixation. Furtherrnanalysis and discussion are needed of carbon accountingmethods, energy researchrnpriorities, ways to link CO_2 removal options to fuel-related mitigation efforts, andrnthe transportation elements of climate policy.