Biofuel's carbon balance: Climatic Change 2013
ABSTRACT. Liquid fuels will remain valued energy carriers well into any upcoming period when CO2 reductions are sought. Biofuels are the presumed replacement for the petroleum-based transportation fuels that dominate liquid fuel use. Lifecycle analysis embeds a closed-loop model of biofuel-related carbon flows, making net CO2 uptake an assumption to be refuted. However, evaluating net CO2 uptake through dynamic industrial and agriforestry supply chains at real-world commercial scales is extremely difficult. All such estimates carry a great deal of doubt and cannot be verified empirically. A different perspective follows by anchoring analysis in the certainty that end-use CO2 emissions from biofuels are essentially the same as those of the petroleum fuels they replace.
A first-order model of the globally coupled bio- and fossil-fuel system reveals conditions for biofuel use to provide an atmospheric benefit. No benefit occurs in the energy sectors where biofuels are used, but rather must be found elsewhere in locations of carbon absorption or retention. The implication is that climate mitigation efforts should focus on such locations and include any mechanisms through which net uptake (an enhanced sink or verifiable offset) can be achieved by biological, chemical, geological or other means. Although biofuels can play a mitigation role when certain conditions are met, deemphasizing biofuel production in favor of terrestrial carbon management may offer more immediate and effective ways to counterbalance the CO2 emitted when using carbon-based liquid fuels of any origin. Climate policies for transportation fuels should be reconsidered accordingly.