|Cropland adjoining patches of forest. All arable land
removes carbon from the atmosphere at varying rates.
This quarrel reflects a new stage in the long-running debate because it does not involve disputes about net energy use or even the food-versus-fuel and land-use change issues raised over the past decade. It is instead a disagreement about the core assumptions to use when examining the question, particularly whether or not biofuels should be treated as inherently carbon neutral. That's the assumption that the CO2 emitted when biofuels are burned does not count because it is biogenic, i.e., newly removed from the atmosphere when feedstocks are grown. My work challenges this assumption, showing that it only holds under certain conditions. De Kleine and colleagues defend the assumption, arguing that it is true unconditionally.
The disagreement is not merely academic. Because new oil production technologies have expanded the supply of economically attractive fossil-based liquid fuels, the business case for biofuels rests increasingly on their value for mitigating CO2 emissions. The stakes are high for both the biofuels industry and for policies to address global warming.