The climate benefits of biofuels such as ethanol and biodiesel have been debated for many years. Attempts to compare these fuels with one another and fossil-derived fuels such as gasoline and diesel confront many uncertainties, not all of which can be resolved through further data analysis. By scrutinizing the greatest sources of uncertainty and grounding analysis in the areas of high certainty such as combustion chemistry and the terrestrial carbon cycle, this paper sheds light on this challenging subject and points the way toward new strategies for addressing CO2 emissions from transportation fuels.
"Carefully examining the locations and magnitudes of fuel-related emissions indicates that the proper policy focus is on the sectors that supply fuel rather than the choice of fuels in the auto sector. Therefore, beyond fundamental R&D, policies to commercialize AFVs are not necessarily required for climate protection at present."
This National Research Council (NRC) report assesses the potential to achieve twin goals of reducing petroleum use and cutting greenhouse gas (GHG) emissions from U.S. cars and light trucks to 80 percent below the 2005 level by 2050.
ABSTRACT. Public policy supports biofuels for their benefits to agricultural economies, energy security and the environment. The environmental rationale is premised on greenhouse gas (GHG, "carbon") emissions reduction, which is a matter of contention. This issue is challenging to resolve because of critical but difficult-to-verify assumptions in lifecycle analysis (LCA), limits of available data and disputes about system boundaries. Although LCA has been the presumptive basis of climate policy for fuels, careful consideration indicates that it is inappropriate for defining regulations.