Factor Analysis of Greenhouse Gas Emissions from Automobiles

Abstract

Three approaches are commonly identified for controlling automobile greenhouse gas (GHG) emissions: reducing travel demand, improving vehicle efficiency and using alternatively (non-petroleum) fueled vehicles (AFVs). Similarly, sector emissions can be decomposed by travel distance, vehicle fuel intensity and fuel GHG ("carbon") intensity. Normalized analysis of these three factors offers valuable insights. For a broad set of conditions, any stringent GHG emissions limit for the automobile sector implies a limit of comparable stringency for fuel carbon intensity. However, carbon intensity is an abstraction of complex supply systems rather than an observable property of fuels (physical energy carriers) themselves. Carefully considering the locations and current magnitudes of fuel-related emissions implies that the proper policy focus is on upstream sectors that supply fuel rather than the choice of fuels downstream in the auto sector. Therefore, other than fundamental R&D, programs to promote AFVs are not currently warranted for climate protection. In addition to managing travel demand and improving vehicle efficiency, the implied climate policy priority is limiting net GHG emissions in fuel supply sectors. Future work is needed to develop GHG management policies for liquid fuel supply systems involving fungible commodities and dynamic global supply chains.