Conceptual and Methodological Issues in Lifecycle Analyses of Transportation Fuels
Human activities associated with the production and use of energy and materials can pollute the air and water. Since the late 1960s concern about regional and local air pollution has led to the adoption of environmental laws and regulations regarding major polluting human activities, such as fuel use for transportation or electricity production. More recently, concern about the impact of human activities on global climate has led to discussions about ways to reduce emissions of the so-called "greenhouse gases" that affect global climate. In the United States and worldwide, the transportation sector is one of the largest sources of urban air pollutants and greenhouse-gases (GHGs). As a result, policy makers and analysts often evaluate the impact of transportation policies on urban air quality and on global climate. The tools available for evaluating impacts on urban air quality (emission-factor models, travel models, and air-quality models) are reasonably well developed, but some of the tools for evaluating impacts on global climate (namely, lifecycle emissions models) are rudimentary and incomplete. This paper discusses some of the methodological and data issues pertinent to using lifecycle analysis (LCA) to evaluate the impacts of transportation on global climate.