Abstract
Summary Consequential life cycle assessment (CLCA) is envisioned as a framework that combines the technological richness of attributional life cycle assessment (ALCA) with basic economic intuition to assess the potential environmental impact of an innovation. However, despite a growing literature, CLCA still lacks general guidelines for system boundary definition. Toward filling this gap, this article invents a new index of vulnerability of the life cycle impact of a product (or activity) to emissions arising from the impact of its large‐scale adoption on market prices. Using corn ethanol as an example, it is illustrated how such an index might aid in the selection of a small set of affected activities for formal consideration in a CLCA. The application to corn ethanol reveals that in addition to land‐cover change, there exist other sources of vulnerability that have not received attention in the context of biofuels. A general procedure for utilizing the vulnerability index as a screening aid for CLCA is outlined. The utility of the vulnerability index is independent of the type of modeling framework (such as multimarket partial equilibrium or computable general equilibrium) that might be employed for a formal CLCA. Finally, this work illustrates how the vulnerability index approach bridges ALCA and CLCA.