Hypothetical Extraction Method in Life Cycle Assessment: Method and Uses

Hypothetical Extraction Method (HEM) is an approach in Input Output Analysis (IOA) used to assess the effects of ‘target’ economic sectors have on other sectors. If we interpret HEM in a Life Cycle Assessment (LCA) context, HEM could be described as ‘assessing the contribution of processes (or groups of processes) to the impact of other processes’, making this another potential Contribution Analysis (CA) approach. In this study, we introduce HEM in LCA and demonstrate how HEM may provide different insights compared to the already existing CA approaches in two example case-studies. We do this by showing how HEM may be applied in LCA in four steps: 1) defining a scenario for extraction, 2) extracting target processes, 3) calculating results for the original and ‘remaining’ system and 4) calculating results for the target processes. We then demonstrate HEM in LCA using different example case-studies and compare HEM against other CA approaches. We also demonstrate process contributions to the target and remaining sections, allowing deeper insight into results. With this study we have shown how and when HEM can be a useful approach for CA in cases where current CA approaches may be lacking, providing an additional CA approach to the LCA practitioner in understanding impacts from their systems.