Marginally Adjusted Average LCA - Bridging the Gulf Between Attributional and Consequential LCA

摘要

Life Cycle Assessment (LCA) can often reveal unexpected or perverse outcomes from environmental initiatives. There are two main approaches to LCA: Attributional (ALCA) typically measures the impacts arising from producing a functional unit of product from average market suppliers and technologies. Consequential (CLCA) measures the marginal impacts to produce an additional functional unit of product, assuming that the resources consumed will come from new marginal supplies/technologies. As a result, ALCA and CLCA studies can give very different outcomes. The choice of method used for different LCA applications has divided practitioners and gives conflicting advice to decision-takers. The premise of this paper is that new production only causes marginal technologies to enter a market if the new producer specifically contracts the new marginal technology resources (e.g. Google sponsoring Solar Power for its operations). If the producer still purchases resources from average markets, then it is the aggregate demand in each market that motivates the entry of new marginal technologies and the effects of any addition should be shared with all co-consumers. The additional resources consumed are really the marginally adjusted average (MAA), not just the marginal. CLCA MAA results will usually closely resemble ALCA results, because entire markets are usually only perturbed to a small degree to meet new demand. In rare cases, where the existing market is substantially perturbed by an added demand, the CLCA results will differ significantly from the ALCA results. Many advantages are given for use of MAA to assess CLCA impacts, not least being to diminish the controversy between ALCA and CLCA outcomes.