Review of criteria for evaluating LCA weighting methods

In the process of selecting where effective environmental measures should be directed, the weighting step of life cycle assessment (LCA) is an optional, controversial, but nevertheless important tool. A set of criteria for evaluating weighting methods has relevance in the process of acquiring meta-knowledge, and thus competence, in assigning relative weights to environmental impact categories. This competence is helpful when choosing between presently available weighting methods, and in creating new weighting methods. Criteria in LCA-related literature are reviewed. The authors have focused on identifying lists of criteria rather than extracting criteria from bulks of text. An important starting point has been the actual use of the term criterion, while at the same time disqualifying certain definitions of the term which are too far removed from the two definitions provided in this article. Criteria for evaluating weighting methods are shown to fall into two general categories. The first being general criteria for weighting methods, demanding that weighting methods have a broad scope, are practical for users and scientists, are scientific and have ethical goals. The second being criteria proposing characteristics of concrete environmental damage which should be taken into account by a weighting method. A noteworthy example is reversibility. While the comprehensive tables of criteria speak for themselves, it can be observed that the need for transparency is particularly highlighted in literature. Furthermore, ISO 14044's statement that the weighting step is not scientifically based would appear to defy a significant proportion of the other criteria reviewed; this, however, depends on its interpretation.