Weighting in life cycle assessments in a global context

The option of weighting impact categories according to ISO 14042 on Life Cycle Impact Assessment (LCIA) is particularly difficult for global organizations, as they have to consider a wide range of values. The motivation for employing weighting is usually based on the desire to simplify LCIA output, especially in circumstances where product system tradeoffs occur. Looking globally at regional variations in legislation, consumer values, monetary valuation, existing weighting sets and expert opinions, no globally agreed upon weighting set is likely to be derived. This is due to both the inherent subjectivity of weighting and local variations in environmental imperatives. Hence, the authors recommend that LCIA quantitative weighting, especially those provided in pre-packaged software instruments, should not be employed. Admittedly, to use a spectrum of LCIA results for internal design decisions, some kind of trade-off analysis has to be performed, especially if comparing competing design alternatives. However, this trade-off analysis should be done separately from the technical LCA study and should reflect values and visions of the global organization, as well as the circumstances of the targeted market, in a qualitative way. For any external communication, none of the quantitative weighting sets can be used.