In Life Cycle Assessment (LCA), according to ISO 14044 (ISO 2006), normalisation and weighting are optional steps of Life Cycle Impact Assessment (LCIA). Those steps allow expressing LCA results aggregating the results (up to a single score), giving different weight to the different environmental impacts.
The step of prioritising and aggregating the results for the 16 environmental impact categories evaluated in the life cycle based Environmental Footprint (EF) - covering e.g. climate change, acid rain, human and eco-toxicity, particulate matter but also impacts due to the use of water, land and resources – has a high relevance.
Weighting supports the identification of the most relevant impact categories, life cycle stages, process and resource consumptions or emissions to ensure that the focus is put on those aspects that matter the most and for communication purposes.
Any weighting scheme is not mainly natural science based but inherently involves value choices that will depend on policy, cultural and other preferences and value systems. No “consensus” on weighting seems to be achievable. This situation does not apply only to weighting in a LCA or Environmental Footprint context, but seems inevitable for many multicriteria approaches.
The objective of this work therefore was to find a convention suitable for the application in the EF context and to develop a method for weighting the Environmental Footprint Impact Categories according to their relevance for the overall environmental problems.
A final recommendation is provided on a weighting set to be used for the EF that includes also aspects of the robustness of the results.
This report includes, from page 46 onward, several annexes and the comments from a consultation of the Environmental Footprint Technical Advisory Board in June 2017.