CONFERENCE REPORT Normalization and weighting: the open challenge in LCA $ Q G U H D V 5 R H V F K 1 & 6 H U H Q H O O D 6 D O D 2 & 1 L H O V - X Q J E O X W K 3 Received: 19 June 2020 /Accepted: 30 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Keywords Aggregation . Normalization . Weighting . ISO . Single score 1 Introduction Drawing the correct conclusions based on environmental indicators can be challenging due to the consideration of a broad variety of environmental impacts, which might show diverging results. Many life cycle assessment (LCA) prac- titioners seek help in interpreting disparate results of life cycle impact assessment (LCIA) in different impact cate- gories by applying normalization and weighting. The stan- dards of the International Organization for Standardization (ISO) do not support the use of normalization and weighting for publishing comparative assertions in LCA. Nevertheless, the increasing need for identifying the most relevant impact categories as well as obtaining unequivo- cal results have led to further research on normalization and weighting, including the calculation of single scores. The 72nd LCA Forum focused on the present state of normalization and weighting in LCA. Statements in ISO 14040, such as those concerning internal and external normalization and hints regarding interpretation, were considered part of the baselines. The forum provided a platform for discussing ongoing developments in the technical specifications for this theme (ISO/TS 14074). In particular, the forum focused on new approaches and ways to boost the acceptance of the use of normalization and weighting and the communication of single scores by a broader community. The current status and main challenges of normalization and weighting were presented in the first session (Section 2). The speakers of the second session showed how normaliza- tion and weighting can be applied to the Product Environmental Footprint (PEF), and how different normaliza- tion and weighting schemes may impact the final results (Section 3). In the third session, the speakers presented some promising developments in normalization and weighting (Section 4), while decision-making implications of using sin- gle scores were discussed in the last session (Section 5). 2 Challenges and opportunities of normalization and weighting Andreas Roesch (Agroscope, Switzerland) introduced the top- ic and summarized the current status and main challenges of normalization and weighting. Normalization and weighting are optional steps in LCIA, but these steps are crucial for providing support information to decision-makers, allowing them to avoid subjective weighting of different environmental impacts. Normalization can be performed at the mid- and endpoint levels, and provides information on the relative relevance of the impact, facilitating the interpretation of the results. Different approaches exist for normalization, and they are classified as follows: (i) global normalization, (ii) production-based normalization (i.e., addressing production- related impacts associated with a region/country), (iii) consumption-based normalization (i.e., including both con- sumption and production impacts associated with a region/ country), and (iv) normalization based on carrying capacity references (Pizzol et al. 2017). Local- and regional-scale im- pact categories, such as freshwater depletion and aquatic eu- trophication, should ideally be related to the carrying capaci- ties of the relevant local and regional territories. Over time, an increasing number of papers and reports have been published on this issue (Sala et al. 2015; Crenna et al. Responsible editor: Matthias Finkbeiner * Roesch Andreas andreas.roesch@agroscope.admin.ch 1 Agroscope, Reckenholzstrasse 191, 8046 Zurich, Switzerland 2 European Commission—Joint Research Centre, Via Enrico Fermi 2749, 21027 Ispra, VA, Italy 3 ESU-services Ltd., Vorstadt 14, 8200 Schaffhausen, Switzerland https://doi.org/10.1007/s11367-020-01790-0 Author's personal copy