Enhancement of environmental distance-to target weighting in life cycle assessment

The need for handling trade-offs as an outcome of complex environmental assessments like life cycle assessment (LCA) is crucial for decision-making. In this context, weighting as an optional element of LCA can support decision-makers in industry, government, and non-governmental organizations. Weighting is defined as "the process of converting indicator results of different impact categories by using numerical factors based on value-choices" (ISO 14044 2006). An increased interest in weighting methods in science, policy, and companies has led to several methodological developments in this field. An example is distance-to-target (DtT) weighting which calculates weighting factors from the distance of desired policy-based or science-based targets to the current environmental situation in a certain region or country. Nonetheless, existing methods still have several gaps and challenges which was the starting point for this thesis, e.g. regarding their focus on a limited amount of countries and regions, the handling of policy targets with different legal characters, and inconsistent time horizons for fulfillment. In addition, the a missing implementation of EU science-based and policy-based targets within the same weighting method. Derived from the gaps and challenges, the overall goal of the thesis is the enhancement of distance-to-target weighting, by developing various regional perspectives and methodological approaches. To achieve this goal, two research questions were formulated. The first research question addressed the issue of how DtT weighting can be improved by the use of different perspectives and methodological adaptations. The second research question focused on how DtT weighting approaches can be implemented in a European context. For the improvement of DtT weighting in LCA, novel global weighting perspectives like the producer-regions and worst-case regions approaches were established, which can be applied next to the existing and widely used consumer-regions approach. With the analysis of short-term targets as well as the consideration of binding targets only into additional weighting sets, important parameters in policy-based weighting showed between 43% - 60% lower weighting results in comparison to the existing practice. Furthermore, the integration of science-based targets into the Ecological Scarcity Method showed a new application for DtT weighting. The practical applicability of all methodological approaches and perspectives was shown with the application in different case studies within this thesis. For the implementation of different DtT weighting approaches in a European context, 123 policy-based eco-factors for a total of 11 environmental issues for the EU were derived based on the Ecological Scarcity Method. In addition, science-based eco-factors based on ecological thresholds (carrying capacities) for Europe and the EU were developed for a total of ten impact categories. The science-based and policy-based weighting approaches can be used in parallel or as stand-alone approaches and can provide an enhanced basis for decision-making. The application in case studies for the EU showed that the environmental issue climate change dominated the science-based weighting results by up to 92%. Whereas EU policy-based weighting results were determined not only by climate change (up to 64%) but also by other air pollutants with their respective potential environmental impacts in photochemical ozone formation, acidification, and terrestrial eutrophication. The different perspectives and methodological approaches developed in this thesis have the potential to foster decision-making in a European context. With the provision of policy-based and science-based weighting sets for the EU, LCA practitioners can apply them to future environmental assessments. With the development of additional perspectives besides the existing consumer-regions weighting, also global value chains and the countries involved, can be incorporated into weighting results.