Investigating methodological aspects of absolute environmental sustainability assessment based on planetary boundaries

The integration of Planetary Boundaries (PBs) in Life Cycle Assessment (LCA) enables the assessment of the environmental sustainability of systems, with the resulting approach termed Absolute Environmental Sustainability Assessments (AESA). This approach has gained significant interest from academia to policymaking, leading to increasing applications but also differing methodologies. To ensure the robustness and comparability of AESA studies, we critically investigate two key methodological aspects related to i) harmonisation of LCA indicators with the PBs control variables and ii) allocation of the Safe Operating Space delineated by the PBs to systems. We use as a case study the EU consumption Footprint to analyse the effects of these methodological aspects on AESA results. Our findings suggest that current consumption patterns in the EU are environmentally unsustainable under an equal per capita principle for all (harmonisation) methods, with at least one boundary transgressed. The extent of boundary transgression varies significantly across methods due to differences in modelling parameters or boundary definition. The choice of allocation principle also significantly affects AESA results, and can even reverse the study's conclusions (e.g. under the Acquired Rights principle). This highlights the utmost importance of employing multiple principles as a sensitivity analysis in AESA studies to ensure robust conclusions. Future work should align individual methods to use similar methodological assumptions, and investigate the merits of developing PB-dependent allocation factors. Regionalisation of boundaries and inclusion of the Biosphere integrity PB are also key limitations that should be investigated. • EU share varies over 1 order of magnitude depending on allocation principle. • Sensitivity analysis of allocation principle is key to interpret AESA results • AESA impact assessment methods yield significantly different results • Future research must harmonise assumptions in impact methods. • EU consumption exceeds PBs under most of the approaches investigated.