Advancing Planetary Boundaries Allocation: Systematic Comparison of Sharing Principles for National-Level Absolute Environmental Sustainability Assessments

The Planetary Boundaries (PBs) framework defines a safe operating space (SOS) for human activities. Allocating the global SOS to national levels is crucial for operationalizing the PBs concept, particularly for Absolute Environmental Sustainability Assessment (AESA). Previous AESA studies have employed different allocation approaches, leading to inconsistent and potentially divergent outcomes. However, there has been a lack of quantitative and systematic comparison of various allocation approaches. To address this, the present study investigates four main sharing principles: equal per capita, ability to pay, grandfathering, and responsibility. In particular, for emission-based approaches (i.e. grandfathering and responsibility), the study also investigates i) the sensitivity of results to the choice of the reference year, and ii) the importance of using PBs-specific allocation factors as opposed to PBs-independent factors based on greenhouse gas emissions. UK consumption is used as a case study and analyzed via an Environmentally Extended Multi-Regional Input-Output model using Exiobase. Results reveal significant variations (up to one order of magnitude) in the allocated SOS (aSOS) across different allocation principles for all 12 control variables analyzed in this study, with grandfathering yielding the largest and ability to pay the lowest aSOS. Using PBs-specific factors instead of GHG-based ones reduces aSOS for land-system change determined by the grandfathering by 30%, while also significantly affecting the aSOS for 5 CVs for the responsibility approach. Our findings highlight the importance of considering multiple allocation approaches for national-level AESA to ensure more comprehensive, equitable, and reliable assessments of environmental sustainability.