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The environmental impacts of food are currently at unsustainable levels. Consumers undoubtedly play a central role in reducing the impacts of the food system to more sustainable levels via dietary changes and food waste reduction. Mathematical optimisation is one approach to identifying less environmentally impactful dietary patterns. A limited number of studies, however, have assessed whether impact reductions offered by optimised diets are enough to remain within planetary boundaries (i.e. attain ‘absolute’ environmental sustainability). Using UK food consumption as a case study, here we employ linear programming to identify nutritionally adequate diets that meet sociocultural acceptability criteria whilst minimising (a) environmental impact transgressions of their allocated share of the safe operating space (SoSOS) for nine planetary boundaries (PBs), (b) cost, or (c) deviation from the current diet. We show that the current diet is unsustainable as it transgresses six or seven PBs, depending on the SoSOS allocation principle. Optimising for minimum SoSOS transgressions yields diets offering significant impact reductions (66 - 95% reduction across all PBs) compared to the current average dietary pattern, but whether they completely mitigate SoSOS transgressions depends on the sharing principle adopted to assign the SoSOS to national food consumption. Additionally, by comparing least-cost and least-transgression solutions, we find a trade-off between cost and environmental sustainability indicating that more sustainable dietary patterns are not currently incentivised by the relative prices of food items in the UK. Our work demonstrates the value in embedding ‘absolute’ sustainability in diet optimisation so that solutions inherently provide a more clear-cut understanding of their broad implications on the environment., Sustainable Production and Consumption, 28, ISSN:2352-5509

Marine eutrophication and hypoxia caused by excess nutrient availability is a growing environmental problem. In this study, we explore marine nitrogen enrichment in the context of Absolute Environmental Sustainability Assessment (AESA), a method combining life cycle assessment (LCA) with environmental boundaries aiming to compare environmental impacts from an activity (product or system) with the safe operating space (SOS) for the activity. Specifically, we aim to increase the spatial resolution and improve life cycle impact assessment (LCIA) models for marine eutrophication for use in AESAs. By estimating a proxy of the areal extent of eutrophication and hypoxia in coastal large marine ecosystems (LME), we increased model resolution from 66 LMEs in the original LCIA method to 289 coastal LME subsegments and updated relevant LME parameters to the new scale (residence time, bottom water volume, reference O2 concentration, primary production rates and depths). The new method was tested and validated by comparing the global and spatially differentiated occupation of SOS by global nitrogen emissions with observations and it showed an improved ability to identify critical areas where the SOS is exceeded, in accordance with observations of hypoxic events. Despite limitations such as the estimation of benthic zone volume and low spatial differentiation of environmental boundaries, the method can be used by AESA and LCA practitioners wishing to assess the impact of nitrogen release on marine eutrophication with a higher and more relevant spatial resolution.

The safe operating space as defined by the Planetary Boundaries framework can be used as an environmental sustainability reference in absolute environmental sustainability assessments (AESAs). In AESAs, the safe operating space must be distributed among human activities so impacts associated with an activity can be related to its assigned share of the safe operating space to assess if the activity can be considered absolute sustainable. To ensure choices concerning sharing principles in AESA are deliberate, there is a need for understanding the distributive justice theory underlying the sharing principles. This study provides a framework for determining and communicating the distributive justice theories that underlie the choice of sharing principles in AESA. To comprehensively describe a sharing principle in relation to distributive justice theories, seven dimensions must be defined, i.e. target, currency, pattern, geographical scope, temporal scope, clauses, and constraints. We conducted a review of sharing principles used in AESAs in relation to contemporary distributive justice theories. 18 studies were identified with 34 sharing principles being applied. The most commonly applied sharing principle is equal per capita sharing of the safe operating space among countries or individuals. This was often combined with utilitarian principles for sharing among industrial units. Based on the review and analysis of the results, we provide recommendations on best practice for defining sharing principles in AESAs systematically based on distributive justice theories and recommendations for further research. The framework developed in this study provide a first step towards a systematic and informed selection of sharing principles used in AESAs.