Absolute sustainability assessment of product life cycles through downscaling of planetary boundary to industry level

Absolute sustainability assessment in LCA is emerging as a new research topic based on planetary boundaries, which span a global “safe operating space” (SOS) of sustainable resource use and pollution. Such assessments... [ view full abstract ]

Absolute sustainability assessment in LCA is emerging as a new research topic based on planetary boundaries, which span a global “safe operating space” (SOS) of sustainable resource use and pollution. Such assessments involve the integration of planetary boundaries in life cycle impact assessment and the calculation of how much SOS studied industries or products can be considered entitled to, in order to assess if they can be considered sustainable in an absolute sense. This study 1) presents a method for calculating industry level SOS entitlement for the Gross value added (GVA) and Grandfathering (GF) approach, and 2) demonstrates the method in a case study of cow milk and soy milk for the environmental issues climate change and freshwater use. 

The GVA approach entails that the entitlement of an industry should be proportional to its contribution to the economy, while the GF approach entails that an industry “inherits” its proportion of the total impact in a past reference year as its entitled proportion of future impacts. The life cycle inventories of the case study were tentatively modelled using EXIOBASE V3. Characterization factors and SOSs for water use (blue water consumption) and climate change were developed based on the most recent planetary boundary estimates. All other parameters required to calculate life cycle impacts and entitlements were sourced from EXIOBASE. The accumulated exceedance of entitled carrying capacities across all industries in the life cycle of the two milk products were calculated. Industries located within the same spatial unit were allowed to “share” local carrying capacity entitlement, meaning that exceeded SOS entitlement of one industry could be compensated by another industry’s un-occupied SOS.

Preliminary case study results show that 1L of cow milk has a much higher climate and water use impact than 1L of soy milk. However, for water use, the unsustainable part of impacts was found to be higher for soy milk than for cow milk when following the GVA approach, due to the relatively high contribution to GVA of the industries in the cow milk life cycle. For the GF approach, the water use of both products appear 100% sustainable. However, the spatial (49 regions) and temporal (annual time steps) resolution of EXIOBASE V3 were found to “hide” potential SOS exceedances in individual watersheds and months, which is a limitation of using this approach to highly local and time-specific environmental issues. For climate change, less than 1% of life cycle emissions were found to be sustainable for both milk products and entitlement approaches.

Our approach can be considered a first step towards absolute sustainability assessments of product life cycles that rely on granting SOS entitlement at the industry level. The approach may be refined to account for more types of environmental issues, to cover other types of entitlement approaches and to improve the spatial and temporal resolution. The approach may also be complemented by assessments that grant a single SOS entitlement to a studied product, based on, e.g., an evaluation of its contribution to meeting human needs.