An axiomatic method for goal-dependent allocation in life cycle assessment

How to apply allocation in an life cycle assessment (LCA) is a long-running and controversial debate. Consensus seems to exist on the fact that the allocation procedure should follow logically from the LCA goal definition. This paper proposes to use an axiomatic method to (1) identify an allocation procedure for co-production, joint treatment, and recycling, that best responds to a specific LCA goal and (2) communicate the rationale applied by the LCA practitioner transparently. The method is illustrated via a case study. The specific goal definition for which a suitable allocation procedure is identified is to evaluate what impacts can be attributed to a product, which could inform a company about potential sources of reputation damage. Subjective assumptions that reflect our vision of “what impacts can be attributed to a product” are described in definitions and axioms. Axioms are formulated that describe the system boundaries of the product system and the partitioning criterion. The derived allocation procedure corresponds to “Allocation at the Point of Substitution,” which is applied in one of the system models of ecoinvent. Partitioning is based on market information, which corresponds to a cause-oriented perspective on “what impacts can be attributed to a product.” Other LCA goal definitions and rationales could require different system boundaries or a different partitioning criterion. The axiomatic method presented in this paper supports the identification of a suitable allocation procedure for a defined LCA goal and the transparent communication of the rationale that backs up this procedure. Building forth on the approach of this paper, a collection of axioms and corresponding allocation procedures could be developed on which consensus might exist within the LCA community. Such goal-dependent allocation procedures could form the basis of future guidance on LCA.