Product lifetime in life cycle assessments of circular economy strategies — A review and consolidation of methodology

Abstract Purpose Product lifetime is central to circular strategies that by lifetime extension could increase products’ environmental performance. In life cycle assessment (LCA), little attention has been paid to product lifetime modelling, although the environmental benefit of lifetime extension can vary greatly with lifetime values. Since product lifetime modelling may have a significant effect on the results, this study identifies and explains existing approaches. The consolidation of methodology for lifetime extension in LCA can support practice as well as further development of methodology. Methods A scoping literature review identified 67 LCA studies of lifetime extension containing 95 cases. The analysis focused on the case description of product lifetime and its integration in LCA calculations. Then, an overview of product lifetime modelling approaches and guidance for selecting them were developed and summarised into a product lifetime modelling framework which follows LCA methodological steps. Results and discussion Lifetime modelling differs in terms of (1) the lifetime definition, specifying in the goal and scope definition whether periods of idleness and the full technical lifetime are included, (2) the lifetime integration in equations either using a single value, no fixed value or distribution over a population in the inventory analysis and impact assessment and (3) the lifetime sensitivity analysis during interpretation. However, unclear descriptions of lifetime definition and missing references to lifetime data sources in 63 and 26% of the cases, respectively, show that reporting of product lifetime modelling is insufficient for unambiguous interpretation of the results. Additionally, significant variations in LCA results observed through lifetime sensitivity analysis underscore the importance of product lifetime modelling in LCA of lifetime extension. Conclusions Product lifetime modelling is not straightforward, as evidenced by the variety of definitions and existing approaches. The developed lifetime modelling framework offers LCA practitioners a more informed and structured approach to modelling lifetime extension in LCA, highlighting the importance of clear methodology requirements and further development. Recommendations Given the significance of product lifetime for LCA of lifetime extension, along with the observed inconsistencies and often insufficient reporting practices, LCA practitioners are encouraged to carefully consider the definition, integration in equations and sensitivity of product lifetime and to report these aspects transparently. The new framework can support these considerations.