Black swans swimming in product streams: method for including unplanned events in life cycle assessment

Abstract

Introduction: Unplanned events such as accidents and more massive black-swan events are contingent to modern technology. However, varying approaches and inconsistent guidelines make the inclusion of unplanned events in life cycle assessment (LCA) uncommon and challenging. This paper discusses the relevance of considering unplanned events in LCA and shows how they can be included in LCA practice. Method: A theoretical background to the concepts of black swans, accidents, and unplanned events is first provided. We then propose a method for how unplanned events can be included in LCA practice, illustrated through three cases: (i) a sabotage in the energy system, (ii) an accident in the use phase, and (iii) a sudden policy change. Results: The results show that unplanned events can be included and may significantly affect LCA results, sometimes even fulfilling criteria for black-swan events. Conclusions: We suggest that unplanned events should be included in LCA when relevant, e.g. as one scenario in LCAs of product systems sensitive to accidents. We also suggest that changes in flows due to unplanned events should be considered in unit processes, so that their impacts become distributed across downstream product systems depending on demand for the unit-process output.