From Pressures to Impacts: - Life Cycle Impact Assessment

Life cycle assessment (LCA) has been developed as a tool for assessment of the environmental impacts which are caused by the pressures from products or systems, viewed in a life cycle perspective, i.e. covering all stages of the life cycle of the product or system from the extraction of raw materials over manufacture or construction through use to disposal or decommissioning and recycling. It is a holistic tool in the sense that it models all relevant environmental impacts from the global (like climate change and ozone depletion) to the local (like land use) and also the loss of resources. The framework for LCA has been standardised by the International Standards Organisation, ISO, which identifies four phases – Goal and scope definition, where the goal is defined, the service to be provided by the studied system is quantified in terms of the functional unit of the study, and the product system is defined, Inventory analysis where data for the physical flows to and from all processes in the life cycle is collected and related to the functional unit, Impact assessment, where the physical flows are translated into impacts on the environment and resource base, and Interpretation where the outcomes of the earlier phases are interpreted in relation to the goal of the LCA. LCA is typically used for comparisons, and in order to facilitate the comparison of the rather diverse environmental impacts which are comprised by the Life Cycle Impact Assessment (LCIA) methodology, procedures have been developed for normalisation and valuation which support aggregation and comparison across the different impacts. The resulting impact scores are seen as representing potential impacts rather than real effects due to: - The lack of knowledge about geographical conditions of most of the processes in the product system and the background conditions of the receiving environment - the aggregation of emissions over time and space - the fact that the emissions in the inventory represent the impacts from a functional unit, which for products often constitutes a minute fraction of the total output from the manufacturing stage. For waste management systems, it is pointed out, that these aspects may be less of a problem than for the typical product systems for which LCA was originally developed, since the environmental impacts from waste management systems are typically dominated by one or a few central waste treatment processes for which both the location, receiving environments and temporal emission profiles can be well known. The emissions of persistent pollutants from landfills does, however, pose special problems to LCIA due to an emission pattern characterised by a very long duration and very low concentrations of the emissions, which is quite different from the typical emission patterns from other processes in the life cycle, and which really requires a more risk-oriented assessment procedure than what is normally applied in LCIA. Finally, some of the topical discussions within the LCIA method development community are introduced, including questions like - How large a part of the environmental mechanism should we model? - For waste management systems (particularly for landfills), it is relevant to include site-specific information in the assessment - is it also possible? - (When) can we develop global recommendations for the life cycle impact assessment?