Midpoints versus endpoints: The sacrifices and benefits

Abstract

On May 25-26, 2000 in Brighton (England), the third in a series of international workshops was held under the um- brella of UNEP addressing issues in Life Cycle Impact Assess- ment (LCIA). The workshop provided a forum for experts to dis- cuss midpoint vs. endpoint modeling. Midpoints are considered to be links in the cause-effect chain (environmental mechanism) of an impact category, prior to the endpoints, at which charac- terization factors or indicators can be derived to reflect the rela- tive importance of emissions or extractions. Common examples of midpoint characterization factors include ozone depletion potentials, global warming potentials, and photochemical ozone (smog) creation potentials. Recently, however, some methodolo- gies have adopted characterization factors at an endpoint level in the cause-effect chain for all categories of impact (e.g., human health impacts in terms of disability adjusted life years for carcinogenicity, climate change, ozone depletion, photochemical ozone creation; or impacts in terms of changes in biodiversity, etc.). The topics addressed at this workshop included the implica- tions of midpoint versus endpoint indicators with respect to un- certainty (parameter, model and scenario), transparency and the ability to subsequently resolve trade-offs across impact categories using weighting techniques. The workshop closed with a consen- sus that both midpoint and endpoint methodologies provide use- ful information to the decision maker, prompt