Life Cycle Impact Assessment Workshop Summary Midpoints versus Endpoints: The Sacrifices and Benefits

TLDR

Midpoints link emissions to environmental impacts and are commonly quantified by factors such as ozone depletion, global warming, and smog potentials, though recent methods now use endpoint factors like DALYs for health and biodiversity. The UNEP workshop convened experts to debate midpoint versus endpoint LCIA modeling, examining how each approach affects uncertainty, transparency, and the ability to resolve trade‑offs across impact categories. Participants agreed that both midpoint and endpoint methods supply valuable decision‑making information, urging the development of integrated tools that combine them.

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, prompting the call for tools that include both in a consistent framework.