On May 25-26, 2000 in Brighton (England), the third
in a series of international workshops was held under the umbrella
of UNEP addressing issues in Life Cycle Impact Assessment
(LCIA). The workshop provided a forum for experts to discuss
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 characterization
factors or indicators can be derived to reflect the relative
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 methodologies
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 implications
of midpoint versus endpoint indicators with respect to uncertainty
(parameter, model and scenario), transparency and the
ability to subsequently resolve trade-offs across impact categories
using weighting techniques. The workshop closed with a consensus
that both midpoint and endpoint methodologies provide useful
information to the decision maker, prompting the call for tools
that include both in a consistent framework. |
