Page 198 - Materials Chemistry, Second Edition

184 R.K. Rosenbaum et al.

like buildings for example), there is also a difference in the lag until their impacts
occur. However, the way LCA is currently conducted, potential impacts are
assessed as if interventions and potential impacts were happening instantly,
aggregating them over time and over the entire life cycle. This means that these
potential impacts need to be interpreted as a “backpack” of potential impacts
attributable to the product or service assessed.
Next to such temporal variability, another potential source of time-related in-
consistency in LCA is the problem of applying different time horizons for different
impact categories. These time horizons are sometimes explicit (e.g. the 20 and
100 years’ time horizons for global warming potentials), but in most cases implicit
in the way the environmental mechanism has been modelled (e.g. over what time
horizon the impact has been integrated). This may result in a mixing of different
time horizons for different impacts in the same LCIA, which may have implications
for the interpretation of LCA results. For example, methane has a lifetime much
shorter than CO 2 . Therefore, depending on the time horizon chosen, the charac-
terisation of methane will change. This is directly connected to the question of how
to consider potential impacts affecting current and immediate future generations
versus those affecting generations in a more distant future.
Another issue concerns the temporal course of the emission and its resulting
impacts. While some impacts may be immediately (i.e. within a few years) tangible
and directly affecting a larger number of individuals (human or not), some impacts
may be very small at any given moment in time, but permanently occurring for tens
to hundreds of thousands of years (e.g. impacts from heavy metal emissions from
landfills or mine tailings). Between these two illustrative extremes, lies any possible
combination of duration versus severity.

10.2.3.10 Spatial Variability and Regionalisation?

Some impacts are described as global because their environmental mechanism is the
same regardless where in the world the emission occurs. Global warming and
stratospheric ozone depletion are two examples. Other impacts, such as acidification,
eutrophication or toxicity may be classified as regional, affecting a (sub-)continent or
a smaller region surrounding the point of emission only. Impacts affecting a small
area are designated as local impacts, water or direct land-use impacts on biodiversity
for example. Whereas for global impact categories the site where the intervention
takes place has no considerable influence on the type and magnitude of its related
potential impact(s), for regional or local impacts this may influence the magnitude of
the potential impact(s) up to several orders of magnitude (e.g. a toxic emission taking
place in a very large and densely populated city or habitat versus somewhere remote
in a large desert). This spatial variability can be dealt with in two ways:

• Identification and modelling of archetypal emission/extraction situations and
their potential impacts (e.g. toxic emission into urban air, rural air or remote air)