Page 205 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 191

NS c ¼ IS c NF c ð10:3Þ

Two different approaches exist for collection of inventory data for the calcula-
tion of NFs (with the exception for global NFs, where both approaches give equal
results):
• Production-based (or top-down), representing the interventions taking place in
the reference region as result of the total activities in the region
• Consumption-based (or bottom-up), representing the interventions that are
caused somewhere in the world as consequence of the consumption taking place
in the reference region (and thus representing the demand for industrial and
other activities within and outside the reference region)
Other ways to derive NF (although somewhat bordering to weighting already)
are to base them on a conceptual “available environmental space”. This can be
determined using, e.g. political targets for limits of environmental interventions or
impacts for a given duration and reference year (i.e. “politically determined envi-
ronmental space” being the average environmental impact per inhabitant if the
political reduction targets are to be met), or a region’s or the planet’s carrying
capacity (i.e. “environmental space” being the amount of environmental interven-
tions or impacts that the region or planet can buffer without suffering changes to its
environmental equilibrium within each impact category). The latter would require
knowing the amount of impact that a region or the planet can take before suffering
permanent damage, which is a concept associated with much ambiguity and hence
very uncertain to quantify. There is increasing focus on science-based targets in the
environmental regulation with the 2 °C ceiling for climate change as the most
prominent example, and this may lead to future consensus building on
science-based targets also for some of the other impacts that are modelled in LCIA.
Political targets are often determined at different times and apply to different periods
of time. In order to ensure a consistent treatment of each impact category, it is
necessary to harmonise the target values available so that all targets for any given
intervention are converted to apply to the same period and reference year. The
targets can be harmonised by interpolating or extrapolating to a reduction target for
a common target year, computed relative to interventions in the reference year.
More details can be found in Hauschild and Wenzel (1998).
Caution is required when interpreting normalised LCA results! Applying nor-
malisation harmonises the metrics for the different impact potentials and brings
them on a common scale, but it also changes the results of the LCA and conse-
quently may change the conclusions drawn from these. Since there is no one
objectively correct choice of reference systems for normalisation, the interpretation
of normalised LCA results must therefore always be done with due consideration of
this choice of normalisation reference. A few main issues that need to be considered
when interpreting normalised LCA results are:
• Depending on the size of and activities reflected in the reference system, dif-
ferent biases may be introduced in the comparison of the impact scores of a