Page 197 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 183

per impact category is possible as for normalised and weighted midpoint indi-
cators while avoiding the need for normalisation and weighting and the associ-
ated increased uncertainty and change in meaning.
3. Misconception: Endpoint characterisation is more uncertain than midpoint
characterisation.
Fact: This may be the case when looking at a limited set of sources of uncer-
tainty and how they contribute to the uncertainty of the value of the indicator.
However, when considering all relevant sources of uncertainty and the relevance
of the indicator for the decision at hand, the choice of indicator has no influence
on the uncertainty of the consequences of the decision. This is discussed in
detail in Chap. 11.

To go from midpoint to endpoint indicator scores, additional midpoint-to-
endpoint characterisation factors (sometimes also referred to as severity or damage
characterisation factors) are needed, expressing the ability of a change in the
midpoint indicator to affect the endpoint indicator. In contrast to the midpoint
characterisation factors which reflect the properties of the elementary flow and
hence are elementary flow-specific, the midpoint-to-endpoint characterisation fac-
tors reflect the properties of the midpoint indicator and there is hence only one per
midpoint impact category. Some LCIA methods only support endpoint character-
isation and here the midpoint and midpoint-to-endpoint characterisation is com-
bined in one characterisation factor.

10.2.3.8 Midpoint or Endpoint Assessment?

Next to the relationship between environmental relevance and various sources of
uncertainty discussed above (and in more detail in Chap. 11), the possibility to
aggregate information from midpoint to endpoint level while avoiding normalisa-
tion has the advantage of providing more condensed information (fewer indicator
results) to consider for a decision, while still being transparent as to which impact
pathway(s) are the main causes of these damages. Instead of perceiving midpoint
and endpoint characterisation as two alternatives to choose from, it is recommended
to conduct an LCIA on both midpoint and endpoint level (using an LCIA method
that provides both) to support the interpretation of the results obtained and which
complement each other respectively.

10.2.3.9 Time Horizons and Temporal Variability?
Environmental impacts caused by an intervention will require different amounts of
time to occur, depending on the environmental mechanism and the speed at which
its processes take place. This means that next to the fact that the numerous ele-
mentary flows of an LCI may occur at different moments in time during the life
cycle of the product or service assessed (which may be long for certain products