Page 31 - Materials Chemistry, Second Edition

2 Main Characteristics of LCA 13

As shown above, decreasing impacts on climate change by substituting fossil fuels
with biofuels has the potential to cause an increase in other environmental issues
such as water scarcity, eutrophication, land occupation and transformation.

2.2.3 Is Quantitative

LCA results answer the question “how much does a product system potentially
impact the environment?” Part of the answer may be “the impact on climate change
is 87 kg of CO 2 equivalents”. The quantitative nature of LCA means that it can be
used to compare environmental impacts of different processes and product systems.
This can, for example, be used to judge which products or systems are better for the
environment or to point to the processes that contribute the most to the overall
impact and therefore should receive attention. LCA results are calculated by
(1) mapping all emissions and resource uses and, if possible, the geographical
locations of these, and (2) use factors derived from mathematical cause/effect
models to calculate potential impacts on the environment from these emissions and
resource uses. The first step often involves thousands of emissions and resource
uses, e.g. “0.187 kg CO 2 , 0.897 kg nitrogen to freshwater, 0.000000859 kg dioxin
3
to air, 1.54 kg bauxite, 0.331 m freshwater…”. In the second step the complexity
is reduced by classifying these thousands of flows into a manageable number of
environmental issues, typically around fifteen (see above). Quantifications generally
aim for the “best estimate”, meaning that average values of parameters involved in
the modelling are consistently chosen (see Chap. 10).

2.2.4 Is Based on Science

The quantification of potential impacts in LCA is rooted in natural science. Flows
are generally based on measurements, e.g. water gauges or particle counters at
industrial sites or mass balances over the processes. The models of the relationships
between emission (or resource consumption) and impact are based on proven
causalities, e.g. the chemical reaction schemes involving nitrogen oxides and
volatile organic compounds in the formation of atmospheric ground level ozone
(smog) or on empirically observed relationships, e.g. between the concentration of
phosphorous in a lake and the observed numbers of species and their populations.
On top of its science core, LCA requires value judgement, which is most evident in
the optional step of assigning weights to different types of environmental problems
to evaluate the overall impact of a product system. LCA strives to handle value
judgement consistently and transparently and in some cases allows practitioners to
make modelling choices based on their own values, for example with respect to the
number of years into the future that environmental impacts should be considered in
the assessment.