135
Differences in qualitative value choices, variation in precision among impact
categories among other LCIA methodological limitations, preclude it from acting as
the sole basis of publicly disclosed comparative assertions of environmental superiority of one specific product over another. But LCIA is useful in general large-scale
industrial sector product descriptions that can be evaluated against one another
especially if this is the stated purpose of the study.
In the LCIA phase, all of the individual inventory flows are classified into the
several environmental impact categories that they contribute to. For example, several gasses beyond carbon dioxide, including methane and nitrous oxide, contribute
to GWP (Kneifel et al. 2018). After each flow is assigned to an impact category, a
characterization factor (CF) must be applied to all of the flows in one category to get
a single equivalency impact score. These CFs reduce down a list of thousands of
flows into a handful of impact categories so that the results of the study can be more
easily understood.
The results of the LCIA phase can be presented as midpoint or endpoint indicators. Midpoint indicators combine the flows into equivalent values of one reference
flow (De Schryver 2011). Again using the example of GWP, kg CO 2 is commonly
used to represent the GWP of all chemicals, not just carbon dioxide. Endpoint indicators attempt to trace the potential impacts to the end of the cause-effect pathway
and quantify the damage done to human health, ecosystem health, and resource
availability (De Schryver 2011). While endpoint indicators can be more illustrative
or easier to comprehend on a quick glance, they also introduce more subjectivity
into the study, whereas the uncertainty of midpoint indicators is much lower (Curran
2012). All of the tools presented in this chapter primarily utilize midpoint indicators.
8.2.1 A Note on Interpretation
Interpretation is the fourth but iteratively repeating phase that specialists must complete when conducting an LCA study. It requires professional judgment to interpret
multiple results produced over successive passes through the other three phases. All
results from the LCI and LCIA phases are evaluated against the framing system
functions, functional unit, and system boundaries defined in the goal and scope
phase. The LCA operator will identify and report limitations and increased uncertainty created by data quality issues based on completeness, consistency, and sensitivity checks. If there is any missing or incomplete information, another pass
through the other phases is required. Once all constituent parts are reasonably complete and determined to be consistent with and supportive of the goal and scope of
the study, the LCA professional presents final qualified conclusions and recommendations to the individual or group who commissioned the study.
8.2 Life Cycle Impact Assessment and Interpretation
Differences in qualitative value choices, variation in precision among impact
categories among other LCIA methodological limitations, preclude it from acting as
the sole basis of publicly disclosed comparative assertions of environmental superiority of one specific product over another. But LCIA is useful in general large-scale
industrial sector product descriptions that can be evaluated against one another
especially if this is the stated purpose of the study.
In the LCIA phase, all of the individual inventory flows are classified into the
several environmental impact categories that they contribute to. For example, several gasses beyond carbon dioxide, including methane and nitrous oxide, contribute
to GWP (Kneifel et al. 2018). After each flow is assigned to an impact category, a
characterization factor (CF) must be applied to all of the flows in one category to get
a single equivalency impact score. These CFs reduce down a list of thousands of
flows into a handful of impact categories so that the results of the study can be more
easily understood.
The results of the LCIA phase can be presented as midpoint or endpoint indicators. Midpoint indicators combine the flows into equivalent values of one reference
flow (De Schryver 2011). Again using the example of GWP, kg CO 2 is commonly
used to represent the GWP of all chemicals, not just carbon dioxide. Endpoint indicators attempt to trace the potential impacts to the end of the cause-effect pathway
and quantify the damage done to human health, ecosystem health, and resource
availability (De Schryver 2011). While endpoint indicators can be more illustrative
or easier to comprehend on a quick glance, they also introduce more subjectivity
into the study, whereas the uncertainty of midpoint indicators is much lower (Curran
2012). All of the tools presented in this chapter primarily utilize midpoint indicators.
8.2.1 A Note on Interpretation
Interpretation is the fourth but iteratively repeating phase that specialists must complete when conducting an LCA study. It requires professional judgment to interpret
multiple results produced over successive passes through the other three phases. All
results from the LCI and LCIA phases are evaluated against the framing system
functions, functional unit, and system boundaries defined in the goal and scope
phase. The LCA operator will identify and report limitations and increased uncertainty created by data quality issues based on completeness, consistency, and sensitivity checks. If there is any missing or incomplete information, another pass
through the other phases is required. Once all constituent parts are reasonably complete and determined to be consistent with and supportive of the goal and scope of
the study, the LCA professional presents final qualified conclusions and recommendations to the individual or group who commissioned the study.
8.2 Life Cycle Impact Assessment and Interpretation