50
3 Exploring Some Fundamentals of Environmental Footprints
the IPOFs have a better performance in the sense that they are able to achieve
this integration without performing a double weighting that would certainly
compromise the validity of the final estimate.
To sum, double counting and double weighting can be avoided by using the IPOFs
rather than using the IVOFs.
3.3.3.2 An Initial Framework for Characterization, Normalization,
and Weighting of the IPOFs
Now, it seems to be clear that the integration of environmental footprints only makes
sense if all involved are members of the IPOF category, to which knowledge of LCIA
would be of great benefit. In the LCA framework, LCIA takes place as a subsequent
step to LCI, where a number of elementary flows are translated into single impact
indicators and, if desired, then weighted and integrated into a comprehensive metric.
Essentially, LCIA consists of three major steps: characterization, normalization, and
weighting. While according to ISO (2006) the weighting is optional and not recommended for comparative assertions communicated to general public because of the
subjectivity and uncertainty, weighting between impact categories greatly facilitates
policy making (Hellweg and Milà i Canals 2014). This is particularly true for analysis
aimed at informing policy makers who are in favor of weighted indicators that make
alternatives easily comparable (Ahlroth et al. 2011). Therefore, footprint weighting
in our view can be considered as part of the established practice although it should
be interpreted with caution (Fang et al. 2015). This is moreover a logical extension
to the idea of the footprint family that is mainly limited to a conceptual discussion.
To cite an example, we assume that, along the life cycle of a product system, all of
the required data are available. In that case, many conceivable IPOFs can be imitated
by multiplying the inventory results with corresponding characterization factors such
as ozone depletion potential (ODP), terrestrial acidification potential (TAP), and
aquatic ecotoxicity potential (AEP). Returning to the mathematical formulation in
Sect. 3.2.1, we calculate a set of IPOFj through:
I P O F j =
i
M i × c f i j
(3.4)
The outcome is impact indicators expressed in equivalent units (e.g., kg CFC-11eq., kg SO 2 -eq., kg 1,4-DCB-eq.), which are common to all contributing substances
within the impact category, but not across impact categories due to incomparable
units. This is why normalization is needed after characterization. The calculation
principle of normalization is transparent (Heijungs et al. 2007): each normalized
footprint nIPOF j is equal to the ratio of the product footprint to the reference system’s
footprint for that category IPOF ref,j :
3 Exploring Some Fundamentals of Environmental Footprints
the IPOFs have a better performance in the sense that they are able to achieve
this integration without performing a double weighting that would certainly
compromise the validity of the final estimate.
To sum, double counting and double weighting can be avoided by using the IPOFs
rather than using the IVOFs.
3.3.3.2 An Initial Framework for Characterization, Normalization,
and Weighting of the IPOFs
Now, it seems to be clear that the integration of environmental footprints only makes
sense if all involved are members of the IPOF category, to which knowledge of LCIA
would be of great benefit. In the LCA framework, LCIA takes place as a subsequent
step to LCI, where a number of elementary flows are translated into single impact
indicators and, if desired, then weighted and integrated into a comprehensive metric.
Essentially, LCIA consists of three major steps: characterization, normalization, and
weighting. While according to ISO (2006) the weighting is optional and not recommended for comparative assertions communicated to general public because of the
subjectivity and uncertainty, weighting between impact categories greatly facilitates
policy making (Hellweg and Milà i Canals 2014). This is particularly true for analysis
aimed at informing policy makers who are in favor of weighted indicators that make
alternatives easily comparable (Ahlroth et al. 2011). Therefore, footprint weighting
in our view can be considered as part of the established practice although it should
be interpreted with caution (Fang et al. 2015). This is moreover a logical extension
to the idea of the footprint family that is mainly limited to a conceptual discussion.
To cite an example, we assume that, along the life cycle of a product system, all of
the required data are available. In that case, many conceivable IPOFs can be imitated
by multiplying the inventory results with corresponding characterization factors such
as ozone depletion potential (ODP), terrestrial acidification potential (TAP), and
aquatic ecotoxicity potential (AEP). Returning to the mathematical formulation in
Sect. 3.2.1, we calculate a set of IPOFj through:
I P O F j =
i
M i × c f i j
(3.4)
The outcome is impact indicators expressed in equivalent units (e.g., kg CFC-11eq., kg SO 2 -eq., kg 1,4-DCB-eq.), which are common to all contributing substances
within the impact category, but not across impact categories due to incomparable
units. This is why normalization is needed after characterization. The calculation
principle of normalization is transparent (Heijungs et al. 2007): each normalized
footprint nIPOF j is equal to the ratio of the product footprint to the reference system’s
footprint for that category IPOF ref,j :