3.2 Investigation into the Inventory and Characterization …
41
Note that, in this chapter, “inventory data” refers to the inputs of the inventory
calculations (e.g., unit process data), “inventory results” in contrast refers to the
outputs of the inventory calculations (e.g., system-wide emissions and extractions),
and the weighted inventory results are out of the scope of these terms. Furthermore,
weighting substances within a footprint, namely, inventory aggregation, should be
distinguished from weighting footprints, which will be discussed in the following
sections. For convenience, we name the former as “(inventory) weighting” and the
latter as “(footprint) weighting”. By contrast, in the field of LCA, the term “weighting” is restricted to what here we call footprint weighting (ISO 2006). Inventory
weighting is not recognized in the LCA standards, but in other tools, for environmental assessment, it may occur from time to time (e.g., Hoekstra and Hung
2002).
In keeping with the framework described above, criteria are developed for selection prior to the evaluation of footprint indicators: (1) documentation of competing
versions; (2) transparency in each of the methodologies; and (3) applicability to classification. For these concerns, a systematic and critical investigation into the inventory
analysis and/or impact characterization will be presented specifically for four footprints: the carbon footprint, the water footprint, the land footprint, and the material
footprint. For each of them, we identify two basic versions. It is worth mentioning that
contrary to common practices, the ecological footprint in this chapter is presented
in a disaggregated form. It means that we choose to separately investigate its abiotic
and biotic components, as will be illustrated below.
3.2.2 Carbon Footprint
3.2.2.1 Climate-Related Carbon Footprint (CF clim )
The widely used climate-related carbon footprint (CF clim ) compiles the inventory
data of greenhouse gas (GHG) emissions (e.g., CO 2 , CH 4 , N 2 O) throughout the
investigated system boundaries, and characterizes and aggregates them into a mass
equivalent metric (e.g., kg CO 2 -eq.) on the basis of their respective global warming
potentials (GWPs)—a global-specific characterization factor representing the integrated radiative forcing over a specified time horizon, with a reference to CO 2
(IPCC2014; Wiedmann and Minx 2008). While being arbitrarily configured by
default to report a time horizon of 100-yr in practice, the GWP is deemed one of the
most established and consensus-based characterization factors in LCIA (Hauschild
et al. 2013; Laurent et al. 2012), and is also used much outside LCA. International
consensus has thus been reached on the characterization modeling used for the CF clim
(Hellweg and Milà i Canals 2014; Ridoutt and Pfister 2013b). For the inventory part,
however, there is much less agreement. In LCA, for instance, the issue of allocation of multi-functional processes is a nagging topic, and there is also disagreement on the accounting of biogenic carbon. In IOA, an example of the controversy
is the choice between commodity-by-commodity tables and industry-by-industry
41
Note that, in this chapter, “inventory data” refers to the inputs of the inventory
calculations (e.g., unit process data), “inventory results” in contrast refers to the
outputs of the inventory calculations (e.g., system-wide emissions and extractions),
and the weighted inventory results are out of the scope of these terms. Furthermore,
weighting substances within a footprint, namely, inventory aggregation, should be
distinguished from weighting footprints, which will be discussed in the following
sections. For convenience, we name the former as “(inventory) weighting” and the
latter as “(footprint) weighting”. By contrast, in the field of LCA, the term “weighting” is restricted to what here we call footprint weighting (ISO 2006). Inventory
weighting is not recognized in the LCA standards, but in other tools, for environmental assessment, it may occur from time to time (e.g., Hoekstra and Hung
2002).
In keeping with the framework described above, criteria are developed for selection prior to the evaluation of footprint indicators: (1) documentation of competing
versions; (2) transparency in each of the methodologies; and (3) applicability to classification. For these concerns, a systematic and critical investigation into the inventory
analysis and/or impact characterization will be presented specifically for four footprints: the carbon footprint, the water footprint, the land footprint, and the material
footprint. For each of them, we identify two basic versions. It is worth mentioning that
contrary to common practices, the ecological footprint in this chapter is presented
in a disaggregated form. It means that we choose to separately investigate its abiotic
and biotic components, as will be illustrated below.
3.2.2 Carbon Footprint
3.2.2.1 Climate-Related Carbon Footprint (CF clim )
The widely used climate-related carbon footprint (CF clim ) compiles the inventory
data of greenhouse gas (GHG) emissions (e.g., CO 2 , CH 4 , N 2 O) throughout the
investigated system boundaries, and characterizes and aggregates them into a mass
equivalent metric (e.g., kg CO 2 -eq.) on the basis of their respective global warming
potentials (GWPs)—a global-specific characterization factor representing the integrated radiative forcing over a specified time horizon, with a reference to CO 2
(IPCC2014; Wiedmann and Minx 2008). While being arbitrarily configured by
default to report a time horizon of 100-yr in practice, the GWP is deemed one of the
most established and consensus-based characterization factors in LCIA (Hauschild
et al. 2013; Laurent et al. 2012), and is also used much outside LCA. International
consensus has thus been reached on the characterization modeling used for the CF clim
(Hellweg and Milà i Canals 2014; Ridoutt and Pfister 2013b). For the inventory part,
however, there is much less agreement. In LCA, for instance, the issue of allocation of multi-functional processes is a nagging topic, and there is also disagreement on the accounting of biogenic carbon. In IOA, an example of the controversy
is the choice between commodity-by-commodity tables and industry-by-industry