2.3 Elaboration of a Footprint Family
19
et al. 2011). It is widely accepted that the life cycle assessment (LCA) is a useful
tool for calculating the carbon footprint, especially at the product level (Wiedmann
and Minx 2008). Some standards such as the PAS 2050 (BSI 2008) and ISO 14,067
(Wiedmann 2009b) have been or are being established on a life cycle basis.
2.3.2.4 Water Footprint
The water footprint is another booming indicator that has gained worldwide popularity in recent years. It is defined as the cumulative virtual water content of all products and services consumed by individuals or communities within a given region
(Hoekstra 2009; Hoekstra and Hung 2002). The real-water content of a product,
in most cases, could be much less than the virtual water content (Chapagain and
Hoekstra 2008). The water footprint can thus be termed in a way similar to that of
the embodied energy, namely, the “embodied water” (Chambers et al. 2000). Two
principal methods have been applied to water footprint accounting: the bottom-up
and top-down approaches (Feng et al. 2011; Hoekstra 2009; Van Oel et al. 2009). The
bottom-up approach belongs to process analysis using detailed descriptions of individual production processes and, conversely, the top-down approach resembles IOA
which is an economic approach adopted in economic and environmental domains
(Feng et al. 2011). The international water footprint standards are simultaneously
under development by the Water Footprint Network (WFN) (Hoekstra et al. 2011)
and the International Organization for Standardization (ISO) 14,046 (ISO 2014).
2.3.3 Comparison of Selected Footprints
Based on a review of original articles on the fundamentals and applications of environmental footprints over the past two decades, here, we examine the differences
and similarities of the ecological, energy, carbon, and water footprints by listing key
issues in Table 2.2. Despite sharing the term “footprint” in their names, the four
footprints differ in more aspects than only in the impacts that are addressed, such as
conceptual roots, research stressors, footprint components, metric units, calculation
methods, and so on. We elaborate on the key differences item by item.
2.3.3.1 Roots and Stressors
(a) In ecological footprint accounting, six footprint components are distinguished
in accordance with major land use types. All of these are built on six ecosystem
services for human well-being: plant-based food production, livestock-based
food production, fish-based food production, timber production, living space
supply, and energy-related CO 2 absorption (Galli et al. 2012; Kitzes et al. 2009;
Moore et al. 2012). Components are weighted with equivalence factors before
19
et al. 2011). It is widely accepted that the life cycle assessment (LCA) is a useful
tool for calculating the carbon footprint, especially at the product level (Wiedmann
and Minx 2008). Some standards such as the PAS 2050 (BSI 2008) and ISO 14,067
(Wiedmann 2009b) have been or are being established on a life cycle basis.
2.3.2.4 Water Footprint
The water footprint is another booming indicator that has gained worldwide popularity in recent years. It is defined as the cumulative virtual water content of all products and services consumed by individuals or communities within a given region
(Hoekstra 2009; Hoekstra and Hung 2002). The real-water content of a product,
in most cases, could be much less than the virtual water content (Chapagain and
Hoekstra 2008). The water footprint can thus be termed in a way similar to that of
the embodied energy, namely, the “embodied water” (Chambers et al. 2000). Two
principal methods have been applied to water footprint accounting: the bottom-up
and top-down approaches (Feng et al. 2011; Hoekstra 2009; Van Oel et al. 2009). The
bottom-up approach belongs to process analysis using detailed descriptions of individual production processes and, conversely, the top-down approach resembles IOA
which is an economic approach adopted in economic and environmental domains
(Feng et al. 2011). The international water footprint standards are simultaneously
under development by the Water Footprint Network (WFN) (Hoekstra et al. 2011)
and the International Organization for Standardization (ISO) 14,046 (ISO 2014).
2.3.3 Comparison of Selected Footprints
Based on a review of original articles on the fundamentals and applications of environmental footprints over the past two decades, here, we examine the differences
and similarities of the ecological, energy, carbon, and water footprints by listing key
issues in Table 2.2. Despite sharing the term “footprint” in their names, the four
footprints differ in more aspects than only in the impacts that are addressed, such as
conceptual roots, research stressors, footprint components, metric units, calculation
methods, and so on. We elaborate on the key differences item by item.
2.3.3.1 Roots and Stressors
(a) In ecological footprint accounting, six footprint components are distinguished
in accordance with major land use types. All of these are built on six ecosystem
services for human well-being: plant-based food production, livestock-based
food production, fish-based food production, timber production, living space
supply, and energy-related CO 2 absorption (Galli et al. 2012; Kitzes et al. 2009;
Moore et al. 2012). Components are weighted with equivalence factors before