5.4 Complementary Use of Environmental Footprints and Planetary …
77
natural capital, of which the failure of maintenance leads to unsustainability. Goodland and Daly (1996) legitimized environmental sustainability by three input–output
rules: (1) harvest within the regenerative capacity of renewable resources; (2) waste
within the absorptive capacity of natural systems; and (3) depletion of non-renewable
resources at a rate less than that of renewable substitutes.
Despite the high transparency, completeness, and acceptability that Goodland and
Daly’s definition provides, a fundamental obstacle to environmental sustainability
assessment (ESA) is the difficulty in predicting how long a life-supporting system
is to be sustainable, rather than in discriminating sustainability and unsustainability
after the fact (Costanza and Patten 1995). This results from a lack of methods for
quantifying the regenerative and absorptive capacity. As a breakthrough to fill in this
gap, the PBF gives, for the first time, numerical results for capacity thresholds at the
global scale. Meanwhile, the footprint metric serves as a counterpart to the boundary
metric by offering background values for environmental issues and thereby helping
to better understand the concept of environmental sustainability.
5.4.2 A Footprint–Boundary ESA (F–B ESA) Framework
To preserve the planet’s environment from facing unexpected or irreversible changes,
a first step would be the development of ways of ascertaining whether human activities are kept within permissible limits. Due to their relative emphases and challenges noted above, neither environmental footprints nor planetary boundaries can
adequately address this complicated issue solely; therefore, they should rather be
used complementarily to make sense of the ESA. In deriving a footprint–boundary
representation of environmental sustainability, clarity on definitions of both environmental footprints and planetary boundaries is required. Although there are already
many attempts for making the two concepts transparent, we contend that any definitions work satisfactorily only if placed in an appropriate context, i.e., none is able to fit
for all purposes. For this reason, environmental footprints and planetary boundaries
will be specified as follows:
• Environmental footprints: a measure of human pressure or impact on the planet’s
environment in relation to resource extractions and hazardous emissions. In
a mathematical context, we indicate the footprint of pressure i (e.g., carbon
emission, water use, land use) as U footprint,i .
• Planetary boundaries: a measure of the regenerative and absorptive capacity of
the Earth’s life-supporting systems, beyond which unacceptable environmental
changes for humanity may occur. Accordingly, we denote the planetary boundary
of pressure i as U boundary,i .
Mathematically, we do two steps:
• Step 1 converts an environmental footprint and/or planetary boundary into a
common metric. For example, U footprint,CO 2 , U footprint,CH 4 , U footprint,N 2 O (in Gt/yr)
are collectively converted into Z footprint,climate (in Gt CO 2 -eq./yr) using the global
77
natural capital, of which the failure of maintenance leads to unsustainability. Goodland and Daly (1996) legitimized environmental sustainability by three input–output
rules: (1) harvest within the regenerative capacity of renewable resources; (2) waste
within the absorptive capacity of natural systems; and (3) depletion of non-renewable
resources at a rate less than that of renewable substitutes.
Despite the high transparency, completeness, and acceptability that Goodland and
Daly’s definition provides, a fundamental obstacle to environmental sustainability
assessment (ESA) is the difficulty in predicting how long a life-supporting system
is to be sustainable, rather than in discriminating sustainability and unsustainability
after the fact (Costanza and Patten 1995). This results from a lack of methods for
quantifying the regenerative and absorptive capacity. As a breakthrough to fill in this
gap, the PBF gives, for the first time, numerical results for capacity thresholds at the
global scale. Meanwhile, the footprint metric serves as a counterpart to the boundary
metric by offering background values for environmental issues and thereby helping
to better understand the concept of environmental sustainability.
5.4.2 A Footprint–Boundary ESA (F–B ESA) Framework
To preserve the planet’s environment from facing unexpected or irreversible changes,
a first step would be the development of ways of ascertaining whether human activities are kept within permissible limits. Due to their relative emphases and challenges noted above, neither environmental footprints nor planetary boundaries can
adequately address this complicated issue solely; therefore, they should rather be
used complementarily to make sense of the ESA. In deriving a footprint–boundary
representation of environmental sustainability, clarity on definitions of both environmental footprints and planetary boundaries is required. Although there are already
many attempts for making the two concepts transparent, we contend that any definitions work satisfactorily only if placed in an appropriate context, i.e., none is able to fit
for all purposes. For this reason, environmental footprints and planetary boundaries
will be specified as follows:
• Environmental footprints: a measure of human pressure or impact on the planet’s
environment in relation to resource extractions and hazardous emissions. In
a mathematical context, we indicate the footprint of pressure i (e.g., carbon
emission, water use, land use) as U footprint,i .
• Planetary boundaries: a measure of the regenerative and absorptive capacity of
the Earth’s life-supporting systems, beyond which unacceptable environmental
changes for humanity may occur. Accordingly, we denote the planetary boundary
of pressure i as U boundary,i .
Mathematically, we do two steps:
• Step 1 converts an environmental footprint and/or planetary boundary into a
common metric. For example, U footprint,CO 2 , U footprint,CH 4 , U footprint,N 2 O (in Gt/yr)
are collectively converted into Z footprint,climate (in Gt CO 2 -eq./yr) using the global