policymakers demonstrate

284 Paul Ekins, Paul Drummond, and Jim Watson
Because natural capital has featured regularly in various definitions of sustainability
and sustainable development, more attention has been paid to the
concept as sustainable development has risen up the public policy agenda. In
this context, considerable efforts have been invested in developing and making
environmental indicators operational (discussed in Section 7.3.3).
Weak and Strong Sustainability
Environmental economics traditionally considers environmental resource
scarcity as a Ricardian ‘relative scarcity’ issue, where biophysical constraints
on economic growth may be overcome by incurring additional cost in the economy
in the short-term (through investment in innovative technology) (Venkatachalam,
2007). This derives from a view that human or manufactured capital
can substitute almost entirely for natural capital and ecosystem services, leadingtotheweak
sustainability conclusion that, as long as the total economic
value of all capital stocks (natural, human and man-made) can be maintained
in real terms, regardless of the distribution between the different types, sustainability
is achieved. An important strand in the sustainability and sustainable
development literatures has called these assumptions into question, particularly
for natural capital. The idea of strong sustainability, more often espoused
in ecological economics, considers that certain elements, aspects are characteristics
of natural resources and the environment, such as uncertainty and the
‘irreversibility’ of some phenomena (e.g., an extinct species cannot be recovered)
(Pelenc and Ballet, 2015) mean that some kinds of natural capital, which
has been called ‘critical’ natural capital (CNC) (Ekins et al., 2003) makes a
unique contribution to welfare or has intrinsic value and therefore cannot be
substituted by manufactured or other forms of capital.
Despite the contrasting theoretical positions taken on these issues, there is
increasing alignment on them in practice in the environmental and ecological
economics literatures. For example, many environmental economists recognize
issues of multi-functionality, irreversibility and uncertainties surrounding natural
capital, and support the idea of maintaining the natural capital stock independently
of man-made capital. Summarizing the literature on the debate between
the validity of the weak or strong sustainability approaches, Dietz and Neumayer
(2007, p. 619) list four reasons why the strong approach to sustainability
may be preferred to the weak: risk and uncertainty, irreversibility, risk aversion
and the ethical nonsubstitutability of consumption for natural capital. However,
proponents of both paradigms appear to agree that it is unlikely to be possible
to conclude which natural capital may be considered ‘critical’ over an indefinite
time horizon (Illge and Schwarze, 2009). A key, long-standing question
remains the extent to which these two concepts may be combined, and how,
to be useful for policy-makers and other stakeholders. Numerous indicators
and indices of sustainability exist, with varied approaches, producing equally