Weak and Strong Sustainability Indicators, and Regional Environmental Resources
approach directly assumes the willingness to exchange natural goods for money which cannot
be seen as a priori given.
Especially neoclassical environmental economics focuses on the so-called weak sustainability
rule assuming total substitutability between natural capital and man-made capital. The weak
sustainability rule has its roots in capital theory (Victor, 1991). The idea behind is that man-
kind has a certain total capital stock at her disposal. This capital stock consists of two com-
ponents:
K = KN + KM (2)
The total capital stock K is set up by KN (natural capital) and KM (man-made capital, manu-
factured capital). The first part (natural capital) is measured by the TEV discussed above.
Man-made capital consists of all physical (machinery, infrastructure) and nonphysical (human
capital) parts of the anthroposphere. An at least constant (non-decreasing) capital stock K is
the indicator for a sustainable development. This weak sustainability rule presupposes that
natural capital and man-made capital can be traded off against one another. As long as the
„worth“ of the capital regardless of its composition is non-decreasing over time, sustainability
is achieved. Interestingly, the empirical studies in this field mainly take the present capital
stock as given, only considering that these entire capital stocks remain at least constant. There
is nearly no consideration whether the actual capital stock may be too low to maintain
(sustain) economic development in the future. Furthermore, assuming that a species only has
one marketable service to offer, there would not be a reason to protect that species if this par-
ticular service can be provided by other (artificial) means.
Equation (2) is an expression of the view that natural goods and services can in principle be
supplied by man-made capital, that means that natural benefits can be artificially produced.
Even if the natural capital depreciates, there is no danger for sustainability if at the same time
man-made capital is being produced to compensate for these losses. The substitutability as-
sumption according to this capital theory approach is a strictly anthropocentric one, and it is
„optimistic“ insofar that even if the technological standard today does not allow a perfect sub-
stitution between natural and man-made capital, with increasing scarcity of natural resources