Epilogue - Thanatia: The Destiny of the Earth's Mineral Resources - page 506

counterbalanced with a deep sense of conservation. Consequently, as Snow (1959)
proposed, the Second Law of Thermodynamics ought to be placed at the core of
literacy classes.
17.2.9 Exergy replacement cost: a good environmental indicator?
With exergy replacement cost one cannot measure the progress in the achievement
of sustainability but instead towards depletion and Thanatia. It can be thus a good
policy guide since it can quantify the annual depletion of the mineral endowment
and explain clearly what are the measures needed to stop it or at least to slow it
down. Effectively it is like a watch measuring the wait until death. One can always
try to decelerate death, but one can never defy it. So how can one ensure that the
exergy replacement cost is a good indicator?
The OECD (OECD, 1994; Hamilton, 2004) proposed a set of criteria that all
good environmental indicators should follow: policy relevance, analytical soundness
and measurability.
Concerning policy relevance, a good indicator must be: a) easy to interpret, b)
show trends over time, c) be responsive to changes in underlying conditions and d)
have a threshold or reference value against which conditions can be measured.
With reference to the aforementioned criteria, the exergy and exergy cost indica-
tors are in the authors' opinion policy relevant. Exergy, the available energy, is easy
to interpret since it is what laypeople call “energy”. As a matter of fact people pay
for exergy not energy. The exergy replacement cost and the exergy cost indicators
can show either aggregated or disaggregated trends over time just by being respon-
sive to any kind of variation. Such variations could include degree of extraction,
improvements in process e ciency, substitution, recycling and whichever changes in
a given material cycle. Finally, Thanatia as a threshold provides the most suitable
reference values to which evolutions in depletion can be measured.
Concerning analytical soundness, indicators should be well supported in techni-
cal and scientific terms. It is obvious that exergy indicators are strongly linked to
the Second Law and therefore satisfy this component.
Concerning measurability, indicators should be: a) calculated from data that
are readily available or available at reasonable cost, b) data should be documented
and of a known quality and c) data and indicators should be updated at regular
intervals.
The data for calculating the annual loss of mineral endowment includes amounts
of extracted material together with composition and ore grade, energy consumed in
mining and beneficiating the ore at the BoL, and the amount of metals and minerals
dumped and dispersed at the EoL. Such information could be found, at least in
part, in the Physical Supply and Use Tables of the U.N. System of Environmental-
Economic Accounts (SEEA) (see Sec. 2.5.1 and Sec. C.1). The data obtained for
exergy replacement costs is as reliable as that provided by SEEA. The calculations