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There has been much debate about the suitability of the said methodologies and
there is as of yet no definite approach. Each one entails non-resolved or controversial
aspects that make them partly unsuitable for assessing abiotic resource depletion
(Valero D. and Valero, 2013). Examples of such deficiencies are for instance the
inability to adequately reflect the loss in functionality related to their use (for
type 1 and 2) (Stewart and Weidema, 2005; Steen, 2006; Yellishetty et al., 2009);
the fact that proven reserves are not static (for type 2) (Stewart and Weidema,
2005); the arbitrariness in the future surplus energy calculation (for type 3) (Strauss
et al., 2006); or the di
culty in understanding the concept of entropy or exergy as
indicators and the issue surrounding the reference environment used for obtaining
exergy values (for type 4) (Stewart and Weidema, 2005).
In Valero D. and Valero (2013), the authors also discussed the strengths and
shortcomings of the above methodologies, comparing them to the Physical Geo-
nomics approach. It is to this the topic now turns.
4.4 The view down the rainbow: grave to cradle
It has been argued that the methods for assessing resource depletion in LCAs must
come from Thermodynamics and must take into account the Second Law (Gößling-
Reisemann, 2008).
Embodied energy and life cycle assessments are quite useful and far reaching
techniques based on Thermodynamics that do not need rigorous definitions of
energy. On the contrary, trying to fit a concept well established in energy eval-
uations and LCAs into the Thermodynamic realm is something which needs to be
done with care. This is because for many unrefined analyses one may use both the
energy and embodied energy concepts interchangeably for exergy and exergy cost.
They are in fact, anything but synonyms. Furthermore, both exergy and exergy
cost require precise definition.
The only rigorous way to build a reference baseline for the calculation of exergies
and exergy costs is through the Second Law. This is required if one wants to
develop a solid theory based on Physics rather than on a more or less reasonable
set of conjectures. As is well known, results derived from a conventional LCA are
relative to the chosen system boundaries with no absolute values existing for a given
good or service. Notwithstanding, if one starts the analysis from a hypothetical
grave in which all the commercial minerals and fossil fuels have been depleted,
i.e., Thanatia, this would then serve both as a boundary limit and as a reference
baseline, appropriate for calculating the exergy and exergy costs of any commodity
at industry's gate. Theoretically speaking, one would then get absolute LCA values
by converging the LCA approach with Second Law analysis through Thanatia as
a reference baseline. Hence, Thanatia could be used as the starting point for the
assessment of abiotic resource depletion.
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