Economic versus Thermodynamic Accounting - Thanatia: The Destiny of the Earth's Mineral Resources - page 57

mon basis, the identification of major loss streams that correspond to ine ciencies
and subsequently led to the first evaluation of their environmental burden.
Other exergy-based approaches are for instance those from Sciubba (2003), Con-
nelly and Coshland (2001) or Cornelissen and Hirs (2002). Sciubba (2003) extended
Szargut's theory, to include non-energy quantities like capital, labour and environ-
mental impact in the calculation. Connelly and Coshland (2001) discussed the ties
between exergy and industrial ecology and proposed exergy-based definitions and
methods for addressing resource depletion. Cornelissen and Hirs (2002) applied
the exergy analysis to the LCA methodology and proposed the exergetic life cycle
assessment. All these approaches provide very useful information for process opti-
misation, as they obtain the exergy costs of production, thereby identifying sources
where energy, materials and harmful emissions can be reduced.
2.6.4 Energy, land and time indicators: a relationship?
The reader has now seen a fair number of physical indicators that propose a yard-
stick or numéraire for accounting purposes and a series of rules and equivalences
to convert their units into the different environmental impacts. Some questions do
still remain: is there some equivalence among these numéraires? Is one numéraire
more relevant than another or even all the others, when it comes to dealing with
environmental problems? How does one add together, using the same units, the
annual rate of Amazonia deforestation, desertification and subsequently the loss
of land for agriculture, natural gas, oil and coal consumption, CO 2 or ozone layer
problems, urban sprawl, etc?
An obvious observation is that environmental problems occur on an Earth, which
has a finite capacity but is daily and timely bathed with sunlight (and thus possesses
some generative capacity).
The sun during 4.5 billion years through the solar constant, 1,367 W=m 2 , 4.921
MJ=m 2 =h or 118.1 MJ=m 2 =day actually represents the global energy cost of life on
Earth. This stable energy flux never lacked during the Earth's history and made its
conversion into Gaia (Lovelock, 1972), a living planet, possible. Since only a small
part of this energy is converted via photosynthesis into biomass, the gross primary
production of the biosphere and its distribution among the principal ecosystems may
be used as an in-surface unit conversion. Such data are provided by many sources.
For instance, Odum (1959) provides the approximate gross primary production of
the biosphere (on annual basis) as 8.4 MJ=m 2 =year or 0.023 MJ=m 2 =day. In
this way, Nature can be imagined as an energy converting machine with a very low
e ciency because the average energy unit cost for producing biomass is 118.1/0.023
= 5,155. Or in other words, Nature needs 5,155 kWh of solar energy in average for
producing 1 kWh of biomass energy.
By using the solar constant one can calculate how much solar energy was needed
to create natural diversity upon the whole Earth's surface (1:2710 8 km 2 of max-