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Damage to Resources caused by depletion of minerals and fossil fuels Unlike the damage categories Human Health and Ecosystem Quality we have not found a more or less accepted unit to express damages to Resources. If the resource quality decreases, economic factors and environmental burdens associated with mining low grade ores will become the real problem. The latter includes the land-use for the mining operation and the amount of energy to extract the resource from the low-grade ore. The availability of land and energy could thus form the real limitations and land-use
and energy use will probably be the most important factors. This is the basis for the proposal of [BLONK 1996].
When we look at alternative energy resources, another additional option is to translate increased energy consumption into increased future land use, as most non-fossil energy sources use a relatively large
area. [ROS 1993] proposes some land-use values for the most important solar and wind based technologies.
[MÜLLER-WENK 1998-1] follows this line of thought. However, instead of land use, he uses the concept of surplus energy. The surplus energy is defined as the difference between the energy needed to extract a resource now and at some point in the future. He calculates the future surplus energy at Q*N, in which Q represents the total amount that has been extracted by mankind before 1990 and N represents the number of times this amount is extracted. Müller-Wenk uses N=5 and N=10 28 .
The choice of the factor 5 is arbitrary, We could also have selected the point on the damage curve at 10*Q or 2*Q, as we assume the damage curve is linear. The consequence of this arbitrary choice is that the absolute value of the surplus energy has no significance. The only purpose of the surplus energy concept is to have a relative measure for the damage the depletion of a mineral or fossil resources creates. In a way the surplus energy is used as a characterisation method, since the choice of N is only used as a reference. As we will see later in the damage assessment, the lack of absolute meaning of the damage to Resources does create some problems in the presentation of questions to the panel.
Surplus energy for minerals
[CHAPMAN AND ROBERTS 1983] analyses the relation between energy use and the lowering of ore grades for the most common minerals. Chapman states there are three effects:
1. The amount of energy needed to change the chemical bonds in which the mineral is found is by definition constant. It is not possible to reduce this energy requirement by efficiency improvements or technological developments.
2. The energy requirements needed to extract, grind and purify an ore goes up as the grade goes down
3. The energy requirements needed to extract, grind and purify an ore goes down with efficiency increases and technological developments.
Chapman shows convincingly that until now the 3rd mechanism is stronger than the second. This means that although the grade of all ores decreases, historically the energy requirements also decrease. Chapman shows that this trend will continue many decades from now. In the case of copper we can extract about 100 times more than mankind has done so far before the actual energy requirements get higher than the present values. For most other metals the situation is even better. Future efficiency increases are not taken into account in LCA. This is consistent with the other damage models. For instance we do not take into account the possibility that the treatment methods of cancer will be improved, when we look at long term exposure. It is also common practice in LCA not to take possible remediation technologies into account.
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| 1. [Blonk 1996] Blonk, T.J. et al. Feasibility of operationalisation of depletion of Abiotic Resources in LCA via the Key Resources Energy and Land, Amsterdam, 1996.
2. [Müller-Wenk 1998-1] Müller-Wenk, R. (1998-1): Depletion of Abiotic Resources Weighted on the Base of "Virtual" Impacts of Lower Grade Deposits in Future. IWÖ Diskussionsbeitrag Nr. 57, Universität St. Gallen, March 1998, ISBN 3-906502-57-0
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