Page 113 - Materials Chemistry, Second Edition

L1644_C03.fm Page 88 Tuesday, October 21, 2003 3:11 PM

3.6 WEIGHTING: SINGLE INDEX APPROACHES

3.6.1 INTRODUCTION
Weighting (in ISO terminology) or valuation (in SETAC workgroup terminology)
is the phase of LCIA that involves formalized ranking, weighting and, possibly,
aggregation of the indicator results into a final score across impact categories.
Weighting or valuation inherently uses values and subjectivity to derive, respectively,
a rank order and then weighting factors with values supporting the aggregation into
a final score. Three types of weighting along similar lines are used:

• Monetary methods, such as mediation costs, willingness to pay, etc.
• Sustainability and target methods, such as in the distance-to-target pro-
cedure
• Social and expert methods

The results of an LCIA in the impact categories explained earlier can be difficult to
interpret in certain cases because they may be contradictory. In these cases it would
be helpful to have one single score.
The prioritization of impact categories often depends on political targets or
business strategies. Weighting is necessary to obtain a single index of environmental
performance of a functional unit. However, the weighting across impact categories
is the most critical and controversial step in LCIA, i.e., a quantitative comparison
of the seriousness of the different resource consumption or impact potentials of the
product, aimed at covering and possible aggregating indicator results across impact
categories.
The weighting methods in LCIA to obtain a single index can be distinguished
and classified according to five types of concepts (Udo de Haes, 1996). Table 3.6
presents a description of these concepts, indicating their advantages and disadvan-
tages. In this frame, no simple truth can decide what works best.
Examples for the proxy approach are the sustainable process index (SPI; Sage,
1993) and the material-intensity per-service unit (MIPS) (Schmidt-Bleek, 1994).
MIPS is a measure of the environmental impact intensities of infrastructures, goods,
and services. Materials and fuels are aggregated by mass and energy content. Impor-
tant cases for the distance-to-target methods are eco-scarcity (Braunschweig et al.,
1994), eco-indicator 95 (Goedkoop, 1995) and EDIP (Hauschild and Wenzel, 1998).
Eco-scarcity is a Swiss method that has also been adapted by Chalmers University
of Technology to suit Swedish conditions. Its units are ECO points per gram of
emission or per MJ of energy. Panel approaches have been used, for instance, by
the German EPA (Schmitz et al., 1995) and in the eco-indicator 99 weighting step
(Goedkoop and Speedesma, 1999). A similar approach, the multicriteria evaluation
(MCE), has been proposed for LCA by Powell and Pidgeon (1994). The abatement
technology concept has been used in the method developed by the Tellus Institute
(1992). It consists of an evaluation of internal environmental costs by means of the
most adequate technology to fulfill the legal requirements. Monetization has been
used as a weighting scheme in some of the damage-oriented methods like environ-

© 2004 CRC Press LLC