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Impact categories, normalisation and weighting in LCA

2. Selection of impact categories

• 2.1 Considerations regarding choice of impact category
• 2.2 References

The selection of impact categories depends on the purpose of the LCA, e.g. what kind of decision is going to be taken based on the LCA. Obviously, the choice also depends on the type of application of the LCA. Basically, selection of impact categories is a matter between the commissioner and the practitioner, and no methodology includes specific guidelines on which impact categories that have to be included in LCA.

Based on a survey of four internationally known methodologies and the draft ISO 14047 (ISO 1999) technical report a comprehensive list of impact categories is established. The list is presented below in Table 2.1. In the comprehensive list it is also indicated if the specific impact categories are considered to be global, regional or local. Further, it is indicated if international consensus regarding the impact category in LCA has been reached.

Table 2.1 Characterisation of impact categories.

1 Nielsen PH and Laursen J has recently (June 2000) submitted with a substantial input regarding classification and characterisation of noise, integration of external noise nuisance from road and rail transportation in life cycle assessment.

A short description of each of the impact categories can be found in chapter 2, Selection of impact categories, in the report "Update on impact categories, normalisation and weighting in LCA." (Stranddorf et al. 2005) and in the detailed chapters in the same report.

As it appears all impact categories (apart from effects of waste heat water and effects on eco-systems) have reached some sort of international consensus regarding classification and characterisation. In both exceptions, it is disputable if the impact categories can be considered as real impacts.

It should be noted that although the above list is comprehensive, it does not include all possible types of impacts. If other types of impacts are of relevance for an LCA study, a suitable method (quantitative or qualitative) for their assessment should be defined and documented thoroughly, fulfilling the general requirements and recommendations in the ISO standards. Except for the remarks in the subsequent section, it is outside the scope of the present guideline to give further recommendations regarding this.

2.1 Considerations regarding choice of impact category

There is a large overlap in the suggested impact categories among different lists, illustrated in Table 2.1. However, the list and its underlying methodology do not guide a practitioner in the exclusion (or inclusion) of impact categories for different applications of LCA.

The ISO 14042 (ISO 2000) provides the following guidance regarding selection of impact categories, category indicators and characterisation models including the criteria for environmental relevance:

• "For most LCA studies existing impact categories, category indicators or characterisation models will be selected in an LCA study, the related information shall be referenced.... ... However, in some cases existing impact categories, category indicators or characterisation models are not sufficient to fulfil the defined goal and scope of the LCA study, and new ones have to be defined. When new impact categories, category indicators or characterisation models are defined, the (same) requirements and recommendations .. also apply".

2.1.1 General recommendation

The aim of any LCA must be to ensure that the results are robust enough to form a basis for further considerations or for a decision.

Of the different methodologies and standards for the recommendation regarding selection of impact categories the ISO 14042 probably provides the most guidance.

Below a few general recommendations are presented:

• The overall recommendation regarding choice of impact categories is to include all the impact categories for which international consensus has been reached.
• Include the internationally recognised impact categories in any LCA study. Exclude any of them only if that can be justified scientifically.
• Depending of the goal and scope it can be necessary to include new impact categories or categories that are not internationally agreed upon to the same extent as the one mentioned as internationally recognised. New impact categories will – however relevant - need the same or more justice than already internationally agreed impact categories.
• Sometimes qualitative assessment is the only way to handle a potential environmental impact. That can either be if there do not exist refined quantitative methods or if the data are not sufficiently accurate. Qualitative assessment is acceptable but could be met with more criticism.

2.2 References

ISO 2000, Environmental management - Life cycle assessment - Life cycle impact assessment. ISO 14042.

ISO TR 14047. Illustrative examples on how to apply ISO 14042 - Environmental management - Life cycle assessment – Life cycle impact assessment. International Organisation of Standardisation, Paris.

Stranddorf, H.K., Hoffmann, L. & Schmidt, A. 2005. Update on impact categories, normalisation and weighting in LCA. Environmental Project no. 995, Danish EPA, 2005.

Nielsen, P.H. & Laursen, J.E.: Integration of external noise nuisance from road and rail transportation in life cycle assessment. In Potting, J. and Hauschild, M. (eds.): Background for spatial differentiation in LCA impact assessment. Environmental Project no. 996. Danish Environmental Protection Agency, Copenhagen, 2005.

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Version 1.0 November 2005, © Danish Environmental Protection Agency