Whereas the classification and characterisation are according to the ISO 14044 mandatory elements within a LCIA, the normalisation and weighting are optional elements. In the following chapter, the 4 elements classification, characterisation, normalisation and weighting within an LCIA are generally described below:
To analyse respectively describe the relevance of single contributions and to relate the different units of an Impact Assessment, a normalisation is necessary. The normalisation calculates this order of magnitude of the category indicator results relative to a reference information.
This better understanding of the relative magnitude for each indicator result of the process, product or life cycle under study is the aim of the normalisation. The normalisation does not define the relevance of the impact categories among each other to evaluate an environmental single score.
The single score requires a cross-category weighting. Therefore the normalisation indicates the share of an impact category (global warming potential, eutrophication,...) caused by a process, product or life cycle related to the total amount of an impact of a defined reference unit (land, continent, world).
The ISO 14044 states that the normalisation may be helpful in, for example,
The normalisation is the conversion of an indicator result by dividing it by a chosen reference value. If no normalisation is done this would implicitly state that the share of the analysed process, product or life cycle to a total amount of each impact category is equal.
ISO 14044 gives some examples of the chosen reference values, which could be:
Most data of the normalisation step is calculated by extrapolating a country specific data. The extrapolation is done using appropriate parameters. Those parameters may be the population (per capita burdens) or the gross domestic product of a country, a continent or a political-economical association. Within GaBi the extrapolations are based on the gross domestic product.
Therefore it can be described by converting indicator results of different impact categories (global warming potential, eutrophication,...) by using numerical factors based on value-choices. It may include aggregation of the weighted indicator results.
Weighting as described within ISO14044 states that it is an optional element with two possible procedures, either
However, weighting is not a science based procedure. It is more subjective and dominated by value-choices to overcome missing scientific knowledge. The basis for the weighting step is a different set of value-choices depending on the national policy, social and societal preferences, a company’s policy or individual preferences. This will lead to different weighting results based on the same indicator results or normalised indicator results.
The ISO 14044 indicates that the data and indicator results should be made available before the weighting step is applied as well as the weighting results to affirm that:
