System expansion and the definition of system boundaries in Product Carbon Footprints of Leather

In this study, the recommendation that the application of a methodological approach known as system expansion justifies starting system boundaries “at the slaughterhouse gate” for leather PCF studies is considered and challenged.

Firstly, a distinction is made between two different types of LCA-based study – consequential and attributional studies – and the way system boundaries are determined in each type of study is seen to be different. The specific procedure and conceptual model for applying system expansion in comparative consequential studies is then presented and analyzed in order to identify the central concepts. In particular, the concepts of utilization of co-products and displacement of alternative production processes and systems are identified as critical in the procedure. The model of system expansion is then considered in a leather-specific context, and the resulting interpretation of the model is seen to vary significantly from that made in the UNIDO Report (where the recommendation was first presented). The choice of product substitution to be studied is seen to be important in a leather context in determining intermediate processes.

While it is clearly essential to consider the intended use of the study and the type of study being undertaken when defining system boundaries, the conclusions of this study are that the UNIDO Report does not do so and, as a result, it uses an inappropriate consequential methodology to support its conclusion on system boundaries in attributional PCF of leather. Secondly, if comparative consequential LCA is used for PCF, there are many complex factors that need to be determined in relation to both utilization and displacement that need to be considered for each study before it can be decided whether the upstream processes can be excluded from a study’s boundaries, and again this has not been done.

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