14. Normalisation

Defined as an optional step in the ISO14044 requirements, normalisation in LCA relates the characterised impact indicator scores of an analysed system to those of a reference system. By putting the LCA results in a broader perspective, it can facilitate their interpretation and communication, and allow checking whether their magnitude looks reasonable. This chapter provides a comprehensive overview of the two major normalisation approaches, internal and external normalisation, encompassing for the latter both production-based and consumption-based inventory methods. Pros and cons are addressed for each approach. Because of its wide use and usefulness, emphasis is put on external normalisation. The chapter details the calculation of external normalisation references, including their scoping, the collection of data for building their associated production-based or consumption-based normalisation inventories, their computation by use of adequate sets of characterisation factors, and their resulting uncertainties. The chapter provides insights in the application of normalisation in practice. After listing the past efforts of establishing external normalisation references for different regions in the world, the use of different normalisation approaches and their possible interpretation in relation to the goals and scope of an LCA study are discussed, along with the potential uncertainties and biases in the normalised scores.