Characterisation is the use of characterisation factors to calculate the amount of an Impact category indicator that corresponds to a Functional unit. This step is a fundamental component of Life Cycle Impact Assessment (LCIA), translating inventory data into meaningful environmental impact results.
In the LCIA phase of a Life Cycle Assessment, characterisation serves as the bridge between the elementary exchanges identified in the Life Cycle Inventory (LCI) and the environmental impacts we seek to understand. The process applies scientifically derived characterisation factors to convert different elementary flows into common units that represent their contribution to specific impact categories. For example, in climate change impact assessment, various greenhouse gas emissions are converted to carbon dioxide equivalents using their respective global warming potentials as characterisation factors.
According to ISO 14040, characterisation is a mandatory element of LCIA, whilst further steps such as normalisation and weighting are optional. Each characterisation factor is derived from a characterisation model that describes the relationship between an elementary exchange and its contribution to an impact category endpoint. These factors reflect the relative contribution that one unit of an elementary exchange makes to the overall impact within a specific category.
The result of characterisation is an impact category indicator result, expressed in the common unit for that category. This allows practitioners to aggregate the contributions from multiple elementary exchanges across the entire product system and relate them back to the functional unit, enabling comparison between different product systems or design alternatives on the basis of their potential environmental impacts.
