A characterisation factor is a numerical coefficient derived from a characterisation model that converts Life cycle inventory analysis result data into quantifiable environmental impacts. These factors serve as the essential translation mechanism within Life Cycle Impact Assessment, enabling practitioners to transform elementary flows into meaningful measures of environmental performance.
According to ISO 14040, characterisation factors are applied to convert inventory analysis results to the common unit of the (Impact) category indicator. This conversion process enables direct comparison and aggregation of different Elementary exchanges that contribute to the same environmental impact category. For example, within the climate change impact category, characterisation factors express the global warming potential of different greenhouse gases relative to carbon dioxide, allowing methane, nitrous oxide and CO₂ emissions to be aggregated into a single indicator measured in CO₂ equivalents.
The characterisation factor describes the relative contribution to the Impact category endpoint from one or more elementary exchanges or other intermediate impact category endpoints. This means that factors can operate at different levels within an impact pathway, either linking elementary exchanges directly to endpoints or connecting intermediate impact indicators within more sophisticated multi-stage characterisation models.
Each characterisation factor is scientifically derived from a characterisation model that represents the cause-and-effect relationships between environmental interventions and their impacts. The quality and scientific robustness of these factors directly influence the reliability of Life Cycle Impact Assessment results, making the selection of appropriate characterisation methods a critical methodological decision in any LCA study.
