Impact assessment is the calculation of the amount of one or more impact category indicators to express the potential environmental impacts of an Activity or a group of activities. This fundamental process in Life Cycle Assessment translates inventory data into meaningful measures of environmental significance.
Whilst the term "impact assessment" can be used broadly across many fields, within the context of LCA it refers specifically to the systematic evaluation of potential environmental consequences. ISO 14040 defines this more precisely as Life Cycle Impact Assessment (LCIA), which is the "phase of Life Cycle Assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product".
The impact assessment process employs characterisation models and characterisation factors to convert Life Cycle Inventory (LCI) results into quantified impact category indicators. These indicators represent potential impacts across various environmental concerns, such as climate change, acidification, eutrophication, human toxicity, and resource depletion. Each impact category addresses a specific environmental issue of concern, and the characterisation factors describe how different elementary exchanges contribute to that category's endpoint.
Impact assessment can be applied at different scales. At the most granular level, it can evaluate a single activity to understand its direct environmental contributions. More commonly, it assesses groups of activities or entire product systems to capture the full scope of environmental impacts across a product's life cycle, from raw material extraction through production, use, and end-of-life treatment.
The results of impact assessment provide decision-makers with quantified, comparable measures of environmental performance, enabling informed choices between alternative products, processes, or policies based on their potential environmental consequences.
