Life Cycle Impact Assessment

The LCIA phase is the evaluation of potential human health and environmental impacts of the environmental resources and releases identified during the LCI. Impact assessment should address ecological and human health effects; it can also address resource depletion. An LCIA attempts to establish a linkage between the product or process and its potential environmental impacts. For example, an LCIA could determine whether one product or process causes more GHGs than other, or could potentially kill more fish.

The key concept in this component is that of stressors. A stressor is a set of conditions that may lead to an impact. For example, if a product or process is emitting GHGs, the increase of GHGs in the atmosphere may contribute to global warming. Processes that result in the discharge of excess nutrients into bodies of water may lead to eutrophication. An LCIA provides a systematic procedure for classifying and characterizing these types of environmental effects.

Why Conduct an LCIA?

Although much can be learned about a process by considering LCI data, an LCIA provides a more precise basis to make comparisons. Thus, we know that large releases of both carbon dioxide and methane are harmful; an LCIA can determine whether 9000 T of CO₂ or 5000 T of methane would have the greater potential impact. Using science‐based characterization factors, an LCIA can calculate the impacts each environmental release has on problems such as smog or global warming. An impact assessment can also incorporate value judgments. In an air non‐attainment zone, for example, air emissions could be of relatively higher concern than the same emission level in a region with better air quality (ISO 2000).

Key Steps of a LCIA

The following steps comprise an LCIA.

1. Selection and definition of impact categories – identifying relevant environmental impact categories (e.g. global warming, acidification, terrestrial toxicity).
2. Classification – assigning LCI results to the impact categories (e.g. classifying CO₂ emissions to global warming).
3. Characterization – modeling LCI impacts within impact categories using science‐based conversion factors (e.g. modeling the potential impact of CO₂ and methane on global warming).
4. Normalization – expressing potential impacts in ways that can be compared (e.g. comparing the global warming impact of CO₂ and methane for the two options).
5. Grouping – sorting or ranking the indicators (e.g. sorting the indicators by location: local, regional, and global).
6. Weighting – emphasizing the most important potential impacts.
7. Evaluating and reporting LCIA results – gaining a better understanding of the reliability of the LCIA results.

The International Organization of Standardization standard for conducting an impact assessment states that impact category selection, classification, and characterization are mandatory steps for an LCIA and data evaluation (step 7) (ISO 1998a). Whether the other steps are used will depend on the goal and scope of the study.