Life cycle assessment (LCA) models the complex interaction between a product and the environment from cradle to grave. It is also known as life cycle analysis or ecobalance.
What is LCA?
The International Organisation for Standardisation (ISO), provides guidelines for conducting an LCA within the series ISO 14040 and 14044. The main phases of an LCA are:
- Goal & Scope definition, the product or service to be assessed is defined, a functional basis for comparison is chosen and the required level of detail is defined.
- Inventory analysis of extractions and emissions. An inventory list of all the inputs and ouputs of a product or service.
- Impact assessment the effects of the resource use and emissions generated are grouped and quantified into a limited number of impact categories which may then be weighted for importance.
- Interpretation, the results are reported in the most informative way possible and the need and opportunities to reduce the impact of the product(s) or service(s) on the environment are systematically evaluated.
Below is a more detailed overview of the four steps involved in an LCA study. For more detailed information about Goal & Scope please see our SimaPro Introduction to LCA.
Goal & Scope
The goal & scope defnition is a guide that ensures the LCA is performed consistently. In this section the most important (often subjective) choices of the study are described in detail i.e. methodological choices,
assumptions and limitations, particularly with regards to the following issues.
- System boundaries
- Multiple output processes/allocation
- Avoided impacts
A life cycle inventory (LCI) includes information on all of the environmental inputs and outputs associated with a product or service i.e. material and energy requirements, as well as emissions and wastes. The inventory process seems simple enough in principle. In practice, however, it is subject to a number of practical issues.
- Geographical variations
- Data quality
- Choice of technology
The inventory list is the result of all input and output environmental flows of a product system. However, a long list of substances is difficult to interpret thats why a further step is needed known as life cycle impact assessment (LCIA). An LCIA consists of 4 steps:
- Classifcation: all substances are sorted into classes according to the effect they have on the environment.
- Characterisation: all the substances are multiplied by a factor which reflects their relative contribution to the environmental impact.
- Normalisation: the quantified impact is compared to a certain reference value, for example the average environmental impact of a European citizen in one year.
- Weighting: different value choices are given to impact categories to generate a single score.
For each substance, a schematic cause response pathway needs to be developed that describes the environmental mechanism of the substance emitted. Along this environmental mechanism a impact category indicator result can be chosen either at the midpoint or endpoint level.
- Midpoint impact category, or problem-oriented approach, translates impacts into environmental themes such as climate change, acidification, human toxicity, etc.
Endpoint impact category, also known as the damage-oriented approach, translates environmental impacts into issues of concern such as human health, natural environment, and natural resources.
Endpoint results have a higher level of uncertainty compared to midpoint results but are easier to understand by decision makers.
Interpretation according to ISO 14044 describes a number of checks you need to make to ensure the conclusions are adequately supported by the data and procedures used in the study. The following checks are recommended:
- Sensitivity analysis
- Contribution analysis