LCIA: Methods, Characterization and Indicators
What this domain tests
Life Cycle Impact Assessment tests method literacy: classification, characterization, midpoint versus endpoint indicators, mandatory and optional elements, and the consequences of method and version choice.
Core rules and concepts
- LCIA converts inventory flows into potential impacts using characterization factors.
- Midpoint indicators stay closer to environmental mechanisms, such as GWP100 or acidification potential. Endpoint indicators model damage to human health, ecosystems, or resources and add uncertainty.
- Common methods include CML, ReCiPe, TRACI, and the EU Environmental Footprint method. They differ in coverage, characterization factors, and recommended use.
- Normalization and weighting are optional and value-based; a weighted single score is not a physical measurement.
- Method version matters. GWP100 factors differ between IPCC assessment reports.
Worked example
A study uses IPCC AR6 GWP100 factors. One kilogram of fossil methane is characterized as about 29.8 kg CO2e, while the same mass under an older AR5 factor would be about 28 kg CO2e. If the study mixes AR6 methane with AR5 nitrous oxide, the carbon footprint is internally inconsistent. The correct reasoning is to fix one method version for all flows and disclose it. If the goal is a public carbon footprint, the chosen version must also match the applicable programme rules.
Traps that cost marks
- Mixing characterization factors from different method versions.
- Comparing midpoint and endpoint scores as if they were the same indicator.
- Treating normalization or weighting as objective science.
- Selecting a method because it gives a lower score rather than because it fits the goal.
- Forgetting that regionalized impacts need spatially explicit factors.