Interpreting life cycle assessment data and results
Using resources • Life cycle assessment and recycling
Flashcards
Test your knowledge with interactive flashcards
Key concepts
What you'll likely be quizzed about
Definition of life cycle assessment (LCA)
Life cycle assessment quantifies environmental impacts associated with all stages of a product’s life: raw material extraction, manufacture, transport, use and end-of-life. The functional unit defines the basis for comparison so results become comparable between different products or processes. LCA outputs appear as impact category values such as carbon dioxide equivalent (global warming potential) or resource depletion, which require interpretation in context.
Functional unit and system boundaries
The functional unit specifies the service provided (for example '1 kg of material' or '1000 hours of light') and normalises results for fair comparison. System boundaries decide which processes appear in the LCA (cradle-to-gate, cradle-to-grave, or cradle-to-cradle). Narrow boundaries exclude life stages and therefore cause underestimation of total impacts; wide boundaries include more processes and therefore increase reported impacts.
Impact categories and indicators
Impact categories group environmental effects such as global warming potential, acidification, eutrophication and human toxicity. Indicators convert inputs and emissions into comparable values (for example CO2e for greenhouse gas emissions). Different indicators emphasise different problems so a low impact in one category can coexist with a high impact in another; comparisons require matching which categories are reported.
Data quality and modelling assumptions
Data sources, age of data, and regional specifics affect LCA results because input emissions and efficiencies vary geographically and over time. Allocation rules for shared processes (for example co-products) and assumptions about product lifetime or recycling rates change final numbers. Low-quality or generic data increase uncertainty and reduce confidence in conclusions.
Comparative interpretation
Comparisons between LCAs require identical functional units, matched system boundaries, and the same impact categories. If comparisons show one option with higher manufacturing impact but lower use-phase emissions, the overall result depends on use duration and performance. Cause → effect logic clarifies outcomes: higher material energy use causes higher manufacturing impact; greater durability causes fewer replacements and therefore lower lifetime impact.
Sensitivity and uncertainty analysis
Sensitivity analysis tests how changes in assumptions (for example lifetime or recycling rate) change results. High sensitivity indicates that small assumption shifts cause large result changes and therefore reduce result robustness. Uncertainty analysis quantifies probable ranges; wide ranges indicate low certainty and require cautious interpretation.
Limitations and ethical choices
LCA excludes some social and economic factors unless specifically included, so it does not provide a complete sustainability judgement. Choices about weighting different impact categories or monetising impacts introduce value judgements that alter outcomes. Time and location dependence of impacts limit global applicability of a single LCA result.
Reading LCA results and graphs
Bar charts and pie charts commonly present impact contributions by life stage or category. Identification of the largest bars or slices shows dominant contributors. Cause → effect interpretation links the large contributor to the process that produces it (for example electricity use in manufacture causes a large share of greenhouse gas emissions).
Key notes
Important points to keep in mind