Introduction to life cycle assessment (LCA)
Using resources • Life cycle assessment and recycling
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Key concepts
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Definition and purpose of LCA
A life cycle assessment (LCA) is a systematic method that quantifies environmental impacts associated with all stages of a product's life. The method assigns impacts to stages such as raw material extraction, manufacturing, distribution, use and end-of-life. LCA provides a basis for comparing products and identifying stages with the largest environmental burdens.
Functional unit and system boundaries
The functional unit defines what is being compared (for example, one shopping bag used once or 100 uses of the same bag). The functional unit controls the comparison so that different materials or designs are assessed on the same basis. System boundaries determine which processes enter the assessment; excluding key stages underestimates impacts.
Common impact categories and data types
Impact categories include greenhouse gas emissions, resource depletion (fossil fuels, metals), water consumption and pollution. Data types include energy use, material quantities and transport distances. Poor data quality or inconsistent units causes misleading comparisons, so transparency in data sources and units is essential.
Comparative LCA: plastic vs paper shopping bags
Manufacture of paper bags consumes more water and energy in pulping and drying, therefore increasing impacts in the production stage. Manufacture of plastic bags uses fossil-fuel feedstocks, therefore increasing impacts from resource depletion and greenhouse gases. Disposal differences cause further effects: paper bags biodegrade or are recyclable in some streams, therefore reducing long-term litter impacts; plastic bags persist and fragment into microplastics, therefore increasing long-term pollution risks. The number of uses changes outcomes: repeated reuse of a stronger plastic bag reduces impact per use, therefore potentially outperforming single-use paper bags when the functional unit is multiple uses.
Interpreting LCA results and limitations
LCA results require interpretation of numerical outputs and graphical summaries. Causes of high impact values may include energy-intensive production, long transport distances or high waste. Limitations include assumptions about usage, uncertainty in emissions factors and omission of social impacts. Differences in system boundaries or functional units cause non-equivalent comparisons, therefore careful matching of these parameters is essential.
Evaluating ways to reduce use of limited resources
Strategies such as increasing reuse, improving recycling rates, switching materials, and reducing material quantity lower impacts per functional unit. Reuse reduces the number of items required, therefore lowering cumulative resource extraction. Recycling reduces demand for virgin raw materials, therefore conserving finite resources and often lowering energy use compared with primary production. Trade-offs arise when recycling or substitution increases energy use or reduces product performance, therefore requiring LCA to identify net benefits.
Key notes
Important points to keep in mind