Life-cycle assessment (LCA) is a systematic method for quantifying the inputs, outputs, and potential environmental impacts associated with a product, process, or service throughout its life cycle. It connects raw-material extraction, manufacturing, distribution, use, and end-of-life treatment rather than examining a single operation in isolation. An assessment inventories material and energy flows, translates them into environmental indicators, and interprets the results within a defined purpose and scope. It evaluates potential impacts, not necessarily observed damage at particular locations. (nepis.epa.gov)
Framework and standards
The international framework is established by ISO 14040, which describes LCA principles and its four phases: goal and scope definition, inventory analysis, impact assessment, and interpretation. ISO 14044 supplies requirements and guidance covering these phases, reporting, critical review, limitations, and optional methodological elements. The phases form an interconnected framework rather than four wholly independent tasks. (iso.org)
LCA helps identify whether an apparent improvement shifts environmental burdens between life-cycle stages or impact categories. Reducing manufacturing impacts, for example, does not establish that the complete product system performs better if use or disposal burdens increase. This life-cycle perspective supports comparisons that would be incomplete when restricted to a factory or its direct emissions. (nepis.epa.gov)
Goal, functional unit, and boundaries
Goal definition specifies the study’s intended application, audience, and reasons for undertaking it. Scope definition establishes the product system, geographical and temporal coverage, data requirements, assessment methods, and exclusions. A central concept is the functional unit: the quantified performance against which inputs and impacts are calculated. Comparisons concern equivalent functions, not necessarily equal numbers or masses of products. For example, packaging systems may be compared by their provision of a specified protective service rather than by one package each. (publications.jrc.ec.europa.eu)
The system boundary determines which processes are included. A cradle-to-grave study follows production through use and end-of-life treatment; cradle-to-gate coverage stops at the manufacturing gate. The chosen boundary must be reported because results covering different stages are not automatically comparable. In product declarations, category-specific rules prescribe the boundary, reporting unit, life-cycle stages, and indicators. (epa.gov)
Life-cycle inventory
Life-cycle inventory analysis quantifies exchanges within the defined system. These include raw materials, fuels, electricity, water, products, wastes, and releases to air, water, and soil. Linked unit processes represent the production network needed to deliver the functional unit. Inventory results can be organized by process, life-cycle stage, or environmental medium. (nepis.epa.gov)
Data may describe specific facilities and suppliers or represent broader production averages. Database records require documentation of their geographical, technological, and temporal applicability. Combining datasets is not merely an arithmetic operation: their definitions and modelling assumptions must be compatible with the study’s purpose. (helpdesk.lifecycleinitiative.org)
Processes producing several useful outputs create an allocation problem. Shared inputs and emissions may need to be divided among co-products. Guidance favours avoiding allocation where possible through process subdivision or system expansion; when allocation remains necessary, the selected physical or other relationship must be justified. Recycling likewise requires explicit rules for assigning burdens and benefits across successive product systems. (publications.jrc.ec.europa.eu)
Impact assessment
Life-cycle impact assessment translates inventory exchanges into indicators of environmental significance. Relevant categories include climate change, ozone depletion, acidification, eutrophication, photochemical ozone formation, toxicity, land use, and resource depletion. Assessment methods connect emissions and resource consumption to potential effects on people, the natural environment, and resource availability. Different categories capture different mechanisms and therefore use different indicators. (publications.jrc.ec.europa.eu)
Classification assigns inventory flows to categories; characterization applies factors expressing their contributions. For climate indicators, greenhouse gases such as carbon dioxide and methane are expressed on a common carbon-dioxide-equivalent basis under a specified method. Optional normalization supplies a reference context, while weighting combines categories using value choices. Such aggregation must not be mistaken for a value-free measurement. (nepis.epa.gov)
Modelling approaches
Attributional LCA describes environmental burdens associated with a product system, using information about its suppliers or representative production averages. Consequential LCA estimates environmental changes resulting from a decision, commonly a change in demand. It therefore includes processes expected to respond to that decision, potentially beyond the immediate supply chain. These approaches answer different questions; neither label alone establishes suitability for every application. (helpdesk.lifecycleinitiative.org)
Their differences affect data selection and treatment of co-products. An electricity model describing an existing supply mix is not equivalent to one estimating the generation that changes when demand increases. The modelling approach must follow the study’s decision context and remain internally consistent. (lifecycleinitiative.org)
Interpretation and applications
Interpretation examines significant contributions, completeness, consistency, limitations, and robustness. Sensitivity analysis tests how results respond to alternative assumptions or parameter values. Transparent reporting records the methodological choices needed to understand results and supports reproducibility. Critical review addresses the study’s methods and documentation, with particular importance for public comparative claims. (pmc.ncbi.nlm.nih.gov)
Applications include material selection, process improvement, and environmental product declarations. A declaration reports LCA-based information under product category rules; comparable units alone do not remove all comparability requirements. Organizational LCA extends the perspective to an organization’s activities and product portfolio, supporting hotspot identification and environmental-performance tracking across its value chain. (epa.gov)