LCA glossary

Life cycle assessment glossary

Brief definitions of common life cycle assessment terms, units, and acronyms, including interpretation limits where they matter.

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A

Allocation #: Procedure used to divide the inputs, outputs, and environmental burdens of a multi-output process between its products or functions. Common bases include mass, energy, and economic value.
Attributional LCA #: LCA approach that describes the environmental burdens associated with a product system, usually by assigning shares of existing processes and supply chains to the studied function.

B

Background system #: Processes usually taken from LCA databases to represent upstream or downstream activities outside the practitioner’s direct control, such as electricity generation or material production.
Biosphere exchange #: Exchange between a process and the natural environment, such as a resource extracted from nature or an emission released to air, water, or soil.

C

Carbon footprint #: Climate-change result for a product, organization, or activity, usually expressed in kilograms of CO₂ equivalent. It covers one impact category, not the full range of environmental impacts considered in an LCA.
Characterization factor (CF) #: Coefficient that converts an elementary flow into its contribution to an impact category. It depends on the substance, the impact method, and often the emission or resource compartment.
Consequential LCA #: LCA approach that estimates the environmental consequences of a decision by modelling the processes and markets expected to change because of that decision.
Contribution analysis #: Examination of which life cycle stages, processes, flows, or parameters contribute most to an inventory or impact result.
Cradle to gate #: Study scope covering extraction of raw materials and production up to the point where a product leaves a specified factory or organization, without its use and end of life.
Cradle to grave #: Study scope covering the full life cycle from raw material extraction through production and use to end-of-life treatment.
Critical review #: Independent examination of an LCA to check whether its methods, data, interpretation, and reporting are consistent with the stated goal and applicable standards. It does not guarantee that every modelling choice is the only possible one.
CTUe (Comparative Toxic Unit for ecosystems) #: Unit used for freshwater ecotoxicity. It represents the potentially affected fraction of species integrated over a volume of water and time, expressed as PAF · m³ · day.
CTUh (Comparative Toxic Unit for humans) #: Unit used for human toxicity. One CTUh represents one statistical disease case in the modelled exposed population. It is an expected potential impact, not a prediction for an identified person.
Cut-off criterion #: Rule used to decide whether a flow, process, or life cycle stage may be excluded from the product system, for example below a documented mass, energy, or environmental significance threshold.

D

Data quality #: Degree to which data fit the study’s purpose. Typical checks cover age, geography, technology, completeness, consistency, precision, and the reliability of the source.
Direct exchange #: Input or output recorded on one process, such as electricity consumed or an emission released there. It describes that process record only; upstream requirements and emissions appear in cumulative inventory results.

E

Elementary flow #: Material or energy entering the product system from the environment without prior human transformation, or leaving it to the environment without subsequent human transformation.
Environmental Footprint (EF) #: European Commission framework and impact assessment method family for measuring the environmental performance of products and organizations over their life cycles.

F

Foreground system #: Processes that are specific to the studied product system and can usually be described or influenced directly by the organization carrying out the study.
Functional unit (FU) #: Quantified description of the function delivered by the product system. It provides the reference against which inventory inputs, outputs, and results are calculated and compared.

G

Global warming potential (GWP) #: Climate-change characterization indicator comparing the integrated radiative forcing of a greenhouse gas with that of carbon dioxide over a specified time horizon, commonly 100 years.
Goal and scope definition #: First phase of an LCA. It states why the study is being done, who will use it, what function is assessed, and which systems, impacts, data rules, and assumptions are included.

I

Impact category #: Environmental issue to which inventory flows are assigned in LCIA, such as climate change, freshwater ecotoxicity, acidification, or resource use.
Intermediate flow (Product flow, Technosphere flow) #: Product, material, energy, or service exchanged between processes inside the technosphere. Unlike an elementary flow, it does not directly cross the boundary with the natural environment.
Inventory result (LCI result) #: Total elementary flows associated with the product system for the chosen reference. Unlike the direct exchanges of one process, it includes the requirements calculated across the modelled supply chain.

L

Life cycle assessment (LCA) #: Method for assessing the potential environmental impacts of a product or service across its life cycle. It connects a defined function to resource use, emissions, and several impact categories.
Life cycle impact assessment (LCIA) #: Phase of LCA that translates inventory flows into indicators of potential environmental impact using impact categories and characterization factors.
Life cycle interpretation (Interpretation) #: Phase that checks the inventory and impact results against the study’s goal, identifies important contributions and limitations, and turns them into conclusions and recommendations.
Life cycle inventory (LCI) #: Phase of LCA that compiles and quantifies the inputs and outputs of the studied product system, including resources, products, wastes, and emissions.
Life cycle thinking (LCT) #: Way of considering effects across a whole value chain instead of shifting a problem between stages, places, or impact categories. LCA is one quantitative tool used to apply it.

N

Normalization #: Optional LCIA step that divides category indicator results by reference values, such as the annual impacts of a region or person, to provide a common scale for interpretation.

P

Potentially affected fraction of species (PAF) #: Modelled fraction of species potentially exposed above an effect threshold. It is used in ecotoxicity indicators and does not represent an observed count of harmed species.
Process (Activity, Unit process) #: Model element that transforms inputs into outputs. A unit process is the smallest process for which input and output data are quantified in a given model.
Product system #: Network of connected processes modelled to deliver the function described by the functional unit. Its boundary determines which parts of the life cycle are included.

R

Reference flow #: Amount of product output required from a product system to fulfil the functional unit. It connects the quantified function to the scale of the inventory model.

S

Sensitivity analysis #: Test of how results change when an important assumption, data value, method, or modelling choice is varied. It helps show which conclusions are robust and which depend on a particular choice.
System boundary #: Set of criteria defining which processes, life cycle stages, and exchanges are included in or excluded from the product system.

T

Technosphere #: Part of the LCA model representing human economic and technical systems, where products, materials, energy, wastes, and services are exchanged between processes.

U

Uncertainty #: Lack of exact knowledge about data, model choices, or parameters. In LCA it can be explored with ranges, scenarios, sensitivity analysis, or probability distributions.

W

Weighting #: Optional LCIA step that applies value-based weights to impact category results, sometimes to combine them into a single score. The chosen weights must be stated explicitly.