LCA glossary

Life cycle assessment glossary

Concise definitions of common terms, units, and acronyms used in life cycle assessment. This glossary will grow with new articles, examples, and questions.

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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

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.
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.

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.

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.

L

Life cycle assessment (LCA) #: Method for compiling and evaluating the inputs, outputs, and potential environmental impacts of a product system throughout its life cycle.
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 inventory (LCI) #: Phase of LCA that compiles and quantifies the inputs and outputs of the studied product system, including resources, products, wastes, and emissions.

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.

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

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.