Climate change — total
kg CO₂-eq/MWhCombines fossil, biogenic and land-use-change greenhouse-gas contributions using climate characterization factors.
Do not read as: direct stack CO₂ alone or a prediction of local climate effects.
Drawing No. EH–ES–009 // Environmental & Safety Engineering
LCA Impact Categories Explained
Reviewed August 2026
What climate change, ecotoxicity, eutrophication, ionising radiation, dissipated water and resource-use indicators actually mean—and what they do not tell you.
Scope Electricity LCAFramework ISO 14040/14044Indicator basis ILCD 2.0Categories explained 15
Key idea: an impact category is a modelled environmental indicator, not a measured impact beside a particular facility. Categories have different units and should not be added together without explicit normalization and weighting.
From inventory flow to impact indicator
LCI → characterization → LCIA result
A life-cycle inventory records elementary flows such as carbon dioxide, sulphur dioxide, nitrogen oxides, phosphorus, metals, radionuclides, energy carriers and water. Life-cycle impact assessment then assigns relevant flows to environmental categories and multiplies them by characterization factors. The result is an equivalent unit that allows unlike substances contributing to the same mechanism to be compared.
For example, a climate-change result expressed as kg CO₂-equivalent combines several greenhouse gases according to the selected method. It is not simply the mass of carbon dioxide emitted at the power plant. The same distinction applies to every category below. The methodology guide explains how boundaries, functional units and assumptions shape the inventory before characterization.
The 15 categories used by the electricity explorer
One table · no composite score
| Theme | Impact category | Display unit | Primary question |
|---|---|---|---|
| Climate & air | Climate change — total | kg CO₂-eq/MWh | What is the life-cycle greenhouse-gas potential? |
| Climate & air | Ozone layer depletion | mg CFC-11-eq/MWh | What is the potential to damage stratospheric ozone? |
| Climate & air | Photochemical ozone creation | kg NMVOC-eq/MWh | What is the potential to form ground-level ozone? |
| Climate & air | Particulate-matter health effects | Disease incidence/TWh | What modelled health burden is associated with particle formation? |
| Ecosystems | Acidification | mol H⁺-eq/MWh | What is the potential pressure from acidifying emissions? |
| Ecosystems | Freshwater ecotoxicity | CTUe/MWh | What comparative toxic pressure may affect freshwater organisms? |
| Ecosystems | Freshwater eutrophication | kg P-eq/MWh | What phosphorus-related nutrient enrichment may occur? |
| Ecosystems | Marine eutrophication | kg N-eq/MWh | What nitrogen-related marine enrichment may occur? |
| Ecosystems | Terrestrial eutrophication | mol N-eq/MWh | What pressure may reactive nitrogen deposition place on land ecosystems? |
| Human health | Carcinogenic toxicity | CTUh/TWh | What comparative toxic effect relates to carcinogenic substances? |
| Human health | Non-carcinogenic toxicity | CTUh/TWh | What comparative toxic effect relates to other toxic substances? |
| Human health | Ionising radiation | kg U-235-eq/MWh | What is the method-specific potential from routine radionuclide emissions? |
| Water | Dissipated water | m³/MWh | How much water is made unavailable to the immediate environment? |
| Resources | Non-renewable energy demand — CED | GJ/MWh | How much non-renewable primary energy is required across the life cycle? |
| Resources | Minerals and metals resource use | mg Sb-eq/MWh | What is the modelled depletion pressure from mineral and metal extraction? |
Indicator selection and units follow the UNECE electricity study's ILCD 2.0 results [1][2]. Land use is withheld from the EngineerHub model because UNECE subsequently corrected that indicator [3].
Detailed interpretation guide
Meaning · unit · principal limitation
Ozone layer depletion
mg CFC-11-eq/MWhExpresses the potential of releases to damage the stratospheric ozone layer relative to CFC-11.
Do not confuse with: ground-level ozone or smog.
Photochemical ozone creation
kg NMVOC-eq/MWhModels ground-level ozone formation from precursor emissions including nitrogen oxides and volatile organic compounds.
Do not read as: a measured ozone concentration beside a plant.
Particulate-matter health effects
Disease incidence/TWhCharacterizes health effects from primary particles and secondary particles formed from precursor emissions.
Do not read as: an observed number of illnesses caused by one facility.
Acidification
mol H⁺-eq/MWhConverts sulphur, nitrogen and ammonia emissions into an equivalent potential to release hydrogen ions.
Do not read as: the pH expected at a specific site.
Freshwater ecotoxicity
CTUe/MWhCombines modelled chemical fate, exposure and effects to compare potential harm to freshwater organisms.
Use cautiously: toxicity indicators can carry substantial inventory and characterization uncertainty.
Freshwater eutrophication
kg P-eq/MWhRepresents phosphorus-related nutrient enrichment that may stimulate excessive biological growth in fresh water.
Keep separate from: nitrogen-driven marine and terrestrial indicators.
Marine eutrophication
kg N-eq/MWhRepresents nitrogen releases that may contribute to nutrient enrichment and oxygen depletion in marine systems.
Site conditions matter: transport and nutrient limitation affect actual consequences.
Terrestrial eutrophication
mol N-eq/MWhCharacterizes ecosystem pressure caused by atmospheric deposition of reactive nitrogen onto land.
Do not read as: soil fertility or useful fertilizer input.
Carcinogenic human toxicity
CTUh/TWhCombines modelled fate, human exposure and carcinogenic effect factors for toxic releases.
Do not read as: a site-specific cancer-risk assessment or observed case count.
Non-carcinogenic human toxicity
CTUh/TWhUses the same comparative fate–exposure–effect framework for potential non-cancer health effects.
Use cautiously: small differences may not be meaningful where inventories or factors are uncertain.
Ionising radiation — human health
kg U-235-eq/MWhCharacterizes potential human-health effects from routine life-cycle radionuclide emissions using the ILCD reference substance.
It is not: sieverts, personal dose, accident risk, waste quantity or kilograms of U-235 released.
Dissipated water
m³/MWhCounts water made unavailable to the immediate environment through evaporation, incorporation or comparable pathways.
It is not: gross withdrawal, discharge, water quality or scarcity-weighted use.
Non-renewable energy demand — CED
GJ/MWhTotals non-renewable primary energy required throughout construction, fuel supply, operation and end-of-life stages.
Method caveat: UNECE notes that the applied CED method groups uranium under “fossil,” although uranium is not a fossil fuel.
Minerals and metals resource use
mg Sb-eq/MWhExpresses modelled depletion pressure associated with mineral and metal extraction in antimony-equivalent units.
It is not: material mass, recyclability, supply-chain criticality, mine toxicity or geopolitical risk.
Can categories be combined?
Only through explicit choices
Normalization
Divides each category result by a reference, such as a regional annual impact or a dataset median. This removes units but introduces a reference choice.
Weighting
Assigns relative importance to categories. Weighting is value-dependent; it can support transparent screening but cannot produce a universally objective environmental ranking.
The Electricity LCA Comparison Tool keeps all 15 indicators visible and offers an optional preference-weighted screening index. Its weights and included categories are explicit, and the result is deliberately not called a “green score.”
Important impacts outside this numerical set
Complementary assessment remains necessary
Land use and biodiversityArea alone does not capture habitat quality, fragmentation or ecosystem sensitivity.
Local water scarcityThe same water consumption can have very different consequences in wet and arid locations.
Waste stewardshipWaste mass, hazard, containment and required management time are not one midpoint indicator.
Severe accidentsLow-probability high-consequence events require risk assessment, not routine LCIA indicators.
Noise and visual effectsProject-specific community effects are normally assessed through siting and environmental review.
Electricity-system effectsStorage, balancing, curtailment, transmission and reliability are outside plant-level generation LCA.
Frequently asked questions
Five interpretation checks
What is an LCA impact category?
An LCA impact category groups inventory flows according to a defined environmental mechanism and converts them into a common characterization unit.
Can LCA impact categories be added together?
Not directly because the categories use different units. A combined result requires normalization and weighting, which introduce explicit methodological and value choices.
Is ionising radiation in LCA the same as public radiation dose?
No. The ILCD result in kg U-235 equivalent is a midpoint characterization indicator, not a dose in sieverts, accident risk or radioactive-waste quantity.
Is dissipated water the same as water withdrawal?
No. Dissipated water represents water made unavailable to the immediate environment. Withdrawal, return flow, water quality and local scarcity are separate considerations.
Does a low carbon footprint mean the lowest total environmental impact?
No. Climate change is one impact category. A technology can perform well for climate change while having different trade-offs in water, resources, toxicity or ecosystem indicators.
References
Primary and methodological sources
- UNECE, Life Cycle Assessment of Electricity Generation Options, March 2022 edition.
- European Commission JRC, European Platform on Life Cycle Assessment and ILCD Handbook resources.
- UNECE corrigendum to the electricity-generation LCA report, July 2022.
- ISO 14040:2006, Environmental management — Life cycle assessment — Principles and framework.
- ISO 14044:2006, Environmental management — Life cycle assessment — Requirements and guidelines.
- Commission Recommendation (EU) 2021/2279 on Environmental Footprint methods.
Continue the LCA analysis
Interconnected EngineerHub resources
Reviewed 27 August 2026 · Indicator basis: UNECE electricity LCA / ILCD 2.0