Glossary›Emissions accounting and measurement›CO2-e (carbon dioxide equivalent)
Glossary term
Cluster D · D21
Tier 1
CO2-e (carbon dioxide equivalent)
Definition
Carbon dioxide equivalent is the common unit that expresses the warming effect of every greenhouse gas as the equivalent quantity of carbon dioxide, using global warming potential values. It allows methane, nitrous oxide, refrigerant gases and carbon dioxide to be added into one total. Australian corporate emissions are reported in tonnes of CO2-e, written tCO2-e.
AASB S2 Appendix B
· paragraphs B21 and B22 ·
In force
On this page
In practice
CO2-e exists because seven gases with wildly different warming effects and wildly different atmospheric lifetimes cannot be added together in their own units. A tonne of methane and a tonne of carbon dioxide are not comparable quantities. Converting both to a common CO2 basis makes a single total possible, and that total is what gets disclosed.
The seven constituent gases the standard works with are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride and nitrogen trifluoride. For a typical Australian mid-market business the material ones are carbon dioxide from fuel and electricity, methane and nitrous oxide from combustion and waste, and hydrofluorocarbons from refrigeration and air conditioning.
Refrigerants deserve a specific mention because they are the line most often missing from a first inventory and they are disproportionately large. A refrigerant with a global warming potential in the thousands means a few kilograms of leakage produces tonnes of CO2-e. An entity with significant cold storage, a large HVAC estate or a refrigerated fleet that reports no refrigerant line has a visible gap, and the underlying data (service records showing top-up quantities) usually exists in a maintenance system nobody thought to ask.
Two notation points that cause real confusion in documents. Tonnes and kilotonnes get mixed within a single report more often than anyone would expect, and the difference is a factor of a thousand in a figure directors sign. And CO2-e is written several ways (CO2e, CO2-e, tCO2e, tCO₂e) which is cosmetic but should be made consistent once across the report, because inconsistent notation reads as a document nobody controlled.
Under AASB S2 Appendix B paragraph B21, an entity using direct measurement converts the seven gases into a CO2 equivalent value using 100-year global warming potential values from the latest IPCC assessment available at the reporting date. Paragraph B22 handles the far more common case where the entity uses emission factors, and provides that where those factors have already converted the gases into CO2-e, the entity is not required to recalculate them. For most Australian reporters that is the operative position: the factor set does the conversion and there is no separate global warming potential step.
What the assurer does with it
The assurer tests unit consistency across the report first, because it is quick and it catches real errors. They check that the total equals the sum of its parts, that scope subtotals foot to the disclosed total, and that units are consistent between the report, the inventory and any comparative.
They then look for the gases that should be present and are not. Refrigerants for an entity with a large HVAC or cold chain estate, methane and nitrous oxide for an entity with significant combustion, and the non-CO2 fraction of any biofuel. A CO2-e total that is arithmetically just the carbon dioxide is a completeness issue disguised as a unit.
They accept a total built from factors that state their CO2-e basis, footed and internally consistent, with units stated. They reject a report mixing tonnes and kilotonnes, a total that does not foot to its components, and a figure labelled CO2-e that is demonstrably CO2 only.
Commonly confused with
CO2 alone. The hyphenated “e” is doing substantial work and dropping it changes the meaning of the figure. A disclosure that says “carbon dioxide” when it means CO2-e is understating what it covers, and the reverse overstates it.
Sources
1
2
Review status
Review required
Last reviewed
15 September 2026
Editorial pass, unsigned
Reviewer required
Carbon accounting specialist
Next scheduled review
1 August 2027
next expected National Greenhouse Accounts Factors release
Part of
Cluster D, Emissions accounting and measurement
49 terms from the head term carbon accounting down to individual Scope 3 categories and the mechanics of factors, boundaries and data quality. The largest cluster in the glossary.
Related terms
The conversion factor that turns each gas into CO2-e
Where the CO2-e conversion has usually already been applied
The ratio the CO2-e total most often appears in
Related questions
Where do Australian emission factors come from?
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The National Greenhouse Accounts Factors, published each year by the Department of Climate Change, Energy, the Environment and Water. They give Scope 1 factors by fuel and Scope 2 electricity factors by state and territory. NGER-registered corporations must use NGER measurement methods for their NGER reporting.
What evidence do we need for each emissions number?
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Every reported number needs a source document you did not create for the report, the activity data drawn from it, the emission factor and its published edition, and the calculation joining them. Fleet fuel needs litres from fuel card statements, electricity needs kWh by site from retailer invoices with the matching state factor, and refrigerants need kilograms by gas type from service records.
Other terms in this cluster
CO2-e (carbon dioxide equivalent)