akar.earthtCO2e: Definition
What is tCO2e (tonne of CO2 equivalent)? How gases are converted with global warming potentials, how to turn carbon into CO2, and common unit errors.
tCO2e (tonne of carbon dioxide equivalent) is the standard unit for measuring greenhouse gases. It expresses any mix of gases as the amount of CO2 that would cause the same warming over a set period, usually 100 years. One carbon credit equals one tCO2e.
Why it matters
Every carbon credit, emissions inventory and climate target is counted in tCO2e. It allows methane from peat fires, nitrous oxide from fertiliser and CO2 from tree loss to be added together. Getting the unit right is basic, but unit errors between carbon and CO2 are still among the most common mistakes in project documents.
How it is calculated
- Other gases: multiply the mass of each gas by its global warming potential (GWP). Methane and nitrous oxide have GWPs far above 1 over 100 years. Programmes specify which IPCC assessment report’s GWP values to use, so check the current rules.
- Biomass carbon to CO2: multiply tonnes of carbon by 44/12 (about 3.67), the ratio of the molecular weight of CO2 to the atomic weight of carbon.
- Biomass to carbon: multiply dry biomass by the carbon fraction, often 0.47.
So one tonne of dry wood holds about 0.47 t C, or about 1.72 tCO2. See CO2 from biomass for worked examples.
Indonesia angle
Indonesia’s market statistics use the same unit: IDXCarbon reports trading volume of 1.9 million+ tCO2e, and both SPE-GRK offsets and PTBAE-PU allowances are denominated in tCO2e. Peat and mangrove projects need careful treatment of methane and nitrous oxide, because rewetting and land-use change affect these gases as well as CO2.
Common mistakes
- Reporting tonnes of carbon as tonnes of CO2, understating by a factor of 3.67, or the reverse.
- Using outdated GWP values.
- Writing “tCO2e” for biomass totals before conversion.
Related terms
See carbon fraction, carbon credit and emission reduction, or browse the forest carbon hub.
Frequently asked questions
How do I convert tonnes of carbon to tCO2e?
Multiply by 44/12, about 3.67. One tonne of carbon equals about 3.67 tonnes of CO2.
What is the difference between tCO2 and tCO2e?
tCO2 counts carbon dioxide only. tCO2e adds other greenhouse gases such as methane and nitrous oxide, converted into the amount of CO2 with the same warming effect.