Carbon Dioxide Equivalent (CO2e)
Summary
A standard unit used to measure carbon footprints, representing the impact of the seven greenhouse gases in terms of the equivalent amount of CO2.
CO2e stands for carbon dioxide equivalent. It is the standard unit used to measure and compare the warming impact of different greenhouse gases in a single, consistent figure.
Not all greenhouse gases warm the planet equally. Methane (CH4), nitrous oxide (N2O), and fluorinated gases (F-gases) are all more potent than carbon dioxide (CO2) over time. To make them comparable, each gas is assigned a Global Warming Potential (GWP) value that converts it into its CO2 equivalent. Methane, for example, has a GWP 28-30 times that of CO2, meaning one tonne of methane is counted as 28-30 tonnes of CO2e.
This matters because:
- Carbon footprints at product and company level are always expressed in CO2e
- Emissions reports under frameworks like the GHG Protocol use CO2e as the reporting unit
- Net zero targets are set and measured in CO2e.
If you are looking at your company’s emissions for the first time, every number you see will almost certainly be in tonnes of CO2e. It is the common currency of carbon accounting.
Once you understand CO2e, the rest of carbon reporting starts to make sense.
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