CO2 versus CO2e

What Is The Difference Between CO₂ And CO₂e?

CO₂ refers to Carbon Dioxide, while CO₂e stands for Carbon Dioxide Equivalent which includes CO₂ and other greenhouse gases.

Carbon dioxide, or CO₂, is a natural, colourless, and odourless greenhouse gas emitted when fossil fuels burn (e.g. natural gas, oil, coal). It is the most prevalent greenhouse gas after water vapour and has become the proxy by which we measure greenhouse gas emissions.

However, carbon dioxide is only one of many greenhouse gases emitted when humans undertake certain activities. Other greenhouse gases are methane, nitrous oxide, and ozone – all of which occur naturally in our atmosphere.

CO₂e Includes Other Greenhouse Gases

CO₂e is a measure that was created by the United Nations' Intergovernmental Panel on Climate Change (IPCC) in order to make the effects of different greenhouse gases comparable because every gas has a different global warming potential.

CO₂e essentially describes the global warming potential (GWP) of all greenhouse gases. CO₂ has a GWP of 1 and methane has a GWP of approximately 25 (on a 100-year time horizon). In other words, for every 1 tonne of methane (CH4) emitted, an equivalent of 25 tonnes of CO2 would be emitted. Put simply, CO₂e gathers all greenhouse gases into one place.

Why is it important to account for CO₂e?

In this way, we can express greenhouse gas emissions as equivalent to CO₂ using the GWP principle. When you see a carbon footprint expressed in terms of CO₂e, it can be known for sure that all greenhouse gases have been included for each activity in scope, and therefore an all-encompassing picture of the environmental impact has been captured.

Most greenhouse gas emission factors are expressed as CO₂e. This means you don’t need to make the conversion from methane GWP to carbon dioxide GWP.