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.
According to the Kyoto Protocol, there are seven primary greenhouse gasses that are contributing to climate change. These are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3). All of these greenhouse gasses have different intensities of effect on the climate. To create a more accessible and usable final number, we combine these effects to produce an overall number of equivalent CO2 (CO2e).
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.