It is the most prevalent greenhouse gas after water vapour and has therefore become the proxy by which greenhouse gas emissions are measured. By definition, CO2 has a global warming potential of 1.
However, carbon dioxide is only one of many greenhouse gases that are emitted when humans undertake certain activities. Other greenhouse gases are methane, nitrous oxide and ozone, all of which occur naturally in earth’s atmosphere. Their global warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere compared to CO2.
To take into account the emission of other greenhouse gases when calculating the level of greenhouse gas emissions, scientists have devised an equivalent measure – CO2e, which literally means carbon dioxide equivalent.
CO2e allows other greenhouse gas emissions to be expressed in terms of CO2 based on their relative global warming potential (GWP).