It is a metric measure used to compare emissions of various greenhouse gases based on the global warming potential of each one of them, defined in decision 2/COP 3 or as subsequently revised in accordance with Article 5.
Carbon dioxide equivalent is the result of the multiplication of tons of greenhouse gases (GHG) emitted by their global warming potential. For example, the global warming potential of methane gas is 21 times greater than the carbon dioxide (CO2)potential. So we say that the CO2 equivalent of methane equals 21.