Greenhouse Gases and Carbon Dioxide Equivalents

There are six major greenhouse gases regulated by the Kyoto Protocol. Of these, the most common in the atmosphere is carbon dioxide. The others are methane, nitrous oxide, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride. Each of these gases differ in their “global warming potential” – that is, their ability to absorb heat in the atmosphere. For example, methane is 21 times as powerful as carbon dioxide, so it has a global warming potential of 21. Similarly, nitrous oxide has a global warming potential of 310. Therefore, a tonne of carbon dioxide emissions is not the same in terms of climate impact as a tonne of another greenhouse gas. Because of this, greenhouse gas emissions are often reported in terms of “CO2 equivalents,” or CO2e. This is determined by multiplying the amount of emissions of a particular gas by the global warming potential of the gas.