Carbon emissions refer to greenhouse gas emissions, carbon dioxide emissions, or, for reporting purposes, carbon dioxide-equivalent emissions. The terms cover the emissions from seven particularly climate-threatening gases as acknowledged by the United Nations: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride, and nitrogen trifluoride. Carbon dioxide is the primary greenhouse gas emitted through human activity, which is why CO2 is often used to encompass all these emissions.