Emissions, when used in this context, means greenhouse gas emissions. This is measured using a universal scale known as carbon dioxide equivalent, or CO2e.

Carbon dioxide is the primary greenhouse gas emitted through human activities, but other greenhouse gases include methane (CH4), nitrous oxide (N2O), chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).