The total amount of greenhouse gases emitted directly and indirectly to support human activities, usually expressed in equivalent tons of either carbon or carbon dioxide.
Carbon footprints are calculated by countries as part of their reporting requirements under the Kyoto Protocol, as well as by companies, regions, or individuals.
Direct greenhouse gas emissions can include tailpipe emissions of CO2 from motor vehicles, methane from landfills, and hydrofluorocarbons from leaking refrigeration or air conditioning equipment. Indirect greenhouse gas emissions arise from coal and other fossil fuel-based energy generated to power residential, commercial, and industrial activities. Indirect emissions also arise from fossil fuel combustion used in the manufacture, transport, storage, disposal, and recycling of commodities and manufactured products.