A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbon dioxide and methane, can be emitted through the burning of fossil fuels, land clearance, and the production and consumption of food, manufactured goods, materials, wood, roads, buildings, transportation and other services.In most cases, the total carbon footprint cannot be calculated exactly because of inadequate knowledge of data about the complex interactions between contributing processes, including the influence of natural processes that store or release carbon dioxide. For this reason, Wright, Kemp, and Williams proposed the following definition of a carbon footprint:

A measure of the total amount of carbon dioxide (CO2) and methane (CH4) emissions of a defined population, system or activity, considering all relevant sources, sinks and storage within the spatial and temporal boundary of the population, system or activity of interest. Calculated as carbon dioxide equivalent using the relevant 100-year global warming potential (GWP100).
The Greenhouse Gas Protocol has extended the range of gases. The standard covers the accounting and reporting of seven greenhouse gases covered by the Kyoto Protocol – carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PCFs), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3).
The global average annual carbon footprint per person in 2014 was about 5 tonnes CO2e. Although there are many ways to calculate a carbon footprint, the Nature Conservancy suggests that the average carbon footprint for a U.S. citizen is 16 tons. This is one of the highest rates in the world, leading to new policies implemented to reduce carbon footprint. Scholars estimated that New York City can eliminate the carbon footprint of its buildings by 2050. Based on city documents and national statistics, a significant measure directly controlled by New York is the elimination of carbon emissions from municipal district heating, which may account for up to 30% of New York city’s reported carbon emissions and 58% of the energy-related carbon emissions.The use of household carbon footprint calculators originated when oil producer BP hired Ogilvy to create an "effective propaganda" campaign to shift responsibility of climate change-causing pollution away from the corporations and institutions that created a society where carbon emissions are unavoidable and onto personal lifestyle choices. The term "carbon footprint" was also popularized by BP.