A carbon footprint is the quantification of energy-related emissions from human activity expressed in units of carbon dioxide (CO2). It includes all the heat, light, power, refrigeration, and transportation emissions associated with the harvesting, manufacturing, use, and disposal of a particular material, product, or service.
Carbon footprints are most closely linked to the burning of fossil fuels. The USGBC estimates that in the next 25 years, CO2 emissions from buildings will grow faster than those from any other sector of the economy, with commercial building emissions predicted to increase 1.8% through 2030. New commercial buildings will add an estimated 12 million metric tons of CO2 per year.