Gases that trap solar heat in the earth's atmosphere and contribute to global mean temperature are considered greenhouse gases. They take their name from the “greenhouse effect,” the term that compares the heat-trapping gases to the glass panes of a greenhouse for the way they warm the atmosphere. According to the National Energy Information Center, “Many gases exhibit these greenhouse properties. Some of them occur in nature (water vapor, carbon dioxide, methane, and nitrous oxide), while others are exclusively human-made (like gases used for aerosols).” Some greenhouse gases, such as methane and nitrous oxide, have more of an impact on global warming than carbon dioxide. In fact, methane (CH4) has 25 times the impact on global warming potential compared with carbon dioxide (CO2), and nitrous oxide (N2O) has 298 times the impact on global warming potential compared with carbon dioxide (CO2).
Studies show that human activities are rapidly increasing the amount of CO2 in the atmosphere, which in turn is increasing global mean temperature. The Intergovernmental Panel on Climate Change (IPCC) cites climate models predicting the effects of higher temperatures, including rising sea levels and greater frequency of heat waves and floods. These events could have severe impact on the biosphere, human health, political stability, and economic development.
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.