What is a Carbon Footprint?
			A measure of the amount of carbon dioxide emitted through the combustion of fossil fuels. A carbon footprint is often expressed as Tons of Carbon Dioxide equivalent (Tons CO2e) or Tons of Carbon Emitted, usually on an annual basis.
	What are Greenhouse Gases?
			The most common greenhouse gas emitted in the United States is carbon dioxide. Other greenhouse gases including nitrous oxide, sulfur hexafluoride, hydrofluorocarbons, perfluorocarbons and chlorofluorocarbons.
	Are Greenhouse Gas emissions increasing?
			Total United States greenhouse gas emissions rose 15% between 1990 and 2006.
	What are the impacts of increasing Greenhouse Gas emissions?
			The United Nations Intergovernmental Panel on Climate Change (IPCC) reported in 2007 that: Warming of the climate system is unequivocal. Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in greenhouse gas concentrations. Eleven of the twelve years in the period (1995-2006) rank among the top 12 warmest years in the instrumental record (since 1850, towards the end of the Little Ice Age). Warming in the last 100 years has caused about a 0.74 °C increase in global average temperature. Average Arctic temperatures increased at almost twice the global average rate in the past 100 years. Sea level rose at an average rate of about 1.8 mm/year during the years 1961-2003. The rise in sea level during 1993-2003 was at an average rate of 3.1 mm/year (It is not clear whether this is a long-term trend or just variability). Computer climate models for projecting surface air warming in the 21st century predict a "low scenario” of 3.2 °F (likely range of 2.0 to 5.2 °F) and a "high scenario" of 7.2 °F (likely range of 4.3 to 11.5 °F). It is very likely that there will be an increase in frequency of warm spells, heat waves and events of heavy rainfall. It is likely that there will be an increase in areas affected by droughts, intensity of tropical cyclones (which include hurricanes and typhoons) and the occurrence of extreme high tides. Sea ice is projected to shrink in both the Arctic and Antarctic. In some projections, Arctic late-summer sea ice disappears almost entirely by the latter part of the 21st century.