In 2010, the United States emitted over 6.8 billion metric tons of greenhouse gases (CO2e). Carbon dioxide accounted for the largest percentage of greenhouse gases (84%), followed by methane (10%), nitrous oxide (4%), and other greenhouse gases (2%). Total U.S. emissions for 2010 totaled 6,821 million metric tons of CO2e and net emissions, taking sinks into account, totaled 5,747 tons CO2e.
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Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2010 (EPA 2012)
Links:
[1] http://www.c2es.org/docUploads/emissions-ghg-2010.png