What are greenhouse gases and how much are emitted by the United States?

Greenhouse gases trap heat from the sun and warm the planet's surface. Of U.S. greenhouse gas emissions, the majority are related to energy consumption, and most of those are carbon dioxide. From 1990 to 2011, energy-related carbon dioxide emissions in the United States increased by about 0.4% per year. The United States produced about 18% of the world's total energy-related carbon dioxide in 2010 — the last year for which comparable data are available.

See full Press Release: http://www.eia.gov/energy_in_brief/article/greenhouse_gas.cfm