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, 87% are related to energy consumption. From 1990 to 2009, greenhouse gas emissions in the United States have grown by about 0.04% per year. The United States accounts for about 20% of the world's total energy-related carbon dioxide..."