What are the sources of greenhouse gases?

In the U.S., our greenhouse gas emissions come mostly from energy use. These are driven largely by economic growth, fuel used for electricity generation, and weather patterns affecting heating and cooling needs. Energy-related carbon dioxide emissions, resulting from petroleum and natural gas, represent 82 percent of total U.S. human-made greenhouse gas emissions (Figure 1).

Figure 1.  U.S. Anthropogenic Greenhouse Gas Emissions by Gas, 2001
(Million Metric Tons of Carbon Equivalent)

http://www.eia.gov/oiaf/1605/ggccebro/chapter1.html