GREENHOUSE GAS EMISSIONS

United States Environmental  Protection Agency published a piece about greenhouse gases overview.  It defines the greenhouse gas emissions as gases that trap heat in the atmosphere. These gases are carbon dioxide, methane, nitrous oxide, fluorinated gases.  The primary sources of greenhouse gas emissions in the United States are:

Electricity production (33% of 2011 greenhouse gas emissions) - Electricity production generates the largest share of greenhouse gas emissions. Over 70% of our electricity comes from burning fossil fuels, mostly coal and natural gas.

Transportation (28% of 2011 greenhouse gas emissions) - Greenhouse gas emissions from transportation primarily come from burning fossil fuel for our cars, trucks, ships, trains, and planes.
Industry (20% of 2011 greenhouse gas emissions) - Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy as well as greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials.

Commercial and Residential (11% of 2011 greenhouse gas emissions) - Greenhouse gas emissions from businesses and homes arise primarily from fossil fuels burned for heat, the use of certain products that contain greenhouse gases, and the handling of waste.

Agriculture (8% of 2011 greenhouse gas emissions) - Greenhouse gas emissions from agriculture come from livestock such as cows, agricultural soils, and rice production.

Land Use and Forestry (offset of 14% of 2011 greenhouse gas emissions) - Land areas can act as a sink (absorbing CO2 from the atmosphere) or a source of greenhouse gas emissions. In the United States, since 1990, managed forests and other lands have absorbed more CO2 from the atmosphere than they emit.