What are common sources of greenhouse gases and what is their global warming potential?

There are four primary greenhouse gases: water vapor, carbon dioxide, methane, and nitrogen oxide, with water vapor being the most common greenhouse gas. Carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) result primarily from human-induced activities. CO₂ is released to the atmosphere primarily due to the combustion of fossil fuels such as coal, gasoline, diesel fuel, and natural gas, and is also produced when solid wastes and wood and wood products are burned.

CH₄ emissions result primarily from the decomposition of organic wastes in municipal solid waste landfills, the raising of livestock, and the operation of wastewater treatment plants.Methane is also emitted in smaller quantitiesduring the production and transport of coal, natural gas, and oil.

N₂O is released during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels. Today, the United States generates and releases more carbon dioxide into the atmosphere than any other country in the world. Each U.S. citizen contributes about 22 tons of carbon dioxide emissions per year, whereas the world average is about six tons. Use of renewable energy sources such as solar, wind, and biomass will substantially reduce the emission of greenhouse gases.

All greenhouse gases contribute to trapping heat in the atmosphere, but some are more effective than others, which is reflected in their global warming potential (GWP). The GWP simply compares the heat-trapping ability of carbon dioxide, methane, nitrous oxide, and other greenhouse gases to carbon dioxide. Carbon dioxide was chosen as the baseline greenhouse gas and assigned a value of 1. Methane and nitrous oxide are 21 and 310 times more effective than CO₂, respectively. Therefore, for every ton of CH₄ or N₂O, the GWP in terms of carbon is 21 and 310 times the amount emitted, respectively. These values are referred to as the carbon equivalent.

WEB SITES (for more information)
www.epa.gov/globalwarming/emissions
www.epa.gov/globalwarming/emissions/national/gwp.html