Gases other than carbon dioxide make up nearly 20% of U.S. greenhouse gas emissions
Note: CO2 equivalent measures different greenhouse gases based on their global warming potential, quantifying how much a particular greenhouse gas contributes to global warming. It is calculated on a relative scale, with other greenhouse gases being compared to a CO2 baseline.
In 2009, U.S. anthropogenic (human-caused) greenhouse gas emissions totaled 6,576 million metric tons carbon dioxide (CO2) equivalent. While CO2 accounts for more than 80% of U.S. emissions, many other different greenhouse gases are emitted. Methane, nitrous oxide, and high global warming potential (GWP) gases account for the other nearly 20% of the total.
CO2 emissions are primarily energy-related. They include emissions from the consumption of petroleum, coal, and natural gas, as well as municipal solid waste. CO2 emissions are also generated from some forms of geothermal power generation. Natural gas production is the second–largest source of CO2, and includes flaring of natural gas from wellheads and scrubbing CO2 from produced natural gas. Industrial processes, such as cement manufacture, also contribute to CO2 emissions.
Other common greenhouse gases include:
- Methane: Similarly to CO2, the majority of methane emissions come from the energy sector, including coal mining, natural gas and petroleum systems, electricity generation, and transportation. Agricultural emissions and waste management emissions are also large sources of methane.
- Nitrous oxide (N2O): The largest source of N2O emissions is agriculture, primarily from soil fertilization and animal waste management. Energy sources also contribute to N2O emissions primarily due to N2O emitted as a byproduct of fuel combustion. Industrial processes and waste management also emit N2O.
- High-GWP gases: Common gases with high global warming potential include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). These gases are commonly used as refrigerants, aerosols, and solvents. Although PFC and SF6 concentrations have decreased greatly since 1990, total emissions of high-GWP gases have continued to increase steadily since 1990. This is due to increases in HFC use; HFCs are being used to replace chlorofluorocarbons and other ozone-depleting compounds. High-GWP gases are much more potent than CO2 in terms of their abilities to trap heat in the atmosphere, and some persist in the atmosphere for thousands of years.
Greenhouse gas emissions in the United States in 2009 were almost 6% below 2008 totals. EIA's Emissions of Greenhouse Gases in the United States 2009 addresses emissions trends in more detail. See EIA's Energy in Brief on greenhouse gases for more information on greenhouse gases in the United States.