What are greenhouse gases and how do they affect the climate?

The major greenhouse gases the United States emitted as a result of human activity in 2009¹ (and their share of total emissions) were:²

• Carbon dioxide (82.8%)
• Methane (11.1%)
• Nitrous oxide (3.3%)
• Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (collectively 2.7%)

There are other greenhouse gases that are not counted in U.S. or international greenhouse gas inventories:

• Water vapor is the most abundant greenhouse gas, but most scientists believe that water vapor produced directly by human activity contributes very little to the amount of water vapor in the atmosphere, and therefore EIA does not estimate emissions of water vapor. Research by NASA suggests a stronger impact from the indirect human effects on water vapor concentrations.
• Ozone is technically a greenhouse gas because it has an effect on global temperature. However, at higher elevations in the atmosphere (stratosphere), where it occurs naturally, it is needed to block harmful UV light. At lower elevations of the atmosphere (troposphere) it is harmful to human health and is a pollutant regulated independently of its warming effects.

These gases are transparent to incoming solar (short-wave) radiation but block infrared (long-wave) radiation from leaving the Earth's atmosphere. Therefore, they trap radiation from the Sun and warm the planet's surface. As concentrations of these gases increase, more warming occurs than would happen naturally.

¹Emissions of Greenhouse Gases in the United States, 2009, EIA's last annual report on total U.S. greenhouse gas emissions.

²Based on "global warming potential."

Learn more:

What are greenhouse gases and how much are emitted by the United States?

Energy and the Environment — Greenhouse Gases

Most recent monthly and annual estimates for Carbon Dioxide emissions from energy consumption.

Last updated: September 20, 2012

 

Other FAQs about Environment

• Does EIA report water vapor emissions data?
• How do I convert between short tons and metric tons?
• How does the hole in the ozone layer affect global warming?
• How much carbon dioxide (CO₂) is produced per kilowatt-hour when generating electricity with fossil fuels?
• How much carbon dioxide (CO₂) is produced when different fuels are burned?
• How much carbon dioxide is produced by burning gasoline and diesel fuel?
• How much of U.S. carbon dioxide emissions are associated with electricity generation?
• What are greenhouse gases and how do they affect the climate?
• What are the energy-related carbon dioxide (CO2) emissions by source and sector for the United States?
• What are the sources of energy-related carbon dioxide emissions by type of fuel for the U.S. and the world?
• Where can I find emission factors for greenhouse gases and air pollutants?
• Why do carbon dioxide emissions weigh more than the original fuel?