U.S. Energy Information Administration - EIA - Independent Statistics and Analysis
Frequently Asked Questions
What are greenhouse gases and how do they affect the climate?
The major greenhouse gases that the United States emitted as a result of human activity and their share of total greenhouse gas emissions in 2013:1
- Carbon dioxide (CO2) = 82%
- Methane (CH4) = 10%
- Nitrous oxide (N2O) = 5%
- Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen triflouride (NF3) = 3%
There are other greenhouse gases that are not counted in United States or international greenhouse gas inventories:
- Water vapor is the most abundant greenhouse gas. Most scientists believe that water vapor produced directly by human activity contributes very little to the amount of water vapor in the atmosphere. Therefore, the U.S. Energy Information Administration (EIA) does not estimate emissions of water vapor. Research by NASA suggests a stronger impact from the indirect human effects on water vapor concentrations in the atmosphere.
- 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, ozone is needed to block harmful ultraviolet light. At lower elevations of the atmosphere (troposphere), ozone is harmful to human health and is a pollutant regulated independently of its warming effects.
Greenhouse gases are transparent to incoming (short-wave) radiation from the sun but block infrared (long-wave) radiation from leaving the earth's atmosphere. This greenhouse effect traps radiation from the sun and warms the planet's surface. As concentrations of these gases increase, more warming occurs than would happen naturally.
1 Based on global warming potential.
Most recent monthly and annual estimates for U.S. carbon dioxide emissions from energy consumption
Emissions of Greenhouse Gases in the United States, 2009, EIA's last annual report on total U.S. greenhouse gas emissions
Last updated: April 2, 2015
Other FAQs about Environment
- Does EIA have projections for energy production, consumption, and prices for individual states?
- 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 is produced by burning gasoline and diesel fuel?
- How much carbon dioxide is produced per kilowatthour when generating electricity with fossil fuels?
- How much carbon dioxide is produced when different fuels are burned?
- Why do carbon dioxide emissions weigh more than the original fuel?
- How much of U.S. carbon dioxide emissions are associated with electricity generation?
- What are U.S. energy-related carbon dioxide emissions by source and sector?
- What are greenhouse gases and how do they affect the climate?
- What are the greenhouse gas and air pollutant emissions factors for fuels and electricity?
- What are the sources of energy-related carbon dioxide emissions by type of fuel for the United States and the world?