Did You Know?

If it were not for naturally occurring greenhouse gases, the Earth would be too cold to support life as we know it. Without the greenhouse effect, the average temperature of the Earth would be about -2°F rather than the 57°F we currently experience.

Many chemical compounds found in the Earth’s atmosphere act as "greenhouse gases." These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth’s surface, some of it is re-radiatedback towards space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and trap its heat in the atmosphere.

Many gases exhibit these greenhouse properties. Some occur naturally. Some are also produced by human activities and some are exclusively human made (for example, industrial gases).

What Are the Types of Greenhouse Gases?

Image of the Earth showing the steps involved in the Greenhouse Effect. 1. Solar radiation passes through the clear atmosphere. 2. Most radiation is absorbed by the Earth's surface and warms it. 3. Some solar radiation is reflected by the Earth and the atmosphere. 4. Some of the infrared radiation passes through the atmosphere, and some is absorbed and re-emitted in all directions by greenhouse gas molecules. The effect of this is to warm the Earth's surface and the lower atmosphere. 5. Infrared radiation is emitted from the Earth's surface.
Source: U.S. Environmental Protection Agency (Public Domain)

The major greenhouse gases the United States emits as a result of human activity and that are included in U.S. and international emissions estimates are:

  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrous oxide (N2O)
  • Industrial Gases:
    • Hydrofluorocarbons (HFCs)
    • Perfluorocarbons (PFCs)
    • Sulfur hexafluoride (SF6)

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. Recent 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.


More About Greenhouse Gases’ Effect on the Climate »