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Important Greenhouse Gases

When the sun shines on the earth, its heat is absorbed and radiated, producing infrared radiation. Certain gases, called greenhouse gases, absorb this radiation and warm the atmosphere. Greenhouse gases are produced both naturally and artificially by humans. Since industrialization, and especially during the 20th century, human emissions have greatly increased and have become a major environmental issue.

  1. Water Vapor

    • Water vapor is the most common greenhouse gas, though it is difficult to know exactly how abundant it is. It is created when high temperatures cause water found in places like lakes and rivers to evaporate. This creates a cycle of warming, called a "positive feedback loop." Warm air can hold more water vapor than cold air. Since water vapor is a greenhouse gas, it further heats up the air and increases the amount of vapor it can hold, creating the cycle.

    Carbon Dioxide

    • Carbon dioxide molecules consist of two oxygen atoms and one carbon atom bonded together. While the gas occurs naturally, humankind is also a major contributor to its occurrence. Humans create carbon dioxide by burning coal, oil, natural gas and wood. This has been a major factor since the Industrial Revolution in the 18th century. Before that time, carbon monoxide was measured at 280 parts-per-million; today, it is at about 370 parts-per-million.

    Methane

    • Methane molecules consist of four hydrogen atoms bonded with one carbon atom. The gas occurs both naturally -- because of swamps, for example -- and as a result of human activity, particularly through growing rice, raising cattle, natural gas use and coal mining. The levels of methane in the atmosphere have been measured since the 1970s. These levels rose by approximately 1 percent between 1978 and 1990 -- and little through 2011.

    Tropospheric Ozone

    • Tropospheric ozone is a gas that descends from the ozone layer in the stratosphere, which is a higher level of the atmosphere, to the troposphere, the lowest level of the atmosphere. While this amount is small, it has been supplemented in the 20th century by ozone-created emissions from vehicles and factories. These emit nitrogen and carbon, which produce ozone when acted upon by sunlight. Ozone is more common in urban areas and is a major cause of smog.

    Nitrous Oxide

    • A nitrous oxide molecule consists of two nitrogen atoms bonded with one oxygen atom. This gas is produced by chemical reactions in the soil and the water, both naturally and through the use of fertilizer. As the use of fertilizer increased in the 20th century, so did the presence of this gas. This gas is also emitted in other processes, including power generation, nylon production, nitric acid production and transportation.

    Chlorofluorocarbons and Other Synthesized Gases

    • Chlorofluorocarbons, commonly known as CFCs, are gases that have been used as refrigerants, aerosol propellants and cleaning solvents since 1928. They do not occur naturally. These gases are harmful to the ozone layer and their use has been and continues to be reduced. Other synthesized gases include hydrofluorcarbons (HFCs), sulfurhexafluoride and carbontetrafluoride.

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