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A greenhouse gas is an atmospheric gas that, when out of balance, can contribute to a greenhouse effect. Greenhouse gases do not allow earth's infrared heat to be reflected back into space. Like the glass in a greenhouse, they let solar heat in and trap the earth's heat, warming the environment. Greenhouse gases include: water vapor, carbon dioxide, methane, and ozone. These four atmospheric gases are the important ones in terms of the greenhouse effect. There are many other greenhouse gases (such as nitrous oxide and chlorofluorocarbons) but they are relatively scarce in the atmosphere.
During the last ten thousand years greenhouse gases have been fairly constant. Since 1750, during the industrial era, forest clearing and burning of fossil fuels has caused an increase in greenhouse gases, most notably carbon dioxide. For thousands of years before the industrial era, carbon dioxide was present in a concentration of 280ppm (parts per million). The current level is 384ppm. The other greenhouse gases have also steadily increased during this period.
There is a global awareness of the problems caused by greenhouse gases and an international attempt to bring the earth's energy budget back into equilibrium. The Kyoto Protocol, which came into force in 2005, sets limits on greenhouse gas production and goals for reduction. The US EPA ranks greenhouse gas contributors by economic sector in this order: industrial, transportation, residential, commercial and agricultural.
How can an individual help to stem the tide of greenhouse gas production? Energy-efficient vehicles, improved building insulation and use of compact fluorescent lights are the big impact items for individuals according to the EPA.
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