Greenhouse gases (GHG) are gases that have the ability to trap infrared radiation and act like a blanket to the Earth. The increased emissions of these gases is what is contributing to global warming.
The main GHG, in terms of human emissions, are the following (http://action.ran.org/index.php)
Carbon Dioxide, CO2
Methane, CH4
Nitrous Oxide, NO2
Sulfur Hexafloride, SF6
Chroflourocarbon, CFC
CO2 is the main concern regarding global warming and comes from energy sources such as coal fired power plants, gasoline combustion, as well as natural gas burning.
CH4 is mainly a product of agricultural practices as well as garbage decomposition. Farm animals release methane as a bi-product of the digestion process.
NO2 sources are similar to those of CO2, as well as fertilizers.
SF6 is produced as an industrial by-product and accounts for less than 1% of GHG emissions.
CFCs gained recognition for the ability to deplete the ozone layer, but are also dangerous GHGs. Sources of this gas are mostly aerosol products and refrigerants. Luckily, this gas is highly regulated, so emissions are very small.
Global warming potential (GWP) is a measure of a gases' ability to trap heat in the form of infrared radiation. It is typically expressed as a multiple of heat trapped compared to a similar mass of CO2. The factor is calculated over certain time periods, usually 20, 100, or 500 years. For example, methane can trap 56 times more heat than CO2 over a 20 year period, while CFCs are upwards of 10,000 times!
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