Greenhouse gases like carbon dioxide and methane are largely transparent to visible light but absorb infrared light very well. Just like the jacket you wear on a cold day, they slow the rate at which Earth loses heat to space, increasing Earth's surface temperature. Not all greenhouse gases are created equal, and some are more effective at slowing heat loss than others.
Global Warming Potential
Multiple factors come into play when determining how potent a greenhouse gas it is. Its lifespan in the atmosphere is important -- a chemical that breaks down quickly should contribute less to long-term climate change than a chemical that persists for a long period of time, for example. The chemical's ability to absorb in the infrared and the wavelengths at which it absorbs infrared light best are also important. A common measure is global warming potential, or GWP, which measures the ability of a predetermined amount of the chemical to trap heat over a specified period of time, usually 100 years. Longer lifespan and better absorption result in a higher GWP.
Some of the most potent greenhouse gases in terms of GWP are fluorinated gases like hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride. These gases last a very long time in the atmosphere and absorb very well in the infrared spectrum. With a GWP of 23,900, sulfur hexafluoride is the most potent of all greenhouse gases. It's used in magnesium production and in the manufacture of semiconductors. The other fluorinated gases also have high GWPs but don't quite rival sulfur hexafluoride. Hydrofluorocarbons have GWPs ranging from 140 to 11,700, while perfluorocarbons have GWPs ranging from 6,500 to 9,200. They are used as refrigerants in place of chlorofluorocarbons since chlorofluorocarbons damage the ozone layer and have been banned.
Although sulfur hexafluoride is the most potent of all known greenhouse gases, its overall contribution to the greenhouse effect is at present less than many other greenhouse gases because this gas has only been released in small quantities. According to the Intergovernmental Panel on Climate Change, as of 2005 atmospheric concentrations of the molecule were close to 5.6 parts per trillion, as compared with CO2 concentrations of about 379 parts per million. Nonetheless, since it's such a potent greenhouse gas sulfur hexafluoride emissions are of special concern.
Together with the other fluorinated gases, sulfur hexafluoride concentrations in the atmosphere are increasing and so, too, is their contribution to the greenhouse effect. Their lifespans in the atmosphere are measured in millennia and they are unusually good at absorbing infrared radiation. Concentrations of sulfur hexafluoride rose from 4.1 parts per trillion in the late 1990s to to 5.6 ppt in 2005. Emission of sulfur hexafluoride in the United States is declining, but emissions of hydrofluorocarbons are on the rise.
About the Author
Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in "Plenty," "San Diego Reader," "Santa Barbara Independent" and "East Bay Monthly." Brennan holds a Bachelor of Science in biology from the University of California, San Diego.
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