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If you've read an article or two about climate change and greenhouse gas emissions, you may have seen the term Global Warming Potential. You've probably deduced that it has to do with the degree to which greenhouse gases cause global warming, but most people are in the dark on how this is measured, so we thought we'd give you a little primer.
According to the EPA, "The definition of a GWP for a particular greenhouse gas is the ratio of heat trapped by one unit mass of the greenhouse gas to that of one unit mass of CO2 over a specified time period."
In other words, the base line for measuring the potency of a chemical is carbon dioxide, and all other chemicals are compared to it.
There are many greenhouse gases, including methane and nitrous oxide, which have global warming potentials of 23 and 296, respectively. Carbon dioxide and other lower GWP chemicals can be taken out of the atmosphere by sinks--a sort of reservoir that collects chemicals. Trees are a primary example of carbon sinks because they take carbon dioxide out of the atmosphere and store it.
But there are no sinks for the three groups of high GWP gases, which are the most potent of greenhouse gases. The three high GWP gases include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).
HFCs have a global warming potential that ranges from 140 to 11,700, and they can persist in the atmosphere from about a year to 260 years, depending on their molecular composition. Most commercially used HFCs, however, have a maximum lifetime of about 14 years-long enough to do plenty of damage.
PFCs pose a far greater risk. The two most common PFCs have global warming potentials of 6,500 (tetrafluoromethane) and 9,200 (hexafluoroethane). Their global warming potential is so high because, at a molecular level, they are very stable so they don't break down easily. In fact, only the powerful UV-rays in the mesosphere, some 60 kilometers above Earth, can destroy these gases, and it takes thousands of years for them to travel the mesosphere. Effectively, once they're out in the atmosphere, they're doing irreparable damage.
As if PFCs didn't sound bad enough, SF6 has a staggering global warming potential of 23,900. It is the most potent gas ever measured by the Intergovernmental Panel on Climate Change.
While high GWP gases have the potential to cause global warming to spin out of control, they accounted for less than 2 percent of U.S. emissions in 2002, according to the EPA, and many uses of these gases are being phased out.
Cara Smusiak writes on behalf of Naturally Savvy.com about how to live a more natural, organic and green lifestyle.
More on Climate Change from Planet Green:
What the Heck are Carbon Emissions, Anyway?
How to Go Green: Carbon Offsets
Al Gore Says You Can Solve Global Warming
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