Greenhouse Gas: Methane is about 21 times more powerful at warming the atmosphere than carbon dioxide (CO2)
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Greenhouse Gas Properties
Methane (CH4) is a principal component of natural gas. It is also formed and released to the atmosphere by biological processes occurring in anaerobic environments. Once in the atmosphere, methane absorbs terrestrial infrared radiation that would otherwise escape to space. This property can contribute to the warming of the atmosphere, which is why methane is a greenhouse gas.
Methane is about 21 times more powerful at warming the atmosphere than carbon dioxide (CO2) by weight (see box below). Methane's chemical lifetime in the atmosphere is approximately 12 years. Methane’s relatively short atmospheric lifetime, coupled with its potency as a greenhouse gas, makes it a candidate for mitigating global warming over the near-term (i.e., next 25 years or so).
Global Warming Potentials
The concept of a global warming potential (GWP) was developed to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to another gas. 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.
As part of its scientific assessments of climate change, the Intergovernmental Panel of Climate Change (IPCC) has published reference values for GWPs of several greenhouse gases. While the most current estimates for GWPs are listed in the IPCC's Third Assessment Report (TAR), EPA analyses use the 100-year GWPs listed in the IPCC's Second Assessment Report (SAR) to be consistent with the international standards under the United Nations Framework Convention on Climate Change (UNFCCC) (IPCC, 1996 Exit EPA). According to the SAR, methane is 21 times more effective at trapping heat in the atmosphere when compared to CO2 over a 100-year time period.
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