– various sources
FACT: The best and most recent science indicates that methane is 33 times more powerful than carbon dioxide as a greenhouse gas, when considered over an integrated time period of 100 years following emission, and 105 times more powerful on an integrated 20 year time period.
The global warming potential or GWP, is a simple metric often used to assess how much more powerful a given greenhouse gas is when compared to carbon dioxide. Back in 1996, the Intergovernmental Panel on Climate Change estimated the GWP for methane as 21, considered over a 100-year time period following emission. As of 2007, the IPCC presented global warming potentials (GWP) for methane of 25 for a 100-year integrated time-frame and 72 for a 20-year integrated time frame after emission. Using a more recent model to better capture how methane interacts with other radiatively active substances, Shindell et al. in a 2009 paper in Science updated these factors to 33 and 105 respectively. These higher values reflect the best, most current science. The GWP for methane is less at the longer time scale simply because methane does not stay in the atmosphere for as long as carbon dioxide.