It has been speculated on that some abrupt and profound changes in the past climate, including the wholesale extinction of species, are down to the sudden collapse of methane hydrate and extreme greenhouse-warming from methane gas in the atmosphere. It is often quoted, as in the Independent today, that methane is "a greenhouse gas 20 times more potent than carbon dioxide ", but this is the case averaged over a 100 year period. Over 20 years, it is 60 times more potent, and if say one kilogramme each of methane and carbon dioxide were released simultaneously into the atmosphere, the global warming potential of methane is nearer 100 times that of CO2.
The latter figure may be deduced as follows from the definition for Global warming potential in: http://en.wikipedia.org/wiki/Global_warming_potential - along with some factors for atmospheric lifetimes for CH4 and CO2 (the latter is quite variable, between 50 and 200 years). From the data in that link, if the warming potential (relative to CO2) for methane is 7 (over 500 years), 23 (100 years), 62 (20 years) - (or the other set of data given) a value of 100 (as deduced below) is reasonable for zero-years, i.e. instantaneous radiative forcing by a given mass of each gas.
Taking the equation that defines GWP (x) in the above link, and then reducing it for t=o (TH=0), you get:
GWP(CH4) = aCH4/aCO2 x MWCO2/MWCH4 = .53W/m^2 ppmv/.015W/m^2 ppmv x 44/16 = 97.2. i.e. about 100. The point is that it's one kg of each gas (i.e. mass not volume) that is assumed to be added to the atmosphere. Since the volume of a kg of a gas depends on the MW of its molecules you need the correction factor as shown, i.e the volume of a kg of CO2 is less than that of a kg of CH4 by the factor of 16/44.
Both gases will over time be removed from the atmosphere, with lifetimes of about 12 years for methane and about 100 years for CO2 (depending on where it is), but I am assuming a kind of steady-state situation where both gases are continually contributed, as seems to be the case, although the amounts of each may vary over time. However, the latter case is complex and goes beyond this simple definition of GWP.
The point is that in terms of assessing the relative GWP of gases relative to CO2, it is important to note the time interval that is being quoted.
Furthermore, if methane is being emitted at up to 100 times background levels in hot-spot regions of the Siberian continental shelf, and the GWP is 100 that of CO2, the effect of this could be catastrophic and climate models will need to be amended to include its influence.
This may well be a striking example of a feedback mechanism in the earth system, where more warming releases more methane and the system runs-away, leading to unexpectedly high, at least local, temperatures with profound influences on the climate of particular regions as the earth heat-machine is tuned in the way it redistributes heat from the equatorial and tropical regions toward and around the poles.
One explanation for the release of methane from the Arctic is that there is an increasing volume of relatively warm water being disgorged from Siberia's rivers as the land-based permafrost melts there. Overall, the Arctic region has felt a rise in temperature of 4 degrees C during the past few decades, with a concomitant decrease in the area of sea-ice there. A significant body of scientists anticipate that the loss of sea-ice which normally reflects sunlight, will result in yet warmer temperatures as the energy is instead absorbed by the open sea.
"Exclusive: The methane time bomb." By Steve Connor. http://www.independent.co.uk/news/science/exclusive-the-methane-time-bomb-938932.html