The role of methane in the "global warming" scenario is rarely properly communicated but it is extremely important, and, in some sense, methane is more important than CO2.
The build up of methane (CH4) over time shows complicated behavior:
There clearly was a period that was relatively flat (see more below) but since about 2008, emissions are steadily climbing.
So how much does Methane contribute to the "Global Warming" propblem.
The cross section of a molecule with respect to its ability to absorb infrared light is important and quite variable from molecule to molecule.
A CO2 molecule is a dumbell shape:
However, the physical size of Methane is much larger and therefore this molecule presents considerably more cross section with respect to outgoing long wavelength IR emission.
The ratio of absorption cross sections between methane and carbon dixoxide is temperature and wavelength dependent on temperature and wavelength, but an aggregate value is around 21.
This value of 21, for 20 years, was the IPCC adopted value for the Global Warming Potential (GWP) of methane. The in 2009 stronger consideration of actual chemical reactions involving
methane and aerosols have shown that aerosol particles (which act as global coolants) rapidly find the reactive surface of a methane molecule and attach themselves, thus removing their global cooling profile. (I guarantee that note a single person teaching any climate change course on this campus is aware of this important development).
The effective of this kind of chemistry feedback is that the GWP
of methane is now 34 which is a 34/21 = 1.6x increase and this is significant (see more below), because its now measured to be leaking out of pipelines and fracking fields!
Sources of Methane Emission:
By Color:
Purple (Wetlands) - lower emissions in drought periods
Green - relatively constant
Orange - these are increasing due to Arctic Warming and ocean warming
Red - human acitivies that increase with population growth directly
Blue - Mostly human actitivies
Note that methane sinks are mostly chemistry based and have reaction rates that have been established over thousands of years. Methane reduction chemistry is not going to accelerate fast enough to handle the increasing emissions.
The period from about 1999 through 2007 showed methane concentration
to be relatively flat(which would be very good news). At the time this was a serious
mystery . One of the strong things that controls terrestrial methane emission is the amount and vitality of wetlands:
Wetlands emission
are key here!
The resolution to the flat period as well as the recent, unfortunate rise in emissions seems to be a combination of
the following two items:
After declining in the 1990s due to the industrial collapse of the Soviet Union,
and the combination of more efficient use of natural gas and efforts to reduce
landfill methane emissions in the West, emissions have risen since 1999 due possibly,
in part, to the booming Chinese economy.
Had it not been for this reduction in methane emissions from wetlands, atmospheric
levels of methane would most likely have continued rising," said Dr Paul Steele, from a
scientist from Australia's CSIRO Marine and Atmospheric Research and one of the paper's
authors. "This suggests that, if the drying trend is reversed and emissions from wetlands
return to normal, atmospheric
methane levels may increase again, worsening the problem of
climate change."
But it now appears that methane emissions are on the rise again
at an annual rate of about 6 ppb(illion).
If the current rates in both CO2 and CH4 continue then by the year 2050 we will have this situation:
CO2 = 399 + 35*2.5 = 487 ppm
CH4 = 1.83 + .006*35 = 2.04 ppm
CO2e = 487 +2.04*34 = 560 ppm
There is, however, potentially, a much worse problem.
A major concern, a positive feedback loop:
Note, however, that "catastrophic" release of CH4 during
period of Ice Ages may be the natural way that the Earth accelerates
from a glacial period:
Known Hydrate deposits. Found typically in continental shelf where
marine organisms (microbes) actively feed on carbon and carbon related
productes to produce methane in the sediments.
And then there is the issue of permafrost melting which contains
much methane (set on fire in the video above).
Spring 2014 saw warmest temperatures ever in Siberia:
and this is significant (see more below), because its now measured to be 
