Methane is over 100 times more powerful as a greenhouse gas than CO2. And when it degrades, a big part of what’s produced is................. CO2.
I don't know where the figure comes from.... the 100X.... but yes, I know it's more powerful. It's turnover rate is also a lot faster, and yes.... it goes towards CO2 and H2O.
The quantities being estimated under Arctic Ice, or part of the ice, are huge, numerically. But I think not more than an order in magnitude....10X....the normal methane being generated from other sources worldwide. And, it's a one-time event, of a sort, that will deplete itself over, say one or two decades, if the ice is all gone.
So, for example, in California, with winter rains, there's a lot of grass north of Bakersfield and Santa Maria all the way to the Delta areas, and some up towards Redding as well. This grass always dries out by June or so, and is a fire hazard until the winter rains come again.
In drying out, a lot of methane is also being released. When the rains come, and the grass decays more, more methane is released. As the humus remains on or in the soil, the release of methane continues.
My point above is that if we let cows eat it, the cow farts are actually less than what would have been released from the decaying grass. Same with every other life form that lives off the grass. Sure, the CO2 taken in by photosynthesis will almost all eventually be returned to the atmosphere.... but the more use we make of the grass, the larger the amount of C stored in the cycle in a "non-CO2" form. The Arctic methane, really is one other reservoir of storage that has kept some CO2 outta circulation for a while.
The second area of caution, I believe, against extrapolating some factor or another to claim a permanent effect or tipping point effect, is the size of CO2 cycle and the size of the sequestration pools, some of while are practically irreversible. Deposits of carbonates under semi-tropical seas, for example. Acid rain releases carbonate of Mg and Ca, but CO2 absorbs proportionally into the ocean as well, and most of that Mg and Ca released is re-deposited in carbonate minerals, and that amount of CO2 is for practical considerations permanently taken out of our air. Well, so carbonate rock to carbonate rock is just a relocation of the stuff, but with the rains there is also some chloride leach from our soils, and a larger amount of carbonate rock being created. Lots of MgCl2 extra in our oceans... some is being consumed by deposition as dolomite or magnesite continuously. The only ways we get that C back into circulation is from continental plate action, subduction, and subsequent volcanism. yah, and in collecting sea shells and burying them in landfills, maybe.
So, the science that calculates combustion and predicts increases in CO2 needs to figure on some being permanently settled in rock. I think the issue is, really, whether we want a petroleum economy to use up all our petroleum already. We might need some later. Like during the next ice age. I say the obvious answer is no. We need to move on to sustainable economies....
I am enthusiastic about the amount of research being done now, much more than ever before. I think we will begin to get good quantitative measures of various cycles, and make better estimates of how we are going to be affected.