SkS has a post up on the decay of permafrost. Catnip to me, of course. It's a good summary, and highlights a number of issues. Here's one I hadn't thought about much:
Commercial activities in the Arctic are large, important to national economies and for the viability of local population centres. Monitoring of permafrost melting and associated greenhouse gas emissions is undertaken by ground instruments and satellites. However, unless technology able to replace melting permafrost with an affordable, durable load bearing foundation can be applied, it should be accepted that virtually all existing buildings and structures located on permafrost with foundations less than 5 metres deep are likely to be damaged or destroyed before 2100.That's the homes and businesses of millions of people; oil, gas, and mining infrastructure, utilities and transport infrastructure, etc. The rapid erosion of the Arctic's 100,000km coastline (which is made of little rocks glued together with the aforementioned permafrost) also gets a good treatment.
They don't precisely estimate the amount of feedback from carbon (methane and carbon dioxide) released by melting permafrost. I don't know the answer either, although I discuss some estimates here and here. If you said 25-100ppm of CO2 in additional carbon by 2200, I don't think anyone could tell you you were wrong. If I find a better estimate, I'll post on it.
1. Why do we never hear about Antarctic permafrost?
Because for complicated reasons it doesn't store very much carbon (touch wood!) Since there are few people there, no one really cares.
2. I'm sick of reading wildly different estimates of the potency of methane as a greenhouse gas compared to CO2. What's the real number?
A molecule of methane traps heat hundreds of times better than a molecule of CO2. But it decays much faster. The really high estimates you see are molecule-to-molecule comparisons; the lower ones are long-term comparisons. The long-term comparisons turn out to be tricky. Methane is worse than CO2; and when it decays it turn into CO2, so it's really a lose-lose proposition.
3. Does melting permafrost release CO2 or methane?
Either CO2 or both. The methane makes headlines but the research I highlighted here suggests the CO2 is actually the bigger problem. More on methane here.
4. Can we stop the melting of the permafrost?
Probably not, given the feedbacks that have already kicked in, and Arctic amplification which we see rapid warming of the North even with radical emissions reductions. Short of large-scale geoengineering, the permafrost is going to go. The additional warming will further accelerate global warming.