Methane's a powerful greenhouse gas but has a very short duration in the atmosphere, compared to CO2 which lasts essentially forever "(for human civilization).
To understand the methane news, you can read this great overview of recent methane news coverage (and its strengths & weaknesses) at Columbia Journalism Review, or drop by RealClimate.org, where the climate scientists have recently written about the methane studies.
The CJR piece indicates methane from permafrost is worrisome but not a time bomb. It quotes journalist Justin Gillis saying "What I learned about ocean methane was reasonably reassuring, with the caveat that scientists would like to know a great deal more about these deposits before declaring for certain that the hazard is minimal", and authors of the Permafrost Carbon Network methane analysis published in Nature saying that (emphases mine) “despite the massive amount of carbon in permafrost soils, emissions from these soils are unlikely to overshadow those from the burning of fossil fuels, which will continue to be the main source of climate forcing.”
The first Real Climate post addresses methane's likely climate effect overall:
"Methane is a powerful greenhouse gas, but it also has an awesome power to really get people worked up, compared to other equally frightening pieces of the climate story.Then they address the methane worst case scenario:
...The methane bubbles coming from the Siberian shelf are part of a system that takes centuries to respond to changes in temperature. The methane from the Arctic lakes is also potentially part of a new, enhanced, chronic methane release to the atmosphere. Neither of them could release a catastrophic amount of methane (hundreds of Gtons) within a short time frame (a few years or less). There isn’t some huge bubble of methane waiting to erupt as soon as its roof melts.
And so far, the sources of methane from high latitudes are small, relative to the big player, which is wetlands in warmer climes. It is very difficult to know whether the bubbles are a brand-new methane source caused by global warming, or a response to warming that has happened over the past 100 years, or whether plumes like this happen all the time. In any event, it doesn’t matter very much unless they get 10 or 100 times larger, because high-latitude sources are small compared to the tropics."
"the methane worst case does not suddenly spell the extinction of human life on Earth. It does not lead to a runaway greenhouse. The worst-case methane scenario stands comparable to what CO2 can do. What CO2 will do, under business-as-usual, not in a wild blow-the-doors-off unpleasant surprise, but just in the absence of any pleasant surprises (like emission controls). At worst comparable to CO2 except that CO2 lasts essentially forever."