This mass extinction has long been linked to a large and abrupt release of carbon dioxide into the atmosphere, but the exact source of this emission has been unknown. (sciencedaily.com)
Since the area of geological disjunctives (fault zones, tectonically and seismically active areas) within the Siberian Arctic shelf composes not less than 1 - 2 % of the total area and area of open taliks (area of melt through permafrost), acting as a pathway for methane escape within the Siberian Arctic shelf reaches up to 5 - 10 % of the total area, we consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. (realclimate.org)
The worry is not so much that there is already an abprupt release (though methane concentrations are on the rise) but that there are pathways for such abrupt release. (realclimate.org)