Methane hydrates are stored in permafrost, and on the ocean floor. Not only have global methane concentrations been skyrocketting (from a historical maximum within the last 10,000 prior to 1900 being 800 ppb, and current data giving us in excess of 2100 ppb), but the highest values have been found around Greenland and the Arctic.
Is the Arctic ice melting because of a self-reinforcing cycle of rising methane, from global warming, from a hole in the ozone layer? It is hard to know, although I think the first theory is the most likely.
But, if it is the methane rising, which is then triggering more methane to rise, then we will have some serious problems to contend to: an extreme rise in temperatures, far in excess of that projected when only taking anthropogenic CO2 into account.