Methane clathrate, also known commonly as methane hydrate, is a form of water ice that contains a large amount of methane within its crystal structure. Potentially large deposits of methane clathrate have been found under sediments on the ocean floors of the Earth, although the estimates of total resource size given by various experts differ by many orders of magnitude, leaving doubt as to the size of methane clathrate deposits (particularly in the viability of extracting them as a fuel resource). Indeed, cores of greater than 10 centimeters' contiguous depth had only been found in three sites as of 2000, and some resource reserve size estimates for specific deposits/locations have been based primarily on seismology. The sudden release of large amounts of natural gas from methane clathrate deposits in runaway climate change could be a cause of past, future, and present climate changes. 
In the Arctic ocean, clathrates can exist in shallower water stabilized by lower temperatures rather than higher pressures; these may potentially be marginally stable much closer to the surface of the sea-bed, stabilized by a frozen lid of permafrost preventing methane escape. The so-called self-preservation phenomenon has been studied by Russian geologists starting in the late 1980s. This metastable clathrate state can be a basis for release events of methane excursions, such as during the interval of the Last Glacial Maximum. A study from 2010 concluded with the possibility for a trigger of abrupt climate warming based on metastable methane clathrates in the East Siberian Arctic Shelf (ESAS) region.