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The clathrate gun hypothesis is the popular name given to the hypothesis that increases in sea temperatures (and/or falls in sea level) can trigger the sudden release of methane from methane clathrate compounds buried in seabeds and that contained within seabed permafrost which, because the methane itself is a powerful greenhouse gas, leads to further temperature rise and further methane clathrate destabilization – in effect initiating a runaway process as irreversible, once started, as the firing of a gun. In its original form, the hypothesis proposed that the "clathrate gun" could cause abrupt runaway warming on a timescale less than a human lifetime,〔 and was responsible for warming events in and at the end of the last glacial maximum. This is now thought to be unlikely. However, there is stronger evidence that runaway methane clathrate breakdown may have caused drastic alteration of the ocean environment (such as ocean acidification and ocean stratification) and of the atmosphere of earth on a number of occasions in the past, over timescales of tens of thousands of years. These events include the Paleocene–Eocene Thermal Maximum 56 million years ago, and most notably the Permian–Triassic extinction event, when up to 96% of all marine species became extinct, 252 million years ago. ==Mechanism== 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 clatrate deposits (particularly in the viability of extracting them as a fuel resource). Indeed cores of greater than 10 cm contiguous depth had only been found in 3 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. The release of this trapped methane is a potential major outcome of a rise in temperature; some have suggested that this was a main factor in the global warming of 6 °C that happened during the end-Permian extinction, as methane is much more powerful as a greenhouse gas than carbon dioxide. Despite its atmospheric lifetime of around 12 years, it has a global warming potential of 72 over 20 years, 25 over 100 years, and 33 when accounted for aerosol interactions.〔(Online )〕 The theory also predicts this will greatly affect available oxygen and hydroxyl radical content of the atmosphere. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Clathrate gun hypothesis」の詳細全文を読む スポンサード リンク
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