Clathrate gun hypothesis

The clathrate gun hypothesis states that as sea temperatures rise the sudden release of methane from methane clathrate compounds buried in the seabeds will cause a drastic alteration of the ocean environment and the atmosphere of earth, as recent analysis concerning the Permian extinction event indicates may have happened in the past.

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Mechanism

Methane clathrate, also called methane hydrate, is a form of water ice that contains a large amount of methane within its crystal structure. Extremely large deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. The sudden release of large amounts of natural gas from methane clathrate deposits in a runaway greenhouse effect could be a cause of past and future climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; it is thought that this is a main factor in the global warming of 6°C that happened during the end-permian extinction[1], 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 62 over 20 years and 23 over 100 years). The theory also predicts this will greatly affect available oxygen content of the atmosphere.

Recent findings

In 2002, a BBC2 'Horizon' documentary, 'The Day the Earth Nearly Died,' summarized some recent findings and speculation concerning the Permian extinction event. Paul Wignall examined Permian strata in Greenland, where the rock layers devoid of marine life are tens of meters thick. With such an expanded scale, he could judge the timing of deposition more accurately and ascertained that the entire extinction lasted merely 80,000 years and showed three distinctive phases in the plant and animal fossils they contained. The extinction appeared to kill land and marine life selectively at different times. Two periods of extinctions of terrestrial life were separated by a brief, sharp, almost total extinction of marine life. Such a process seemed too long, however, to be accounted for by a meteorite strike. His best clue was the carbon isotope balance in the rock, which showed an increase in carbon-12 over time. The standard explanation for such a spike – rotting vegetation – seemed insufficient.

Geologist Gerry Dickens suggested that the increased carbon-12 could have been rapidly released by up-swellings of frozen methane hydrate from the seabed. Experiments to assess how large a rise in deep sea temperature would be required to sublimate solid methane hydrate suggested that a rise of 5°C (9 F) would be sufficient.

Possible release events

Two events possibly linked in this way are the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. However, warming at the end of the last ice age is thought not to be due to methane release.

Related mechanism: dissolved methane release

Focusing on the Permian-Triassic boundary, Gregory Ryskin [2] explores the possibility that mass extinction can be caused by an extremely fast, explosive release of dissolved methane (and other dissolved gases such as carbon dioxide and hydrogen sulfide) that accumulated in the oceanic water masses prone to stagnation and anoxia (e.g., in silled basins).

References

• Benton, Michael J.; Richard J. Twitchett (July 2003). "How to kill (almost) all life: the end-Permian extinction event". TRENDS in Ecology and Evolution 18 (7): 358-365. doi:10.1016/S0169-5347(03)00093-4., cited by 21 other articles.

• Release of methane from a volcanic basin as a mechanism for initial Eocene global warming, Henrik Svensen1, Sverre Planke1,2, Anders Malthe-Sørenssen1, Bjørn Jamtveit1, Reidun Myklebust3, Torfinn Rasmussen Eidem2 and Sebastian S. Rey2; Nature 429, 542-545 (3 June 2004)

• Warming the fuel for the fire: Evidence for the thermal dissociation of methane hydrate during the Paleocene-Eocene thermal maximum, Deborah J. Thomas1, James C. Zachos2, Timothy J. Bralower3, Ellen Thomas4 and Steven Bohaty5 ; Geology; December 2002; v. 30; no. 12; p. 1067-1070

• Methane-driven oceanic eruptions and mass extinctions, Gregory Ryskin, Northwestern University. Geology; September 2003; v. 31; no. 9; p. 741-744

• Temperature sensitivity and time dependence of the global ocean clathrate reservoir, Archer, D.; Buffett, B., Department of Geophysics, University of Chicago IL, American Geophysical Union, Fall Meeting 2004

In fiction

• The book Mother of Storms by John Barnes offers a fictional example of catastrophic climate change caused by methane clathrate release.
• In The Life Lottery by Ian Irvine unprecedented seismic activity triggers a release of methane hydrate, reversing global cooling.
• The hypothesis is the basis of an experiment in Death By Degrees.
• In Transcendent by Stephen Baxter, averting such a crisis is a major plotline.
• The novel The Black Silent by author David Dun features this idea as a key scientific point.
• In the anime Ergo Proxy, a string of explosions in the methane hydrate reserves wipes out 85% of human life on Earth.

See also

• Clathrate compound
• Extinction event
• Bermuda Triangle

Historical events

• Biology News: Gassy emissions no longer in suspect dock for melting the last ice age
• Linking continental-slope failures and climate change: Testing the clathrate gun hypothesis