Editing Extinction event (section)

====Global warming====
{{Main|Extinction risk from global warming}}
This would have the opposite effects: expand the area available for [[Tropics|tropical]] species; kill [[temperate]] species or force them to migrate towards the [[Polar circle|poles]]; possibly cause severe extinctions of polar species; often make the Earth's climate wetter on average, mainly by melting ice and snow and thus increasing the volume of the [[water cycle]]. It might also cause anoxic events in the oceans (see below).

Global warming as a cause of mass extinction is supported by several recent studies.<ref>{{cite journal | vauthors = Mayhew PJ, Jenkins GB, Benton TG | title = A long-term association between global temperature and biodiversity, origination and extinction in the fossil record | journal = Proceedings. Biological Sciences | volume = 275 | issue = 1630 | pages = 47–53 | date = January 2008 | pmid = 17956842 | pmc = 2562410 | doi = 10.1098/rspb.2007.1302 }}</ref>

The most dramatic example of sustained warming is the [[Paleocene–Eocene Thermal Maximum]], which was associated with one of the smaller mass extinctions. It has also been suggested to have caused the [[Triassic–Jurassic extinction event]], during which 20% of all marine families became extinct. Furthermore, the [[Permian–Triassic extinction event]] has been suggested to have been caused by warming.<ref>{{cite journal | vauthors = Knoll AH, Bambach RK, Canfield DE, Grotzinger JP | title = Comparative Earth History and Late Permian Mass Extinction | journal = Science | volume = 273 | issue = 5274 | pages = 452–457 | date = July 1996 | pmid = 8662528 | doi = 10.1126/science.273.5274.452 | s2cid = 35958753 | bibcode = 1996Sci...273..452K }}</ref><ref>{{cite journal | vauthors = Ward PD, Botha J, Buick R, De Kock MO, Erwin DH, Garrison GH, Kirschvink JL, Smith R | display-authors = 6 | title = Abrupt and gradual extinction among Late Permian land vertebrates in the Karoo basin, South Africa | journal = Science | volume = 307 | issue = 5710 | pages = 709–714 | date = February 2005 | pmid = 15661973 | doi = 10.1126/science.1107068 | s2cid = 46198018 | citeseerx = 10.1.1.503.2065 | bibcode = 2005Sci...307..709W }}</ref><ref>{{cite journal | vauthors = Kiehl JT, Shields CA |date=September 2005 |title=Climate simulation of the latest Permian: Implications for mass extinction |journal=Geology |volume=33 |issue=9 |pages=757–760|doi=10.1130/G21654.1 |bibcode = 2005Geo....33..757K }}</ref>

===== Clathrate gun hypothesis =====
{{Main|Clathrate gun hypothesis}}
[[Clathrates]] are composites in which a lattice of one substance forms a cage around another. [[Methane clathrate]]s (in which water molecules are the cage) form on [[continental shelf|continental shelves]]. These clathrates are likely to break up rapidly and release the methane if the temperature rises quickly or the pressure on them drops quickly – for example in response to sudden [[global warming]] or a sudden drop in sea level or even [[earthquake]]s. Methane is a much more powerful [[greenhouse effect|greenhouse]] gas than carbon dioxide, so a methane eruption ("clathrate gun") could cause rapid global warming or make it much more severe if the eruption was itself caused by global warming.

The most likely signature of such a methane eruption would be a sudden decrease in the [[Isotope analysis|ratio of carbon-13 to carbon-12]] in sediments, since methane clathrates are low in carbon-13; but the change would have to be very large, as other events can also reduce the percentage of carbon-13.<ref>{{cite magazine | vauthors = Hecht J | title=Methane prime suspect for greatest mass extinction | magazine=[[New Scientist]] | date=2002-03-26 | url=https://www.newscientist.com/article/dn2088-methane-prime-suspect-for-greatest-mass-extinction/}}</ref>

It has been suggested that "clathrate gun" methane eruptions were involved in the [[Permian–Triassic extinction event|end-Permian extinction]] ("the Great Dying") and in the [[Paleocene–Eocene Thermal Maximum]], which was associated with one of the smaller mass extinctions.