Editing IPCC:AR6/WGI/Chapter-5 (section)

===== 5.4.9.1.3 Methane release from clathrates =====

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The total global clathrate reservoir is estimated to contain 1500–2000 PgC ( [[#Archer--2009|Archer et al., 2009]] ; [[#Ruppel--2017|Ruppel and Kessler, 2017]] ), held predominantly in ocean sediments, with only an estimated 20 PgC in and under permafrost ( [[#Ruppel--2015|Ruppel, 2015]] ). The present-day CH <sub>4</sub> release from shelf clathrates is &lt;10 TgCH <sub>4</sub> yr <sup>–1</sup> ( [[#Kretschmer--2015|Kretschmer et al., 2015]] ; [[#Saunois--2020|Saunois et al., 2020]] ). Despite polar amplification (Chapter 7), substantial releases from the permafrost-embedded subsea clathrates is ''very unlikely'' ( [[#Minshull--2016|Minshull et al., 2016]] ; [[#Malakhova--2017|Malakhova and Eliseev, 2017]] , 2020). This is consistent with an overall small release of CH <sub>4</sub> from the shelf clathrates during the last deglacial transition, despite large reorganizations in climate state ( [[#Bock--2017|Bock et al., 2017]] ; [[#Petrenko--2017|Petrenko et al., 2017]] ; [[#Dyonisius--2020|Dyonisius et al., 2020]] ). The long time scales associated with clathrate destabilization makes it ''unlikely'' that CH <sub>4</sub> release from the ocean to the atmosphere will deviate markedly from the present-day value through the 21st century ( [[#Hunter--2013|Hunter et al., 2013]] ), corresponding to no more than additional 20 ppb of atmospheric CH <sub>4</sub> (i.e., &lt;0.2 ppb yr <sup>–1</sup> ). Another possible source of CH <sub>4</sub> is gas clathrates in deeper terrestrial permafrost and below it ( [[#Buldovicz--2018|Buldovicz et al., 2018]] ; [[#Chuvilin--2018|Chuvilin et al., 2018]] ), which may have caused recent craters in the north of Russia ( [[#Arzhanov--2016|Arzhanov et al., 2016]] , 2020; [[#Arzhanov--2017|Arzhanov and Mokhov, 2017]] ; [[#Kizyakov--2017|Kizyakov et al., 2017]] , 2018). Land clathrates are formed at depths greater than 200 m ( [[#Ruppel--2017|Ruppel and Kessler, 2017]] ; [[#Malakhova--2020|Malakhova and Eliseev, 2020]] ), which precludes a substantial response to global warming over the next few centuries and associated emissions.

Thus, it is ''very unlikely'' that CH <sub>4</sub> emissions from clathrates will substantially warm the climate system over the next few centuries.

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