Clathrate gun hypothesis

K–Pg

Tr–J

P–Tr

Late D

O–S

Millions of years ago

Marine extinction intensity through time. The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the “Big Five” extinction events are clickable hyperlinks; see Extinction event for more details. (source and image info)

The clathrate gun hypothesis is the popular name given to the hypothesis that rises in sea temperatures (and/or falls in sea level) can trigger the sudden release of methane from methane clathrate compounds buried in seabeds and 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.^[1]

In its original form, the hypothesis proposed that the “clathrate gun” could cause abrupt runaway warming in a timescale less than a human lifetime,^[1] and might be responsible for warming events in and at the end of the last ice age.^[2] This is now thought unlikely.^[3][4]

However, there is stronger evidence that runaway methane clathrate breakdown may have caused drastic alteration of the ocean environment and the atmosphere of earth on a number of occasions in the past, over timescales of tens of thousands of years; most notably in connection with the Permian extinction event, when 96% of all marine species became extinct 251 million years ago.^[5]