A cage of flammable ice
Beneath the seafloor of the Arctic Ocean lies a vast and unusual substance: methane hydrate. This material, also known as "flammable ice," is a crystalline solid where water molecules form a lattice structure that traps a large amount of methane gas inside. These deposits, or clathrates, are stable only under conditions of high pressure and low temperature, such as those found in deep ocean sediments or beneath permafrost.
Estimates of the total amount of carbon locked away in global methane hydrates vary widely, but they are immense. Some calculations suggest the amount of carbon is more than twice that found in all known fossil fuel reserves combined. The general chemical formula for a methane hydrate is CH4·nH2O, with the "n" representing a variable number of water molecules, often around 5.75 to 6. Under standard atmospheric pressure, one cubic meter of solid methane hydrate can release about 164 cubic meters of methane gas. These deposits form from methane that migrates up from deep within the earth or is produced by the decay of organic matter in sediment layers.
The theoretical trigger
The Clathrate Gun hypothesis proposes that these stable methane hydrate deposits can become destabilized by warming ocean temperatures. A sufficient increase in temperature can break down the ice-like cages, leading to a large-scale release of methane gas from the seabed into the water column and potentially the atmosphere. Since methane is a strong greenhouse gas—over 80 times more powerful than carbon dioxide over a 20-year period—a massive release could trigger a feedback loop, where the released methane causes further global warming, which in turn destabilizes more clathrates.
This mechanism has been proposed as a potential driver for rapid warming events in Earth's geological past. The most cited example is the Paleocene-Eocene Thermal Maximum (PETM), which occurred around 56 million years ago. During the PETM, global temperatures rose by 5 to 8 degrees Celsius in a geologically short period, an event some scientists believe was caused or amplified by a catastrophic methane release from hydrates. The hypothesis is also linked to the end of the "Snowball Earth" period around 635 million years ago and the Permian-Triassic extinction event.
Firing blanks?
The current scientific consensus on the immediate threat is that a catastrophic, rapid release is unlikely in the near future. Most methane hydrate deposits are buried deep in sediments, meaning it would take centuries to millennia for a warming signal from the ocean surface to reach them. Studies indicate that up to 90% of methane released from the seafloor is oxidized by microbes in the water column and converted into carbon dioxide, a less potent greenhouse gas, before it can reach the atmosphere.
However, the situation in the shallow Arctic shelves is being actively researched. Here, hydrates can exist in shallower waters, stabilized by the extreme cold. Scientists have observed active methane plumes bubbling from the seafloor in the East Siberian Arctic Shelf and other locations. While current models suggest a slow, chronic release rather than an abrupt "gunshot," the behavior of these vast, shallow deposits in a rapidly warming Arctic remains a significant uncertainty in climate models.