Mehane hydrates - a.k.a. methane clathrates - are an important part of global methane storage (see)
They are commonly found in permafrost deposits and on and under the sea floor, being a frozen, naturally‐occurring, and highly‐concentrated form of methane linked with water molecules.
For stability, they require low temperatures (typically < 15 °C) and moderately high pressures. When warmed, the trapped methane is released and ultimately enters the atmosphere - where it is a potent 'greenhouse' gas. This greenhouse effect leads to higher global temperatures which in turn releases more methane from the hydrates. Thus, they may be a profound factor in the case of positive-feedback 'runaway' global warming.
Some climatologists suggest that runaway methane hydrate release was responsible for the 6°C global temperature rise at the end of the Permian period, which caused mass extinctions. [ ref. Trends in Ecology and Evolution, volume 18, issue 7, pp358-365, ]
Although the science behind the storage and release mechanisms are well understood, at present the quantity of naturally stored methane hydrate worldwide is unknown. With expert estimates varying by a factor of more than 30 times.
Current midrange estimates put the global quantity at around 2.4 trillion tonnes of CH4 [ Source: Review of Geophysics Volume 55, Issue1 ]
These uncertainties make accurate calculations of potential global warming models considerably more problematic.
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