take thousands of years to warm the ocean and the sediments enough to cause
massive releases, only lots of drilling rigs.
Returning to the 4 GtC release scenario, assume such a release occurs over a one-
year period sometime in the next 50 years as result of slope failure. According to the
Report of the Methane Hydrate Advisory Committee, “Catastrophic slope failure
appears to be necessary to release a sufficiently large quantity of methane rapidly
enough to be transported to the atmosphere without significant oxidation or
dissolution.”
In this event, methane will enter the atmosphere as methane gas. It will have a
residence time of several decades and a global warming potential of 62 times that of
carbon dioxide over a 20-year period.
This would be the equivalent of 248 GtC as carbon dioxide or 31 times the annual
man-made GHG emissions of today. Put another way, this would have the impact of
nearly 30 years worth of GHG warming all at once. The result would almost
certainly be a rapid rise in the average air temperature, perhaps as much as 3°F
immediately. This might be tolerable if that’s as far as things go. But, just like
15,000 years ago, if the feedback mechanisms kick in, we can expect rapid melting of
Greenland and Antarctic ice and an overall temperature increase of 30°F.
For point of reference, the average temperature of the Earth (atmosphere, land and
top layer of the ocean) in 2004 is around 60°F. The methane hydrate release
projected here would raise the temperature to around 90°F or more. Such high
temperatures would undoubtedly destabilize all of the other methane hydrates in
the ocean and arctic permafrost, some 10,000 GtC or 620,000 GtC equivalent as
carbon dioxide. This would have the impact of 78,000 years worth of GHG warming
over a few decades. The temperatures reached and sustained would most likely
cause a rapid die off in ocean phytoplankton and other sea life as well as most land
plants and animals, including humans. The result would be a mass extinction and
mark a major transition point in the Earth’s geological history.
Although a 1000 or 10,000 GtC methane release in one year or over several decades
is very unlikely, a 4 GtC release is entirely plausible. Even if the feedback
mechanisms that were operative 15,000 years ago became partly active, the outcome
could be just as disastrous as the scenario outlined above.