If the Arctic tundra thaws (see the graphic below), climate scientists believe it may represent an irreversible tipping point that sends climate warming out of control.  The methane released would take at least 250 years to first be converted into CO2 and then be pulled into the oceans and plant life where it can be removed by fixation.  Methane is 21 times more powerful a greenhouse gas than CO2.  So, release of one ton of methane is like releasing 21 tons of CO2.  In a reference article here:  (http://www.wunderground.com/resources/climate/melting_permafrost.asp),  it states: “[A]s of 2011, no climate model incorporates the effects of methane released from melting permafrost, suggesting that even the most extreme climate scenarios in the models might not be extreme enough.”  This article also covers methane hydrates that climate scientists say may, as a result of warming oceans, begin to melt and release the methane trapped in more shallow ocean beds such as the Arctic ocean.

Locations where permafrost exists in the Arctic (northern high latitudes). Source: Philippe Rekacewicz, 2005