Arctic Melt Releasing Methane

Methane would be CH4, and there's lots of it stored in the Arctic.  Or was stored.  The article states that CH4 is the second most important greenhouse gas behind CO2.  There is much more CO2 being emitted than CH4, but CH4 is 72x more efficient at trapping heat than CO2.  This is called its Global Warming Potential and has to be stated over a particular time horizon.  The 72x relates to a 20 year period.