Permafrost + heat = methane

A good science source re the current unthawing of the ground in the arctic is  Centre for Arctic Gas Hydrate, Environment and Climate (CAGE)
 "The Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) is investigating the role of gas hydrates in arctic areas, and the effects they will have on oceans and our global climate in the future.
The research centre is located at UiT The Arctic University of Norway in Tromsø, which is the northernmost university in the world."

 https://cage.uit.no/