Melting of the northern permafrost could release a large amount of mercury (estimated around 800 gigagrams). (https://news.ycombinator.com/item?id=16330219 http

Melting of the northern permafrost could release a large amount of mercury (estimated around 800 gigagrams). (https://news.ycombinator.com/item?id=16330219 https://news.ycombinator.com/item?id=16330219) There is also worry of a positive feedback loop that could cause global warming to spiral out of control. (https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis)