Permafrost is a clump of ice that is below the surface, which is considered permanent ice in cold regions. With global warming, in places like Siberia in Russia, craters are formed, and these craters occur, because permafrost thaws and there is no more support for the soil above, and thus it yields forming craters.
There are several signs of global warming, and the consequences of this man-made event. Several regions lose their ecological balance, like the regions of Siberia. The ice in the cold regions needs to cool the imbalance of the globe. And so the ice mass considered permanent, melts, reducing the cooling power of the planet.
The melting of Permafrost is yet another sign of the dark future that lies ahead.