It is referred to as the Long Cold as well.
As is told, at one point where the world before ceased and a period of darkness began, all dwellers of the surface got cold and the beasts of untold power and cruelty brought and end to all things, pausing time in a non-stop blizzard of death and chaos. For an undetermined period, no new life could start and what few things remained did so at a stand still with their own existance, left to wait until the thaw when ultimately the lack of what was before drove them mad. There was no known end, but in time consciousness returned to the foresaken world of the Avantsphere, and the clarity spread slowly until the present day, still reaching to corners of darkness yet to be purged from the cold of endless night. Evidence of this time can still be found in the depth of great ravines where black ice holds pools of darkness frozen even now.