So Heavensward is basically Coerthas the expansion?

[Omegakiyohime]

Yep you're right. I forget the lore but why was Coerthas covered in snow and ice? Can't be just Bahamut's Rage.

I'm not sure if it was anything more than vast temperature changes due to the fall of Dalamud. Due to certain events that would constitute a spoiler, a lot of aether got released back into the world so that may play a part as well.