These areas have always been habitable, for some value of habitable. They just used to have a lot of year-round ice that has now melted off. Caribou craps on

These areas have always been habitable, for some value of habitable. They just used to have a lot of year-round ice that has now melted off. Caribou craps on the ice, hunter looses a spear, snow covers it up, snow turns to ice. Lather, rinse, repeat.