As all you know it is now uninhabitable by men and mer. What do you think, what caused the cooling?

In before ancient aliens.

I always theorized the Kamal had something to do with it.

That is, if the Kamal aren't the descendents of proto-nords anyway.

The frost dragons began to overpopulate, and had a "debate" about who should clear out and colonize other territories. Everyone lost.

Atmora=northern Akavir. The Nords settled there in early spring, the Kamal thawed out in summer and drove them out, and by the time they returned, it was winter.

Source?

Orkey happened.

I always liked the theory that it was related to Kamal in some way. Although it was still green around the time of the Nords war with the Falmer so maybe they had something to do with it.

I've never thought of this before, but it would be kind of neat for seasonal cycles on every continent to be different, based on the mythopoetic differences of the people who live there.

Also, this makes me think of "Winter is coming." That's always a plus.

My imagination. Makes a decent amount of sense though, what with the Dragon Cult garb looking an awful lot like Akaviri Dragonscale, the similarities between Thu'um and Akaviri kiai, and the fact that Akavir is Dragon Land.

[Headcanon]Snow Hell, originally part of a glacier of Atmora, broke off during the time period when Alduin ate the life-span of the Nords and drifted to sea until hitting akavir. Though they didn't manage to get their life-span back due to being far from the other Atmorans. The Kamal slowly went insane with blood thirst and anger, using the ice to prevent them from dying of old age they managed to make every spring and summer a hell for the akaviri while returning how when autumn hits out of fear of missing the time to freeze themselves again.[/headcanon]

It froze, and that's about all we know. The how and why is currently unknown, and I'd suspect it'd remain that way for a long while.

If anyone tells you different, they're using headcanon or have a source I'm currently unaware of.

Damn, and I was gonna say "Winter came."

My guess? Whatever mythopoeic forces that bound the stone of Snow-Throat to the condition of Skyrim's social well-being decided to take not any chance in fragmenting the Nords society. The children had to move out of their home, and so on.

The last expedition to Atmora resulted in the expedition group finding a frozen landscape devoid of all life, they probably didn't spend long there since living conditions were horrible, probably even short term living conditions.

also according to the Monomyth Lorkhan shattered Atmora into many

http://www.uesp.net/wiki/Lore:The_Monomyth

"Auriel could not save Altmora, the Elder Wood, and it was lost to Men. They were chased south and east to Old Ehlnofey, and Lorkhan was close behind. He shattered that land into many. Finally Trinimac, Auriel's greatest knight, knocked Lorkhan down in front of his army and reached in with more than hands to take his Heart. He was undone. The Men dragged Lorkhan's body away and swore blood vengeance on the heirs of Auriel for all time."

Jyggalag brought Order.

Ah, I just wasn't sure if there was an in-game reference or something. That's an interesting theory, though; it would make Akavir significantly bigger than I had thought previously.

By getting jyggy-with-it?

But of course!

As far as I'm concerned, Atmora went the same way Aldmeris did: it deteriorated due to loss of magical energy (or sunlight, in this case). Aldmeris devolved into Tamriel, Atmora (a forested continent) devolved into a frozen wasteland. Just natural forces.

In this quote, "that land" that you refer to Lorkhan shattering is Old Ehlnofey, Aldmeris, which we already knew was sundered. The only mention of Atmora/Altmora here is that the Elves lost it to Men and had to leave.

Mythic inverse curve - Aldmeris swung padomaic, Atmora went full Anuic.