I was recently looking at the history of the Nords when I came across their original location of Atmora. I understand that a civil war happened there which caused many to leave but are there people still living there in the fourth era, or is it a frozen wasteland?

Next question is about Morrowind. Articles I have read proclaim the eruption of Red Mountain to be catastrophic and thousands fled from Morrowind, however how else did the eruption impact Morrowind and the Dunmer? I know that Argonians invaded during the chaos but were the Dunmer able to retain political stability? How many Dunmer are still there?

If my info is wrong please excuse my errors, I recently started studying Elder Scrolls Lore, I am more of a Fallout guy

I don't remember exactly what is the state of Atmora and I don't feel like checking it out so I will just answer the question about Morrowind ( but if I remember correctly by fourth era Atmora is completly frozen [ and not neccesarily by ice] and no one lives there)

From what we seen and heard in both Skyrim and Dragonborn, Dunmers seem to be slowly recovering even on the vvanderfell itself from what I remember. That said bunch of big changes have happend both in the field of religion and politics ( which tend to intertwine together anyway).

For one thing the old temple worshiping Almsivi was taken over by dissidient priests and transformed in to a new temple that returned to the worship of reclamations, not everyone is happy with that.

On a political scene, House Redoran seems to be the major force right now. House Hlaalu lost the status of the great house to the new Great House Sadras, and House Indorill became synonymous with the New Temple.

Ever since Ysgrammor landed on Skyrim, Atmora has been uninhabitable to all life (except giants in out of game sources).

As for Morrowind, the book, Lord of Souls, deals with the immediate repercussions of what occurred. The Saxhleel were able to get as far north as Vivec City, and a lot of dumner fled to Solstheim. In Skyrim, particularly the DLC 'Dragonborn', much of what you ask is addressed. Currently, House Redoran is the top dog house, likely due to taking in fleeing Dunmer to bolster their rank and being up north, allowing them time to build up a counterforce. Hlaalu has been removed as a Great House, due to their collaboration with the Empire, which fell hard at the end of the 3rd era. Indoril exists largely in name only. For all practical purposes, it is now The Temple, who is divided on whether to worship the Tribunal as saints or to see them as blasphemers and heretics of the Three Good Daedra.

Morrowind, as a whole, is still rebuilding, but they're getting their strength back. The 'Mournhold' of Morrowind is now Blacklight, I believe, which is the capital of House Redoran.

We don't have too many concrete sources on the political state of Morrowind. Hellmouth already mentioned http://www.imperial-library.info/content/infernal-city-lore-notes and http://www.imperial-library.info/content/lord-souls-lore-notes, which visit Morrowind and talk a little bit about what it's like in the 4E40s. I've linked to the lore notes in the previous sentence, if you don't own the books and don't feel like buying them. You'll also be interested in http://www.imperial-library.info/content/red-year, which contains personal accounts of the crisis, and http://www.imperial-library.info/content/history-raven-rock, which deals with Dunmeri settlements and politics on Solstheim. In terms of minor details, http://www.imperial-library.info/content/house-redorans-reply mentions that Morrowind currently has 74 colonies, and http://www.imperial-library.info/content/great-war mentions that in 170 Morrowind had still not fully recovered from Red Mountain's eruption.

As for Atmora, it is indeed a frozen wasteland. http://www.imperial-library.info/content/pocket-guide-empire-third-edition-atmora.