Knight Mariel,
I believe our disagreement arises largely in our definition of "civilization" as well as the general lack of information on pre-migration Atmora. The 'official' criteria for civilizations are as follow. It is important to note that a civilization does not have to have them all (several native American civilizations did not poses a system of writing for example).
Cities: While we do not know of any cities in Atmora, Ysgamor established Saarthal shortly after his arrival, suggesting that the knowledge was already present in their society.
Full-time labor specialization: again, no direct information is available. Again, the Atmoran's ability to build ships and cities suggests that specialization was present.
The ability to produce and store surplus food: No information is available on this. However, I would suspect that the very survival of the Atmorans during the harsh Atmoran winter (coupled with the suggestion of specialization) that they posesed atleast a basic concept of surplus.
The beginning of social control based on a central government and class structures: Leadership by Ysgamor and the civil war in Atmora suggests this was the case.
Trade over long distances: While we have no direct support of trade from Atmora we know of its theoretical possibility given their ability to settle Tamriel.
Writing and a system of notation: none, from what we know.
The beginning of science: some science possibly required to navigate, but any more then that is unknown.
You must also keep in mind that Atmora was not always an uninhabitable wasteland. In the early years of Atmora it might have adequately supported life and lead to the development of a civilization. Atmora's Aldmeri name, Elder Wood, suggests that it was once a fully habitable place.
Saarthal could've been an earlier settlement before Ysgramor, building ships, boats, skiffs are not signs of civilization, again they're hunters, blah, blah, blah...
Just to end my contribution this:
"Even before the frost fall, Atmora was apparently not a temperate place. The early Nedic peoples who came from Atmora were hunters with no knowledge of agriculture. A land where every denizen was a predator doubtless insured that only the most brutal and savage survived. It is easy to see how these traits passed the raider men and down to the nature of the Arena of Tamriel."
Yeah, so for anyone who's going to it's out-of-Atmora, hush. I know.
And although A(l)tmora was one of the first kingdoms of the elves, they left a long time ago, leaving humans to become what is described in the 3rd PGE.
Anyway, Knight Mariel, out!