However MK wrote From The Many-Headed Talos to explain the change:
Not a very good explanation if you ask me. It's not so much a justification as it is Bethesda's way of saying "Yeah, sorry that Cyrodiil doesn't look anything like what it did in any lore prior to Oblivion, but we can explain it! See? Talos did it!"
Is it just me, or are these threads becoming very common?
They popped up quite a lot before the game was announced to, since at the time, it was already widely accepted that the Elder Scrolls V was likely to be set in Skyrim, but it may be that there's a renewed interest in them now since we now officially KNOW the game is being made and KNOW it's set in Skyrim.
But regardless, I think we can safely assume that the game won't be ALL snow, not because of what the lore says on Skyrim, even though I'm sure it allows for more diversity in the province than that. Because Bethesda has already shown that they're willing to contradict what past lore says about the landscapes of the province the game takes place in if it suits their vision with the design, and I'm sure Bethesda knows that players would get bored with the game quickly if it was ALL snow and ice. I mean, even Bloodmoon had green grass in the south and got more and more like your stereotypical snow and ice land as you got further north. Now, I don't doubt that we'll see lots of snow, and mountains, for that matter, but I doubt it will be all we'll see. I wouldn't bet on getting the same level of diversity in landscapes as Morrowind offered, but I'd say that we don't have to worry about being stuck with snow everywhere.
Howerver based on cyrodil (Further north you got the colder it got!) it is the safest bet to say Skyrim will be covered in snow!
The problem with this notion is that it fails to take into account that how far north or south you go is not the only factor that determines climate. In particular, while the Jerall Mountains, the region of Cyrodiil that bordered on Skyrim, are in fact the northern-most part of Oblivion's map, they're also, as the name would imply, mountains, not to mention they're also far from the sea. and in general, areas of higher elevation, like mountains, tend to be colder than lower ones, so while the Skyrim border may have been all nice and snow, that does not necessarily mean everything north of it must be as well.