The Ancient Elves also had the Arcane Warrior class, which allowed them to channel their magic inward and make their weapons and bodies stronger from within, rather than just shooting magic from their hands (like creating ice blasts and fireballs and other things).
Maybe they had other ways of turning their magic inward? Like regulating internal body temperature to deal with different environments, like you said.
I wouldn't be surprised. 
I seem to remember from somewhere that the elves of Thedas are supposed to be highly adaptable. It might mean that, generally speaking, elves aren't bothered as much by extremes in temperature, even though other aspects of the environment (muck, sharp stones, dry, dusty air, etc) might still be problematic. It would also explain why the devs decided Dalish should run around without shoes (but what about the Dalish boots from Origins??????). How Solas avoids severe foot injury is beyond me...
Hm. Another thought I have had, since playing The Descent and Jaws of Hakkon:
The dwarves are "children of the Stone," which may or may not be the Titans.
The humans are "children of the Maker," though whether you believe the Maker exists in the context of Thedas is subjective.
Now... humans are kind of jacks of all trade, and dwarves definitely have an affinity with earthy things and stone.
Elves, on the other hand... their affinity is with the Fade. So, if we were to go out on a limb and assume that the Maker is real (whatever the Maker might turn out to be) and the dwarves were created by the Stone, then it seems most likely that the elves were created either from the Fade or from something in it. I still think the first elves (possibly the Creators, minus Ghilan'ain) could have been spirits who became "real." But if not... what would their creation myth be? Who or what was the intelligence behind the elves? So far, everyone else has such a story, except qunari.
And as for qunari... I suspect that they might be the first race, not the elves. And then the elves enslaved them. Wait, what? you ask... but those supposedly Tevinter and ancient elven bridges in the Emprise both feature qunari ladies. There's a similar statue somewhere (and it's HUGE) in the Hissing Wastes. Maybe more than one. Why would Tevinters sculpt massive statues of qunari beauties? And it does appear that they predate Tevinter in some cases. If I'm right, then the qunari haven't changed tremendously in appearance, but clearly something has changed about them--Kieran notices. Maybe they're really altered elves. Maybe they are something else entirely. Hard to say.
Regarding the Scaled Ones: Did the Avvar conspiracy theorist from Jaws of Hakkon not also write something about lizard people? He also babbled about moon men. Maybe we shouldn't be so quick to entirely write him off. This is Thedas we're talking about, after all. And there are those paintings scattered around the Emerald Graves that depict lizard-men, too (though they look less human than what the dwarf in the codex entries of Descent described).
And speaking of other races... what are the Fex exactly and will we ever see them in-game? Maybe they'd have some bearing on all of this...
If only Solas were more willing to stick around and tell the truth about who he is. Then maybe we could answer some of these things. Not all of them, of course. But some.