From what I understand, Argonians are indeed cold-blooded. This means that they should die in cold weather, or at the very least suffer some serious health problems. Being cold-blooded just means that their bodies are affected by external temperatures way more than warm-blooded races, who can generate their own heat and regulate temperature. That's why lizards and snakes sunbathe on a morning and mostly live in warm places - sort of like charging up their internal battery
Most real-world cold-blooded animals allow themselves to freeze during winter and thaw out during spring, with the help of some handy chemicals in their bloodstream which acts a bit like anti-freeze. Of course it's always cold in Skyrim so Haa Rei couldn't just hibernate all the time (as much as he'd like to). I'm not sure about fish and other cold water creatures, but I guess they have a similar sytem.
An in-game book I found in ESO claims that Argonians don't seem to have as much trouble in the snow as you'd think, and the Altmer author thinks it's something to do with Hist sap which Argonians ingest as hatchlings. So Argonians can still feel the cold, and it most likely makes them a little sluggish, but they can still function in colder areas at least as well as an Imperial or a Bosmer.
ESO has been such a treasure trove of info about Argonians - I've just been super excited the whole time
This post has been edited by hazmick: Jun 18 2015, 07:44 PM
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