I'm not saying it is flawless. I'm saying that you are wasting effort trying to move it into some arbitrary "believability zone." It's completely unnecessary. Granted, I don't have an ecology degree so it doesn't bother me because I don't know enough about the subject to be offended by its wrongness.I didn't say it's unplayable. In fact, I said it's easily fixable by just shortening the amount of time it's been going on.
But if you think any civilization would still be this intact after two years on four daily hours of twilight and temps averaging 50 below - or that there would be any significant wildlife or plant life left alive (the adventure is full of animals) - I'm not sure what to tell you. I mean, you're completely wrong, but whatever. The place would be a desert of ice. It doesn't ruin the adventure (which seems to be overall a good one) because like I said, easy to change.
I really like the 5E hardcovers - all of them, even the dodgy ones like Waterdeep: Dragon Heist and Horde of the Dragon Queen. But each of them, to varying degrees, has nonsensical flaws that are exactly that: flaws. The climate here is a flaw - they went too far. Auril is a bigger one - they didn't write her any goals.
I don't understand the compulsion some fans have to deny that any flaws in these adventures are there, and to defend them against the slightest criticism.
But, you do care and it is wrong of me to tell you you shouldn't. Different strokes. I'm glad you found a solution that works for you.