Fair enough point on the climate.<br/><br/>As for the reason civilization ended, how about zombies? I've always been fond of that, and it does create a persistent threat to worry about. Barring that, I think a plague would make sense; natural or maybe even man-made? Terrorist plot, maybe?<br/><br/>Ideas about the shelter: They could have used vehicles and such to block up the ground entrances to the airport, and live in there? In either extreme of climate, that might be a better idea than living inside a huge metal tube, which could get very hot or cold.<br/><br/>Then again, they could very well just have a sort of ring of airplanes; time to rest, just go up, and close the hatch. Probably damn near impossible for zombies to bang their way inside, and I'd imagine their's a way to bolt the doors shut from the inside; never been on a plan, so I wouldn't know, though.<br/><br/>Also, how big of an airport are we talking about? I imagine we're not doing something like LAX, where their's literally over a hundred  restaurants, and stores and the like.