Coldlander by Jacob Tanner

Yarla, a middle-aged has-been, lives so far from the failing Low Temperature Temple that it's almost inhospitable for coldlanders like herself. Ice nearly melts, and it's getting worse, when she'd prefer things a few hundred degrees colder. But when a stranger from the boiling-hot side of the planet arrives with a key to the Temple, she begrudgingly takes it upon herself to travel south and fix what is broken. With her new hot-suited ally, Lazarus, she must fight her way to the Temple through deadly wildlife, the rude coldlander culture, her own impatience, the consequences of age, and one very unhelpful teenage girl.