Thanks everyone, more good ideas.
I especially like Alchemist's suggestion. Might be interesting, although not necessarily those particular words, since part two would be even more freezing than part one
But gives me some ideas, I'll have to think about it for a bit.
Good news though, that by deciding to cut the book in two, it means I'm just about done with the first book - only technicalities and some improvements to the first half to go - and I'll already have the second half mostly done by the time I start submitting the first book. I'm liking this idea of marketing it as YA.