Nordic: you are more resilient to cold, you need lets say 20less heat on all body parts. Costs 2 points
Southern: more resilient to heat, you get -10 heat on body parts when you reach the “too warm” limit. Costs 1 point.
So both could be traits, or you could work in that Nordic would be less heat tolerant, while the southern would be less cold tolerant.
Keep in mind, names and numbers can and prob should be changed, but im just throwing the idea out that it is posible for people to be more hot/cold resistant if not both and that it could help out ingame if you either end up wearing too much or too little heat items.