I think we have to assume that the snowfields on which the battle in Frost Giant's Daughter is fought represent either the mountains on the Aesir Vanir border, or that the battle was fought in winter. It can't always be like that across the land, or you wouldn't have people never mind beer. The Nordheimers are not nomadic savages; they are barbarians, but they have extensive smithying, goldworking and other abilities, since they fight with steel and wear pretty heavy armour. You are probably looking at Scandanavian climates: cold winters, but farmable in summer. There will be a warrior class of thegns who do most of the fighting, and a farmer class of carls who do most of the farming (aided by thralls, no doubt). These class divides will probably be quite fluid though.