"Man, as an animal, is indeed, a tropical animal. But man, as distinguished from animals, is not at his best in the tropics or very near them. His fight upward in civilization has coincided in part at least with his march northward over the earth into a cooler, clearer, more bracing air." - Vilhjalmur Stefansson (The northward course of empire, 1922).
The book is an elaborate crack-pot argument celebrating the unappreciated richness of the Arctic rather than a geopolitical survey of empires, their temperatures and the inevitable polar thrust of society you would perhaps expect. It opens with the above graph and it's hard to not to smile.