Jed, the Gulf Stream has shifted before, north, in the middle ages. It caused a major global power realignment, because it brought the great codfish schools with it — and moved that source of national wealth marginally out of reach for the vessels of Spain and Portugal at the time. England and the cities of the Hanseatic League benefited, to the extent that by the mid-1300s, the League had taken over global control of the salt fish trade.
