between the years 800 and 1200 AD there were as something called the Medieval Warm Period...which warmer than it is now (followed by the little ice age caused by the maunder minimum). during that time enough of Greenland was exposed as to make agriculture possible along the southern coast of Greenland, which can not be done today because of the colder temps today...
My question is, where did the Polar Bears go back then?
That was before Darwin, so they hadn't evolved yet.