I saw a great show last night on the Vikings. Whoever posited that the Vikings stayed warm because the climate was warmer at teh time the went to Greenland.
Core samples of lake bottoms, analysis of ice cores, of the Sttlers teeth, of bone evidence and historical data proves that the temperature of the settlement was relatively high for a few hundred years.
Teh settlement failed when the weather got colder during a mini ice age. TEH Vikings continued to farm in the same manner and wore the same woven wool clothes. MEanwhile, the innuit and Icelandic vikings changed from farming to hunting and fishing. They began to wear furs and waterproof seal skin boots. The innuit had a surplus of food and the Greenland Vikings died.
So they were tough, but not adaptable enough to withstand a drop in temperatures.