“although a disturbing factor of a much larger global warming effect”
So, in 300AD this area must have been free of ice. Just like Greenland was when Lief Erickson went there and established a settlement. Then it got colder and covered with ice. What caused the Earth to get colder? Then it got warmer. Maybe it has absolutely nothing to do with “greenhouse gases” such as CO2.
More than likely this would have to do with volcanic action and the cycles if sunspot activity.
But, lets not get well known cyclical events get in the way of a good climate change story. LOL.