Note that most historians do not believe that the end of the Medieval warm period was the trigger of the collapse of the Greenland settlement, but rather that was the abandonment of trade routes to Greenland that caused its collapse.

I still think that the changing temperature was likely a factor but perhaps just a small one. It certainly would have got harder to eek out an existence on the island.

As you say though a bigger factor was Portuguese traders gaining access to African elephant ivory which was easier and cheaper to procure than walrus ivory which was the cash crop of the Greenland settlement.