Eirik the Red may have called it "Greenland" to fool people into going out there, but the evidence shows that it was warmer in the Mediaeval Warm Period than it is today.

In fact, I quote from Wikipedia:

What is verifiable is that the ice cores indicate Greenland has experienced dramatic temperature shifts many times over the past 100,000 years — which makes it possible to say that areas of Greenland may have been much warmer during the medieval period than they are now and that the ice sheet contracted significantly.

The fact that Greenland's ice sheet is in decline again is evidence that the world is warming, but the question is whether or not mankind is responsible for most or all of that warming and whether or not the trend is a fluctuating one or a linear progression.