According to Fox News, a new study has found that Greenland was indeed green at one time. The title of the article was "DNA Test Indicates Very Green Greenland". So, that being a topic of interest in climate change, I was interested to know more. The details were very revealing, indeed:

"These findings allow us to make a more accurate environmental reconstruction of the time period from which these samples were taken, and what we've learned is that this part of the world was significantly warmer than most people thought," Martin Sharp, a glaciologist at the University of Alberta, Canada, and a co-author of the paper, said in a statement. The base of the ice is mixed with mud and it was this mud that Willerslev's team studied. The DNA, dated to between 450,000 and 800,000 years ago, may be the oldest yet recovered, according to the team. DNA found previously in the Siberian permafrost has been dated to 300,000 to 400,000 years ago. However, because of uncertainties in interpreting the age estimates, they could not rule out the possibility that the newly found DNA dates to the last interglacial, 130,000 to 116,000 years ago. - Fox News

So, the last time Greenland was actually "green" was hundreds of thousands of years ago. This tells me that it was not "green" only 1000 years ago when Vikings settled there. I continually end up discussing this issue with skeptics and I always go back to the fact that most of the evidence involving Vikings in Greenland is anecdotal. Now, there's finally a scientific evaluation of Greenland's past, and it shows a "green" Greenland well before Vikings existed, much less discovered the island. This would be the type of evidence I would be looking for as acceptable proof that Greenland was warmer during medieval times. However, it has yet to be provided.