Greenland's Norse were killed off by global cooling

"A cold snap in Greenland in the 12th century may help explain why Viking settlers vanished from the island."  That according to this Reuters story: Greenland cold snap linked to Viking disappearance.  Norse settlements in Greenland were remarkably advanced, and were developed enough that there was a regular Catholic bishopric established on the island in the village of Gardar in 1124.

The Reuters article attempts to turn the story of the end of the Greenland Vikings into a cautionary tale about global warming, which appears to be a bit of a stretch.  If anything, global warming would have been a huge help to the Norse of Greenland. Instead, the unfortunate Norsemen were hit with a long spell of global cooling. This made not only their economic connections with Europe more tenuous, it made their survival on the island more and more difficult as the terrain become more and more inhospitable.

Here's a link to a documentary on the Norse civilization of Greenland and its disappearance after nearly 500 years: