The Viking colonies on Greenland were during a relatively warm period, but the difference was rather minor... it's not like now Greenland is covered in snow and

The Viking colonies on Greenland were during a relatively warm period, but the difference was rather minor... it's not like now Greenland is covered in snow and ice and then it wasn't, the glaciers weren't any smaller then, they were actually a bit bigger. But during this warm period that lasted a couple of hundred years the summers were a bit longer and probably more sunny. The Viking settlements were in the far South of Greenland, actually further South than their prior home on Iceland, on land that's quite green in Summer today as well (just visit Greenland's official tourism site to see what it looks like). Tundra vegetation is actually excellent pasture, very mineral and protein rich... enough so to have supported lots of the largest mammalian mega-fauna!