USDA zone 6 worldwide

I was looking at a world map of USDA zones. It's pretty amazing to see where zone 6 meanders. Most of us are pretty familiar where it lies in the U.S. From the east coast going west it goes through all of Newfoundland, New York, Philly, D.C., just below St. Louis, Albuquerque, above Phoenix northward to Portland, Vancouver and just a little spot in the southern coast of Alaska.

It picks up again in Sapporo Japan, just below Seoul Korea, in a narrow band across China through Tajikistan, Afghanistan, Iran, Interior Turkey and around the Caspian and Black seas to Ukraine, Romania, much of eastern Europe including Hungary, Slovakia, Austria, Czech Rep. Poland and most of Germany. All of Denmark up to southern Sweden and interior Norway all the way up to the Bering sea, the northern 3/4 of Iceland and a huge section of the coastline of southern Greenland!

Also some interior sections of Argentina in South America.

What really surprised me was how far north it went in Norway--to the very northern most coast line. I mean this should all be tundra. This must be above the Artic Circle. And Greenland? I could easily believe that Iceland could be zone 6 with all the geothermal vents but Greenland? I thought it was all covered with ice. Who knew?