When Eric the Red led the Norwegian Vikings to Greenland in the late 900s, it was an ice-free farm country–grass for sheep and cattle, open water for fishing, a livable climate–so good a colony that by 1100 there were 3,000 people living there. Then came the Ice Age. By 1400, average temperatures had declined by 2.7 degrees Fahrenheit, the glaciers had crushed southward across the farmlands and harbors, and the Vikings did not survive.