Nuuk, Greenland is showing its first spring green today, on the last day of spring.

Vikings farmed southern Greenland 900 years ago during the Medieval Warm Period, but the climate is much too cold now to support farming.

Lisa J. Graumlich, who examines the ring patterns of foxtail pine trees and western junipers in the Sierra Nevada, has compiled a detailed record of the year-to-year variation in temperature and precipitation over the last thousand years.

She has seen in the North American trees the feathery but unmistakable signatures of the Medieval Warm Period, a era from 1100 to 1375 A.D. when, according to European writers of the time and other sources, the climate was so balmy that wine grapes flourished in Britain and the Vikings farmed the now-frozen expanse of Greenland

In Unexpected Places, Clues to Ancient and Future Climate – Warming? Tree Rings Say Not Yet –…