There was a warm period between about 800-1300 AD. During this period, some parts of the globe may have been warmer than they are today, such as the North Atlantic. The effects of the warm period were particularly evident in Europe, where grain crops flourished, alpine tree lines rose, many new cities arose, and the population more than doubled.
Excavations have shown the presence of birch trees during the early Viking period. The Vikings took advantage of the climatic amelioration to colonise southern Greenland in 985 AD, when milder climates allowed favourable open-ocean conditions for navigation and fishing. Erik the Red explored Greenland from Iceland and gave it its name. He claimed land in southern Greenland and became a chieftain in about 985 AD. Greenlanders brought grain seed, probably barley, oats and rye, horses, cattle, pigs, sheep and goats. The southern coastal area was forested at the time. Greenland settlements lasted about 500 years before cooling during the Little Ice Age ended the settlements. From 1000 to 1300 AD the settlements thrived under a climate favourable to farming, trade, and exploration. A cooling, steadily deteriorating climate began after 1300 AD and farming became impractical. A bishop who travelled there about 1350 AD found that the settlement was completely abandoned. The church abandoned Greenland in 1378 AD because ships could not get through the sea ice between Iceland and Greenland.
During the Medieval Warm Period, wine grapes were grown as far north as England or North America, where growing grapes is now not feasible, and about 500 km north of present vineyards in France and Germany. Wheat and oats were grown around Trondheim, Norway, suggesting that the climate was about 1°C warmer than it is at present.
Evidence also suggests that some places were very much cooler than today including the tropical pacific. This arid period may have depopulated the Great Plains of North America.
Graphic source: EASTERBROOK,, Evidence-Based Climate Science, Nature, 2016