History of past warming - Greenland had farms

From WUWT:
Greenland and AGW
In 1991, two caribou hunters stumbled over a log on a snowy Greenland riverbank, an unusual event because Greenland is now above the treeline. (1) Over the past century, further archaeological investigations found frozen sheep droppings, a cow barn, bones from pigs, sheep and goats and remains of rye, barley and wheat all of which indicate that the Vikings had large farmsteads with ample pastures.

The Greenlanders obviously prospered, because from the number of farms in both settlements, whose 400 or so stone ruins still dot the landscape, archaeologists guess that the population may have risen to a peak of about five thousand. They also built a cathedral and churches with graves which means that the soil must have been soft enough to dig, but these graves are now well below the permafrost (2).

So There was a 'Medieval Warming Period' which AGW alarmists not want to ignore. Not only that, it went from warmer than now to much colder than now.

It is well-known from written reports that temperatures must at times have been considerably lower than in the Medieval Warming Period since Frost Fairs were often held on the frozen Thames until 1814 and in 1658, during the coldest period of the Little Ice Age, King Karl X Gustav of Sweden led an army across the frozen Danish waters to lay siege to Copenhagen.

It was also at this time that the Viking settlements in Greenland gradually died out. The Medieval Warming Period is usually agreed to have lasted from approximately 900 to approximately 1300 AD and from then onwards the climate cooled again. Glaciers grew, sea ice advanced and marine life migrated southwards as it did so, leaving the Greenlanders with a smaller and more difficult catch. The summers became shorter and progressively cooler, limiting the time cattle could be kept outdoors and increasing the need for winter fodder which became less available. Trade between Greenland, Iceland and Europe became more difficult and finally ceased.

So the possibility that temperatures were higher in the past in any part of the world was a thorn in the sides of those Climatologists who are wedded to the whole idea of Anthopogenic Global Warming (AGW), also known as Climate Change.

Unfortunately for them, an English Climatologist, Hubert H Lamb, first formulated the idea of a Medieval Warming Period (MWP) in 1965 and other surveys have found that this warming did not just occur in the northwestern hemisphere but was global (6). Lamb founded the UK Climate Research Unit (CRU) in 1971 and until the mid 1990s the MWP was undisputed fact and was shown even in the IPPC progress report of 1990.

But Dr David Darning (University of Oklahoma College of Earth and Energy) in his recent testimony to Congress (7) said ‘…I received an astonishing email from a major researcher in the area of climate change. It said “We have to get rid of the Medieval Warm Period”’ And this the ‘warmist’ Climatologists certainly tried to do.

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Countering IPCC Climate viewpoints. 
Summary: The earth's climatic Geosphere is NOT unstable and adjusts to changes. There will be no 'runaway' anything, at the present situation.