What was done
The authors report paleolimnological inferences regarding Holocene climatic variability from a small lake in southern Greenland - Qipisarqo Lake (61°00'41"N, 47°45'13"W) - based on lake sediment physical-chemical properties, including magnetic susceptibility, density, water content, and biogenic silica and organic matter concentration.

What was learned
In the words of the authors, "the interval from 6000 to 3000 cal yr B.P. was marked by warmth and stability."  Thereafter, the climate cooled "until its culmination during the Little Ice Age."  From 1300-900 cal yr B.P., however, there was a partial amelioration during the Medieval Warm Period, which was associated with an approximate 1.5°C rise in temperature.  Following another brief warming between A.D. 1500 and 1750, the second and more severe portion of the Little Ice Age occurred, which was in turn followed by "naturally initiated post-Little Ice Age warming since A.D. 1850, which is recorded throughout the Arctic" and "has not yet reached peak Holocene warmth."

The authors note that "colonization around the northwestern North Atlantic occurred during peak Medieval Warm Period conditions that ended in southern Greenland by A.D. 1100."  Norse movements around the region thereafter, however, "occurred at perhaps the worst time in the last 10,000 yr, in terms of the overall stability of the environment for sustained plant and animal husbandry."

What it means
As the planet cooled following the warm and climatically-stable period of the mid-Holocene, earth's climate became more and more erratic, culminating in maximum variability during the Little Ice Age, which spelled the end of the Norse settlements of Greenland that had occurred during the more benign Medieval Warm Period.  The demise of the Norse colonies was clearly the result, in the words of the authors, of "the most environmentally unstable period since deglaciation."  Their further observation that "current warming, however rapid, has not yet reached peak Holocene warmth," should only heighten our hopes for a brighter climatic future awaiting us around the next corner of time.