The Norse came to a new land around the end of the first millennium, borne on the backs of their Viking long ships and lured away from Iceland by the promise of Erik the Red's Greenland. The land was indeed green when they landed—and stayed that way for several centuries until natural variations in the planet's climate cooled the world's largest island by 4 degrees Celsius. Years of such cool summers doomed the Greenland Norse, and their outpost froze to death by 1500.



The Norse "were primarily farmers who relied on the summer hay production to feed their livestock through the long Greenland winter," says geologist William D'Andrea at the University of Massachusetts Amherst, who presented new confirmation of this cooling and starving scenario in the May 30 issue of Proceedings of the National Academy of Sciences. "If summers got shorter and/or colder than the Norse were used to and their hay production was not able to meet their demands—and if this happened over a sustained period of time—it would have been difficult for them to maintain their way of life."



Climate change has likely played a role in the shifting fortunes of all human civilizations in Greenland, from the Saqqaq who thrived there via caribou hunting thousands of years ago to today's Inuit, buoyed by a lengthening growing season and new discoveries of oil and gas. Using mud cores from two lakes in Kangerlussuaq, Greenland—Brya So and Lake E—D'Andrea and his colleagues found evidence showing that significant shifts in average temperatures correlate with the rise and fall of Greenland cultures.



The scientists specifically measured alkenone—a fat produced by blooming algae in the northern lakes under specific conditions—as a proxy for the lakes' water temperature, which in turn reflects ambient air temperatures. This record in algal oil shows that average summer temperatures in the past 5,600 years have varied by as much as 5.5 degrees C. A cooling swing in those temperatures coincides with the Saqqaq culture fading from the scene and the Dorset arriving—a culture that thrived in the cold thanks to snow knives, sledge shoes and other technologies. Back-to-back warming and cooling swings led to that culture's exit about 1800 years ago, perhaps following shifting hunting grounds, whereas general warming coincided with the Norse migration to Greenland a few hundred years later. Then 550 years ago, as average temperatures cooled again, the Norse were gone.



"You have an interval when the summers are long and balmy and you build up the size of your farm," says D'Andrea of the Norse interlude. "Then suddenly, year after year, you go into this cooling trend and the summers are getting shorter and colder and you can't make as much hay. You can imagine how that particular lifestyle may not be able to make it."



Greenland is still inhabited, of course, by Inuit people who migrated to the region as recently as a millennium ago. These people are currently enduring some of the most rapid climate change on the planet, which has had benefits ranging from a longer growing season, like the one that aided the Norse, to newly accessible oil deposits that promise potential financial independence. "The Arctic is undergoing major changes," D'Andrea notes. "Just like in the past, some people will benefit and others will lose out."



Of course, it is the burning of such oil that has led to this warming in the first place, thanks to increasing concentrations of atmospheric greenhouse gases. Already, those increasing concentrations of greenhouse gases are warming the planet's overall climate to the point that the meltdown of Greenland's ice sheet is speeding up, which could raise global sea levels a meter by 2100 at present rates, among other impacts. "This area of the Arctic has warmed significantly since the 1990s," says glaciologist Gordon Hamilton of the University of Maine, Orono. "If [the ice sheet] is responding to the warming ocean, that is going to persist for decades to come. That's not an easy switch to turn off."



That warming indeed looks set to continue and will ultimately doom, at the very least, Greenlanders' traditional way of life. But the changes in Greenland this time may prove to be global. "If we don't keep the Greenland Ice Sheet intact, we will lose a lot of coastline," argues Rafe Pomerance, a senior fellow at environmental group Clean Air-Cool Planet. Yet, earlier this month a meeting of the nine Arctic Council nations focused more on squabbles over newly accessible natural resources in the rapidly warming region than mitigating the causes of climate change. Pomerance adds, "The fate of Greenland and Antarctica's ice sheets has an enormous impact on the world."