This is going to be a little painful, but stick with me for a brief tour of how the obscure history of the disappearance of a civilization informs our emerging scientific understanding of climate change. Let’s begin with a subject we know quite a lot about-the expansion of Norse culture across vast areas of remote island and coastal geography throughout the northern North Atlantic, including the Orkneys, Shetlands and Faroe islands off Scotland, to mention just a few of the archipelagoes they dominated until they reached Iceland in approximately 874. With no locals to subdue in Iceland, the Norse explorers took up the more sedentary pursuits of fishing and farming and often began feuding, as they had on islands elsewhere, over territory when good farmland ran short.
One of these squabbles resulted in a murder and the subsequent expulsion of Erik the Red from Iceland in 982, whereupon he loaded up his Viking longboat with family members, livestock and tools and set off in search of an island further to the west that had been vaguely described in the oral traditions of Icelandic sagas. After weeks of voyaging, Erik and his followers reached a high mountainous coast of spectacular peaks covered by blindingly white alpine glaciers. They were unable to land due to the heavy sea ice along the shore, so they turned south and followed the coastline around a rugged promontory later named Cap Farvell (Cape Farewell), where an enormous area of southern fjords opened up lined with fringing green pastures. Erik called the newly discovered region Greenland, and three years later led a flotilla of 25 longboats back to colonize the new land.
It so happened that Erik and his followers discovered Greenland at a propitious time, since their arrival coincided with what we understand to have been an abrupt change in the climate of Europe, which climatologists now call the Medieval Warm Period. Beginning in 950 AD, give or take depending on location and lasting for the next 300 to 400 years, the alpine glaciers all across Europe began retreating back up the valleys they had long occupied. But more important, the length of the growing season increased throughout Europe, enabling more food crops to be harvested per acre and more nutritious grains to be planted further north than ever before. The effect of the warming climate had an even more pronounced effect on survival for the Greenland Norse.
Sea ice, which flowed in suffocating packs southward on the East Greenland Current and could choke off all commerce between Norway and the Norse in the southern fjords, would dissipate most every summer long enough for these remote colonies to send shipments of walrus ivory, gyrfalcons and seal furs back home in exchange for critical supplies of salt and iron tools they could not produce themselves.
Then, after 500 years of settlement, the once flourishing Greenland Norse civilization, which peaked at between 4,000 and 5,000 settlers, disappeared almost overnight without a trace at some point between 1350 and 1425. The disappearance of the Greenland Norse is one of history’s most intriguing mysteries, and also one of the important stories to understand by those who are concerned about climate change-especially the prospects of abrupt climate change.
We may never know what happened to the Greenland Norse, but we do know that the Medieval Warm Period, which lasted from 950 to 1350, ended abruptly and was followed by the Little Ice Age, during which average temperatures plunged across Greenland, Iceland and Europe for the next half a millennia between 1350 and 1880, give or take. In Greenland, the persistence of winter sea ice that did not melt or disperse in the summer choked off the Norse colonies from all contact with Europe for centuries, and was almost certainly a critical factor in their civilizational collapse.
George Denton, a University of Maine geologist has studied glaciers on six continents and is a co-author of The Fate of Greenland-Lessons From Abrupt Climate Change, along with his colleagues, glaciologist Richard Alley and Wally Broecker, the grand old man of climate change research as well as this columnist. We all were fortunate enough to travel with the late Gary Comer, founder and chairman of Lands’ End on research voyages to Greenland that Comer funded. On the basis of these voyages and other research from the Comer Abrupt Climate Change Program, Denton, Broecker, Alley and their colleagues have proposed a new theory that links changes in ocean and atmospheric conditions in the regions around Greenland as one of the flex points in the world’s “climate switch.”
Most of us were taught that the climate changes almost imperceptibly from an ice age into a warm period and back again over hundred or thousands of years. Perhaps this is why so many of us find it difficult to take the threat of climate change seriously in our lifetimes. But more recent discoveries during the past two decades from ice core research have revealed that the biggest changes in regional temperatures around Greenland and elsewhere in the world occurred in as little as a decade or two. In other words, the global climate system appears to operate in one of two modes-the warm mode or the cold mode-and changes abruptly between the modes as if a switch had been flipped.
Broecker, Denton and Alley have proposed that changes in the location and speed of the North Atlantic ocean currents Broecker has named the “conveyor” which bring heat from the tropics into the far north on the tongues of the Gulf Stream, occasionally slows down when atmospheric changes over the vast Pacific Ocean and smaller Atlantic periodically reorganize themselves. When the conveyor slows down in the North Atlantic and shifts position southward, the ocean around Greenland gets colder in a hurry. Sea ice that forms every winter extends southward, enveloping Greenland, and sea ice no longer melts in the summer. Sea ice over the North Atlantic creates a “feedback” loop in the climate system because the ice reflects sunlight and heat back into the atmosphere, making the summers colder, which further increases the mass of sea ice and so on and so on. With sea ice covering the northern North Atlantic even in the summer, the belt of winds that circle the globe and control the distribution of heat and precipitation across the globe shift position, such that much of the Asian monsoon falls over the ocean rather than on land, plunging vast areas of China, for example, into drought.
Climate feedbacks are how we are now beginning to understand abrupt climate change: small changes in atmospheric and ocean temperatures build up over long periods of time until a threshold is reached, triggering a feedback loop that changes the climate quickly from warm to cold or cold to warm. Climate scientists who have studied these abrupt changes in the past, which have occurred “naturally,” are worried that increasing carbon dioxide levels in the atmosphere could trigger not just a gradually warming planet, but abrupt changes, that could have deeply tragic consequences for many of those who, like the Norse, live at the edge of a sustainable existence.
The Fate of Greenland is available to order from Archipelago located at 386 Main Street, Rockland.
Philip Conkling is president of the Island Institute in Rockland, Maine.