Field Notes From a Catastrophe: Man, Nature, and Climate Change (6 page)

When Steffen planned Swiss Camp—he built much of the place himself—it was not with global warming in mind. Rather, he was interested in following meteorological conditions on what is known as the ice sheet’s “equilibrium line.” Along this line, winter snow and summer melt are supposed to be precisely in balance. But in recent years, “equilibrium” has become an increasingly elusive quality. During the summer of 2002, for example, melt occurred in areas where liquid water had not been seen for hundreds, perhaps thousands, of years. The following winter, there was an unusually low snowfall, and in the summer of 2003, the melt was so great that, around Swiss Camp, five feet of ice were lost.

When I arrived at the camp, the 2004 melt season was already under way. This, to Steffen, was a matter of both intense scientific interest and serious practical concern. A few days earlier, one of his graduate students, Russell Huff, and a postdoc, Nicolas Cullen, had driven out on snowmobiles to service some weather stations closer to the coast. The snow there was warming so fast that they had had to work until five in the morning, and then take a long detour back, to avoid getting caught in the quickly forming rivers. Steffen wanted to complete everything that needed to be done ahead of schedule, in case everyone had to pack up and leave early. My first day at Swiss Camp he spent fixing an antenna that had fallen over in the previous year’s melt. It was bristling with equipment, like a high-tech Christmas tree. Even on a relatively mild day on the ice sheet, which this was, it never gets more than a few degrees above freezing, and I was walking around in a huge parka, two pairs of pants plus long underwear, and two pairs of gloves. Steffen, meanwhile, was tinkering with the antenna with his bare hands. He had spent the last fourteen summers at Swiss Camp, and I asked him what he had learned during that time. He answered with another question.

“Are we disintegrating part of the Greenland ice sheet over the longer term?” he asked. He was sorting through a tangle of wires that to me all looked the same but must have had some sort of distinguishing characteristics. “What the regional models tell us is that we will get more melt at the coast. It will continue to melt. But warmer air can hold more water vapor, and at the top of the ice sheet you’ll get more precipitation. So we’ll add more snow there. We’ll get an imbalance of having more accumulation at the top, and more melt at the bottom. The key question now is: What is the dominant one, the more melt or the increase?”

Greenland, the world’s largest island, is nearly four times the size of France—840,000 square miles—and, except for its southern tip, lies entirely above the Arctic Circle. The first Europeans to make a stab at settling it were the Norse, under the leadership of Erik the Red, who, perhaps deliberately, gave the island its misleading name. In the year 985, he arrived with twenty-five ships and nearly seven hundred followers. (Erik had left Norway when his father was exiled for killing a man, and then was himself exiled from Iceland for killing several more.) The Norse established two settlements: the Eastern Settlement, which was actually in the south, and the Western Settlement, which was to the north. For roughly four hundred years, they managed to scrape by, hunting, raising livestock, and making occasional logging expeditions to the coast of Canada. But then something went wrong. The last written record of them is an Icelandic affidavit regarding the marriage of Thorstein Ólafsson and Sigridur Björnsdóttir, which took place in the Eastern Settlement on the “Second Sunday after the Mass of the Cross,”in the autumn of 1408.

These days the island has just over fifty-six thousand inhabitants, most of them Inuit, and almost a quarter live in the capital, Nuuk, about four hundred miles up the western coast. Since the late 1970s, Greenland has enjoyed a measure of home rule, but the Danes, who consider the island a province, still spend more than three hundred million dollars a year to support it. The result is a thin and not entirely convincing first-world veneer. Greenland has almost no agriculture, or industry, or, for that matter, roads. Following Inuit tradition, private ownership of land is not allowed, although it is possible to buy a house, an expensive proposition in a place where even the sewage pipes have to be insulated.

More than 80 percent of Greenland is covered by ice. Locked into this enormous glacier is 8 percent of the world’s fresh water supply. Except for researchers like those at Swiss Camp, no one lives on the ice, or even ventures out onto it very often. (The edges are riddled with crevasses large enough to swallow a dogsled or, should the occasion arise, a five-ton truck.)

Like all glaciers, the Greenland ice sheet is made up entirely of accumulated snow. The most recent layers are thick and airy, while the older layers are thin and dense, which means that to drill through the ice is to descend backward in time, at first gradually, and then much more rapidly. A hundred and thirty-eight feet down, there is snow that fell during the time of the American Civil War; 2,500 feet down, snow from the time of the Peloponnesian Wars, and, 5,350 feet down, snow from the days when the cave painters of Lascaux were slaughtering bison. At the very bottom, 10,000 feet down, there is snow that fell on central Greenland before the start of the last ice age, more than a hundred thousand years ago.

As the snow is compressed, its crystal structure changes to ice. (Two thousand feet down, there is so much pressure on the ice that a sample drawn to the surface will, if mishandled, fracture, and in some cases even explode.) But in most other respects, the snow remains unchanged, a relic of the climate that first formed it. In the Greenland ice, there is nuclear fallout from early atomic tests, volcanic ash from Krakatau, lead pollution from ancient Roman smelters, and dust blown in from Mongolia on ice age winds. Every layer also contains tiny bubbles of trapped air, each of them a sample of a past atmosphere.

Much of what is known about the earth’s climate over the last hundred thousand years comes from ice cores drilled in central Greenland, along a line known as the ice divide. Owing to differences between summer and winter snow, each layer in a Greenland core can be individually dated, much like the rings of a tree. Then, by analyzing the isotopic composition of the ice, it is possible to determine how cold it was at the time each layer was formed. Over the last decade, three Greenland cores have been drilled to a depth of nearly two miles, and these cores have prompted a wholesale rethinking of how the climate operates. Where once the system was thought to change, as it were, only glacially, now it is known to be capable of sudden and unpredictable reversals. One such reversal, called the Younger Dryas, after a small Arctic plant—
Dryas octopetala
—that suddenly reappeared in Scandinavia, took place roughly 12,800 years ago. At that point, the earth, which had been warming rapidly, was plunged back into ice age conditions. It remained frigid for twelve centuries and then warmed again, even more abruptly. In Greenland, average annual temperatures shot up by nearly twenty degrees in a single decade.

As a continuous temperature record, the Greenland ice cores stop providing reliable information right around the start of the last glaciation. Climate records pieced together from other sources indicate that the previous interglacial, which is known as the Eemian, was somewhat warmer than the present one, the Holocene. They also show that sea levels during that time were at least fifteen feet higher than they are today. One theory attributes this to a collapse of the West Antarctic ice sheet. A second holds that meltwater from Greenland was responsible. (When sea ice melts, it does not affect sea level, because the ice, which was floating, was already displacing an equivalent volume of water.) All told, the Greenland ice sheet holds enough water to raise sea levels worldwide by twenty-three feet. Scientists at NASA have calculated that throughout the 1990s the ice sheet, despite some thickening at the center, was shrinking by twelve cubic miles per year.

The Greenland record reveals that temperatures have often swung wildly. Credit:
The Two-Mile Time Machine,
Princeton University Press, after K. Cuffey and G. Clow
, Journal of Geophysical Research,
vol. 102 (1997).

Jay Zwally is a NASA scientist who works on a satellite project known as the Ice Cloud and Land Elevation Satellite (ICESat). He is short and stocky, with a round face and a mischievous grin. Zwally is a friend of Steffen’s and about ten years ago, he got the idea of installing global-positioning-system receivers around Swiss Camp to study changes in the ice sheet’s elevation. He happened to be at the camp at the same time I was, and the second day of my visit we all got onto snowmobiles and headed out to a location known as JAR 1 (for Jakobshavn Ablation Region) to reinstall a GPS receiver. The trip was about ten miles. Midway through it, Zwally told me that he had once seen spy-satellite photos of the region we were crossing, and that they had shown that underneath the snow it was full of crevasses. Later, when I asked Steffen about this, he told me that he had had the whole area surveyed with bottom-seeking radar, and no crevasses of any note had been found. I was never sure which one of them to believe.

Reinstalling Zwally’s GPS receiver entailed putting up a series of poles, a process that, in turn, required drilling holes thirty feet down into the ice. The drilling was done not mechanically but thermally, using a steam drill that consisted of a propane burner, a steel tank, and a long rubber hose. Everyone—Steffen, Zwally, the graduate students, me—took a turn. This meant holding on to the hose while it melted its way down, an activity reminiscent of ice fishing. Seventy-five years ago, not far from JAR 1, Alfred Wegener, the German scientist who proposed the theory of continental drift, died while on a meteorological expedition. He was buried in the ice sheet, and there is a running joke at Swiss Camp about stumbling onto his body. “It’s Wegener!” one of the graduate students exclaimed, as the drill worked its way downward. The first hole was finished relatively quickly, at which point everyone decided—prematurely, as it turned out—that it was time for a midday break. Unless a hole stays filled with water, it starts to close up again, and can’t be used. Apparently, there were fissures in the ice, because water kept draining out of the next few holes that were tried. The original plan had been for three holes, but, some six hours later, only two had been drilled, and it was decided that this would have to suffice.

Although Zwally had set out to look for changes in the ice sheet’s elevation, what he ended up discovering was even more significant. His GPS data showed that as the ice sheet melted, it didn’t so much sink as start to accelerate. Thus, in the summer of 1996, the ice around Swiss Camp moved at a rate of thirteen inches per day, but, in 2001, it had sped up to twenty inches per day. The reason for this acceleration, it is believed, is that meltwater from the surface makes its way down to the bedrock below, where it acts as a lubricant. (In the process, it enlarges cracks and forms huge ice tunnels, known as “moulins.”) Zwally’s measurements also showed that, in the summer, the ice sheet rises by about six inches, indicating that it is floating on a cushion of water.

At the end of the last glaciation, the ice sheets that covered much of the Northern Hemisphere disappeared in a matter of a few thousand years—a surprisingly short time, considering how long it had taken them to build up. At one point, about fourteen thousand years ago, they were melting so fast that sea levels were rising at the rate of more than a foot a decade. Just how this happened is not entirely understood, but the acceleration of the Greenland ice sheet suggests yet another feedback mechanism: once an ice sheet begins to melt, it starts to flow faster, which means it also thins out faster, encouraging further melt. Not far from Swiss Camp is the huge river of ice known as the Jakobshavn Isbrae. In 1992, the Jakobshavn Isbrae flowed at a rate of 3.5 miles per year; by 2003, its velocity had increased to 7.8 miles per year. (Similar findings were announced recently by scientists measuring the flow of ice streams on the Antarctic Peninsula.) On the basis of Zwally’s findings, James Hansen, the NASA official who directed one of the initial 1970s studies on the effects of carbon dioxide, has argued that if greenhouse gas emissions are not controlled, the total disintegration of the Greenland ice sheet could beset in motion in a matter of decades. Although the process could take centuries to fully play out, once begun it would become self-reinforcing, and hence virtually impossible to stop. In an article published in the journal
Climatic Change
in February 2005, Hansen, who is now the head of the Goddard Institute for Space Studies, wrote that he hoped he was wrong about the ice sheet, but added, “I doubt it.”

As it happened, I was at Swiss Camp just as the global-warming disaster movie
The Day After Tomorrow
was opening in theaters. One night, Steffen’s wife called on the camp’s satellite phone to say that she had just taken the couple’s two teenage children to see it. Everyone had enjoyed the film, she reported, especially because of the family connection.