For one team of young U.S. researchers working on the Greenland Ice Sheet Project II, almost all of them new to the science of polar ice drilling, the moment they had been waiting for arrived in the middle of the summer of 1992. After more than five weeks, members of the crew had acclimated themselves to the conditions at Summit and were coordinating their tasks about as well as could be expected of any group at an elevation of 10,400 feet in subzero cold. They were working in a glorified snow cave known as "the science trench," field-testing and processing the 5.2-inch core for later laboratory examinations that would subject polar ice to a multifarious array of chemical and physical analyses.

At the front of the processing line, Kendrick C. Taylor, a young geologist from the Desert Research Institute in Reno, Nevada, was running a direct electrical current through the core. This ingenious electrical conductivity measurement (ECM) technique had been invented by Claus Hammer, a Danish geophysicist and an experienced member of the team of European scientists who were drilling a twin ice core just 20 miles east of the U.S. site. Kendrick applied electrodes to the side of the core that had been shaved smooth. He watched as the acidity variations of the ice changed the strength of the current and made green wiggles on the screen of his computer.

Every inch of the two-mile core would be tested for its electrical conductivity, and a continuous profile of the ice sheet would be assembled. Out of the green wiggles came a pattern of annual layers, as small but regular variations tracked subtle seasonal differences in the ice's acidity. A spike in the readings might signal the presence of aerosols from a volcanic eruption somewhere in the Northern Hemisphere. A dip might indicate the fallout of airborne soot wafting across the ice sheet from distant forest fires. Taylor had connected the device to a speaker for a time, giving the researchers an audible sense of the variations in the signal's strength as the electrodes moved down the core. This first-pass procedure didn't identify the causes of these spikes, but it quickly generated a continuous profile that located interesting places for other researchers to look.

In line behind Taylor was Richard B. Alley, a young geoscientist who was applying the oldest test in the books. Following in the footsteps of the pioneers who had first examined polar ice, Alley was looking through the ice and seeing what he could see in the diffused rays of light emanating from a fluorescent bulb on the other side of the core. In the literature, this critically valuable albeit imperfect procedure has been dressed up in

Sunday clothes and given the name of "visual stratigraphy." Like anything so entirely human, however, it really is as much art as science, demanding personal patience and practice and defying attempts to objectively replicate its results photographically or archive its data electronically.

Alley was looking for anything interesting that might show up, of course, but first and foremost he was counting back the age of the ice by identifying the individual layers along the core. He passed the core sections in front of fluorescent lights that showed the variations in lightness and darkness caused by differences in physical properties such as trapped air bubbles or lines of dust. Besides leaving regular variations in electrical conductivity, the Arctic seasons' dramatic differences, summer's perpetual sunlight and winter's perpetual darkness, left behind a telltale visual signature in the ice. Summer snowfall was coarser than winter snowfall, and this difference in texture was preserved as a subtle layering effect as snow turned to ice, allowing Alley's practiced eyes to discern the passage from one year to the next.

This rookie Penn State professor had looked at more polar ice than most Americans in the science trenches at the time, having spent two field seasons in Antarctica working on a Ph.D. thesis on how snow turns to ice. In fact, Alley was one of the few young American scientists at GISP2 with any prior experience in

Temperatures in Central Greenland

This profile of temperatures in central Greenland during the past 100,000 years, reconstructed from oxygen isotope measurements along the GISP2 ice core in the mid-1990s, illustrates a climate pattern that is very different than the slumbering stability that researchers traditionally envisioned for ice ages. Notice the Younger Dryas, the last abrupt cold period before the current warm era, and the brief "cold snap" 8,000 years ago. Reprinted from National Research Council, Abrupt Climate Change: Inevitable Surprises, National Academy Press (2002).

Greenland ice. In the summer of 1985, as a graduate student, Alley had been one of a small U.S. contingent that helped a team of Danish experts survey the ice cap as part of the process of selecting the best site for what eventually became the European GRIP and U.S. GISP2 projects.

As almost everyone had expected of the Summit of Greenland, the ice under the site already had proven its value as an ancient climate archive, delivering up continuous sections that were beautiful, as polar ice cores go, and superior to the cores from Dye 3 and Camp Century. Far from the divide and the principal accumulation area of the glacier, the annual layers in the shorter cores taken from the earlier drilling sites were subject to more distorting effects of ice flow. At the twin Summit drilling sites, scientists were able to easily observe eras of climate just halfway down through the ice sheet that in the earlier cores were razor-thin layers near bedrock. By the middle of the summer of 1992, the Americans had drilled through a mile of ice, although they were still waiting to encounter what they had spent all of this money and time on and come all this way to see.

Where was the ice that would prove—or disprove—the truth of abrupt climate change? For more than a decade, the idea that climate could change noticeably within a single human lifetime had been bandied about among climate scientists but taken seriously by only a few. Not many researchers had actually seen the data from Camp Century and Dye 3, which had been the subject of long discussions about what, among many, circumstances could make them faulty. In any case, even those who were intimately familiar with the evidence would concede that episodes of abrupt climate change were "only suggested rather than proven" by the earlier cores. So where was the section of core that would settle the arguments once and for all?

The Greenland ice sheet concealed the secret of rapid climate change almost perfectly. This critical layer of ice, just a few feet thick, was suspended almost exactly in the center of the ice sheet at Summit—about a mile below the ice sheet's surface and a mile above bedrock. Drilling back in time, there were really no signs of it coming. The ice they were studying at the time looked a lot like the ice that had fallen as snow during the last 10,000 years. Yet they knew they were close.

They knew they had the critical layer of ice in their snow cave. Wanda Kapsner, a Penn State graduate student, had been taking thin sections about every 20 meters along the lengths of core laid out in the cave. She told Alley, "This section is in Holocene ice and the next section 20 meters down is in Ice Age ice, and so between these two is where you're going to find it."

This team of scientists was about to complete their six-week stint at Summit, and a new team was about to take its place. So it was up to project leader and paleoclimatologist

Paul Mayewski to decide which team was going to handle this important ice. On hearing the news from Kapsner, Mayewski told Alley, "Fine, before we get out of here, we're going to do that ice."

The ice that had formed from falling snow during the transition from the last of the cold, dry, windy ice ages to the first of the warm, wet calms of the modern 10,000-year-long Holocene climate is 1,678 meters, just over a mile, down the GISP2 core. Rendered in ice, what exactly would it look like, this boundary of epochs? The young American scientists had read the literature from Chet Langway, Willi Dansgaard, Hans Oeschger, Wally Broecker, and others, and they had heard from the Europeans, who were about a year ahead of them in drilling at Summit. Yet still they were not entirely prepared for what they saw that day in the ice, for the suddenness of it.

"You did not need to be a trained ice core observer to see this," recalled Alley. "Ken Taylor is sitting there with the ECM and he's running along and his green line is going wee, wee, wee, wee—Boing! Weep! Woop! And then it stays down." Dust in the windy ice age atmosphere lowered the acidity of the core to a completely new state. "We're just standing there and he just draws a picture of it," Alley said.

Spontaneous celebration was followed by a sudden and unexpected quiet. "I think we cheered," recalled Alley, "and then we were all a little sobered. Because it was just so spectacular. It was what we'd been looking for, and there it was, and then we're sitting there. Holy crap."

The instant of recognition that summer of 1992 had a raw feel to it, although eventually the disquiet would find concrete expression in numerous articles and presentations as the scientists became accustomed to the large truth of abrupt climate change and immersed themselves in its fine details. Alley recalled later: "Those of us who were down there in that trench at that time knew right then that our picture of the world had changed. There's a whole bunch of us who came out of that ice core project who have since dedicated ourselves to understanding abrupt climate change."

"My attitude changed profoundly," Kendrick recalled five years later in an article for American Scientist magazine. Before that experience in Greenland, he wrote, "I used to believe that changes in climate happened slowly and would never affect me."

Reviewing the evidence from Greenland and later results from ocean sediments, Taylor observed that in a span of just 20 years many regions of the world had experienced the changes he had first seen in the ice. "There was no warning," Taylor wrote. "A threshold was crossed, and the climate of much of the world shifted abruptly from cold to warm. This was not a small perturbation; our civilization has never experienced a climate change of this magnitude or speed."

Later, archaeologists and anthropologists would give human dimension to the evidence of change in that section of Greenland ice core. On one side were the atmospheric remnants of the climate of the Younger Dryas, a cold and windy, dry and unstable regime that had driven the Neolithic human clans to turn to agriculture. On the other side was the warm and wet and calm climate of the Holocene that during the past 11,000 years had cradled the rise of civilization. What Taylor and Alley saw was a boundary that looked nothing like the subtle progression of blurring that might have been left by a congenial process of gradual climate change. Holy crap. The line in the ice, just a few inches thick, looked more like a trap door falling shut. In the GISP2 science trench, the tray holding the section of core rolled down the assembly line and then it was Alley's turn at the ice. "It slides across in front of me and I'm trying to identify years: 'That's a year, that's a year and that's a year, and—woops, that one's only half as thick.' And it's sitting there just looking at you. And there's a huge change in the appearance of the ice, it goes from being clear to being not clear, having a lot of dust."

Long before chemical analyses would be conducted in more commodious laboratory environments in Europe and the United States, the scientists in the snow cave that day knew what this relic of ancient atmospheric processes would mean in terms of the science of climate. Reduced to a matter of inches, along a section of ice that went from clear to opaque, was environmental change of singular power and scope. "We knew what you'd see very clearly with an isotope record or a chemical record," said Alley. "We knew just standing there looking at it that it was huge, it was very fast, it did this bounce "

The bounce was part of climate change on a timescale that had never been seen before. In the summer of 1992, the quality of the GISP2 core and the sensitivity of the electrical conductivity measurements made it possible for Taylor to obtain more than 15 samples for every annual layer in the ice that had fallen as snow more than 10,000 years ago. In one sense, the bounce was part of a pattern of discovery that historians of science would recognize. Every time researchers had found a new way to a more sharply focused view of climates past, episodes of change emerged that had not been seen before. With each more finely detailed rendering, the climate system had emerged as more varied and more precariously balanced.

The following February, in Nature, Taylor described a "flickering" pattern between colder and milder conditions that lasted 10 or 20 years and typically terminated in less than 5 years. "The transitions between century or longer warm and cold periods are characterized by abrupt fluctuations in alkaline dust concentrations that occur over periods of less than 10 years," Taylor wrote. During the warm Dansgaard-Oeschger events of the ice age and "at main climate transitions, the part of the climate system influencing the ECM is behaving like a flickering switch that fluctuates between two states before stabilizing."

A "reordering of atmospheric circulation" seemed the most likely agent for such rapid changes, especially a change in the speed of winds bearing calcium carbonate dust over the ice sheet. Changes in atmospheric circulation also seemed the likely cause of dramatic change in another climate parameter. In the summer of 1992, this one stuck out of the ice core when U.S. researchers got their first look at the seam between the Younger Dryas and modern climate.

Alley's eyeballing and Taylor's ECM readings agreed: The changes in thickness of the individual layers in the ice were unmistakable. It may have been the fastest climate change ever seen. In April 1993, in a brief article in Nature, Alley, Kendrick, and their team reported that during the transition from the Younger Dryas to the Holocene, the amount of snow falling over the summit of Greenland had doubled, and the change seemed "to have occurred in three years with most of the change in one year." The researchers estimated that the sharp change in layer thickness at 1,678 meters, about a city block more than a mile deep in the ice sheet, corresponded to 11,640 years ago.

Again, the speed of events seemed to rule out the more slowly changing elements of the climate system such as solar radiation, atmospheric CO2 changes, or glacier retreat. "Causes must be sought in threshold levels in the climate system or in especially fast-acting components of the climate system including restricted, sensitive 'trigger' regions of deep oceanic convection, and atmospheric circulation patterns," Alley wrote.

Whether it jumped or was pushed, there was no doubt that the atmosphere had changed over the North Atlantic. On July 9, 1993, Mayewski and several members of the team reported in Science that numerous chemical analyses of the Younger Dryas ice "provide evidence of an extremely dynamic atmosphere thus far unparalleled in the Holocene. Investigation of the forcing of such an extreme environmental state offers a new view of climate change." Temperatures had warmed during the transition, of course, although a study by Wanda Kapsner in 1995 showed that rising temperatures alone could not account for the doubling of snowfall. The cold polar front had retreated northward, and the storm track was more squarely over Greenland.

In 1997, after more detailed laboratory work, Taylor reported in Science that changes at lower latitudes had taken place perhaps 15 years before the last jump to the Holocene in Greenland. Climate proxies related to areas outside the Arctic apparently changed before proxies of Arctic climate. Taylor said he couldn't tell "if the climate transition started at lower latitudes or if earlier changes that we are unable to detect occurred in more northern regions."

Chemical analyses of ice that had registered a spike in electrical conductivity measurements pointed to the eruption of a volcano that either was nearby in Alaska or Iceland or was a large explosive event elsewhere, 11,660 years ago. "We do not believe the [approximately] 10-year cooling associated with this eruption would have been sufficient to tip a precariously poised climate system to a warmer state," Taylor wrote, "but the coincident occurrence of the eruption and climate transition is intriguing." In ice representing the following 15 years, other chemical evidence pointed to a decrease in dust, indicating either an increase in moisture in areas outside the Arctic where the dust originated or a general drop in wind speeds.

A full field season ahead of the Americans, 40 members of a European team that included such polar ice pioneers as Willi Dansgaard and Hans Oeschger reached into silty ice at the bottom of the ice sheet at Summit in the summer of 1992. In contrast to the Americans, who first focused on the data of the Younger Dryas, the Europeans took a more comprehensive theoretical approach to their climate profile and its implications for modern conditions.

Taking in this first view of the climate profile from top to bottom, they came across features that were entirely familiar to Dansgaard and Oeschger. Echoing their earlier findings, the sudden spikes of warmth depicted a climate shifting "between two apparently quasi-stationary climate stages." It must have been a deeply satisfying recognition. The 23 warm "interstadials," or "Dansgaard-Oeschger events," that first appeared 25 years earlier in the oxygen isotope analyses of Camp Century ice were just where the Europeans expected to find them along their Summit core.

Reporting their first results in Nature that September, Sigfus Johnsen declared an end to the debate over the reality of this long, irregular series of abrupt climate changes that punctuated the last ice age. The common argument—that they were figments of Camp Century and Dye 3 records that had been skewed by deformation of ice layers near bedrock—found no support in the superb climate archive at Summit. "The results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt," Johnsen wrote. Rapidly, time and again, temperatures had climbed about 12.6°F, although still 9°F below modern levels, and in irregular steps over the next 500 to 2,000 years returned to ice age cold.

Johnsen raised a point that would haunt other researchers. If the abrupt changes turn out to reflect "a randomness" in the climate system, if two or more patterns are possible from a given set of variables, "climate modelers will have to reconsider the feasibility of predicting natural climate change."

Computer modelers would struggle for years with the problem that Johnsen described as randomness. Their most powerful simulations are highly complex mathematical creations that capture many processes. These numerical weather prediction models are the best things that have ever happened to weather forecasting, but they have their limits. On the timescale of weather, the atmosphere exhibits a kind of chaotic behavior that typically causes the skill of even the best forecasts to deteriorate after a few days. Johnsen's speculation about the origin of the abrupt-change "interstadials" was not good news to researchers who had higher hopes for the predictability of climate. The idea of "two or more possible flow schemes for a given set of primary parameters" reminded everyone of the kind of chaotic nonlinear behavior that imposes limits on weather forecasting.

Modelers, who might take refuge in the idea that warm climates behave differently than ice ages, weren't going to find much encouragement from Johnsen either. The last millennium had seen a medieval warm period in Europe that was followed by a "little ice age" during which sea ice frequently surrounded Iceland. The cold temperatures had been succeeded by a warming that culminated in the 1920s with an abrupt rise in temperatures—"too abrupt to be explained by the increasing greenhouse effect." These oscillations had been smaller than ice age changes, to be sure, but followed the same "sequence of events (gradual cooling followed by abrupt warming)."

The Europeans were first to examine a section of ice far down their Summit core that the leaders of both projects considered a prime target for research. Below the depth of 2,788 meters (1.7 miles),they found ice that had fallen as snow the last time Earth's climate was as warm as the modern Holocene. The "interglacial" warm era known as the Eemian began about 135,000 years ago and ended with the beginning of the last ice age 110,000 years ago. Because other paleoclimate proxy records suggested a time of relative stability when global temperatures were somewhat warmer than during the Holocene, the Eemian period had long been considered an important "analogue" for the future of modern climate under the influence of an intensifying greenhouse effect. The findings from the European core, announced in Nature in the summer of 1993, surprised everyone.

The same episodes of rapid and large change that characterized the last ice age ran straight through the Eemian period and into the earlier ice age. Down in the core below 2,750 meters, in ice that the Europeans were confident represented the period of Eemian warmth about 120,000 years ago, oxygen isotope data showed two especially large and sudden plunges toward ice age cold. In one episode, average temperatures apparently plunged 25°F for about 70 years. The only period of relative stability during the Eemian came during the last 2,000 years of its warmest stage.

"The unexpected finding that the remainder of the Eemian period was interrupted by a series of oscillations, apparently reflecting reversals to a 'mid-glacial' climate, is extremely difficult to explain," the Europeans wrote. "Perhaps the most pressing question is why similar oscillations do not persist today, as the Eemian period is often considered an analogue for a world slightly warmer than today's." Given the history of the last 150,000 years, they wrote, the past 8,000 years "has been strangely stable."

In an accompanying commentary, American climatologist James W. C. White, a stable-isotope specialist, asked if the Eemian record in the Europeans' ice core was a glimpse of our own future. "Whatever the answer to that question, the speed with which the climate system can shift states gives us pause. Adaptation—the peaceful shifting of food growing areas, coastal populations and so on—seemed possible, if difficult, when abrupt change meant a few degrees in a century. It now seems a much more formidable task, requiring global cooperation with swift recognition and response."

As journalist Richard A. Kerr noted in Science, the news from Greenland shattered the conventional view among climatologists of the warm intervals between ice ages as "benign interludes." On the front page of the New York Times, science writer Walter Sullivan reported: "To the astonishment of climate specialists, an analysis of ice extracted from the full depth of the Greenland ice sheet has shown that except for the 8,000 to 10,000 years since the last glacial epoch, the climate over the past 250,000 years has changed frequently and abruptly." Michael Morrison, associate director of the U.S. project, where bedrock had been reached just two weeks earlier, told Sullivan that the Americans expected to confirm the European findings.

It was not until U.S. researchers got a close look at the deep sections of their core that they noticed serious discrepancies between the new long climate profiles. The U.S. core gave the same general impression of instability during the Eemian warm period, but when researchers examined the data in detail, they found no real agreement in the sequence of individual climate episodes. From the surface all the way down to 2,780 meters, through 90 percent of the depth of the ice sheet, the two finely resolved climate variation profiles agreed with one another in almost lock-step precision. Then, unexpectedly, at a point that was still 200 meters above bedrock, agreement broke down completely.

In December, two reports in Nature broke the unhappy news. Taylor for the U.S. team and Claus Hammer for the Europeans coauthored a report that described major discrepancies in their electrical conductivity measurement data for the ice cores at the depths below 2,750 meters. And a paper by Pieter M. Grootes, White, Johnsen, and others reported similar problems with the oxygen isotope readings at the Eemian depths. Everyone was confident that the upper 90 percent, where both cores agreed, represented two highly detailed, accurate records of climate going back 110,000 years that were unaffected by ice flow. However, with the integrity of the last 10 percent of at least one ice core, and possibly both, in doubt, the Europeans' interpretation of their Eemian results was in serious trouble. Arguing that evidence of disturbance seemed more apparent in the Americans' core, several members of the European team held out for the integrity of their own data back through the Eemian.

Yet just as the conformity of the two climate profiles proved the reality of abrupt change for the last 110,000 years, their nonconformity proved critically valuable in detecting faulty data in older ice. The circumstances threw a new light on the seemingly extravagant decision to simultaneously undertake two large and nearly identical ice coring projects in central Greenland. Without a twin of the same ice, the ability to quickly test one against the other, climate science might have been led down a long and unrewarding road.

Later studies finally persuaded scientists on both projects that ice flow had distorted the sequence of the annual layers in both cores below about 2,800 meters. Strong evidence came in 1995 in a study by Alley and others of the physical properties of the deep sections of both cores. Most convincing was an analysis by the French glaciologist Jérôme Chappellaz of the atmospheric gases trapped in the air bubbles. Chappellaz compared concentrations of methane in the supposed Eemian-age Greenland cores with bubbles of the same age in ice from the Vostok core in Antarctica. Because methane, a climate "proxy" for the extent of continental wetlands, is globally mixed in the atmosphere, the Greenland and Antarctic data should agree in general direction even if the amplitude of the signal is different. By 1997, the issue was no longer in doubt: Where both of the Greenland cores showed large and rapid variations in methane trapped in their deep ice bubbles, Chappellaz reported, "the Vostok record shows no such variations."

In an effort to overcome the "Eemian problem" in the ice, to extend the sharply focused view afforded by polar ice through the last period of warm climate, the Americans and Europeans joined in 1996 to finance the drilling of a third central Greenland ice core. Drilling at a promising location north of the Summit site, the North Greenland Ice Core Project proved even more frustrating. After seven years of stuck drills and other stops and starts, in the summer of 2003 NorthGRIP drillers finally reached bedrock at a depth of 3,085 meters. There, unexpectedly, they found that heat rising from some unknown geothermal process had melted the Eemian ice.

In the end, of course, whatever the ice may have revealed of the Eemian period, leaders of both projects recognized that they had rewritten the history of climate over the last 110,000 years. Scores of international scientists had analyzed polar ice as never before, producing two long, reliable, and continuous profiles of ancient climate with a clarity that was unprecedented. No longer was there any doubt about the warm Dansgaard-Oeschger events. Twenty-four episodes stood out clearly, as did 13 separate Heinrich events that dramatically plunged the Northern Hemisphere into especially severe cold and dispatched armadas of icebergs across the northern Atlantic. Scientists would spend years poring over the results, comparing them with other climate archives, looking for ways to explain this warming or that chill.

More interesting to the larger community of climate scientists—and to nonscientists— was the unmistakable pattern that emerged. This was not the record of ancient climate that anyone had been taught to expect. It was not just that the climate was subject to more variation than was generally supposed, although the idea of so much change during an ice age was certainly a surprise. More surprising, of course, and most interesting was not the fact of change but its suddenness.

"From the central Greenland ice cores we now know that the Earth has experienced large, rapid, regional to global climate oscillations through most of the last 110,000 years on a scale that human agricultural and industrial activities have not yet faced," an international group of leading climate scientists wrote in a special issue of the Journal of Geophysical Research devoted to detailed studies of both cores. The work reported was part of a flood of new information that poured out into a growing community of climate scientists who were increasingly attuned to changes taking place in the atmosphere and around the world. The Dane Claus Hammer, the American Paul Mayewski, David Peel of the British Antarctic Survey, and Dutch-born Minze Stuiver wrote: "The ice-core records tell a clear story: humans have come of age agriculturally and industrially in the most stable climate regime of the last 110,000 years. However, even this relatively stable period is marked by change. Change—large, rapid, and global—is more characteristic of the Earth's climate than is stasis. Until we understand the operative mechanisms, it will not be possible to understand current change or predict future change."

So the secret of the Greenland ice was out. No longer was abrupt climate change the hypothesis of a small group on the strength of debatable data. The evidence was unusually reliable and voluminous, taken from twin sites analyzed by two large, well-organized research teams from more than 40 university and national laboratories. As Taylor described the collaboration, "We shared samples, spent time in one another's labs, replicated one another's results, proposed ideas, tore them apart and then jointly proposed better ones."

Many scientists encountered abrupt climate change for the first time when they read the papers by the Europeans and Americans in the scientific journals in 1993. In December, the Greenland scientists made joint presentations and gave interviews during the fall meeting of the American Geophysical Union in San Francisco. Reporting on the meeting, many newspapers around the world published their first articles on the subject.

Among climate researchers, the news from Greenland encouraged a range of new studies. Researchers like Taylor and Alley would go looking for longer high-resolution records of climate history in Antarctic ice. Oceanographers and other investigators would search out and find more evidence of abrupt change in ocean sediments and a variety of other climate archives around the world.

The remarkable successes of the European and U.S. ice core projects at Summit are commonly seen as occasions of original discovery. Scientists familiar with the paleoclimatology literature would see them more accurately as verification of the earlier work in the 1960s and 1970s by Dansgaard, Oeschger, and Langway. Perhaps it is in the nature of such "Big Science" projects, like glaciers moving down a mountain, to obliterate the records of earlier exploits with their massive progress. Science, after all, is not a museum of ideas, but a process of finding out how the world works. You test ideas discard what doesn't seem to work, and move on. Scientists have a keen sense of their debt to those investigators whose ideas and data they employ, but they don't necessarily have a keen sense of history—even the history of their own discipline. So perhaps it was only natural that no one in the mid-1990s seemed to see the success of the Greenland ice core projects as the culmination of investigations that began 63 years earlier in a very lonely place called Eismitte.

What would it mean to Ernst Sorge, the German researcher who dug the first trench down from his cave in the ice cap that winter of 1929? Or to the expedition's organizer Alfred Wegener, the father of continental drift, who died on the ice that winter—would he recognize this new paradigm in climate science?

The passage of 63 years can be a long time in a rich and actively pursued science, of course—although, as almost everybody knows, it's really no time at all on the geological scale. Who would have thought that 63 years is time enough for climate to change?

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