Abrupt climate change finds a theorist

The new methods of reconstructing climates past not only have inspired reinterpretations of history but have also cast the future in a new light. They have transformed the study of ancient climates into the study of the very nature of climate—the ways it distributes heat and water around the planet and the dimensions and pace of its changes.

Nothing stimulated the field of paleoclimatology more than the reports in the early 1980s by Swiss and French physicists and climatologists of their analyses of the composition of the bubbles found in polar ice cores. Researchers suddenly realized something that many had not even dreamed possible: Not only was polar ice an archive of the isotopic footprints of past climates, it was a storehouse of the climate system's most ephemeral feature—the air itself. The bubbles in the ice were tiny time capsules of "fossil" atmospheres that were trapped inside the glacier when the coarse old snow turned to solid ice about 100 meters down. They could be assigned ages, and unlike proxy evidence, the chemical composition of this trapped air could be analyzed directly.

These technically demanding geochemical analyses were accomplished by the Swiss physicist Hans Oeschger and the French physicist Claude Lorius. Independently of one another, Oeschger, analyzing Greenland ice, and Lorius, analyzing Antarctic ice, measured the level of carbon dioxide in the air bubbles.

For the first time, scientists from a broad range of specialties began to recognize polar ice as a source of climate information that was timely and global in scope. Carbon dioxide, a gas that is well known for its radiative "greenhouse" properties even in minuscule concentrations, remains in the atmosphere hundreds of years. Long-lived gases are dispersed evenly around the world by the mixing actions of the atmosphere. Even scientists who were skeptical of the oxygen isotope analyses of the ice and their evidence for abrupt change realized that the air pockets held clues to what was becoming the most compelling environmental question of the day: How will Earth's climate respond to industrial pollution?

The answer to this critical question hinged on the chemical composition of the atmosphere and on its history. In the face of rising global temperatures and mounting evidence, predictions of climate scientists had radically changed. Concern about Earth's natural long-term orbital variations forcing it toward a new ice age had given way to a vision of global warming provoked by human pollution from the burning of hydrocarbon fuels. Driving this change in thinking were three sets of critical data that came together within a decade.

In 1973, a landmark study by Charles D. Keeling of the Scripps Institution of Oceanography reported the first direct measurements of changing carbon dioxide concentrations in the atmosphere. Measured from his laboratory atop Mauna Loa, Hawaii, atmospheric CO2 had climbed steadily from 312 parts per million in 1958 to 330 parts per million in 1972. These meticulous readings and the inexorable rise of the famous "Keeling curve" would become central to the issue of global warming.

Beginning in 1980, European polar ice laboratories produced the first convincing picture of how the composition of the atmosphere had changed through history and clues to the relationship of these changes to global temperatures. In 1980, researchers reported results of the first analyses of an Antarctic ice core that measured the concentration of carbon dioxide gas in the atmosphere during the nineteenth century. In these "preindustrial" times, scientists reported, the atmospheric CO2 concentration was between 280 and 290 parts per million.

In 1982, the other shoe dropped. European labs reported that about 20,000 years ago, during the coldest depths of the last ice age, the atmosphere contained about 30 percent less carbon dioxide, about 200 parts per million.

"The discovery of natural oscillations in greenhouse gases from fossil air trapped in polar ice ranks as one of the most important advances in the field of climate and earth science," wrote geologist Thomas M. Cronin, author of Principles of Paleoclimatology, a leading text on the subject. Together with Keeling's measurements, he wrote, "These discoveries about natural and human-induced fluctuations in potentially climate-altering atmospheric gases sent shock waves throughout the paleoclimate community that still reverberate."

Now the relevance of the past to the present was no longer a subject of conjecture. At universities and government laboratories, new technologies were applied to the mysteries of the ice. Old institutional barriers gave way as specialists who had been only vaguely aware of one another's work found themselves in long conversations about the surprising results from Bern and Grenoble. Among a whole generation of young earth scientists, polar ice was becoming famous. For the first time, paleoclimatologists occupied the same conference rooms as scientists who were focusing on the increasing concentration of greenhouse gases in the contemporary atmosphere. And along the way, almost incidentally, a larger and more receptive audience heard about the Greenland ice cores and their evidence for abrupt climate change.

Comparing the Dye 3 core with the Camp Century ice and with new results from lake sediments in Switzerland, Willi Dansgaard and Hans Oeschger had identified 24 episodes of abrupt change during the last ice age. These times of sudden warming took on a characteristic, somewhat straight-sided rectangular shape in the profile of the ice cores. Whatever their cause, the switches in oxygen isotope readings apparently were recording the same sequence of events. Temperatures shot up to a level that indicated a distinctly milder climate, although not as mild as the modern climate of the last 10,000 years, the Holocene. Fairly soon after this spike, temperatures would begin an irregular slide back from this new level of warmth. Then, after several centuries, more or less, they would plunge back just as suddenly to ice age cold.

In the minds of these ice core researchers, a new conception was taking shape. The sharp, erratic changes seemed to show a climate that was shifting in and out of two distinct modes or states of operation, like a badly driven jalopy lurching between gears. In a 1984 paper, Oeschger, Dansgaard, Chet Langway, and others observed that these events "can be linked to oceanic changes, namely advances and retreats of cold polar water in the North Atlantic Ocean." The southward advance of polar water coincides with colder climate in Europe, they noted, and its retreat northward with a warmer Europe. "This strongly suggests that the continental climate shifts were an effect of changes of the surface conditions of the North Atlantic Ocean." But researchers were more inclined to think of the oceans as reservoirs of "thermal inertia" and climate stability rather than agents of sudden change. What could cause the ocean surface conditions to shift so rapidly?

No one in climate science was more interested in this question or better prepared to consider it than the American geochemist Wallace S. Broecker. Since the 1950s, Broecker had been following two research paths—paleoclimatology and ocean circulation. About all these subjects seemed to have in common was the fact that both were amenable to investigation by the new technology of radioactive isotopes of carbon. As a graduate student in charge of Columbia University's new radiocarbon laboratory, Wally Broecker was among the first researchers to use 14C dating techniques to explore both subjects.

In 1957, his doctoral thesis described the use of 14C dating techniques in both fields of research. Analyzing samples obtained with a 200-liter ocean water sampler developed by oceanographer Maurice Ewing, director of the Lamont Geological Observatory, Broecker was able to estimate the ages of volumes of seawater taken from different depths. From this data emerged a picture of the pattern and pace of ocean circulation. Inspired by radiocarbon dating of samples he had taken in Nevada from caves around a prehistoric lakebed, he also included a chapter entitled "Evidence for an Abrupt Change in Climate 11,000 Years Ago." As a professor at Columbia and a researcher at Lamont, Broecker had spent the next 20 years developing ways to measure the rate of circulation of the oceans and techniques to correlate various far-flung clues to climate events that marked the transition from the ice age some 11,000 years ago.

When Oeschger and Lorius reported that the ice age atmosphere contained a third less carbon dioxide, Broecker pounced on the results. While there had been "much discussion about the influence of the anthropogenic 'greenhouse' gases on future climate," Broecker wrote, until the results from the polar ice bubbles, researchers had "little of substance" to link paleoclimate to paleochemistry. "I realized right away that the driver for these changes must reside in the oceans," he recalled. After 20 years, the link between atmospheric CO2 and ice age temperatures still has yet to be satisfactorily explained; "the driver" has yet to be identified. Ironically, even though, as Broecker put it, "the prize has yet to be grasped," his fascination with the subject led to his most famous scientific contribution.

All of his years of research into the chemistry of the ocean and the mysteries of paleoclimatology came together in 1984 as he sat in a lecture hall at the University of Bern, watching and listening to Hans Oeschger puzzle over the pattern he was seeing in the Greenland ice core. Years later, Broecker would recall the defining moment.

Oeschger was showing a graph of the Dye 3 climate profile from Greenland that depicted the numerous abrupt warmings during the last ice age that would become known as "Dansgaard-Oeschger events." The graph, which showed atmospheric CO2 levels changing along with temperatures, suggested to Oeschger a system jumping back and forth between two different modes of operation. Broecker recalled: "Realizing that the CO2 jumps required changes in the operation of the ocean, I said to myself, 'Could the key lie in a turning on and off of deep water formation in the northern Atlantic?' And as quick as that, my studies in oceanography and paleoclimatology merged." Again, Broecker's theoretical instincts would prove to be better than the underlying data. Researchers lost confidence in the CO2 readings that seemed to rise and fall along with the Greenland warming events during the last ice age, especially after they failed to appear in the Antarctic ice. By then, however, Broecker was on his way to developing the first enduring explanation of abrupt climate change.

In 1985, in a defining article in the British journal Nature, Broecker took the subject from the sidelines and onto center stage in paleoclimatology. In the hands of its leading theorist, the focus of the science and its research agenda were about to be given a new look. Different events were going to be seen on a different timescale. The ocean sediments and their long but blurry geological reach, so helpful to the investigation of ice age rhythms, were going to have to make room for the polar ice cores and their shorter, more finely detailed mysteries of rapid change. With coauthors Dorothy M. Peteet and David Rind, Broecker rephrased the question posed by Oeschger, "Does the ocean-atmosphere system have more than one stable mode of operation?"

Broecker pointed out that the Greenland ice cores detected changes during the last ice age that hadn't been seen before—"many brief events during which climatic conditions returned about halfway to their inter-glacial state." While such fine detail would be lost in the typical sediment core taken from the open ocean, he noted, this did not mean that the ice cores and the sediment cores were really in conflict with one another. "However, as these idiosyncrasies of the ice-core record were not seen in other records, the initial temptation was to pass them off as climate 'noise' without global significance. A rapid succession of findings has since changed this view of the noise, now the focus of much interest."

The Dye 3 results, reported in 1981, had confirmed that the wiggles in the oxygen isotope profile that first showed up 10 years earlier in Camp Century ice were real warming events. The rapid changes also showed up in the ice core analyses of other chemical proxies—in dust and in concentrations of wind-blown aerosols of sulfate, nitrate, and chloride. And the oxygen isotope evidence for the most recent rapid event in both cores also appeared in calcium carbonate analyses from lake sediments in Switzerland, supporting Willi Dansgaard's view, expressed years earlier, that the Greenland ice and the European pollens were recording the same rapid cooling event—the Younger Dryas. With this paper, Broecker began to describe the Younger Dryas as a climate event that was larger in scope and more consequential than his colleagues might assume from its obscure origin in the fossil pollens of Scandinavia. Signs of the dramatic climate tumble back toward ice age cold also had turned up in Spain, northern Italy, and northern Canada, although not in the United States. It may be a regional climate phenomenon, limited to the North Atlantic, but "the situation may be more complicated." Although the Younger Dryas wasn't detected in the Antarctic ice taken from a core at Byrd Station, there was evidence for such an event in the mountains of South America and in New Zealand. This convergence of Broecker's research paths inspired a sustained effort to develop a theory of abrupt climate change—in particular, to explain the Younger Dryas. Broecker sketched a mechanism that described an intricate interplay between the movement of water vapor in the atmosphere and the transfer of heat in the oceans. The scenario linked atmospheric processes to a global interconnected system of large-scale ocean currents. Oceanographers call this system the thermohaline circulation. This joining of the Greek words for heat and salt signifies that the currents are driven by variations in temperatures and levels of salinity. In 1961, the famous oceanographer Henry Stommel had proposed that this global circulation has two stable states.

North Atlantic Ocean water is saltier than North Pacific Ocean water. The North Atlantic gives up more fresh water to evaporation

The Great Ocean Conveyor

First drafted by Wallace S. Broecker, this diagram illustrates how differences in water temperature and salinity transport water—and heat—among the world's oceans. Notice the key role of the North Atlantic as an important "cog" in the conveyor system. In two critical areas, where heat is released to the atmosphere, surface water becomes more dense, sinks to the ocean depths, and begins flowing southward. Reprinted from National Research Council, Abrupt Climate Change: Inevitable Surprises, National Academy Press (2002).

than it receives through precipitation and runoff from adjoining rivers. The opposite is true of the Pacific. At the same time, the North Atlantic's surface water is warmer than the Pacific's at the same latitude. As Broecker wrote, "Water is being distilled off the 'warm' Atlantic and condensed on the 'cold' Pacific" by the storms and winds of the atmosphere. Because of this constant freshening, the North Pacific's waters do not develop the same layering of different densities. Cold water from its great depths wells up along its continental margins and in a great clockwise gyre flows back over its surface toward the Equator. In the North Atlantic, the pattern of circulation is more distinctly vertical. In the North Atlantic, the big warm surface currents, the Gulf Stream and the North Atlantic Drift, carry heat from the Tropics toward the pole and the cold abysmal currents carry excess salt southward from the Atlantic to the Pacific and Indian oceans.

Broecker focused on a critical juncture in the system—the far North Atlantic, the Labrador and Nordic seas, where water from the surface encounters the Arctic westerlies off Canada. Now cold and salty, the current sinks to the abyss, forming the dense southward flow that oceanographers call North Atlantic Deep Water. The evaporative cooling of the surface water transfers from the ocean to the atmosphere an amount of heat that Broecker estimated to be equivalent to 30 percent of the Sun's warmth that far north. Northern Europe, which is meteorologically "downstream" of this process, enjoys a climate that is warmer than other regions at such high latitudes.

Using the new computer model of the general circulation of the atmosphere, developed at the Goddard Institute for Space Studies in New York, Broecker, Peteet, and Rind built the most persuasive case yet for the role of ocean circulation in rapid climate change. They noted that, according to a variety of evidence from deep-sea sediments, the formation of this North Atlantic Deep Water "was reduced greatly" during the coldest depths of the last ice age. But what of the abrupt warmings, Broecker wondered: "Is it possible then that the brief warm events recorded in the ice cores represent periods during which the glacially weakened northern Atlantic deep-water source was rejuvenated?" The scientists couldn't test that question directly on the computer model without more evidence of the geographical distribution of the climate impacts of warm events. But they could test the opposite circumstances—the last big rapid event, the sudden cold of the Younger Dryas.

The researchers plugged into the Goddard Institute model the colder sea surface temperatures estimated for the North Atlantic during the depths of the last ice age. The computer generated cooler temperatures across Europe and far northeastern North America in a pattern that looked like the pollen record of the Younger Dryas. Of course, it wasn't proof that a shift in the North Atlantic's circulation had provoked the cold of the

Younger Dryas or the ice age warm events. But as scientists are fond of saying when using computer models, the results were consistent with the evidence.

To Broecker it was tempting to speculate that Oeschger's two modes represented two states of operation of ocean circulation. During the ice ages—the glacials—the North Atlantic was cold because the circulation was weak or even reversed, he supposed, and during the warm interglacials the North Atlantic was warm because the circulation would be strong. During the "Oeschger oscillations," as he called them in this paper, climate seemed to settle temporarily at some halfway point before slipping back into the ice age. Broecker tentatively outlined a scenario of abrupt warmings and cold snaps driven by changing ocean temperatures, ice cap melting, and shifting seawater salinity.

As Broecker noted, scientists had generally assumed that the climate system's response to "any gradual forcing will be smooth," but if Oeschger was right about the system having more than one stable mode of operation, "then the situation is more complex." If Oeschger was right, atmospheric computer models were going to have to become more sophisticated and incorporate the physics of the ocean to allow researchers to explore the more complex interactions in the climate system, and scientists were going to have to learn more about its components. If Oeschger was right, the great challenge facing climate science—anticipating future change—not only was more complicated, but its solution might well be more urgent. Broecker began to wonder about the implications of ever-increasing concentrations of carbon dioxide in the atmosphere. Are sudden mode switches likely in such a future?

The information was tenuous, he acknowledged, and thinking in terms of these abrupt mode changes was not going to be easy, but "we must begin to explore this alternate track." The new approach meant that scientists were going to have to design better computer models, achieve a better understanding of the climate system's various parts, and "extract all possible information from the paleoclimatic record." More polar ice cores were going to have to be drilled. More money was going to have to be spent. More scientists were going to have to be involved. "Unless we intensify research in these areas," Broecker wrote, "the major impacts of CO2 will occur before we are prepared fully to deal with them."

In the mid-1980s, Broecker began a long, fruitful exploration of "this alternate track" of abrupt climate change. A transformation was under way. While other scientists devised new ways to tease information from archives of climate in glacial ice and ocean sediments and in tree rings and sea corals, Broecker would assimilate the data and give it theory—a physical mechanism that explained the data. The polar ice cores and the refinement of methods of analyzing ocean sediments were bringing into focus new features of climate with new causes and effects, and a new terminology was taking shape, much of it coined by Broecker.

To distinguish the abrupt episodes of relatively short-term change from the variations that marked the grand ice age cycles, abrupt changes became known as "millennial-scale" events because they seemed to last about a thousand years, more or less. The term itself is a bit of geological artifact, in a sense. To scientists accustomed to thinking in units of geological time, calling something "millennial scale" was meant to imply brevity.

Broecker coined the name "Dansgaard-Oeschger" oscillations, or D-O events, for the series of sudden warmings through the last ice age. The term recognized Willi Dansgaard's pioneering oxygen isotope analyses of the ice core that first revealed the temperature changes, as well as Hans Oeschger's landmark interpretations of these events.

Before long, the terminology of the new science would include other coinages for other abrupt climate oscillations. The young German researcher Harmut Heinrich, examining layers he detected in Atlantic Ocean sediments, identified a series of sudden plunges to especially cold temperatures during the last ice age. The sediment layers were composed of debris scraped off by the grinding of the Laurentide ice sheet in Canada and rafted far across the North Atlantic by armadas of icebergs. Broecker named these cold outbreaks of icebergs "Heinrich events."

But the centerpiece of the new science remained that mysterious stab of cold that so dramatically interrupted the 4,000 years of warming from the last ice age, the Younger Dryas. On land and at sea, evidence for this last and most accessible rapid climate change 11,000 years ago continued to accumulate, enlarging its reach and its global significance. By 1985, Broecker had satisfied himself that an abrupt shutdown of the ocean circulation in the North Atlantic was responsible for ice age cold suddenly spreading back across Europe. But what would cause such a catastrophe?

In the mid-1980s, Broecker put the pieces of the puzzle together. His explanation of the Younger Dryas changed contemporary thinking about the character of Earth's climate. The message from the Greenland ice cores was clear: the behavior of climate during the last ice age was nothing like the epoch of slumbering stability that was commonly accepted. Nor were the great ice sheets it formed subject only to ponderous advance and decay in concert with the variations of Earth's orbit. Just as the Camp Century and Dye 3 cores implied, sudden large swings between exceptional cold and exceptional warming marked 100,000 years of climate history. What Broecker brought to the science was the first plausible explanation for these events.

The Younger Dryas, Broecker said, was caused by the sudden massive flooding into the North Atlantic of meltwater from the Laurentide ice sheet that covered much of North America. Some 2,000 years of warming had led to the formation of an enormous lake across much of Canada, south and west of the world's largest glacier. About 11,000 years ago, the retreat of the ice closed off the lake's southern outlet through the Mississippi River basin into the Gulf of Mexico and opened a new channel eastward through the St. Lawrence into the North Atlantic. This sudden freshening of the surface water altered its density balance, preventing it from sinking to the ocean's depths and blocking the northerly flow of the warming current from the Tropics.

Climate scientists would spend years debating the details of this scenario and filling in the missing pieces. Broecker's bold line of thought drew widespread interest and brought a new focus to paleoclimatology. For the first time, climate scientists had a coherent explanation for abrupt changes, one that invoked a close interplay between processes in three realms of the climate system: the atmosphere, the ice sheets, and the oceans. And it brought together the evidence from three very different lines of investigation: ice cores drilled from the Greenland ice sheet, sediments plumbed from the seabed of the North Atlantic, and fossil pollen layers in the old bogs and lakebeds of northern Europe.

A new time dimension was being forced onto earth science, one remarkably close to the old catastrophist fantasies that geologists had fought so hard to disassociate themselves from earlier in the century. So much for the time-honored maxim of Aristotelian thinking: Natura non facit saltum—nature does not make leaps. When it comes to changing climate, it turns out that making leaps is exactly nature's way. In 1989, the time dimension was given a precise new scale by another study of the Camp Century and Dye 3 ice by Dansgaard, the American James W. C. White, and Sigfus Johnsen of Iceland. Examining the core sections representing the cold-to-warming transition that marked the end of the Younger Dryas, these researchers concluded that most of the "abrupt and radical changes" had happened in the span of only 20 years.

Like Hans Oeschger in Switzerland, Broecker was quick to relate the lessons of abrupt change to the growing dialogue about the climate impact of the rising atmospheric concentrations of carbon dioxide and other greenhouse gases. He sought to extend these new lines of thought to the broader community of climate scientists and to alert policy makers and the public to the disquieting new discoveries in the paleoclimate record. Broecker is an entertaining speaker and an acknowledged leader in his field, and everyone listened politely. But none of these audiences found his message particularly welcome, primarily because his news was not good.

Many fellow earth scientists, steeped in the conservative tradition of geological time, were slow to react. Many preferred the relatively safe haven of ice age dynamics to the difficult and politically noisy realm of contemporary environmental science. Broecker's bold hypothesis seemed almost apocalyptic, a rash and untested scenario that added a new level of uncertainty and controversy to a subject that already was too uncertain and controversial. Climate science's ambition to predict the future was going to be more difficult to achieve than many supposed, he warned, and perhaps decades farther in the future. More than that, the future itself was likely to be more dangerous. For computer modelers and others looking for a baseline of natural variation to simulate the impact of the industrial age on climate, the physics of gradual change was going to be difficult enough to absorb. What Broecker offered was something even more intractable—a more lethal and more willful system controlled by the tangled dynamics of chaos. About all that Broecker promised was more years of hard work and, at the end of this longer and bumpier road, a future of greater uncertainty.

In a 1987 commentary in the journal Nature, Broecker wrote that as they contemplated the future, climate scientists had been "lulled into complacency by model simulations that suggest a gradual warming over a period of 100 years" and by the oxygen isotope record in deep-sea cores that gave the impression that the response of the climate system to changes wrought by subtle alterations of Earth's orbit of the Sun is smooth and gradual. "Only recently have we begun to realize that this impression is a false one," he wrote. Looking back, clues were there in the North Atlantic seabed in the changing species of planktonic organisms that probably reflected sudden changes in sea surface temperatures during the past 100,000 years. "It took more than this, however, to make us take these abrupt changes seriously," Broecker confessed. "The evidence that turned our heads came from holes drilled through the Greenland ice cap."

Employing an analogy he would use more than once, Broecker wrote: "We play Russian roulette with climate, hoping that the future will hold no unpleasant surprises. No one knows what lies in the active chamber of the gun, but I am less optimistic about its contents than many."

What the world needed was a cadre of young scientists dedicated to intensifying investigations of a range of climate issues, including a more careful examination of the evidence of change in ocean sediments and ice cores. "Although we don't know nearly enough about the operation of the Earth's climate to make reliable predictions of the consequences of the build-up of greenhouse gases, we do know enough to say that the effects are potentially quite serious," he warned. A climate that experienced sudden leaps could deal wildlife a serious blow. Our food supply might be at risk. "To date, we have dealt with this problem as if its effects would come in the distant future and so gradually that we could easily cope with them. This is certainly a possibility," he wrote, "but I believe that there is an equal possibility that they will arrive suddenly and dramatically."

For all its dark warnings and pessimism, Broecker's message struck a responsive chord among young graduate students entering the earth sciences. Here was an uncrowded field, a virtually new science with a new sense of consequence and urgency to embrace. As more and more young scientists turned to the Greenland ice core records and sought to develop their own lines of research, a problem that had been simmering for years quickly became more serious. There was not enough Greenland ice to go around. As more scientists began to focus on the climate profile from the ice sheet, the origins of the cores became a more serious issue. None of the deep-core ice had been drilled from scientifically optimum locations on the ice sheet.

As a young and essentially unproven line of research, ice core drilling in Greenland had always been forced to compromise with logistical convenience. The enterprise, cumbersome and costly, had benefited for years from the willingness of the U.S. Army's Corps of Engineers to explore the ice as part of its strategic interest in Greenland. But that support had come at a price. In the 1960s, the first core to bedrock had been drilled in northwestern Greenland at a site that was chosen primarily because of the nearby location of Camp Century, the "City Under the Ice," the military's elaborate experiment with habitation in the ice cap. In the 1970s, after military interest faded, Langway, Dansgaard, and Oeschger, who had searched the ice sheet for ideal sites for drilling to bedrock, presented the National Science Foundation (NSF) with specific ideas about extracting a core from a site chosen for maximum scientific benefit—the summit of the ice sheet. Again, however, even as the U.S. civilian science funding administrators committed $10 million to a second surface-to-bedrock core, the scientists of the Greenland Ice Sheet Program were required to settle for a much inferior southeastern drill site, far from the summit, because it was logistically convenient to a Distant Early Warning radar station known as Dye 3.

By the late 1980s, the scientific landscape was very different. "We've got people tripping over each other to do this research," Herman Zimmerman, an NSF program manager, told journalist Elizabeth Pennisi in 1989. So intense was the international competition for ice samples and research participation in a drilling program in Greenland that Broecker, Dansgaard, and Oeschger concluded a bold and ambitious agreement. Two separate ice cores would be drilled at Summit, just 20 miles from one another. The NSF would finance GISP2, a $25 million multidisciplinary project involving researchers from 12 U.S. universities. For a like amount, a European consortium would undertake the Greenland Ice Core Project, GRIP. The great northern ice cap was about to reveal its secrets. And the science of climate change would never be the same.

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