by Sarah Dry
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Thanks to Dansgaard’s idea and the developments in isotopic analysis on which it relied, ice cores became, in Dansgaard’s poetic phrase, frozen annals of the earth’s past. Ice cores were perhaps the most sublime of paleoclimate records, with their evocation of the cold poetry of ancient snows, but there were many other, equally amazing, if less haunting, records of the past, some of which stretched even further back in time. In the hunt for more clues, paleoclimate scientists analyzed layers of mud and sediment taken from the ocean floor that preserved the shells of ancient sea creatures called foraminifera that had built their shells out of isotopically diverse elements. They bored into ancient trees, counting the bands of tree rings that documented the changes experienced by trees that had lived since well before Christ. They studied pollen deposited on winds that had blown thousands of miles, leaving a record of which plants had flourished and therefore an indication of the climate conditions. Getting a tree to give up its secrets took different skills and required different assumptions than finding a way to make ancient mud speak of long-past climates. The strength of the signal varied, as did its precision. The old mud was, by its very nature, blurrier than the rings of ancient trees, but while the trees could be used, en masse, to go back 11,000 years, the mud stretched more than 1.5 million years.
It was a simultaneously stimulating and contentious time. There was a heightened self-consciousness of the need for interdisciplinarity, but the challenge of working across disciplinary boundaries remained. An important conference took place at Brown in 1972. Dansgaard, who did not attend, sent in his results, which were included in the proceedings. Despite the productivity of the meeting, the tension was also evident. Two kinds of researchers found themselves in a room together for what felt like the first time. On the one hand were researchers who searched for “climate analogues,” past episodes that looked like the present climate and which could provide some indication of what was to come. On the other were scientists who wanted to determine the physical causes of those patterns—to get underneath the patterns and explain their origins. It was unclear which direction the field would go. The editors of the volume that came out of the conference thought it wise to allow both strands to flourish. “These two different approaches to research on climate change must run their own courses until such time as the validity of general theories is well demonstrated.”33 Time would tell which approach would win.34
Much was up for grabs. Where Louis Agassiz had posited a single ice age, and James Geikie and James Croll had argued for multiple ice ages, to researchers like Dansgaard and Broecker, the paleoclimate data indicated that climate was, in a certain sense, always changing. Seen in the context of a temperature curve that, however tentatively, extended back some 100,000 years, any climatic stability looked temporary. The old idea of a stepped climate, extending back to Lyell, was abandoned. In its place was a new way of thinking about climate as something that was, in a certain sense, undergoing constant change. It was becoming increasingly clear that, as Barry Saltzman put it, “there has always been so much variability of the climate that it seems doubtful that we can ever speak of a single climatic norm for the Earth. Judging from the past, the climate we are experiencing today is almost certain to be transient, giving way to something different in the future.”35 The new way of seeing the earth’s past—and by extension its future—as a constantly changing system represented a massive reorganization in the way scientists thought about the earth.
When Broecker had warned in 1975 of the possibility of global warming, he did so against a backdrop of fears about not global warming but global cooling. A string of colder than normal years prompted some scientists to worry that another ice age was imminent, as the natural global climatic cycle entered a cooler stage. The potentially catastrophic effects on the global food supply prompted front-page-level anxiety in 1972 against a backdrop of Soviet grain crises. Climate was changing, and which way it might change seemed, for a moment at least, to be up in the air.
The abrupt warming episodes revealed by Camp Century and other ice cores drilled in the late 1960s and 1970s came from the oldest ice, which sat at the bottom of the ice sheet. As a consequence, the records were often smeared or distorted by the pressure of the ice as it dragged along the bedrock—just where it was most critical to see it clearly. What was the nature of the earth’s changing climate in the past? How variable had it been? What patterns in its changes might be found? More ice cores were needed in order to solve a mystery only just coming into focus. Cooperation between American and European consortium projects proved difficult to secure. The science around ice cores was so exciting that each nation wanted a bite of the apple. In 1987, two different proposals emerged to drill in central Greenland. Far from discouraging this duplication of effort, Dansgaard recognized it as an important way to validate the results of each individual core. Much as Piazzi Smyth’s stereo-photographs had done more than a century earlier, the ensuing ice-core projects, named GRIP and GISP2, would provide a check on each other.36 Both projects got underway in 1989, just twenty miles apart from each other, in the very center of Greenland, where the ice would be thickest and hopefully the least distorted by sliding. While they failed to produce the really old climatic information researchers had been hoping for, these cores produced stunning results confirming the abrupt changes that earlier cores had suggested.
The data from these new Greenland ice cores further galvanized Broecker’s thinking. Once he’d been primed to see the changes in the Greenland cores, he began to look for similar changes in many other paleoclimate proxies. “One after another, other archives showed the same thing,” recalls Broecker. “Greenland led the way. No one would ever have thought that that had happened. If Dansgaard hadn’t, we’d probably have had a much harder time realizing these things.”37 Broecker named the abrupt changes captured in the Greenland cores Dansgaard-Oeschger (D-O) events because they were found both in ice cores that the Dane had helped unlock and for which Hans Oeschger had developed techniques for analyzing the gases trapped within. With additional confirmation from ice cores drilled in Antarctica, Broecker’s idea that many of the cycles in Greenland’s cores represented global changes, and that the D-O events were startlingly abrupt cycles of change, seemed to be confirmed (even if the short 120-year cycles were never found anywhere else).
FIG 7.7. The three musketeers of ice core research: Willi Dansgaard, Chet Langway of the CRREL, and Hans Oeschger, circa 1980.
The cause of these sudden events, both the D-O events and a series of even more dramatic shifts called Heinrich-Bond cycles, is still debated. Broecker’s best guess, and still a prominent hypothesis today, was that a shift in the way the ocean circulates caused by an influx of melted ice in the North Atlantic could have caused a dramatic drop in temperature. While the currents in the top 100 meters of the ocean are driven by winds, down in the depths of the ocean it is the density of water that determines its motion. When water at the poles cools, gets saltier, and sinks to the bottom of the ocean, it sets up a chain reaction that draws in warmer, fresher water to replace it. The cycle transfers huge amounts of energy around the globe and, Broecker realized, could be responsible for a very fast and dramatic shift in the climate if something were to disrupt it.38
The lessons of the ice cores were coming through loud and clear. Change came first, and from it all else followed. This new understanding of the planet, based on ice cores and other paleo sources, began to make its way—like the melting of ice in a glacier—into the deepest recesses of the growing network of national and international bodies dedicated to thinking about the earth as a system. Systems thinking and change-thinking went hand-in-hand—the changes revealed by the ice cores needed systems of interlocking mechanisms like the ones Broecker explored to explain them.
At the same time, a growing environmental consciousness made the changes happening in the present thanks to the activities of humans feel increasingly urgent. Not
only did human activity seem to be increasing in its pace, but it was increasingly evident that it had the potential to effect change on a planetary scale. Global change became the organizing principle of a series of influential workshops held in the early 1980s. This was the moment when all roads seemed to lead, as NASA put it, on a Mission to Planet Earth. Inspired in part by the new availability of observations of Earth taken from space in the 1960s and 1970s, these meetings captured the feeling of the time and would have a lasting influence on what came next.
“The earth is a planet characterized by change,” declared the participants of a NASA workshop on “Global Change: Impacts on Habitability,” held at Woods Hole in June 1982, “and has entered a unique epoch when one species, the human race, has achieved the ability to alter its environment on a global scale.”39 The long run of resource extraction and exploitation that had fueled most of human development was, it seemed, coming to an inevitable end. “The next valley,” warned the participants, “is now occupied.” The need for working across disciplines was paramount. “We have now reached a point where the boundaries of each discipline are overlapping, and the next step forward can only come from an interdisciplinary research program.”40 The next summer, another workshop took place, and with it came another impassioned plea for whole-earth thinking: “The earth is changing even as we seek to understand it,” reported the participants of a meeting funded by the International Council for Science to investigate the establishment of an International Geosphere/Biosphere Program, “in ways that involve the interplay of land and sea, of oceans, air, and biosphere.” Only by seeing the earth as a “single system” could there be any hope of understanding the problem.41 That statement of the need for a new way of seeing the earth had behind it the intellectual heft of Roger Revelle—the man who had first raised the alarm about increasing concentration of carbon dioxide.
The most influential report, however, came from NASA’s three-year-old Earth System Sciences Committee, chaired by Francis Bretherton, the theoretical oceanographer who had helped guide the design of the Mid-Ocean Dynamics Experiment. Recent developments, Bretherton wrote, had “converged to reveal to us—indeed, to force upon us—a new view of the Earth as an integrated system, whose study must transcend disciplinary boundaries.”42 At a meeting of the project’s modeling group at the incongruous location of the Snow Bunny Lodge, in Jackson Hole, Wyoming, team members alternated between skiing and sketching out a diagram showing “how all the pieces of the planet work.”43 One of the participants, caught up in the intensity of the discussion, momentarily forgot that the diagram in progress was being projected on the hotel room wall. He corrected an equation with marker directly on the wall, at some cost to NASA, who footed the bill to repaint it.
The Bretherton diagram, which took its name from the chair of the committee that produced it (though Francis Bretherton did not himself play a direct role in creating the diagram), was an attempt to capture the complex interactions between the various elements of an earth system. These feedbacks showed how each component of the system could affect and be affected by each other. Together, these feedbacks created the variability in climate that Dansgaard’s ancient ice cores had revealed. Notably, the diagram brought both the biogeochemical and the physical aspects of the earth system together—the living ocean and land and the swirling air and water upon which that life depended. Ocean dynamics was connected to both atmospheric physics and marine biogeochemistry, for example, while terrestrial ecosystems drew from the soil and global moisture while affecting tropospheric chemistry. At the center of it all sat global moisture. It was water that made Planet Earth, uniquely in the solar system, it seemed, a planet of change.44
FIG. 7.8. The so-called Bretherton diagram, an influential product of NASA’s 1986 Earth System Sciences committee, showing physical and biogeochemical systems linked together. Human activities are represented by a single box to the right.
While it wasn’t the first time anyone had considered it important to link the living earth with the physical earth, the diagram appeared at a moment of elevated self-consciousness. The 1960s and 1970s were crucial decades in the development of an awareness about climatic change that had affected the entire planet over a mind-boggling array of timescales, from decades to hundreds of thousands of years. Paleoclimatology was a broad church, bringing ice core, trees, mud, and pollen studies under the same roof. Broader still was the new science of climatic change which brought geologically minded practitioners seeking to understand the past ice ages together with more physically and chemically oriented earth scientists who were working to predict the effects of a human-induced rise in CO2.45 It may not be too much of an exaggeration to say that the big discovery of twentieth-century climate science was not that humans had the ability to change the climate but, as the tools of paleoclimatology were showing, that the climate itself was always changing.
In this context, it seemed more important than ever to try to show, as the Bretherton diagram did, how living things affected and were affected by the movement of water and heat through the system. To that end, the diagram also included a single box representing human activities, which affected the climate system via land use, pollutants, and carbon dioxide, and which was, in turn, affected by the outputs of the system in the form of climate change and terrestrial ecosystems. This little box represents a significant milestone in global change research. To be sure, it is as reductive a representation of human activities as it is possible to imagine. By squeezing all of human affairs into a literal black box, humanity seems to function as little more than a cog in the great mechanism of the planetary climate system. While this may have indicated a certain humility about human impacts on the planetary scale, it also demonstrated a strikingly blithe attitude toward the complexity of human activity. Looking back, it is hard not to read this box as an indication of the naiveté of those who came up with the diagram, vis-à-vis the social sciences. And yet, crude as it was, the inclusion of this box represented a sea change in the way climate scientists understood their science. By including human activities within the earth system, these scientists were not only acknowledging that human beings had the potential to alter the planet in extremely significant and consequential ways. They were also indicating that the tools of climate science alone would not be enough to describe the nature of the earth system, much less to design programs that could limit or reverse a warming trend.
The Bretherton diagram became famous among the influential group of scientists and administrators working within or alongside earth system programs at NASA, and as part of the International Biosphere/Geosphere Program established by the International Council for Science in 1987.46 Most fundamentally, the diagram conveyed in simple, graphical form a vision of the planet as a system—an engineer’s Earth made up of interlocking parts. The implication of the diagram was a pragmatic one: If the earth was a system, each part of that system could be treated as a modular element. In this way, the Bretherton diagram reduced the otherwise overwhelming complexity of a global climate system into a diagram that could be used, as an electrician might use a wiring chart, to diagnose crucial locations in the system—or tipping points—upon which study and intervention could be focused.
This vision of the planet was similar to Stommel’s ocean—a complex machine with many moving parts, but nonetheless a machine in which parts could be profitably studied independently of one another. It was a pragmatic and mechanistic vision of the planet suited to engineers. What the Bretherton diagram did not do was promulgate a vision of a living planet, or a planet which, Gaia-like, constituted a living being and in some sense acted to conserve life. Instead, it captured the vision of the planet as seen by a group of engineers and scientists who had been empowered by the national and international agencies they worked for to try to solve a problem. That problem was to understand the natural variability of the earth in time to be able to address the additional problem—crudely but significantly captured in the single b
ox—of the effect of human activity on the system. For all its reductionistic framing of human affairs, the report and associated diagram were a claxon announcing the existence of a new field in which human activity was inextricably linked with complex climate processes. The earth was not one thing, nor was it many things. It was, instead, “an integrated system of interacting components,” of which human beings were nominally, if only crudely, seen as forming a part.47 This was the beginning of a new field that called itself Earth system science. Each of the key words in this phrase was loaded with implications for how NASA, which had already positioned itself as a key knowledge-producing organization of this new science, saw the future of the sciences of the earth.
The vision of the earth generated by the Apollo space missions was not merely, or even primarily, a vision of unity and shared responsibility for a fragile living earth which Stewart Brand promulgated with his Whole Earth Catalog. The image of Earth from space was, in this sense, a planet calling out not for salvation or the development of a shared planetary consciousness, but for management. What was being managed was a system characterized by change. The discovery of change as an integral feature of the earth’s climate system was simultaneous with the development of methods for engineering or managing that change. To put this another way, the discovery of anthropogenic climate change was simultaneous with the discovery of natural climate change. The ability to recognize abnormal change was predicated on the vision of past natural change that the paleoclimatologists—not least the ice-core scientists—revealed. And the structure that scientists from a range of disciplines used to combine and compare these newly available observations was that of Earth system science. Change was built into this system, and the subtitle of the report was a “program for global change,” punning on the need for action to address humanity’s role in perturbing this system as well as the need to study change on a global scale. “The people of the Earth are no longer simple spectators to the drama of Earth evolution,” went the story, “but active participants on a worldwide scale.”48
