History on Ice
Updated: May 31, 2021
How climate science has staked its claim in history— and what it leaves out.
In 1969, researchers announced that they had obtained ‘one thousand centuries’ of climate record from a core of ice one foot in diameter and nearly one mile long that had been drilled from the top to the very bottom of the northern Greenland ice sheet. Using a bit of scientific sleight of hand, the researchers, led by Willi Dansgaard, had found a way to use measurements of the ratio of oxygen isotopes in the ice to infer the temperature at the time that ice had fallen as snow. The tale told by the ice was an unexpectedly dramatic one. When traced on a graph, it revealed a series of ridged oscillations, a bit like the skyline of New York City. Closer examination revealed what seemed to be regular cycles of certain duration—at 13,000, 940 and 120 years. Like a recently discovered cache of old manuscripts, the ice seemed to be telling a story about how the climate worked that begged further study and explanation.
Precisely what the story of past climate is, and what import it has for the future, is a question not only for scientists. Historians also have an important role to play in framing our understanding of the past in relation to the current challenges posed by climate change and the future that our decisions today will bring about.
Climate scientists and historians have much in common. Both are intensely interested in understanding the dynamics of what happened in the past—in determining which causes accounted for which effects—so that they might better understand the present and even the future. Both work hard to find new records of the past. Sometimes their evidence looks very similar; climate scientists excavate old ships’ logs and weather records from musty shelves, the historian's domain, to put them in dialogue with other climate records. But much of the evidence used by climate scientists must be extracted from the most remote and forbidding environments on Earth. In search of proxy records of past climatic conditions, researchers climb arid mountains to core into slow-growing, tough trees whose alternating rings tells stories of long-ago rainfall and drought. They haul up samples of muddy ocean sediment from deep seas to scrutinize traces of former atmospheres. Or they spend months in sub-zero temperatures, drilling frozen columns of ice out of the mile-thick ice sheets of Greenland and Antarctica.
It's worth it to climate scientists to make these efforts to gather data from the past because it is difficult—not to say impossible—to experiment on the climate in the present. The global scale and interconnectedness of the Earth’s systems mean any physical experiments are necessarily partial. This is the reason so much time and energy is spent on climate modelling, which serves as another way to fill the experiment-deficit of climate science. For climate scientists who seek to understand the mechanics of climate, the past is a laboratory for theoretical experiments. There’s plenty of both space and time with to test assumptions and seek patterns, just as the Greenland ice core allowed researchers to do. This is important because climate is a system that reveals its true nature through time and across space. The deeper the past is, the more useful the experiment. The past record, fragmentary as it is, also has the benefit of being a faithful simulation; it is the only model we know to be completely authentic, tuned exquisitely to the physics of the real world because it is the real world. With ice cores and mud cores, tree rings and stalactites, ancient air bubbles and fossilized pollen, scientists have been able to turn the Earth’s very form into master-histories written of the Earth, by the Earth. In this way, they have translated ‘mere’ matter into a messenger of past dynamics, making still and silent things speak and move once more, like old film footage for which a new projector has been constructed.
I admit to feeling wonder in the face of such skilful and persistent scientists, and in the light of their hard-won archives. But it’s feeling that soon gives way to skepticism about the true similarities between climate science and history. It’s not that the ice and all the other remarkable proxy records can’t teach us a great deal. But they can’t teach us everything we need to know about human history and all that history implies for the future. It’s too easy to forget that our assumptions and our skills are always at work in determining what counts, in our histories of the earth’s climate, as global, as continuous, or as highly-resolved. And this is to say nothing of the ends—such as predicting future climates—to which these climate histories are put, ends which are inevitably shaped by our values, our anxieties, our ambitions.
Scientists tend not to be as explicit about the assumptions their histories are based on—and the aims for which they are intended—as we might want them to be. And though historians are no more exempt from making assumptions than any other human beings, it is part of our training to make those assumptions explicit. When we make historical claimes or arguments, we work to make our own perspective, and that of intervening generations, as clear as possible. History of science has a special role to play in highlighting the way that knowledge itself is generated, under conditions of both so-called normal science and of contestation and mistrust, which has characterized much of the recent history of climate science. In this sense, the story of history remains always unfinished because it is always shaped by the moment in which it is being written. When climate scientists write their histories of the planet, on the other hand, they aim to produce a singular history which, if necessarily fragmentary, approaches the limit of the truth of what happened.
I fear that the climate scientists’ version of Earth history has begun to dominate other versions—and visions—of what history is. This can be seen in the current attempt to identify a chronological starting point for the Anthropocene. There’s little agreement so far; 1610, 1789 and 1945 have all been mooted for various reasons. Regardless of the disagreement over specific dates, many commentators (within both scientific and humanities disciplines) agree that it makes sense to look for a physical location in the material record of the planet of the moment when humans became planetarily dominant. It seems a peculiar and even dangerous irony that in this moment of extreme self-consciousness about the human causes of climate change, so many seem inclined to reduce human history to the merely material. The Anthropocene dating push reveals a strange blind spot that characterizes much of this new way of thinking about the earth: Even as commentators assert the exceptional scale and force of human technology and the science from which it is derived, they fail to recognize the significance of human-meaning making.
As wonderful as the knowledge we can gain from the ice is, and as impressive as the skills of those who extract it are, I’d rather not go there, conceptually speaking. We won’t find the answers to our most pressing questions in the ice, no matter how hard we look. I say this with full respect for and appreciation of the work of climate scientists. We need to generate as much knowledge as we possibly can about how the Earth’s climate works. I just don’t want to cede the very idea of history to climate scientists and their way of working. Our understanding of the past can never be finished in the same way that we can never date the beginning of the Anthropocene. We are always standing on our own skis—heading into the past from whatever mountain we find ourselves standing on today.
Sarah Dry (St Johns) is a writer and historian, and a 2003 Gates scholar in the History and Philosophy of Science.