Cold

by Bill Streever

  Here in the Scottish Highlands, pipkrakes have sculpted steps into the slopes. These steps are anything but subtle. Pipkrakes lift the smaller grains of soil away from larger pebbles and rocks. At a slower pace, pipkrakes lift the pebbles away from the rocks, and at an even slower pace, they lift the smaller rocks away from the bigger rocks. In Canada, pipkrakes have lifted rocks weighing upward of one ton. On steep slopes with scattered vegetation, the fine soil pushed to the top blows away. The pebbles tumble downslope. The rocks settle back into place. All of this occurs at differing paces. The end result can be solifluction, the slow and irregular sliding of a hillside. Under the right conditions of soils and slopes and moisture, solifluction leaves what looks like a regular pattern of cryoturbation steps. These steps sometimes form diamond patterns on the slopes, but they also form long parallel terraces, each progressively lower platform a step away from and a step below the next. It appears as if some bored druid or some Iron Age tribe had carved steps up the sides of these mountains.

  Moving downward, we take a shortcut across scree, loose rock and gravel splintered by ice. On scree, it is difficult to remain upright. My companion, her hands still numb from the Raynaud’s, is afraid of falling, rightfully scared because her numb hands will be little help in breaking the fall. I scurry ahead. Below the scree, I find a hollow of deflated soil that shaves a notch off the wind and nap while waiting for her to catch up.

  Recognition of the Pleistocene Ice Age is a surprisingly recent phenomenon. Two hundred years ago, no one would have suggested that ice sheets many miles thick had once covered most of Britain, most of Norway and Switzerland, New York City and Boston. People knew of ice sheets in Greenland, and they were learning about the ice of the far north. James Cook and others had sailed far enough south to have been stopped by Antarctic ice. They knew of alpine glaciers, and they knew of the huge boulders scattered around the lowlands — the erratics sitting on top of soil, with no hint of how they might have gotten there, miles from the nearest source of this sort of rock, far too big to carry. There was some thought that the boulders had been carried there by ice, but floating ice during the biblical Flood rather than vast ice sheets hundreds or thousands of feet thick and stretching hundreds of miles to the north. As for other signs of glaciation — the strange hills of soil that would become known as moraines, the baskets of eggs called drumlins, and the odd scoring often found across the faces of exposed bedrock — they were easy enough to overlook and ignore.

  Charles Darwin, after learning about ice ages, chastised himself and others for missing the obvious. “I had a striking instance how easy it is to overlook phenomena,” he wrote, “however conspicuous, before they have been observed by anyone…. Neither of us saw a trace of the wonderful glacial phenomena all around us; we did not notice the plainly scored rocks, the perched boulders, the lateral and terminal moraines.”

  The observer who pointed out the obvious was Louis Agassiz, a Swiss scientist. As a student in Munich, he cataloged fish from the Amazon for one of his professors. This did not mean traveling to the Amazon itself. Agassiz traveled instead through pickled samples, sketching whole fish and scales and bones. He explored the vistas of a laboratory bench and named the fish that he encountered in those wanderings. In 1829, while still a student and despite never having been to Brazil, he published Brazilian Fishes, making his first mark as a naturalist. Ten years later, by then widely recognized for his work, Agassiz vacationed near Bex in the Swiss Alps. There the geologist Jean de Charpentier ran a salt mining operation. Charpentier, in part through his association with an engineer named Ignatz Venetz, was convinced that the Swiss glaciers had shrunk over time. He took Agassiz to look at boulders along the faces of existing glaciers, then showed him others farther downhill, dumped there sometime in the past. They were of a kind of rock that might not occur for miles around, and as often as not they were stuck precariously on valley walls or left standing in odd positions. They were erratics. The two men also saw curved beds of gravel and earth — moraines — along the faces of glaciers that matched those farther downslope, and they saw grooves and scratches cut into bedrock.

  A year later, in 1837, Agassiz presided over a meeting of the Natural History Society of Switzerland. In his introductory speech, when he was expected to talk about fossil fish, he sprang the idea of an ice age. Although Charpentier knew that the alpine glaciers had once covered more of the Alps than they currently did, Agassiz went further. He described a sheet of ice extending from the North Pole to the Mediterranean. He knew that some would view this as harebrained. “I am afraid,” he said, “that this approach will not be accepted by a great number of our geologists, who have well-established opinions on this subject, and the fate of this question will be that of all those that contradict traditional ideas.”

  Three years went by before Agassiz published Études sur les Glaciers. “In my opinion,” he wrote, “the only way to account for all these facts and relate them to known geological phenomena is to assume that… the Earth was covered by a huge ice sheet that buried the Siberian mammoths and reached just as far south as did the phenomenon of erratic boulders.” He was wrong about many things. “The development of these huge ice sheets must have led to the destruction of all organic life at the Earth’s surface,” he wrote. “The land of Europe, previously covered with tropical vegetation and inhabited by herds of great elephants, enormous hippopotami, and gigantic carnivore, was suddenly buried under a vast expanse of ice, covering plains, lakes, seas, and plateaus alike.” In fact, the Ice Age was not sudden, it did not bury all of Europe under ice, and it did not destroy all organic life, but his general premise was correct. Made famous by this premise, he moved to the United States to take a professorship at Harvard. He died in 1873 and was buried in Cambridge, Massachusetts, under a granite erratic shipped from a moraine in Switzerland. Its transport across the Atlantic made it the most erratic of erratics. By that time — nearly six decades after the Year Without Summer and Shelley’s Frankenstein, a few years before Greely and a handful of his men barely survived their experience in the Arctic, and fifteen years before the School Children’s Blizzard — the existence of a great ice age was considered a fact. The world knew of the Pleistocene glaciations.

  Speculations about the cause of the Ice Age abounded. James Croll, a self-educated Scotsman who had run a tea shop and worked as a millwright before becoming known for his scientific contributions, wrote, “We may describe, arrange, and classify the effects as we may, but without a knowledge of the laws of the agent we can have no rational unity.” Some thought that the sun might change over time. Others wondered if the earth might occasionally drift through cold regions of space. Some thought that the earth might have somehow rolled, so that the poles were at the equators. But Croll built his work on a proposal put forward in Charles Lyell’s famous Principles of Geology in 1830. Lyell had skeptically suggested that someone should look into the possible influence of astronomical conditions. Someone, Lyell had suggested, should do the math. Croll decided that he was the someone for the job.

  This was in a time before computers, but it was known that the earth’s orbit was elliptical and that the ellipse changed over time. As other planets tugged at the earth, its orbit could become more round or more stretched. When its orbit was stretched, the earth would be farther from the sun during the winter and might receive less light. It was also known that the earth’s axis was tilted; the earth leaned at an angle to the sun, making winter days shorter than summer days. More important for Croll, it was known that the earth’s axis wobbled over time. And Croll knew that periods of extensive glaciation during the Ice Age had in fact come and gone and come and gone through repeated cycles, that the Ice Age was not a single event but rather a pattern of events that had to be explained. Building on the work of others, he looked for a cause that could explain these cycles of relative cold and relative warmth, or more correctly, relative cold and relatively less cold. He saw that the combination of changes in the earth’s
orbit and a wobbling axis would lead to at least mild changes in the heat coming into the Northern Hemisphere. He realized that slight cooling could mean more snow. He knew snow to be a nearly perfect reflector of heat. On a cold, clear day, warmth from the sun that hits snow is reflected back into the air and lost. And he believed that as glaciers grew, wind patterns would change and that this could lead to changes in oceanic currents.

  Croll had many of the facts correct, but his timing was off. As geologists learned more about the coming and going of cold, they saw that the cycles from Croll’s work did not match what they saw on the ground. Croll’s math was out of kilter with the earth’s behavior, and his ideas were discarded. But, as sometimes happens in science, his ideas were later resurrected. Milutin Milankovitch, a Serbian mathematician and engineer known as an authority on the properties of concrete, decided that his talents could best be used in developing a mathematical theory of the earth’s climate. Working through the chaos of the First World War, spending part of that time as a prisoner of war, using new information on just how much energy the sun delivers to the earth, Milankovitch reworked what Croll had started. In 1920, he wrote A Mathematical Theory of the Thermal Phenomena Produced by Solar Radiation, a book with a title that doomed it to limited circulation. But among the few readers of the book was Wladimir Köppen. Köppen’s daughter was married to Alfred Wegener, the man responsible for the theory of continental drift, who would later, in a historical footnote, die on the Greenland ice. Köppen and Wegener realized that Milankovitch’s work could be extended to the distant past. They wanted him to run the calculations to six hundred thousand years before the present. The results were consistent with the history of the Ice Age as it was then understood. In 1941, Milan kovitch published another book with another catchy title, Canon of Insolation and the Ice Age Problem. The Second World War broke out. The manuscript was at the printer when the Germans invaded Yugoslavia. The printing shop was flattened, but the manuscript survived more or less intact and was printed and distributed during the German occupation. From the memoirs of Milankovitch: “Our civilized existence had disintegrated into a life of hard grind.”

  Like Croll’s work, Milankovitch’s efforts were eventually dismissed. In a repeat of Croll’s situation, new evidence suggested that the timing from Milankovitch’s models did not match what had happened on the ground. But the parallel with Croll extended to the resurrection of Milankovitch’s work. In 1976, a trio of scientists showed that the on-the-ground record matches a set of overlaid astronomical cycles: changes in the earth’s orbit over a hundred-thousand-year cycle, changes in the earth’s tilt over a forty-three-thousand-year cycle, and wobble of the earth’s tilt over a twenty-thousand-year cycle combine to correspond to some degree with what is known about climate history during the hundreds of thousands of years of the Pleistocene Ice Age.

  Circle the earth in late winter, and what do you see? In the Northern Hemisphere, half the land is covered with snow, and a third of the ocean is frozen. We are in the midst of a warm spell, we are worried about global warming, but the fact remains that even in summer, whole regions remain covered with snow and ice. An area of land five times the size of Texas is in the permafrost zone, underlain by permanently frozen ground. If the mathematical predictions are right, we are at the tail end of an interglacial period, dramatically increasing its warmth with greenhouse gas emissions. But nevertheless we remain in what a geologist one hundred thousand years in the future would clearly recognize as part of the Pleistocene Ice Age. If the Ice Age does not die a natural death, and we do not kill it with greenhouse gases, renewed glaciation will come within a few thousand years.

  This Ice Age at its worst, when what would become New York City was under ice, and woolly mammoths strolled over what would become great cities, was not as horribly cold as it might have been. For truly cold weather, one has to go back seven hundred million years, back to the time of Snowball Earth.

  It is September twenty-third. Back in Anchorage, leaves on the birch trees have turned yellow. It has been raining while I was away. It is raining now. Everything is soaking wet at the lower elevations. Everyone is speculating about a very snowy winter. “A few degrees colder,” people say, “and this would be snow.” In the mountains, at elevations above the road system, snow already covers the ground. A certain class of women, not quite able to wait for the really cold weather, already wears fashionable full-length coats. People are putting on their spiked snow tires. The spikes click and clack as they contact wet pavement.

  My pet caterpillars, Fram and Bedford, stayed in the refrigerator while I was in Britain. They seem a bit subdued but otherwise fine. I give them fresh willow leaves to eat. They crawl on the leaves, but they have no appetite. For them, it is close to winter. It is nearly time to freeze up.

  Friends come to dinner. One of them brings me a copy of the Anchorage Daily News, dated September ninth. I had been driving on the ninth, crossing Scotland’s glacier-formed landscape. “Lodge Owner Trapped by Lawnmower Dies,” the headline says. Andrew Piekarski had been cutting the grass at his lodge thirty miles from Anchorage. He was on a riding mower. Nighttime temperatures in his area were dropping into the thirties. On a small hill, the mower toppled and pinned him to the ground. He lay under the mower all night, unhurt but trapped and slowly freezing to death. A state trooper was interviewed. “He couldn’t get it off his legs,” the trooper reported, “and he couldn’t get out from under it and he died from exposure, from hypothermia.” As Piekarski slowly froze, there would have been time for existential thinking. Before the hypothermia slowed his thinking, before the stupor, before the hallucinations of warmth, he must have considered the absurdity of his situation, the odd reality of deadly hypothermia before the end of summer.

  I show off Fram and Bedford to my dinner guests. The two caterpillars remain listless. It is clear that they are ready to sleep. I have two jewelry boxes, and I line each with willow leaves. I put Fram in one box and Bedford in the other. After a brief ceremony, I put them in the freezer, behind the frozen peas and under a slab of salmon, condemning them to a snowball cocoon for winter.

  Reconstruction of past climates is not a simple business. Even today, three centuries after Daniel Fahrenheit developed the mercury thermometer, understanding recent global climate change leads to controversy. Which thermometers are reliable? Do thermometers near cities reflect local warming or real patterns in global temperature change? Do the number of measurements taken in the Northern Hemisphere outweigh and overwhelm those taken in the Southern Hemisphere? Is the average temperature the important number? Or the hottest day? Or the coldest day?

  There are dozens of ways to reconstruct past climates. In western Europe, the timing of the grape harvest has been recorded for hundreds of years. Late harvests reflect cold, wet summers. Emmanuel Le Roy Ladurie, author of Times of Feast, Times of Famine: A History of Climate Since the Year 1000, wrote, “Bacchus is an ample provider of climatic information. We owe him a libation.” Where records exist, grape harvest data can be backed up by grain harvest data. Another climate historian visited forty-one art museums to look at more than six thousand paintings dating from the beginning of the Little Ice Age. In the paintings, he saw a slow increase in cloudiness from the late 1400s until about 1750. Low clouds settled in after 1550 but cleared away around 1850.

  Much can be said without written history or paintings. Tree rings can be measured, often stretching back a century or more. Corals, too, leave growth rings. In both cases, wide rings indicate good growing conditions, while narrow rings indicate cold. The chemical composition of ice cores says something about the climates when the ice formed. Cores pulled from Antarctic ice can span four hundred thousand years. Past sea levels say something. When it is cold, water is locked in ice, and sea levels drop. River channels extending out onto today’s continental shelves speak of lower sea levels during past cold snaps and glacial periods. Beach terraces on hillsides speak of higher sea levels and past warm spells and inter
glacials.

  And there is geology. There are erratics and moraines. There is bedrock scored by the action of ice. There are fossils of animals and plants with known temperature tolerances. There are sand wedges, originally formed as long-ago ice wedges, identical to those of today’s Arctic. There are dropstones — stones carried by ice over a sea or a lake and dropped to the bottom when the ice melts, there deforming soft mud, leaving an unmistakable sign of ice and cold. There is topographical graffiti left by massive flooding that followed warm spells and broken ice dams. The Channeled Scablands of eastern Washington State were scrawled across the landscape when the ice dam that formed Lake Missoula melted thousands of years ago. Water from the lake ripped across what is now the northwestern United States. For a few hours, water flowed at a rate something like sixty-five times that at which today’s Amazon River flows. During these few hours, soil disappeared and boulders were suspended like particles of clay. Gouges hundreds of feet thick were cut into the earth.

  There is this inescapable fact: the farther back in time one goes, the more speculative climate reconstruction becomes. It is easy enough to find signs of the most recent glaciations of the late Pleistocene Ice Age, to see hints of its many glacial and interglacial swings, but dip farther into prehistory, and records are obliterated. Rocks are worked and reworked, clues are muffled, and fossils are scarce or even absent. The earth has been around for something like four and a half billion years. It took the first billion years for life to invent itself. This was simple life, more like a living slime than something biblical. It took another three billion years for more complex life to form, the kind of life that leaves abundant fossils, the kind of life with hard shells and bones and exoskeletons. Throughout this time, continents drifted. Tectonic plates rode about like loose barges, occasionally colliding, one forced downward and one upward. And there was erosion from wind and water and ice. The rocks enshrining the planet’s history were recycled, cast away like dusty books remaindered from a publisher’s warehouse.