Birth and Death of the Holocene

It is just the latest of many climate phases of the Quaternary Period. The 103rd major shift in climate-driven global oxygen isotope values, to be precise, since the official-designated beginning of the Quaternary Period, 2.58 million years ago. And, many of those major phases, as we have seen, include dozens of climate oscillations far greater in scale than humans have witnessed since written records began. Nevertheless, it is our warm phase, that within which our civilization has grown, and hence it has been separated as a distinct epoch, the Holocene, a little over 0.01 of a million years long. Its counterpart is the Pleistocene Epoch, in which reside those other 2.57 million years of Quaternary time, and those other 102 major climate oscillations. Thus, we live—at least as far as formal geological nomenclature goes—in a privileged time. When this epoch began, Homo sapiens had already existed for some 150,000 years. As a species its prospects might not have seemed bright: this creature lacked anything terribly impressive in the way of claws or teeth or thick fur or armour. But by being ingenious at developing what one might describe as artificial claws and teeth—axes and spears and arrows—it could kill and eat mammals considerably larger than itself. In those early days, it might not have prospered, exactly, but it clung to existence, seemingly weathering at least one very bad patch, several tens of thousands of years ago, when its numbers dropped almost to extinction levels. It survived the climate oscillations of the late Pleistocene—the droughts and floods and episodes of bitter cold and killing heat—by adapting its behaviour or migrating as best it could. Its migrations from its place of origin, Africa, were on an epic scale. The many thousands of individual and collective stories of hope, fear, endurance, courage, tragedy, and (less commonly) triumph are all lost. What remains is the evidence that humans, by the beginning of the Holocene, had spread widely over Europe and Asia, ousting (it seems) their kindred hominin species, Homo neanderthalensis and Homo erectus.

The Glacial World

It is a scene of devastation, as far as the eye can see. Swathes of bleak landscape, with strewn boulders embedded in a sticky mass of sandy clay. Here and there are signs of a little more order—distinct spreads of gravel or patches of fine sand. Mostly, though, it looks as though every type of sediment, from fine clay to house-sized blocks, has simply been stirred together and spread across the land. Remove the crops and topsoil of gentle Leicestershire and Suffolk, or of central Germany or Kansas, and this is what lies beneath. Between the ordered sedimentary strata of the distant geological past and the ordered calm of the present is evidence of an only-just-elapsed catastrophe, and two centuries ago, when the science of the Earth was young, the naturalists of those days pondered on what it might mean. There were those like the young William Buckland, both Reader in mineralogy at Oxford and priest (he went on to become Dean of Westminster), who saw in it evidence of the biblical Deluge. Or Jean André de Luc, mentor to the wife of George III, who considered that the large blocks had been fired, like Roman ballista, from the mountains by some powerful but mysterious explosions. Or Sir James Hall, a savant of Edinburgh, who thought that the blocks had been carried into position by tsunamis, generated when large areas of sea floor (he supposed) suddenly popped up like blisters—he was clearly of an intellectually playful disposition. Or Leopold von Buch, who invoked catastrophic mudflows (one such, indeed, did take place in an Alpine valley, the Val de Bagnes, just after von Buch’s paper on this topic was published, when a natural dam burst, scattering mud and boulders far down the valley, and killing many people). But it was that extraordinary polymath, Johann Wolfgang von Goethe (a one-time Superintendent of Mines, if you please) who was among the first to sense what had been going on, when he associated the scattered blocks with a great expansion of the Alpine glaciers he was familiar with, and coined the term Eiszeit —the Ice Age.

Into the Icehouse

The frozen lands of the north are an unforgiving place for humans to live. The Inuit view of the cosmos is that it is ruled by no one, with no gods to create wind and sun and ice, or to provide punishment or forgiveness, or to act as Earth Mother or Father. Amid those harsh landscapes, belief is superfluous, and only fear can be relied on as a guide. How could such a world begin, and end? In Nordic mythology, in ancient times there used to be a yet greater kingdom of ice, ruled by the ice giant, Ymir Aurgelmir. To make a world fit for humans, Ymir was killed by three brothers—Odin, Vilje, and Ve. The blood of the dying giant drowned his own children, and formed the seas, while the body of the dead giant became the land. To keep out other ice giants that yet lived in the far north, Odin and his brothers made a wall out of Ymir’s eyebrows. One may see, fancifully, those eyebrows still, in the form of the massive, curved lines of morainic hills that run across Sweden and Finland. We now have a popular image of Ymir’s domain—the past ‘Ice Age’—as snowy landscapes of a recent past, populated by mammoths and woolly rhinos and fur-clad humans (who would have been beginning to create such legends to explain the precarious world on which they lived). This image, as we have seen, represents a peculiarly northern perspective. The current ice age is geologically ancient, for the bulk of the world’s land-ice had already grown to cover almost all Antarctica, more than thirty million years ago. Nevertheless, a mere two and a half million years ago, there was a significant transition in Earth history—an intensification of the Earth’s icehouse state that spread more or less permanent ice widely across the northern polar regions of the world. This intensification— via those fiendishly complex teleconnections that characterize the Earth system—changed the face of the entire globe. The changes can be detected in the sedimentary strata that were then being deposited around the world.

Between Greenhouse and Icehouse

There is a celebrated Flemish painting by Pieter Bruegel the Elder in the Kunsthistorisches Museum in Vienna. It depicts the age-old battle between Carnival and Lent. Carnival—a time of high spirits, led in this vision by a fat man on a beer-barrel, carousing and brandishing a pig’s head on a spit—is opposed by Lent, deflating the happy excitement and bringing in a time of sobriety and abstinence. Bruegel’s understanding of these opposed rhythms of rural life in the sixteenth-century Netherlands was acute: he was nicknamed ‘Peasant Bruegel’ for his habit of dressing like the local people, to mingle unnoticed with the crowds, all the better to observe their lives and activities. Bruegel’s vision of the age-old rhythm of life, in the form of an eternal oscillation between two opposing modes, may be taken to a wider stage. From the late Archaean to the end of the Proterozoic, the Earth has alternated between two climate modes. Long episodes of what may be regarded as rather dull stability, best exemplified by what some scientists refer to as the ‘boring billion’ of the mid-Proterozoic, are punctuated by the briefer, though more satisfyingly dramatic, glacial events. This alternation of Earth states persisted into the last half-billion years of this planet’s history—that is, into the current eon, the Phanerozoic. If anything, the pattern became more pronounced, as if it had become an integral part of the Earth’s slowly moving clockwork. There were three main Phanerozoic glaciations—or more precisely, there were three intervals of time when the world possessed large amounts of ice—though in each of these, the ice waxed and waned in a rather complex fashion, and none came close to a Snowball-like state. Thus, these intervals often now tend to be called ‘icehouse states’ rather than glaciations per se. Between these, there were rather longer intervals—greenhouse states—in which the world was considerably warmer; though again, this warmth was variable, and at times modest amounts of polar ice could form. Of the Earth’s Phanerozoic icehouse states, two are in the Palaeozoic Era: one, now termed the ‘Early Palaeozoic Icehouse’ centred on the boundary between the Ordovician and Silurian periods, peaking some 440 million years ago; and a later one centred on the Carboniferous and early Permian periods, 325 to 280 million years ago.

Earth as a Snowball

Our attempts to reconstruct the climate of the distant Archaean in Chapter 1 might seem a little like reading a volume of Tolstoy’s War and Peace recovered from a burnt-out house. Most of the pages have turned to ash, and only some scattered sentences remain on a few charred pages. The Proterozoic Eon that followed began 2.5 billion years ago, thus is not quite so distant from us in time. We know it a little better than the Archaean—at least a handful of pages from its own book have survived. And this book is long—the Proterozoic lasted nearly two billion years. This is as long as the Hadean and Archaean together, and not far short of half of Earth’s history. Like many a soldier’s account of war, it combined long periods of boredom and brief intervals of terror—or their climatic equivalents, at least. The latter included the most intense glaciations that ever spread across the Earth. Some of these may have converted the planet into one giant snowball. The earliest traces of glaciation on Earth are seen even before the Proterozoic, in rock strata of Archaean age, 2.9 billion years old, near the small South African town of Pongola. These rocks include sedimentary deposits called tillites, which are essentially a jumble of rock fragments embedded in finer sediment. The vivid, old-fashioned term for such deposits is ‘boulder clays’, while the newer and more formal name is ‘till’ for a recent deposit and ‘tillite’ for the hardened, ancient version. Many of the ancient blocks and boulders in the tillites of Pongola are grooved and scratched—a tell-tale sign that they have been dragged along the ground by debris-rich ice. This kind of evidence is among the first ever employed by scientists of the mid-nineteenth century, such as Louis Agassiz and William Buckland, to tell apart ice-transported sediments from superficially similar ones that had formed as boulder-rich slurries when rivers flooded or volcanoes erupted. Ice, then, appeared on Earth in Archaean times.

The Last Greenhouse World

Ellesmere Island today is a destination only to a particular type of tourist: rich enough to afford the most exclusive of package tours, and hardy (or ascetic) enough to yearn for the spiritual purity of an icy wasteland, rather than the sensual pleasures of a Mediterranean seashore. The island is large—twice the size of Iceland. Yet, its largest settlement, Grise Fjord (or, in the local Inuktitut language, Aijuittuk—‘the place that never thaws’) has but some 140 souls—while its smallest, Eureka, bizarrely but somehow appropriately, was listed in 2006 as having precisely none. Squeezed between northern Canada and Greenland, Ellesmere Island is well within the Arctic Circle, and its northern tip is not much more than 700 kilometres from the North Pole. A land of mountains, fjords, glaciers, and ice-fields, it has been dubbed ‘the horizontal Everest’. In the short summer, the Sun never leaves the sky, and temperatures might, on brief sunny days, exceed 20 °C. When the winter months come, the Sun never rises, and temperatures drop below –40 °C. The only tree that can grow, here and there, is the dwarf Arctic willow, usually knee-high, while the mammals—musk ox, caribou, seals—have attracted Inuit hunters for some 4,000 years (and more lately, Viking explorers too). It was the handsomely whiskered First Lieutenant Adolphus Washington Greely (1844–1935) of the United States Army who discovered the ancient forest that had lain there, deeply buried, for fifty million years, a forest as expressive of bygone glories as any Arthurian legend. As part of the First International Polar Year, in 1882, he had been given charge of a party of soldiers, and tasked with making magnetic and meteorological measurements in the far north. They explored the Greenland coast, and traversed Ellesmere Island from east to west, stumbling upon the forest in the course of these journeys. The voyage killed most of his men, and almost killed him. When the relief crews arrived, two years late (the expedition had not been ideally planned) only six men, including Greely, were left alive. They had survived—just—by eating their own boots and, it seems, the remains of their dead colleagues.

Primordial Climate

We are lucky, on Earth. We are lucky because we—as complex and self-aware organisms—are here. We are sustained, given air to breathe, and water, and food, by a very ancient planet: a planet past its midpoint, a planet that is nearer death than birth. Our species is a latecomer. It took some three billion years to bridge the gap from a single-celled organism (originating in this planet’s youth) to a multicellular one, and then a little over half a billion more to arrive at the diversity of species on Earth today, including Homo sapiens . In all this time, the chain of life has remained unbroken. The Earth has been consistently habitable, with an atmosphere, and land, and oceans. Since life began, our planet has never been truly deep-frozen, nor have the oceans boiled away. The Earth is the Goldilocks planet. One recalls, here, the children’s story, where the young heroine of that name walks into the house of the three bears, and in their absence tries out successively their bowls of porridge, their chairs, and their beds. Each time the first and second choices are too hot or cold, large or small, hard or soft—and the third choice is just right . The Earth has been, so far and all in all, just right for life: not just right at any one time, but continuously so for three billion years. There have, though, been some close calls: times of mass extinction. But, life has always clung on to bloom once more. That makes the Earth’s history more remarkable than any children’s story. Other planets have not been so lucky. Mars seems to have been a planet with an appreciable atmosphere, and—at least intermittently—running water over its surface, and may even have begun to incubate life. But the atmosphere was stripped away by the solar wind. Its early lakes and rivers became acid, charged with sulphates. Then, most of the water evaporated and was carried off into space; what little was left became locked away as permafrost and in thin ice-caps. Mars does have weather, including spectacular, planet-wide dust-storms.

The Anthropocene Begins

What is the future for the planet, and for climate? Gazing into crystal balls is a pastime that humans have a fascination for. It is also one in which they have a dismal record. A generation or two ago, there were predictions of cities made of glass or plastic, clothes of aluminium or asbestos, flying cars, the fall of nationalism and the rise of world government, the demise of religion, and robots taking over our tasks and ushering in an age of universal leisure for all. So much for all that. When we move, then, to the almost limitless complexities and intersecting feedbacks of Earth’s climate system, one might be forgiven for throwing in the towel straight away. This is a system, we must eternally remember, of which we have only partial understanding, even as we see today’s weather patterns spin off from it. Go back into the deep past, and that climate and those long-vanished weather patterns leave only traces in strata that are, in large part, invisible to the naked eye. And of the future, of course, we have no samples, no deep boreholes, no fossils: the canvas is blank—indeed, as yet there is no canvas at all. Yet, from those ancient stratal traces we can construct a picture of events that is both vivid and (within our levels of uncertainty) true. There is no reasonable doubt that 20,000 years ago massive ice sheets spread out from the poles—or, that 125,000 years ago there was a climate on Earth as temperate, within a degree or so, as the one we enjoy today. So, there are patterns, real patterns that we can use as guides to help us try, with the utmost caution and scepticism, to create pictures, scenarios, sketches of the climate of the future. One might imagine alternative futures—or create them—particularly with the help of those elapsed realities. For instance, one might take that striking five-million year slice of climate history put together by Lorraine Lisiecki and Maureen Raymo (see Ch. 8 ).

The Last of the Warmth

The Pan-American Highway rises in the far north of the Americas at Prudhoe Bay, Alaska and, except for a small gap in Panama, runs the entire length of the two American continents to terminate at Ushuaia in southernmost Argentina. Along its way it travels nearly 50,000 kilometres, from the polar landscape of the far north, through the boreal forests of Canada, the temperate plains and hot deserts of the USA and Mexico, and on further into the tropical zones of Central and South America, until it reaches the sub-polar landscape of Tierra del Fuego. The American landscape was not always like this. To travel along the Pan-American Highway some three million years ago, in the Pliocene Epoch, would have revealed a different world. It was a little warmer than our own. Far away, the Greenland ice sheet covered only a small part of that land mass. At the other end of the world, there was less ice covering the West Antarctic than we are familiar with today. Going south, from Prudhoe Bay along the Pan-American Highway of the Pliocene, there was none of the scrub tundra now seen by the ice road truckers. Forests then extended far to the north, covering vast areas of northern Canada and Alaska, and draping the coastal margins of Greenland. They stretched, too, into Siberia, a mass of forest extending thousands of kilometres from Norway to Kamchatka. There was almost no tundra in the north, except for a few patches in Greenland and on the far northern extremities of Siberia. Instead the polar sun rose across that well-nigh endless green Pliocene forest. Such a prehistoric journey south along the Pan-American Highway would take one across the grasslands of temperate America. These are truly ancient, having been long established even then. Patterns of seasonal temperature and rainfall, though, allowed forests to grow where none are present today. There were no humans to cut down the trees or hunt the animals that lived in the forests. There were no Great Lakes either, for no northern ice had grown yet, to scour out their floors and fill them with melt water.

The Ice Returns

Among the marvellous fossils retrieved from Seymour Island—a thin strip of land near the northern tip of the Antarctic Peninsula, is a giant penguin that lived forty million years ago. Called simply ‘Nordenskiöld’s giant penguin’, after one of the great early Antarctic explorers, it is not the kind of animal you would like to meet down a dark alley late at night. Standing at nearly the height of an average man and with a long beak to match, it was much taller than the modern Emperor penguin. Nordenskiöld’s giant penguin was a portent of a cooling climate. Its bones—many of which now reside in the collections of the Natural History Museum in London—have been found within the Eocene mudrocks of Seymour Island. This island holds a special affection for palaeoclimatologists. It was here, in the late nineteenth century, that some of the first Antarctic fossils were found. These give a glimpse of what that continent was like before it became an icy wilderness. Seventy million years ago, wide Cretaceous forests, inhabited by dinosaurs, flourished in Antarctica. Even as little as fifty million years ago, the kinds of tree and shrub that thrive today in Patagonia once covered the hills and slopes of the mountainous Antarctic Peninsula. Their fossilized remains are found in the rocks of Seymour Island. In the summer months the island is warmed by the faint Antarctic sun, its surface melting like a chocolate cake at a picnic. The resulting muddy quagmire is worth persevering with. It yields the most wonderful fossils of ancient plants, among them Auracaria, the warmth-loving monkey-puzzle tree. Antarctic scientists have another, ulterior motive for visiting Seymour Island; those in the know are aware that the Argentine Base at Marambio is famous for its steaks. They are the best on the continent, and everyone hopes to get invited in. How then did Antarctica change from a continent of lush forests to a frozen wasteland? After all, this part of ancient Gondwana had already drifted over the southern polar region during the Cretaceous. Thus, Antarctica is not simply a frozen wasteland because it lies at the Pole.