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The Anthropocene Rupture

A rupture in Earth history

First, the science. The Geological Time Scale divides the Earth's history into ages, epochs, periods, eras, and eons in ascending order of significance. The International Commission on Stratigraphy is considering officially adding a new epoch, the Anthropocene, to the scale. Stratigraphers - geologists who specialize in the study of rock layering - are perhaps the most tradition-bound members of a somewhat conservative profession; yet their decision has the most radical implications.

The principal reason for Earth scientists' belief that the planet has shifted out of the previous epoch, the Holocene, lies in the rapid increase in the concentration of carbon dioxide in the atmosphere and its cascading effects throughout the Earth System. The system-changing forces of ocean acidification, species loss, and disruption of the nitrogen cycle add to the case. Human disturbance of the climate system is now detectable from the beginning of large-scale coal burning at the onset of the Industrial Revolution. The rise in atmospheric concentrations of carbon dioxide was gradual for the next 150 years, but became steep after World War II. Now a range of indicators shows sharp and unambiguous human disturbance to the Earth System from the end of World War II.1 The post-war period stands out, writes Earth scientist Will Steffen, "as one of the most remarkable in all of human history for its rapidity and pervasiveness of change."2 Other Earth System scientists express it a little differently: "The last 60 years have without doubt seen the most profound transformation of the human relationship with the natural world in the history of humankind."3

Long-term trends in global economic growth, resource use, and waste volumes show a sharp upturn after World War II, a period dubbed the "Great Acceleration" and that continues today. For this reason, expert opinion now dates the beginning of the new epoch from around 1945 rather than the end of the eighteenth century as first proposed.4 From a strictly stratigraphic point of view (the one most germane to the official decision on the new epoch), a million years hence the sharpest marker in the rock record will be the sudden deposition of radionuclides across the Earth's surface as a result of nuclear explosions in 1945, known as the "bomb spike." Although the nuclear age has not itself changed the functioning of the Earth System, the layer of radionuclides laid down in 1945 does mark the dawn of the era of US global hegemony and the astounding period of material expansion of the post-war decades, that is, of capitalism's sublime success. We now understand what that success meant for the Earth System. It is measured most simply and strikingly by the Keeling Curve, showing the secular increase in carbon dioxide concentrations in the atmosphere. Earth scientist James Syvitski puts it succinctly: "By any unbiased and quantitative measure humans have affected the surface of the Earth at a magnitude that ice ages have had on our planet, but over a much shorter period of time."5 The course of the Earth System has been changed irrevocably.

To understand why these changes are effectively permanent consider global warming alone. Humans have redistributed the Earth System's stock of carbon, a vital element that profoundly affects the climate. Large reserves of carbon that had over millions of years been immobilized as fossils deep beneath the Earth's surface have been dug up, burned, and released in the system, where they will remain mobile in the atmosphere, oceans, and biosphere. It will probably be hundreds of thousands of years before most of this carbon can be rendered immobile again. In the meantime, the pulse of carbon dioxide emitted into the atmosphere over a century or two is bringing changes that have everlasting consequences. Because they naturally draw carbon dioxide out of the atmosphere, the oceans are already a third more acidic than they were before humans began burning fossil fuels on a large scale. Over a time-scale of many thousands of years, rising acidity disturbs the natural process of deposition of calcium carbonate on the deep seafloor.6 The destabilization of ice masses, such as glaciers and the Greenland ice-sheet, is not something that can be reversed except over tens of thousands of years. The possibility of an ice-free Earth over the next few centuries, bringing much higher sea levels, cannot be ruled out. Such a reconfiguration of the Earth System can be undone only over many millennia, if at all. In the words of 22 earth scientists writing in Nature, "the next few decades offer a brief window of opportunity to minimize [but not prevent] large-scale and potentially catastrophic climate change that will extend longer than the entire history of human civilization thus far."7

A long time after humans disappear, or shrink to a position where we are no longer interfering in the Earth System, the great processes that drive planetary change - orbital forcing, plate tectonics, volcanism, natural evolution, and so on - will overwhelm human influences. But the planet will not settle into a state that looks anything like the Holocene - the 10,000-year epoch of mild and constant climate that permitted civilization to flourish. It has been diverted onto a different trajectory. Experts are already suggesting that the changes caused by humans in recent decades are so profound and long-lasting that we have entered not a new epoch but a new era - the Anthropozoic era - on a par with the break in Earth history brought by the arrival of multicellular life.8

So 1945 marks the turning point in the sweep of Earth's history at which the geological evolution of the planet diverged from one driven by blind forces of nature to one influenced by a conscious, willing being, a new human-geological power. We are accustomed to the idea of humans as the agents that make history, and use the term "pre-history" for the period from the emergence of early humans to the invention of writing. Now we must concede what seemed impossible to contemplate - humans as agents changing the course of the deep history of the Earth, or rather of the Earth's deep future, an event giving rise to what might be called "post-history."

Although we are preoccupied with what the Anthropocene may mean for the future of humans, the present decades mark a transition in which Earth's biogeological history itself enters a new phase, because the Earth's history has become entangled with human history so that "the fate of one determines the fate of the other."9 In a few short decades we have seen the entire history of the Earth - from its formation through to its eventual vaporization when the Sun finally explodes - split irrevocably into two halves - the first 4.5 billion years in which Earth history was determined by blind natural forces alone, and the remaining 5 billion years in which it will be influenced by a conscious power long after that power is spent. If humans disappear, then the great forces that drive the Earth System will continue and eventually erase the more obvious impacts of humans on the landscape. Even so, signs of the influence of humankind - its rise, fall, and enduring legacy - will be evident, not least in a disturbance in the rock record, a freakish band of a few hundred thousand years somewhere in the middle of the 10 billion-year record of the Earth.

Volition in nature

In all previous instances, transitions from one division to the next in the Geological Time Scale came about because of the gradual evolution of natural forces or, at times, a single massive event. These forces are unconscious and unintentional so that the feedback effects from one element to another are not filtered but exert their influence directly (albeit in complex ways). However, if the human imprint on the Earth System is so far-reaching that Homo sapiens now competes with the forces of nature in its impact on the way the planet as a whole functions, the human imprint is the effect of a force fundamentally unlike physical ones such as weathering, volcanism, asteroid strike, subduction, and solar fluxes. This new "force of nature" contains something radically different - the element of volition.

Global anthropogenic impacts, such as increases in carbon dioxide in the atmosphere and disturbance to the nitrogen cycle, do not just happen but are the consequences, intended or otherwise, of decisions taken by human minds. In nature, as we have always understood it, the forces of nature are unconscious and involuntary; no decisions are made, so to comprehend humanity as a geological force we need to consider its distinctive quality, its volitional element. Humankind is perhaps better described not as a geological force but as a geological power, because we have to consider its ability to make decisions as well as its ability to transform matter. Unlike forces of nature, it is a power that can be withheld as well as exercised.

So for the first time in the Earth's 4.5 billion-year history we have a non-physical force (which brings about physical effects) mixed in with physical forces, although it is not so much added to the pre-existing natural forces but in some sense infuses them and modifies their operation. And this new force can...