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      A Second Copernican Revolution

      In terms of some key environmental parameters, the Earth System has moved well outside the range of the natural variability exhibited over the last half million years at least. The nature of changes now occurring simultaneously in the Earth System, their magnitudes and rates of change, are unprecedented. The Earth is currently operating in a no-analog state.

      —AMSTERDAM DECLARATION ON GLOBAL CHANGE¹

      The word Anthropocene has been coined three times.

      In 1922, the Soviet geologist Aleksei Petrovich Pavlov proposed Anthropocene or Anthropogene as a name for the time since the first humans evolved about 160,000 years ago. Both words were used by Soviet geologists for some time, but they were never accepted in the rest of the world.

      In the 1980s, marine biologist Eugene Stoermer used the word in some published articles, but no one seems to have followed his lead.

      The third time’s the charm. Atmospheric chemist Paul J. Crutzen reinvented the word in February 2000, at a meeting of the International Geosphere-Biosphere Program in Cuernavaca, Mexico. Will Steffen, then executive director of the IGBP, was a witness:

      Scientists from IGBP’s paleoenvironment project were reporting on their latest research, often referring to the Holocene, the most recent geological epoch of earth history, to set the context for their work. Paul, a vice-chair of IGBP, was becoming visibly agitated at this usage, and after the term Holocene was mentioned yet again, he interrupted them: “Stop using the word Holocene. We’re not in the Holocene any more. We’re in the … the … the … (searching for the right word) … the Anthropocene!”²

      Five years earlier, Crutzen had won a Nobel Prize for work that helped prove that widely used chemicals were destroying the ozone layer in Earth’s upper atmosphere, with potentially catastrophic effects for all life on Earth. In his acceptance speech, he said that his research on ozone had convinced him that the balance of forces on Earth had changed dramatically. It was now “utterly clear,” he said, “that human activities had grown so much that they could compete and interfere with natural processes.”³ His interjection at the IGBP meeting in 2000 crystallized that insight in a single word, Anthropocene. “I just made up the word on the spur of the moment,” he says. “Everyone was shocked. But it seems to have stuck.”⁴

      Crutzen was something of a scientific superstar: according to the Institute for Scientific Information, between 1991 and 2001 he was the world’s most-cited author in the geosciences.⁵ There is no question that his high profile drew attention to his articles on the Anthropocene, and eventually helped win broad acceptance for the idea.

      Steffen, Crutzen, and environmental historian John McNeill subsequently explained the need for a new word this way:

      The term Anthropocene … suggests that the Earth has now left its natural geological epoch, the present interglacial state called the Holocene. Human activities have become so pervasive and profound that they rival the great forces of Nature and are pushing the Earth into planetary terra incognita. The Earth is rapidly moving into a less biologically diverse, less forested, much warmer, and probably wetter and stormier state.⁶

      “A no-analog state,” “planetary terra incognita”—these phrases are not used lightly. Earth has entered a new epoch, one that is likely to continue changing in unpredictable and dangerous ways. That’s not an exaggeration or a guess: it’s the central conclusion of one of the largest scientific projects ever undertaken, one that requires us to think about our planet in an entirely new way.

       Earth as an Integrated System

      Though it has gone unnoticed by most people and unmentioned in mainstream media, scientific understanding of our planet has radically changed in the past three decades. Scientists have long studied various aspects of Earth, using the methods of geology, biology, ecology, physics, and other disciplines. Now many are studying Earth as an integrated planetary system—and discovering that human activity is rapidly changing that system in fundamental ways:

      Crucial to the emergence of this perspective has been the dawning awareness of two fundamental aspects of the nature of the planet. The first is that the Earth itself is a single system, within which the biosphere is an active, essential component. In terms of a sporting analogy, life is a player, not a spectator. Second, human activities are now so pervasive and profound in their consequences that they affect the Earth at a global scale in complex, interactive, and accelerating ways; humans now have the capacity to alter the Earth System in ways that threaten the very processes and components, both biotic and abiotic, upon which humans depend.⁷

      Studying Earth as a system became possible and necessary in the 1980s. It became possible when new scientific instruments became available—in particular, satellites designed to gather data about the state of the entire Earth and computer systems capable of collecting, transmitting, and analyzing vast quantities of scientific data. It became necessary when scientists and others realized that nuclear weapons, ozone-destroying chemicals, and greenhouse gases could radically remake the world: human activity was causing not just change but global change, with potentially disastrous consequences.

      Following discussion of global change at meetings of the International Council of Scientific Unions (ICSU) in Warsaw in 1983 and Ottawa in 1985, a series of international symposia and reports recommended creation of a coordinated international research program on global change. As a member of the American Geographical Union wrote, the need went beyond scientific curiosity:

      It

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