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Era … has begun:

      • in a few generations humankind is in the process of exhausting fossil fuel reserves that were generated over several hundred million years,

      • nearly 50% of the land surface has been transformed by direct human action, with significant consequences for biodiversity, nutrient cycling, soil structure and biology, and climate,

      • more nitrogen is now fixed synthetically and applied as fertilizers in agriculture than is fixed naturally in all terrestrial ecosystems,

      • more than half of all accessible freshwater is used directly or indirectly by humankind, and underground water resources are being depleted rapidly in many areas,

      • the concentrations of several climatically important greenhouse gases, in addition to CO₂ and CH₄, have substantially increased in the atmosphere,

      • coastal and marine habitats are being dramatically altered; 50% of mangroves have been removed and wetlands have shrunk by one-half,

      • About 22% of recognized marine fisheries are overexploited or already depleted, and 44% more are at their limit of exploitation,

      • Extinction rates are increasing sharply in marine and terrestrial ecosystems around the world; the Earth is now in the midst of its first great extinction event caused by the activities of a single biological species (humankind).¹⁹

      The pamphlet presented the Anthropocene concept tentatively—it said the changes have “led to suggestions,” not that a new geological period had definitely begun. This likely reflected unwillingness by the other three sponsors to endorse a concept that was new to them.

      This caution extended to the Declaration on Global Change the conference adopted. Although it said that “the Earth System has moved well outside the range of the natural variability exhibited over the last half million years at least,” and that “Earth is currently operating in a no-analog state,” the Declaration did not mention a new geological epoch or use the word Anthropocene.²⁰

      After the Amsterdam conference, Paul Crutzen submitted a more strongly worded article to Nature, one of the world’s most widely read scientific journals. The oddly titled “Geology of Mankind,” published in January 2002, was the first peer-reviewed paper to specifically argue that a new geological epoch had begun.

      Again Crutzen listed ways in which human activity was changing the face of Earth, including:

      • A tenfold human population growth in three centuries.

      • Maintaining 1.4 billion methane-producing cattle.

      • Exploiting 20–50 percent of Earth’s land surface.

      • Destruction of tropical rainforests.

      • Widespread dam building and river diversion.

      • Exploitation of more than half of all accessible fresh water.

      • A 25 percent decline of fish in upwelling ocean regions and 35 percent in the continental shelf.

      • A 16-fold increase in energy use in the twentieth century, raising sulphur dioxide emissions to over twice natural levels.

      • Use of more than twice as much nitrogen fertilizer in agriculture as is used naturally in all terrestrial ecosystems combined.

      • Increasing atmospheric concentrations of greenhouse gases to their highest levels in over 400,000 years.

      He pointed to global consequences, including acid precipitation, photochemical smog and global warming of 1.4 to 5.8 degrees Celsius during this century. He was careful to add that “these effects have largely been caused by only 25% of the world population.”

      Barring a global catastrophe such as a meteorite impact, world war, or pandemic, Crutzen wrote, “mankind will remain a major environmental force for many millennia,” and so “it seems appropriate to assign the term ‘Anthropocene’ to the present, in many ways human-dominated, geological epoch.”²¹

       A New Synthesis

      Meanwhile, an eleven-person team headed by Will Steffen had begun the complex and time-consuming task of synthesizing a decade’s work by thousands of scientists into a single volume that would be largely accessible to a non-expert audience. Steffen says the main text was “a true synthesis, as we did not assign chapters to individual authors but rather wrote the whole book as a single, integrated narrative with all authors contributing to the whole book.”²² The team also commissioned and included short essays by individual experts to highlight important aspects of the subject.

      Completed early in 2003 and published in 2004, Global Change and the Earth System: A Planet Under Pressure (not to be confused with the earlier pamphlet of the same name) was an invaluable contribution to broad understanding of the Earth System—and despite the many scientific advances that have been made since, it remains essential reading for anyone who wants to understand the scientific basis for declaring a new epoch, the Anthropocene.²³

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      The Great Acceleration

      We know that something went wrong in the country after World War II, for most of our serious pollution problems either began in the postwar years or have greatly worsened since then.

      —BARRY COMMONER¹

      At some point the IGBP team that prepared Global Change and the Earth System decided that their book should “record the trajectory of the ‘human enterprise’ through a number of indicators” from 1750 to 2000.² The result was 24 graphs—twelve showing historical trends in human activity (GDP growth, population, energy consumption, water use, etc.) and twelve showing physical changes in the Earth System (atmospheric carbon dioxide, ozone depletion, species extinctions, loss of forests, etc.) over 250 years.

      The authors were surprised by what they found: Every trend line showed gradual growth from 1750 and a sharp upturn from about 1950. “We expected to see a growing imprint of the human enterprise on the Earth System from the start of the Industrial Revolution onward. We didn’t, however, expect to see the dramatic change in magnitude and rate of the human imprint from about 1950 onward.”³ They pointed this out in the book:

      One feature stands out as remarkable. The second half of the twentieth century is unique in the entire history of human existence on Earth. Many human activities reached take-off points sometime in the twentieth century and have accelerated sharply towards the end of the century. The last 50 years have without doubt seen the most rapid transformation of the human relationship with the natural world in the history of humankind.⁴

       Millennium Ecosystem Assessment

      While the IGBP was preparing its synthesis report, another global scientific project was completing its work. The Millennium Ecosystem Assessment (MEA), coordinated by the United Nations Environment Program, was launched in 2001 to collect and synthesize “authoritative scientific knowledge concerning the impact of changes to the world’s ecosystems on human livelihoods and the environment.”⁵ Nearly 1,400 scientists from around the world contributed to the seven synthesis reports, four technical volumes, and many supporting papers that the MEA published in 2004 and 2005.

      One of the project’s most important conclusions was highlighted in a final statement from the MEA Board in March 2005. After noting that human societies have always changed the natural systems of the planet to meet their needs, the Board declared that “throughout human history, no period has experienced interference with the biological machinery of the planet on the scale witnessed in the second half of the twentieth century.”⁶

      The MEA Synthesis Report on Ecosystems and Human Well-Being made the same point, and listed significant examples:

      Over the past 50 years, humans have changed ecosystems more rapidly and extensively than in any comparable period of time in human history, largely to meet rapidly growing

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