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
2
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 demands for food, fresh water, timber, fiber, and fuel. This has resulted in a substantial and largely irreversible loss in the diversity of life on Earth….
• More land was converted to cropland in the 30 years after 1950 than in the 150 years between 1700 and 1850. Cultivated systems (areas where at least 30% of the landscape is in croplands, shifting cultivation, confined livestock production, or freshwater aquaculture) now cover one-quarter of Earth’s terrestrial surface.
• Approximately 20% of the world’s coral reefs were lost and an additional 20% degraded in the last several decades of the twentieth century, and approximately 35% of mangrove area was lost during this time (in countries for which sufficient data exist, which encompass about half of the area of mangroves).
• The amount of water impounded behind dams quadrupled since 1960, and three to six times as much water is held in reservoirs as in natural rivers. Water withdrawals from rivers and lakes doubled since 1960; most water use (70% worldwide) is for agriculture.
• Since 1960, flows of reactive (biologically available) nitrogen in terrestrial ecosystems have doubled, and flows of phosphorus have tripled. More than half of all the synthetic nitrogen fertilizer, which was first manufactured in 1913, ever used on the planet has been used since 1985.
• Since 1750, the atmospheric concentration of carbon dioxide has increased by about 32% (from about 280 to 376 parts per million in 2003), primarily due to the combustion of fossil fuels and land use changes. Approximately 60% of that increase (60 parts per million) has taken place since 1959.
Humans are fundamentally, and to a significant extent irreversibly, changing the diversity of life on Earth, and most of these changes represent a loss of biodiversity.
• More than two-thirds of the area of 2 of the world’s 14 major terrestrial biomes and more than half of the area of 4 other biomes had been converted by 1990, primarily to agriculture.
• Across a range of taxonomic groups, either the population size or range or both of the majority of species is currently declining.
• The distribution of species on Earth is becoming more homogenous; in other words, the set of species in any one region of the world is becoming more similar to the set in other regions primarily as a result of introductions of species, both intentionally and inadvertently in association with increased travel and shipping.
• The number of species on the planet is declining. Over the past few hundred years, humans have increased the species extinction rate by as much as 1,000 times over background rates typical over the planet’s history (medium certainty). Some 10–30% of mammal, bird, and amphibian species are currently threatened with extinction (medium to high certainty). Freshwater ecosystems tend to have the highest proportion of species threatened with extinction.
• Genetic diversity has declined globally,
