Facing the Anthropocene. Ian Angus
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, particularly among cultivated species.7
Naming the Turning Point
Almost simultaneously, two large-scale global scientific projects—the International Geosphere-Biosphere Program and the Millennium Ecosystem Assessment—independently identified the middle of the twentieth century as a turning point in Earth history. As the IGBP report said, “The last 50 years have without doubt seen the most rapid transformation of the human relationship with the natural world in the history of the species.”8
In 2005, Will Steffen and Paul Crutzen of the IGBP, together with environmental historian John McNeill and others who had participated in the MEA process, attended an intensive one-week seminar in Dahlem, Germany, with the aim of deepening their understanding of the history of the relationship between humanity and nature. Their workshop, chaired by Steffen, drew on findings from the IGBP and MEA to argue that “the 20th century can be characterized by global change processes of a magnitude which never occurred in human history.” After quoting the MEA, their workshop report gave those processes a name:
These and many other changes demonstrate a distinct increase in the rates of change in many human-environment interactions as a result of amplified human impact on the environment after World War II—a period that we term the “Great Acceleration.”9
Steffen later wrote that the name Great Acceleration was a deliberate homage to The Great Transformation, Karl Polanyi’s influential book on the social, economic, and political upheavals that accompanied the rise of market society in England:
Polanyi put forward a holistic understanding of the nature of modern societies, including mentality, behavior, structure, and more. In a similar vein, the term “Great Acceleration” aims to capture the holistic, comprehensive, and interlinked nature of the post-1950 changes simultaneously sweeping across the socioeconomic and biophysical spheres of the Earth System, encompassing far more than climate change.10
A Two-Stage Anthropocene?
The first peer-reviewed account of the Great Acceleration was the provocatively titled article, “The Anthropocene: Are Humans Now Overwhelming the Great Forces of Nature?” by Steffen, Crutzen, and McNeill, published in 2007. They argued that the Anthropocene had developed in two distinct stages.
Stage 1: The Industrial Era, from the early 1800s to 1945, when atmospheric CO2 exceeded the upper limit of Holocene variation; and Stage 2: The Great Acceleration, from 1945 to the present, “when the most rapid and pervasive shift in the human-environment relationship began.”
(They also—over-optimistically, I’d say—predicted that a third stage, “Stewards of the Earth,” would begin in 2015.)
Steffen, Crutzen, and McNeil left no doubt that their answer to the question in their article’s title was an emphatic yes:
Over the past 50 years, humans have changed the world’s ecosystems more rapidly and extensively than in any other comparable period in human history. The Earth is in its sixth great extinction event, with rates of species loss growing rapidly for both terrestrial and marine ecosystems. The atmospheric concentrations of several important greenhouse gases have increased substantially, and the Earth is warming rapidly. More nitrogen is now converted from the atmosphere into reactive forms by fertilizer production and fossil fuel combustion than by all of the natural processes in terrestrial ecosystems put together….
The exponential character of the Great Acceleration is obvious from our quantification of the human imprint on the Earth System, using atmospheric CO2 concentration as the indicator. Although by the Second World War the CO2 concentration had clearly risen above the upper limit of the Holocene, its growth rate hit a take-off point around 1950. Nearly three-quarters of the anthropogenically driven rise in CO2 concentration has occurred since 1950 (from about 310 to 380 ppm), and about half of the total rise (48 ppm) has occurred in just the last 30 years.11
The term Great Acceleration quickly caught on among Earth System scientists as a descriptive name for the period of unprecedented economic growth and environmental devastation since World War II. Their “two stages” model has not survived, however; as we’ll see in chapter 4 many Earth System scientists, including Steffen, Crutzen, and McNeill, have concluded that the Anthropocene actually began in the middle of the twentieth century, that the beginning of the Great Acceleration is also the beginning of the Anthropocene.
FIGURE 2.1: Earth System Trends
Updates of the 2004 Great Acceleration graphs were published in 2015. As in the original graphs, all the trend lines show hockey stick-shaped trajectories, turning sharply upward in the middle of the twentieth century.12
FIGURE 2.2: Socioeconomic Trends
Acceleration Update
The original Great Acceleration graphs, published in 2004, showed social and environmental trends from 1750 to 2000. In January 2015, Will Steffen