Living in the Anthropocene Read online

  A few examples will underscore the reality of the Great Acceleration. Our forebears took many millennia to reach a population of one billion, which occurred around 1800 or 1820. It then took more than a century for human numbers to reach two billion (around 1930). Soon, in the middle of the twentieth century, an unprecedented frenzy of survival and reproduction began, and the human population tripled in the span of one lifetime. It reached three billion by 1960 and four billion by 1975, and thereafter it added a new billion every twelve to thirteen years. Meanwhile, total energy use quintupled between 1950 and 2015. In those sixty-five years, people burned a quantity of fossil fuels that had taken 150 million years to accumulate. More than three-quarters of the anthropogenic greenhouse gas emissions in human history occurred during those sixty-five years. The world’s motor vehicle fleet grew like kudzu, from forty million to nine hundred million, over the same time span. These and many more accelerating trends made the post-1950 world very different from all that had come before it. Collectively, they vaulted us into a new time period in both human history and the history of Earth: the Anthropocene.

  Figures 1–8. These eight graphs collectively show that the middle of the twentieth century was a transitional moment for several indicators, or driving forces, of global environmental change. For those who embrace the concept of the Anthropocene and endorse a mid-twentieth-century birthday for it, these graphs provide persuasive evidence. Several more such charts appear on the website of the International Geosphere-Biosphere Programme. (OECD: Organisation for Economic Cooperation and Development; BRICS: Brazil, Russia, India, China, and South Africa.) From W. Steffen et al., “The Trajectory of the Anthropocene: The Great Acceleration,” Anthropocene Review 2 (2015): 81–98. Used with permission of Sage Publishers.

  “The Anthropocene” at present means all things to all people. Arguments simmer about how old it is. The weight of the evidence suggests that the Anthropocene began in the mid-twentieth century, but some scientists argue for a much older Anthropocene, beginning with the harnessing of fire, the late Pleistocene extinctions, or the dawn of agriculture. Others prefer an Anthropocene dating to the Columbian Exchange (beginning in 1492), when sailors carried ark-loads of species of animals, plants, and microbes from one continent to another, leaving a lasting mark in the paleontological record. Still others see the Industrial Revolution (ca. 1780–1850) as the decisive period that sets the Anthropocene apart, thanks to the rapid adoption of fossil fuels and the subsequent greenhouse gas emissions that were generated on an ever-larger scale in those years.

  Arguments about the antiquity (or novelty) of the Anthropocene are also arguments about its essence. For most of those who regard atmospheric chemistry as the most relevant marker of global change, an Anthropocene that begins with industrialization makes the most sense. For those who require that the Anthropocene leave a signal in the paleontological record and who see the history of life on Earth as the key variable in demarcating intervals of time, the late Pleistocene extinctions or the Columbian Exchange make more sense.

  If one tries to mesh all the relevant variables and to avoid privileging any particular discipline’s outlook and preferred forms of evidence over others, the Great Acceleration seems to be the best birth date for the Anthropocene. Taking a “basket of variables” approach, as the International Geosphere-Biosphere Programme recently did, underlines the many respects in which the mid-twentieth century marks a point of inflection on rising curves. Beyond the upticks in rates of population growth and energy use, which together may lie at the heart of the matter, a long list of relevant variables describe a similar trajectory: carbon emissions, methane emissions, fertilizer consumption, ocean acidification, and nitrogen loading of coastal waters, among others. It is the collective weight of all these variables that separates the Anthropocene from what came before, rather than any single one. Their simultaneous and interwoven acceleration trajectories, beginning about 1950, blasted us into the Anthropocene.

  The Great Acceleration is doomed. The remarkable trends that most of us have lived with all our lives will not last long. In some cases, finite supply is the issue. The world does not have enough fresh water to allow another quadrupling of water withdrawals (as occurred from 1950 to 2010). There are not enough good sites left to support another sextupling of the world’s large dams. There are not enough fish to permit another quintupling of the marine fish catch. In other cases, saturation or equilibration is the issue. The proportion of the global population living in cities, now at more than 50 percent, cannot more than double (as happened from 1950 to 2010). Total human population could in theory triple once more, as it did in that same period, but no one imagines it will, because urbanization, formal female education, and other social changes have sharply reduced couples’ reproductive ambitions. Globally, human fertility is only a little more than half of what it was in 1970. So for all these reasons and several others, the Great Acceleration will come to a close. Indeed, many of its trends have already leveled off (dam building, marine fish catch) or begun to decline.

  The Anthropocene, however, will live on. Even if the human population starts to fall some fifty or sixty years hence (as some speculate it will), even if by 2075 we have banished fossil fuels to the margins of a low-carbon energy system, even if green parties win every election, the Anthropocene will live on. That is because, for a long time to come, there will still be billions of people using the global environment as a source of materials and a sink for wastes, even if at restrained rates, and for a long time to come, the carbon already emitted into the atmosphere will continue to trap heat and warm Earth’s surface and its oceans. Less certainly, increasing skill in manipulating human and other genomes could give a new tint to the Anthropocene, raising the efficiency with which we eliminate some species (pesky mosquitoes, perhaps) and alter others.

  Thus, of all the possible understandings of the Anthropocene, the one that best matches the evidence is the post-1950 Anthropocene, born of the Great Acceleration. Historians may leave it to others to reflect upon whether the Anthropocene is on balance a good or a bad thing and how long it might last. Those questions require a clear look into the future, and historians have trouble enough seeing into the past.

  THINKING LIKE A MOUNTAIN IN THE ANTHROPOCENE

  SCOTT L. WING

  Aldo Leopold’s posthumously published book A Sand County Almanac (1949) includes an essay entitled “Thinking Like a Mountain.” In it, he recounts shooting a wolf as a young man. Watching the “fierce green fire” in her eyes die helps him to consider the deeper meaning of the wolf’s existence—or, as he puts it, to think like a mountain. In this essay of only 878 words, Leopold gave twentieth-century conservationists two powerful but distinct metaphors. The fierce green fire speaks of the emotional effect of losing the wildness that wolves represent. Thinking like a mountain suggests a more detached point of view but one that appreciates the interplay of the wolf and its ecosystem. In the decades after he shot the wolf, Leopold writes that he has “watched the face of many a newly wolfless mountain, and seen the south-facing slopes wrinkle with a maze of new deer trails…seen every edible bush and seedling browsed, first to anaemic desuetude, and then to death.” What he has learned, and what the mountain has always known, is that extirpating predators leads to explosive growth of herbivore populations, overbrowsing, reduced vegetation, and loss of soil—in short, a cascade of unintended, long-term consequences considered undesirable by the humans who initiated them. Leopold’s essay stretches the minds of readers unaccustomed to thinking about the biological and landscape changes that can be precipitated by removing a keystone predator from an ecosystem.

  The thinking mountain of the essay’s title recognizes ecological complexity, but its spatial frame is regional rather than global and its time scale more human than geologic. Looking back, though, we see that A Sand County Almanac was published near the onset of the dramatic upward inflection in human resource use and global effects often referred to as the Great Acc
eleration, making it one of the first conservationist texts of the Anthropocene. Three score and eight years is not a long time to watch a new epoch unfold, but the changes in the environment that have taken place in those years may justify a reevaluation of Leopold’s classic metaphor.

  The idea behind the Anthropocene is conceptually simple: the changes we are now making to Earth are on a par with the shifts in the global environment that mark the beginnings of previous geologic time periods. (By convention, stratigraphers define each period of the geologic time scale by its beginning, or base, with the end of one being defined by the beginning of the succeeding period. No gaps or interregna are allowed in geochronology.) Although there is plenty of scholarly debate about naming a formal Anthropocene epoch, there is no doubt that the changes humans have been causing to Earth systems since the mid-twentieth century are comparable in type and magnitude to past changes that we use to recognize the beginnings of new phases of Earth history. Indeed, some of these earlier changes reflect perturbations of the very same processes we are now altering, even though their rates and ultimate causes are different.

  The beginning of the Eocene epoch (approximately fifty-six million years ago), for example, was accompanied by a major release of carbon, with attendant global warming and ocean acidification, an event called the Paleocene-Eocene Thermal Maximum, or PETM. Although the amount of carbon released at the onset of the PETM was greater than the amount that humans are likely to generate except in the most extreme future scenarios, the rate of carbon release today is probably ten times faster. The rapid shift in carbon chemistry (the ratio of 12C to 13C) at the onset of the PETM now forms a convenient marker for the base of the Eocene, as do the changes in the composition of fossil faunas and floras that it caused. The effects of the PETM on Earth’s climate and biota lasted for more than a hundred thousand years. In a parallel fashion, the change in the ratio of carbon isotopes caused by burning fossil fuels will form a permanent sedimentary marker for recognizing an Anthropocene epoch, as will the massive changes in biodiversity, sedimentation, nutrient supply, and ocean chemistry that are resulting from human activities.

  Since 1949, we have gained much greater insight into how the integrated Earth-life system works. Geologists have contributed to this understanding by reconstructing past global environmental changes and the interaction of environmental change with life. Earth system scientists have developed the ability to monitor environmental change globally in real time—giving us a sense of how, and how fast, the Earth’s system is shifting. Powerful computers can now simulate the interconnected processes that influence the global environment, producing predictions of future change. As a result, we know not only that we are increasing carbon dioxide (CO2) in the atmosphere every year but also that much of that carbon dioxide will still be in the atmosphere in the year 3000, that most of the resulting increase in temperature and sea level will still be in force in the year 12,000, and that a full return to background carbon dioxide won’t occur for more than a hundred thousand years. Human effects on the global environment are large and unprecedented and are producing a welter of unintended consequences. Even more important, though less widely appreciated, is that these human-induced changes will persist for far longer spans of time than the historical, or even archaeological, record that shapes our thinking.

  The revolution in Earth system science that has taken place since 1949 should have radically altered our sense of who we are. The new insights haven’t undone the Copernican revolution, which removed us from the center of the solar system, or the Darwinian revolution, which revealed that we exist because of the same evolutionary processes that generated all life on Earth, but current understanding of the Earth’s system does show that we are no longer a bit player in the story of this planet, and that the influence of our actions now will change the global environment for at least hundreds of human generations to come.

  The distant future will never be as salient as tomorrow. Nevertheless, in the Anthropocene we have to learn to anticipate and adapt to the long-term consequences of our actions and to avoid taking actions with dire consequences. Although some imagine that the rapid changes we are causing in the global environment are an existential threat—that we will drive ourselves extinct—this scenario is a very remote possibility. A planetary population that has more than doubled since the mid-twentieth century and will likely reach more than nine billion in the next thirty years is the opposite of endangered. Visions of human extinction are more escapism than reality: believing in the apocalypse means you don’t have to plan for the future. The apocalypse may be a dark fantasy, but even without an existential threat there is enormous potential for human misery in a hotter future with flooded coastlines, longer droughts, more violent storms, fewer forests and coral reefs, and fewer species. Only the most resigned cynic or bloated egotist could conclude that short-term benefits to current generations trump the long-term costs to the many generations to come.

  If it is clear that we will not “destroy the planet,” as it is sometimes put, it is also clear that we don’t have the capacity to return it to a “state of nature,” if that implies no human influence. The seven billion of us now on the planet use between a quarter and a half of global net photosynthetic productivity and have left far less than half of Earth’s land area in a wild or seminatural state. Even with dramatically more sustainable practices, the portion of the planet and its resources devoted to supporting humans will almost certainly increase as the human population continues to swell. Any attempt to rapidly return the planet to an imagined prehuman state would cause enormous human suffering. Furthermore, change is inevitable. Earth history shows us that climate veers from warm to cold, that the composition of the atmosphere changes, and that cataclysms happen. Rather than justifying anthropogenic global change, however, this perspective shows just how hard it is to survive such rapid change. Slowing the rate at which we alter global life-support systems may seem a modest goal, but it would allow more time for adaptation to changes that cannot be avoided, as well as time for natural negative feedbacks to counteract some of the changes we are forcing.

  Researchers of the Earth’s system have been focused, appropriately, on developing a better understanding of the vast and interconnected processes that create our environment, and they have made a great deal of progress since the publication of A Sand County Almanac. Although there are many problems left to solve, knowledge about planetary life-support systems has progressed far more rapidly than society’s willingness to use this knowledge. The biggest challenge facing humanity is that our political, social, and economic systems are shortsighted. Long-term planning typically considers years or decades, but the global environmental processes we are now influencing play out over centuries, millennia, or more. We need to instill a sense of geologic time into our culture and our planning, to incorporate truly long-term thinking into social and political decision making. This is what “thinking like a mountain” should come to mean in the Anthropocene. If we succeed in transforming our culture, residents of the later Anthropocene will look back on the early twenty-first century as a time of human enlightenment, when people learned to truly think like mountains by anticipating their long-lasting and complex effects on the world. The moral price of our knowledge and influence is that we must use them responsibly to shape our future and that of the planet. We must take a much longer view of our legacy than we ever have before.

  THE UNDERWATER ANTHROPOCENE

  DOUGLAS J. McCAULEY

  Scientific dialogues on the Anthropocene rarely extend below the high-tide line. This terrestrial bias is perhaps justifiable, as we have been altering terrestrial ecosystems since the African diaspora gained momentum about fifty thousand years ago. Today, croplands and pastures take up about 40 percent of Earth’s land surface, while the forty million miles of road (a distance equivalent to 165 trips to the Moon) that we have laid out across the world have left less than 10 percent of the planet’s land surface remote. The terrestrial port
ion of the world has been brought unambiguously under the dominion of our species.

  By almost all measures, however, the mark of the Anthropocene has been lighter in the oceans. California, my home, provides an illustrative example. Humans assisted with the extirpation of terrestrial megafauna (e.g., eleven-ton mammoths, ground sloths more than ten feet tall) from the region about fourteen thousand years ago. We then proceeded to drive California’s wolves and grizzly bears extinct (the latter our state animal and flag symbol). But today, just offshore and within eyesight of metropolitan skylines, thirty-three-ton gray whales undertake one of the longest mammal migrations on the planet, 550-pound giant sea bass vocalize at divers, and white sharks investigate the palatability of about one and a half California beachgoers annually. While deeply altered, the oceans retain a wildness that has become rare in much of the terrestrial world.

  What delayed and muted the arrival of the Anthropocene in the oceans? The simple answer is that it is harder to change the oceans—at least for us terrestrial apes. Examples of nonhuman great apes affecting aquatic ecosystems are uniformly underwhelming: orangutans can catch disabled catfish, and bonobos scoop up the occasional aquatic animal when swamp foraging. But because we humans rely more on our brains than on tooth or claw, we eventually overcame the significant physical barriers that normally prevent terrestrial animals from hunting efficiently in ocean ecosystems. We invented our first deep-sea fishing technologies (e.g., bone fishhooks) and were catching pelagic fish at least forty thousand years ago. But it wasn’t until after the Second World War, when we repurposed wartime marine technologies to industrialize fishing fleets, that we profoundly amplified our impact on the oceans and arguably first wet the feet of our global human footprint.