The Green Marble

Earth System Science and Global Sustainability

David Turner

• Editorial: Columbia University Press
• Año: 2018
• ISBN:
  9780231542845
• Categoría: Physical Sciences
• Categoría: Geology & Earth Sciences

Humans have difficulty thinking at the global scale. Yet as we come to understand our planet as a single, interconnected, complex system and encounter compelling evidence of human impact on Earth's climate and biosphere, the need for a truly global effort is increasingly urgent. In this concise and accessible text, David P. Turner presents an overview of global environmental change and a synthesis of research and ideas from the rapidly evolving fields of earth system science and sustainability science that is suitable for anyone interested in humanity's current predicaments and what we can do about them.

The Green Marble examines Earth's past, contemporary human disruption, and the prospects for global environmental governance. Turner emphasizes the functioning of the biosphere—the totality of life on Earth—including its influence on geologic history, its sensitivity to human impacts, and its possible role in ameliorating climate change. Relying on models of the earth system that synthesize vast amounts of monitoring information and recent research on biophysical processes, The Green Marble describes a range of scenarios for our planetary home, exploring the effects of anthropogenic greenhouse gas emissions and factors such as economic globalization. Turner juxtaposes cutting-edge ideas from both the geosciences and the social sciences to illustrate how humanity has arrived upon its current dangerous trajectory, and how we might pull back from the brink of civilization-challenging environmental change. Growing out of the author's popular course on global environmental change, The Green Marble is accessible to non-science majors and provides a framework for understanding the complex relationship of humanity to the global environment.

1

EARTH SYSTEM SCIENCE

In every age there is a turning point, a new way of seeing and asserting the coherence of the world.

—J. Bronowski (1974)

THE CHALLENGE OF GLOBAL ENVIRONMENTAL CHANGE

Planet Earth can seem quite small. It takes only 90 minutes for an Earth-orbiting satellite to accomplish one global circuit. A single photograph can capture the entire Earth, with recognizable continents and oceans. Google Earth can take the virtual you nearly instantaneously to the top of Mount Everest or the depths of Death Valley.

Size is relative, of course, and in a sense our planet is rapidly becoming ever smaller. With the existing global transportation and communication networks, we can physically make our way to almost any location on the face of the planet within a day or two. The Internet allows us to communicate in text, sound, and images with billions of people around the world. The media keep us informed of breaking news locally and globally. In my professional life, satellite data give me near real-time information on weather and major biosphere disturbances everywhere on the planet.

The Earth is getting smaller in other fundamental ways. Until very recently, our species had only a minor influence on the global biogeochemical cycles of water, carbon, nitrogen, and other elements critical to life. However, in the past century we have become one of the dominant forces in those cycles (W. C. Clark, Crutzen, and Schellnhuber, 2004; Vitousek, Mooney, Lubchenco, and Melillo, 1997b). We are increasing the atmospheric carbon dioxide (CO2) concentration by burning fossil fuels and converting forest land to cropland. Industrialized agriculture and fossil fuel combustion are now introducing into the environment more plant-available nitrogen per year than is produced by natural processes. We now use in one way or another 50 percent of global freshwater flow in streams and rivers. These anthropogenic impacts on the environment are changing the operation of the Earth system in ways unfavorable to advanced technological civilization (Barnosky et al., 2014). Perhaps more ominous in the long run than our influences on the global biogeochemical cycles is that we are driving species of plants and animals extinct at a vastly higher rate than is indicated in the paleorecord over much of evolutionary history.

As ecologists have said for decades, the problem starts with a human population that has been increasing for roughly the past 10,000 years—since the end of the last ice age. There are now over seven billion of us, and the projected balance of births and deaths will likely continue to favor population increase throughout this century. Equally significant, the ecological footprint per individual—i.e., per capita resource consumption—has increased dramatically in parallel with the number of people. About 20 percent of the global population has achieved a moderate to high standard of living (albeit leaving billions living quite precariously), but the cost in terms of environmental degradation has been enormous (MEA, 2005). If several billion additional people attain what is considered the modern lifestyle by exploiting resources in a manner similar to the lucky two billion, humanity will soon be living on a planet of weed-like species with a warmer climate than has been found on Earth in over 30 million years.

In recent decades, we have begun casting around for ways of thinking that might ameliorate our perverse impact on the environment and change the current trajectory. In broad terms, one aspect of the solution is to “think globally.” That slogan traces back at least as far as the “think global, act local” motto of Friends of the Earth, an environmental organization founded by activist David Brower in 1969. “Think Global, Act Local” was also the title of an influential essay published in 1972 by French microbiologist René Dubos (1901–1982). He promoted the concept at the United Nations Conference on the Human Environment in 1972.

The meaning of the “act local” part of the aphorism is straightforward. It means to work at saving specific geographic areas from environmental degradation. Friends of the Earth is built around the concept of people in specific areas organizing to protect those areas. To “think global” is the other side of the coin (Mol, 2000). It could be interpreted as an admonition to be aware of global-scale environmental problems, such as climate change, that are a manifestation of many local decisions. The expression serves as a reminder to foster solidarity on environmental issues among the wide variety of human cultures dispersed around the planet (N. Gough, 2002). However, to think at the global scale remains a challenge. In part this is likely because our brains were designed by biological evolution primarily to apprehend and respond to local events over short time frames, usually involving small groups of people and simple cause-and-effect relationships (Ehrlich and Ehrlich, 2009). Thinking about global environmental change inevitably requires us to stretch our capacity for imagination and for abstraction. This book is an effort to develop a foundation for thinking globally.

IMPACTS, FEEDBACKS, AND GOVERNANCE

We will pay special attention to three intertwined themes.

The first is human impacts. Earth has existed for more than four billion years. At the time of our recent arrival, it had evolved a well-established biosphere and a complex web of global biogeochemical cycles. However, humanity is rapidly changing how the Earth system operates. We are said to be entering a new geological period—the Anthropocene (Crutzen, 2002; Crutzen and Stoermer, 2000). In seeking to manage our global-scale impacts, we must understand the background functioning of the Earth system and the relative magnitude of our influences on it. Reciprocally, human-induced changes in the Earth system are beginning to negatively impact human welfare, and projections to 2100 and beyond suggest much worse to come.

Second is the concept of feedback. In common usage, the term refers to a reply or comment that conveys an evaluative message. A teacher gives students feedback on their essays. More formally, it refers to reciprocal interactions between different components of a system. In a negative feedback relationship, a change in one part of a system induces a change in another part that dampens the original change. This type of feedback is seen when an increase in the atmospheric CO2 concentration induces an increase in biosphere photosynthesis, which then increases the rate of CO2 uptake from the atmosphere and dampens the CO2 rise. The alternative is a positive feedback relationship in which the original change induces a change in another part of the system that amplifies the original change. This is seen when climate warming causes more forest fires that increase emissions of greenhouse gases. With respect to the Earth system, we are especially interested in feedback relationships that regulate the global climate; these include biophysical processes that change with climate warming and serve to amplify or dampen the warming. The study of Earth’s history and recent dynamics offers many clues.

The last theme is governance—specifically, global environmental governance. The meaning of “governance” is more inclusive than “government” because the former accounts for a broader range of actors in the self-regulation of a social body. A system of global environmental governance will ultimately include intergovernmental organizations, states, civil society, and engaged citizens. A critical question here is how to build an institutional framework to manage the relationship between humanity and the rest of the Earth system.

THINKING METAPHORICALLY

Considering our inherent difficulty in thinking globally, perhaps a good way to start is simply in terms of familiar similes and metaphors.

Probably the most deeply rooted metaphor about Earth is the vision of Earth as mother. We can intuit that cave painters of the prehistoric era, by going underground, were attempting to connect with the generative power of the Earth—possibly in the belief that through their drawings they were fertilizing it (Frankl, 2003) or releasing the animal spirits within (Lewis-Williams, 2002). We of course cannot know for sure what they were thinking, but even among extant hunter-gatherer cultures there is often a sentiment of reverence for Earth’s fecundity. The mother metaphor is still used widely in contemporary culture: Mother Earth was referred to in the Paris Agreement on climate change, James Lovelock chose Gaia (the Greek goddess of Earth) as the name of his revolutionary hypothesis about planetary homeostasis (which we will examine in chapter 3), and one of historian Arnold Toynbee’s mighty tomes was titled Mankind and Mother Earth.

Cultivation of plants for food began about 10,000 years ago, a step that introduced a fundamental change in the relationship of humans to their environment. In the hunter-gatherer era, the bounty of nature was there for the taking. With cultivation, the change was made to actively managing nature. At that point, the reigning metaphor became Earth as garden. This was not the Garden of Eden, but rather the garden that produces dinner. In a sense, cultivation began our separation from nature because we became the subject and Earth became the object that we sought to control. But cultivation also requires a certain intimacy with nature because we are motivated to understand it (albeit to exploit it more efficiently), and possibly protect it (to ensure a harvest).

The urge to understand nature, so as to better manipulate it, led to the discovery and rapid expansion of the scientific worldview in recent centuries. The dominant metaphor has thus become Earth as machine. Enlightenment-era French philosopher René Descartes (1596–1650) described both the human body and Earth itself as machines. In that view, we have a mostly instrumental relationship with the natural world and manipulate it as needed for our own objectives. The key feature of the machine metaphor is reductionism. We take nature apart, identify the mechanisms that drive it, and reorder them to meet our needs. A key weakness is that a machine is made by an agent outside the machine, but in the case of Earth, humanity is a part of the Earth system.

In recent decades, the consequences of the machine metaphor have become manifest on a global scale through pollution, natural resource degradation, and environmental change. The latest mythological figure evoked to characterize our relationship with the Earth is Medea (Ward, 2009). She was the mother in Greek mythology who killed her children. Along with the Gaia hypothesis, we will consider the Medea hypothesis in chapter 3.

Alternative models that have emerged as antidotes to the reductionist thinking of the machine metaphor include Earth as home and Earth as system. The iconic image of sunlit Earth against a background of endless dark space (the “blue marble”) has become a reminder of Earth’s beauty and fragility. An especially poignant early photograph of Earth from space was made from the Apollo 13 spacecraft as it limped back from an unsuccessful mission to the moon. Traditionally, a home is worth preserving and, if necessary, worth fighting for.

The power of the system metaphor is in identification of structures composed of parts and wholes, and finding the causal relationships and feedback relationships among the parts and between each whole and its environment. Humans are just one part of a larger system in this view. The emerging field of Earth system science aims to disentangle the hierarchy of parts and whole that make up the Earth system, to model the dynamics of this system’s behavior, and to inform the evolution of a sustainable global civilization.

THE SEMANTICS OF THE SPHERES

One way to think about parts of the Earth system is in terms of spheres, and to continue our project of thinking globally in a more scientific sense, let’s consider the sphere. Perhaps the most characteristic feature of Earth is its roughly spherical shape. This geometric form is quite common in nature and remarkable in any of its manifestations (Volk, 1995). The most startling thing about the sphere is its symmetry. From the perspective of energy balance and materials cycling, the sphere is a satisfying object of study because there is closure; i.e., it can readily be studied as a whole. An additional intriguing feature of a sphere is what happens on its surface as substances or energy forces grow and distribute themselves. First, density gradually increases; but once the surface is covered, the pressure of interaction increases, and the likelihood of new phenomena is enhanced.

Awareness in the Western world that we live on a sphere traces back to the Greek philosophers. Pythagoras (570–490 BCE) observed that mast tops appeared first when ships came into view on the horizon. Aristotle (384–322 BCE) knew that different stars became visible as a person traveled south, and...