[Adapted from a talk given in December at Hopkins's
School of Public Health's
First, of course, the idea of a sustainable future implies a future that is geologically sustainable, a future that is responsive to the limits of Earth's ability to provide 9 or 10 billion people with food, water, and natural resources. To achieve that we need to learn as much as we can about how the biosphere, atmosphere, hydrosphere, and solid Earth function-- about how resources are produced, climate controlled, rainfall distributed, disease transmitted, and so on.
But imagining sustainability in that largely pragmatic sense will not be enough. Sustainability will raise some of the most difficult moral questions that we've ever faced--questions about the value of other species and of ecosystems, what resources to save for future generations, what level of equity among nations is fair and sustainable, and so on. We'll need to think deeply about just what it is that makes life worthwhile, what gives life meaning beyond mere existence, where the appropriate balance lies between the "legitimate rights" of one culture and the "moral dignity" of another.
Questions like those are the domain of ethics and religion, not science. And one of the things that seems to mark us as being human is that questions like that matter to us. We can't just ignore them. No approach to sustainability that tries to ignore them could work for long. In addition, some of the steps needed for sustainability will be unpopular, and our political will to undertake them may depend upon seeing them as moral imperatives. So it seems to me that an achievable vision of the future will also need to be seen as being morally or theologically sustainable.
And so I see our vision of sustainability being worked out in the unfamiliar terrain linking science, or to be partial, geology, with religion and ethics, or theology. Although I'll start from these two very divergent perspectives, I hope to show that there is much more common ground between geology and theology than most of us would think.
A good starting point is the by now iconographic image of Earth from space taken by the Apollo astronauts. It fundamentally changed our view of Earth and of ourselves by demonstrating that the metaphor of the endless frontier no longer applies. In its place we see a small, isolated world, breathtaking in its beauty, an exquisite jewel set against the velvety black immensity of space. For the first time we saw Earth as a complex system of rock, soil, and water, veiled by a gossamer-thin layer of air, and inhabited by billions of fellow creatures, large and small. And we began to see that all species on Earth are related by an intricate web of biogeochemical cycles in which the chemicals needed for life--carbon, water, calcium, nitrogen, phosphorous, potassium--are recycled in a complex series of biological, chemical, and geological processes, mostly powered by solar energy. Though we had intellectually understood these points before, those Apollo photographs burned that new image into our consciousness in a way we could no longer ignore. We began to know in our hearts that we are all radically dependent upon that biogeochemical system and so are radically dependent upon one another.
To understand that recycling system we can start with the familiar food chain, more accurately known as a food web. Food webs tend to vary a lot from one ecosystem to another, but there are a few features common to all. Surface ecosystems all begin with primary producers--plants--which use solar energy to convert CO2 into organic matter. Consumers--first herbivores, then carnivores--ultimately derive the energy they need from those plants. But the food web doesn't end there. Animals produce waste products and plants produce dead organic matter. If that material were allowed to accumulate, we who live in Eastern forest systems would be up to our eyeballs in leaves and other organic debris; the carbon and nutrients they contain would be lost, and eventually the whole system would grind to a halt. So a third part of the system--the fungi and bacteria known as decomposers--play a key role by consuming all that dead organic material and converting the carbon and nutrients to a form in which they can be used again by the primary producers.
On a planetary scale, all ecosystems are linked by a global carbon cycle, in which carbon is cycled in both the terrestrial and marine biospheres, and the two are linked by fluxes through the atmosphere and the river systems. The origins of this biogeochemical system are lost in the mists of time, but carbon isotopes from rocks in Greenland suggest that photosynthesis had already begun 3.85 billion years ago and that at least a primitive terrestrial carbon cycle had begun to operate.
Today, this carbon cycle regulates the amount of atmospheric CO2 which, along with water vapor and other greenhouse gasses, absorbs infra-red radiation emitted by Earth and leads to an average surface temperature of 17°C, roughly the most efficient temperature for carbon-based life. Without that greenhouse effect, Earth's temperature would be -18°C, and the oceans largely covered with sea ice, reflecting more incoming solar radiation, and cooling Earth so much that life as we know it would probably never have developed.
The greenhouse effect has kept Earth's surface temperature within the 40°C temperature range required for life for nearly 4 billion years, despite the fact that the intensity of solar radiation has increased by approximately 20 percent; despite the fact that the atmosphere has changed from an early, reducing composition to its present oxygen-rich composition; and despite the fact that the species mix on Earth has been radically altered in five major extinctions in the last 500 million years. The most intense of which happened 250 million years ago and eliminated about 80 percent of the species then alive. The other extinctions weren't quite that strong, but utterly changed the makeup of the terrestrial system.
The key requirements for a sustainable life system are pretty daunting. The Earth must be close enough to the Sun that its temperature is in the range of liquid water. Its gravity field must be strong enough to retain an atmosphere that gives a surface pressure in the field of liquid water (unlike Mars, or the Moon). Its daily rotation be fast enough that diurnal temperature variations are not too extreme (unlike the Moon). It must have a crust light enough to form large continental masses, but thin enough to permit plate tectonics to operate (unlike Mars).
The temperature requirement is not a very severe limitation-- given a solar system, some planet will be at about the right distance from the Sun. But the other requirements are much more difficult to satisfy. In detail, they depend upon precisely which planetesimals collided to form Earth, exactly what the bulk composition of the aggregate was, and precisely how each of those collisions happened during the final stages of planetary accretion about 4 billion years ago. Even small differences in the trajectories of those colliding planetesimals would have led to a different Earth, quite possibly one unable to sustain life. But even an Earth perfectly attuned to nurturing life might not have produced us. Were it not for the fact that the Mesozoic reptiles were largely eliminated by a meteorite impact 65 million years ago, mammalian evolution might never have gotten under way.
And because we are among the youngest of the mammals--modern
humans appeared only 150,000 years ago--we obviously are not
essential to the existence of life on Earth. Aside from a few
bacteria, viruses, and parasites that have learned to live at our
expense and some domestic species that we have bred into
dependence, few of our fellow creatures would miss us if we were
It seems to me that there are two ways of reading this geological story: One, the more conventional reading, is that we are totally dependent on the continuing operation of the biogeochemical system, but the system is in no way dependent upon us.
The other reading, less conventional, but no less important, is simply to stand stunned by the beauty, intricacy, and the incredible contingency of the story, the creativity of the system, the sheer exuberance of life, and finally to stand in awe at the sheer privilege of our being here, able to sense that exuberance and feel that awe. As scientists, we are privileged to see the delicacy and beauty of nature more clearly than most, and I often think we should be less reticent about expressing this side of our work. In the end helping to articulate our sense of that beauty and the feeling of privilege that it engenders may be our most important contribution.
But the point I want to stress is that although these two
readings of the story are dramatically different, both point to
the central importance of life, and both suggest that we should
do all that we can to nurture the system that sustains life.
To respond to that common mandate, we need a sense of how vulnerable the system is to our increasing impact, and how urgently we need to reduce that impact.
Assessing the system's vulnerability is difficult. On one level the system itself is extraordinarily stable. It has continued to sustain life on Earth for nearly 4 billion years, despite the transition to an oxidizing atmosphere, five massive extinctions, a 20 percent increase in the intensity of solar radiation, and so on. It will obviously be very difficult for us to destroy the system.
But of course the question for us is whether we might perturb the system so that it can no longer sustain us. Although the system itself has lasted a long time, individual species have not. Of the 500 million to 1 billion species that existed at one time or another, 97 percent have become extinct, due mostly to their inability to respond to changes in the system, especially changes in climate. Again, we get a sense of our privilege at being here, and a sense of our vulnerability.
Unfortunately, we can't say exactly what confers survivability on a species, but we do have some important clues.
We might start by thinking about the relationship between individual species and an ecosystem as a whole. The welfare of individual species is critical to the system--the system exists only in that it is instantiated by a particular set of species. Yet no species can exist apart from a healthy ecosystem. The welfare of the system depends both on the welfare of individual species and on the effectiveness of the biochemical processes linking species together.
At the same time, the classical idea of a "balance of nature" like that of a uniform system in stable equilibrium is wrong. Natural ecosystems tend to be distinctly patchy, the nature of the key processes tends to change with the spatial and temporal scales at which we view them, and they seem to have multiple equilibrium configurations. Perhaps the best criterion of system health is adaptability, the ability to respond creatively to stress, to move easily from one stable configuration to another as needed.
At the species level, generalist species seem to be more adaptable--and more robust--than those that have adjusted to very specific niches. On that criterion, humans would seem to score pretty well, but as we begin to approach Earth's carrying capacity we severely limit our room for maneuvering in response to change. The risk is that we may do our job too well. If we succeed in identifying precisely what our needs are and precisely where in parameter space Earth's capacity to meet those needs is maximized, we could become more vulnerable to change and to variation in the parameters of the global system.
And the importance of adaptability makes an ecosystem's health very difficult to measure. It means that we can't just measure some parameter of the system today and compare it with some supposedly "pristine" state of the system in the past. Healthy systems are constantly changing in response to the seasons, to climatic cycles, and to human forcing factors like deforestation in the Amazon or re-forestation in New England. So change by itself is not necessarily an indication that something is wrong with the system.
Perhaps the best we can do is to compile a variety of indices designed to compare our impact on different sectors of the global ecosystem with the capacity of that sector. A 1997 paper in Science by Peter Vitousek and others comes pretty close. They show that we have transformed nearly half the land on Earth's surface (put differently, we're using nearly half the land's biological production), that we have produced about 20 percent of atmospheric CO2, that we use over half of the available fresh water, and fix over half of the amount of nitrogen fixed globally, and so on.
The finding regarding marine fisheries is one of the most dramatic. When I was growing up in the '50s, the sea was thought of as the ultimate source of food--if we ever outstripped the limits of terrestrial agriculture, the endless oceans stood ready to sustain us. Over half the fisheries were undeveloped. Today, yields in more than half of commercial fisheries have either plateaued or are declining. Our first real experiment in managing global sustainability seems to be going seriously awry. We could tick off other indices--urban air quality, infant mortality--and we could get involved in a prolonged debate of the importance of each. But that debate would miss the point.
The point is that geology has a message for us: That although we are utterly dependent upon the functioning of the global system, we are stressing the system in several critical ways, and there's evidence that we are approaching some of the limits of what the system can provide. Few of these limits are rigid. Most involve tradeoffs, and ask us to set priorities. But as global population expands by another 3 or 4 billion over the next century, stresses on the system are going to increase. And those stresses will get even worse if people who now consume less than we do try to match our lifestyle.
Enough geology for the moment. What does theology have to do with all of this? A great deal. Though we obviously need science to help us understand how the global system works--for example, to inform us of the probable consequences of increasing the CO2 content of the atmosphere--many of our decisions will depend less on our science than on our values--on how much we care about ecological damage; about health issues linked to global warming; about the welfare of people living at or near sea level in Bangladesh, the Nile delta, or the island states; and especially about issues of social justice and generational equity.
So with that new set of questions in mind, let's return to the image of Earth from space. Through that thin veil of cloud, we can now see that faint smear of green as billions of creatures, living together as neighbors in the global ecological family. We begin to see that the ancient tale that humans were created in a fertile and well-watered garden set in a vast desert was in part correct. And the theological affirmation that we need to learn to till the garden and keep it begins to sound reasonable. In theological language, we are called to act as stewards and we have been given the responsibility of "dominion" over other creatures on Earth.
But theology also challenges us to go beyond a purely ecological view of sustainability, and to acknowledge that authentic human existence requires more than the basic physical needs that Earth can supply. A meaningful life should include the freedom to enjoy loving relationships with others, the opportunity to find fulfillment in learning what we are good at and in doing it well. In order to provide those opportunities, theology would insist that sustainability can ultimately be achieved only in a society that values justice and equity.
But here we encounter a problem. Sustainability is obviously a global problem; it is not enough to consider it from the perspective of any one religious tradition. We need to engage a global community, one which now includes some 200 religions and many for whom no religion is decisive. We need a way of thinking and speaking that can connect with all segments of that population and which can operate at the personal, communal, and global levels.
In trying to address such a broad range of traditions, we have a language problem. The language of religion, or faith, tends to be particular to each tradition, and tends to be problematic for people outside that tradition, perhaps especially so for those who espouse no religious tradition. Even that term faith has so many overtones that it has become problematic. The theologian Paul Tillich has suggested a way of solving that problem that I find helpful. He suggests that instead of speaking in terms of faith, we speak in terms of what he calls an ultimate concern, that instead of talking about having faith we talk about being ultimately concerned about something, something that for us is our ultimate basis for discernment, our ultimate criterion for deciding how to order our lives.
As Tillich sees it, the truth of an ultimate concern can be assessed in two ways, one objective and one subjective. Objectively, he insists that we judge our ultimate concern on the basis of its ultimacy, on the degree to which its content is really ultimate. Subjectively, he suggests that we judge it on the basis of its power to move us, to impel us to respond out of the very depths of our humanity, with all our heart, all our soul, and all our mind.
Because Tillich's approach sort of levels the playing field between religious and secular thought systems, it helps us to identify areas of common ground and areas of complementarity between geology and theology. Geology would insist that our ultimate concern must include the continuing health of the global Earth system. Theology would agree that as Earth's stewards our ultimate concern must impel us to work toward sustainability, but a new kind of sustainability, one which goes beyond the mere functioning of the natural system to include an explicit dimension of social justice. Theology would then go on to say that if we accept this concept of sustainability as our ultimate concern, we should feel a compulsion to work for sustainability with all of our hearts, our minds, and our souls. Mere assent to the importance of sustainability is not enough; we are called to move beyond assent to an active commitment to work to bring that state into being. Religion is not about doctrine; it is about practice. If our concern is truly ultimate, we are compelled to act.
But here we encounter a problem with both geological and
theological dimensions. Although we recognize that we are
radically dependent upon the Earth system, we are also deeply
aware of our ignorance of the details of how the system
functions, and though we may agree that we have to act, we
are not at all sure just how to act. The problem is even more
acute when we confront the issue of social justice. |
Here theology has a second message. It doesn't matter that we are uncertain about how to proceed or that we doubt whether we can succeed. Doubt tends to be a constant companion of concerns that are truly ultimate. We must simply do the best that we can, in spite of our doubts. And again that means that we must mobilize more than just our minds. We need to involve our hearts and our souls as well. Theology invites us to act with care, energy, and deep joy at the almost incredible privilege of being called as partners in the continuing process of creation.
For religious people, the path to involving our hearts and our souls is a familiar one. We pray, or meditate, or follow some spiritual practice that engages our hearts and our souls. For more secular people, the path may lie in different directions. Some find the courage to act in a deep sense of commitment that emerges from their research. Others may sense it in a quiet walk in a near-primeval forest or in cultivating a garden. Others in the depth of their love for their family or community.
That sense of connectedness that engages the whole person is what a theologian would call revelation. And, unfortunately, revelation is widely misunderstood. Many assume it is a process that abandons reason. But that's not it at all. Revelation is a process that involves the whole person--it's a confluence of reason with affective response, the experience of having all of our cognitive tumblers fall into place at once, when we suddenly see the world from a new and transforming perspective. H. Richard Niebuhr put it this way: Revelation is the "experience that makes all other experience intelligible," the one event that gives meaning to everything else. It's sort of like falling in love.
Revelation can emerge from either secular or religious insight, but as Tillich notes, every revelation--whether grounded in secular or religious thought--is always humanly distorted, a partial image of reality. So although our commitment to an ultimate concern may give us the courage to act in spite of uncertainty, it does not--it must not--be taken to confer certainty. Here religion can learn a lot from science. Any meaningful way of imaging reality carries the risk of our becoming too committed to it. Our images can all too easily be taken to be reality, rather than the meaningful glimpses they are. And religious thought has proven to be all too vulnerable to that form of self-deception. Accepting any system of belief or image of reality too rigidly is idolatry, and religious history is full of glaring examples, examples that have inhibited the growth of understanding instead of fostering it. Like science, religious thought must be willing to test its deepest commitments in light of human experience, to be, in the language of one tradition, "reformed and always reforming."
So, finally, what I am arguing today is that we should try to imagine a sustainable future in terms of a confluence of geology and theology, or, more broadly, of science and religion. There is a surprising amount of common ground, but even where differences remain the two are complementary rather than contradictory. We need to honor and take advantage of the differences. Both geology and theology see the need for including ecological sustainability in our ultimate concern. Geology can provide concrete data and help us to understand that need more precisely and deeply. Theology can show us that sustainability must incorporate a commitment to social justice. Both suggest that we should feel a sense of privilege at being here, and a sense of humility born of the inadequacy of our understanding. Both rely on reasoned reflection of our experience. Geology serves as a model of the need to test, revise, and reshape our understanding of how the world works, at times rejecting our most cherished ideas. Theology encourages us to take seriously our affective responses to the beauty of nature and life, and to allow the power of those emotions to give us the courage we need to live creatively.
We need to recognize that science and religion are each essential parts of what it is to be human, and that if our vision of a sustainable future is to respond authentically to our humanity, our vision must be shaped by both. I pray that both will have the humility to recognize that each will be wrong, perhaps much of the time; that we learn from our missteps and from each other; and that we judge one another for the best that we offer, not the worst. And I pray that we can find the courage to act creatively despite our doubts. Our future depends upon it.
Fisher's essay on this topic will appear in The Earth Around Us: Maintaining a Liveable Planet, due out in April from W. H. Freeman and Company.
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