An open access publication of the American Academy of Arts & Sciences
Fall 2001

Perspectives on Environmental Change: A Basis for Action

Michael Brendan McElroy
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Michael B. McElroy is a professor in the division of engineering and applied sciences and the department of earth and planetary sciences at Harvard University. He is also director of the Harvard University Center for the Environment.


We live at a unique point in the history of planet Earth. After almost four billion years of evolution, a single species, Homo sapiens sapiens, has evolved with the capacity to think, to contemplate not only its place in the universe but also potentially to control its own destiny and that of other species as well. What sets our species apart is our brains. We have the facility to absorb, process, and organize prodigious amounts of information. With language, written and spoken, we can pass information from person to person, extending knowledge and experience from generation to generation across the ages. With art and literature we can stimulate the imaginations of our fellow humans. With science we can explore the complex processes that developed in the first few seconds of the universe, in the aftermath of the big bang. We can hope to understand the events that led to the production of the elemental subatomic building blocks of matter, the synthesis of the elements, and the eventual accretion of matter in orderly macroscopic structures we identify as planets, stars, and galaxies. We can track the life cycle of a star from birth, to death, to rebirth. We can enumerate the factors that set our planet apart from other bodies of our solar system. We can reconstruct the history of the earth and speculate as to the events that led to the early appearance of life and the forces that shaped its subsequent evolution. We can hope to unravel the principles that govern life itself. And soon we may have the capacity to manipulate our genes, perhaps to eliminate disease or at least postpone its onset.

Yet there is a dark underside to this record of accomplishment. The achievements of our science are astounding, the future scarcely imaginable. In a world of specialization there is a risk, though, that we may lose sight of our place in nature, that we may begin to view ourselves as above it all—as supernatural. We have developed an undeniable capacity to transform the earth, to alter, for example, the composition of the atmosphere on a global scale with uncertain but surely inauspicious implications for the climate. We have the power to eliminate in a geological instant species that took billions of years to evolve. The critical question is whether we have the wisdom and ethical maturity to employ our scientific and technological skills with discretion. As the late Roger Revelle remarked, we have embarked on an unplanned global experiment and our ability to predict the consequences is deficient. We need to step back and take stock if we are to avoid serious mistakes. We need a moral compass: there are ethical as well as technical issues to be addressed if we are to chart a responsible course to the future.

Do we have the right to alter the composition of the global atmosphere if we are unable definitively to assess in advance the consequences? If the changes in atmospheric composition for which rich nations are largely to blame result in a change in climate and if the negative effects of this climate change are experienced most acutely by those less advantaged, is there a duty for the responsible parties to provide compensation? Do we have a moral obligation to preserve the diversity of life forms on Earth? If our actions lead to elimination of entire ecosystems on the planet, tropical rain forests for example, should our children unborn have the right to hold us accountable? What are the rules by which we should live and be judged? What is our proper place in nature? If posterity is to serve as jury, to whom do we answer as judge? If there are no penalties, why should we care? Science alone cannot provide answers to these questions. Nor can we expect a definitive response from our colleagues in economics.

For the economist, the value of the rain forest lies in the monetary returns to be reaped by harvesting its resources. Its timber has value. So also have the unique genetic materials it harbors, resources that might be exploited in the future to develop medicines to help combat disease. We could propose to measure the aesthetic worth of the forest by estimating fees tourists would be prepared to pay to enjoy its wondrous diversity and complexity. But surely there is more to the continued existence of the rain forest than a value measured simply in dollars and cents. Thomas Berry argues that the natural world is “our primary revelatory experience.” He decries the emphasis by the religious establishment on “verbal revelation to the neglect of the manifestation of the divine in the natural world.”1 To destroy the rain forest, or any other unique feature of the natural world, is, in Berry’s perspective, a sin, an insult to the Creator, an impediment restricting permanently our ability to contemplate and communicate with the Divine. It would be difficult to attach a monetary value to such a far-reaching impact.

This essay is concerned specifically with changes in the global environment resulting from diverse forms of modern industrial activity. We begin with an attempt to place the contemporary human influence in a larger historical context. Our human species is a product of close to four billion years of evolution. Only recently, however, in the past century or so, have we developed the capacity to alter the environment on a global scale. We choose to emphasize the challenge posed by the impact of human activity on the climate system. Yet, as we shall indicate, there are other issues that demand attention.

The properties of climate depend to an important extent on the composition of the atmosphere. The atmosphere today is composed mainly of diatomic oxygen and nitrogen. These gases are transparent to sunlight and transparent also to longer wavelength infrared radiation emitted by the surface of the earth. If the atmosphere were composed exclusively of oxygen and nitrogen, the surface of the earth would be freezing cold, incapable of supporting life as we know it. Earth’s relatively mild climate results from the presence in the atmosphere of small concentrations of polyatomic gases capable of absorbing infrared radiation emitted by the surface. These gases serve to insulate the surface from the cold temperatures of outer space. By loose analogy with the function of glass in a greenhouse, they are referred to as greenhouse gases. Water vapor is the most important of the contemporary greenhouse gases. The supply of water vapor depends, however, on temperature. If Earth were cold, concentrations of water vapor would be too low to have a significant impact on the climate. The presence of a concentration of water vapor sufficient to raise the surface temperature of the earth by a significant amount depends, thus, on the presence of other greenhouse gases, notably carbon dioxide, methane, and nitrous oxide. As we shall see, concentrations of these gases are increasing at a historically unprecedented rate today.

The nature of the disturbances responsible for these changes and the potential implications for the climate are discussed below. A critique of policy options currently underway to address the issue of climate change also follows, highlighting the need for an ethical perspective to complement the contemporary emphasis on science, technology, and economics. As discussed further below, addressing the challenge of global environmental change will require an evolution of social organizations comparable to the physical evolution of Earth and the evolution of life itself. Private parties, governments, educational institutions, religions, and business all have essential roles to play. If we are to be successful, we argue, our actions must be guided not simply by science and economics but also by an abiding sense of universal ethical responsibility.


The earth is approximately 4.6 billion years old. It evolved from the spinning mass of gas and dust that constituted the original solar nebula. As it formed, the planet began to heat up, responding in part to energy released during gravitational accretion, in part to the input of heat associated with the decay of radioactive elements such as uranium, thorium, and potassium. Heating of the interior led to instability with lighter material underlying heavy. This resulted in a spontaneous adjustment, an organized pattern of vertical motion with lighter material rising in some regions to be replaced by heavier stuff sinking elsewhere. Heavier elements such as iron settled to the core. More volatile elements such as hydrogen, carbon, nitrogen, and the noble gases concentrated in the near surface region forming the primitive atmosphere, ocean, and crust. Chemical differentiation, driven by the changes in pressure and temperature accompanying vertical motion, resulted in the formation of the distinct zones identified today with the core, lower and upper mantle, crust, atmosphere, and ocean. Regions of uplift were associated with divergence of crustal materials at the surface; preexisting crustal material was pushed apart as fresh matter reached the surface. Conversely, regions of downward motion were associated with convergence of surface material. Segregation of light from heavy minerals led to the appearance of continents and ocean basins. The lighter minerals that formed the continents floated like rafts on the underlying heavier material composing the mantle. Crustal matter was organized in a number of coherent structures, referred to as plates. As fresh material was added to individual crustal plates by upward motion, old material was removed by compensatory downward motion elsewhere. The configuration of crustal plates evolved significantly over the course of geologic time responding to changes in the strength and spatial pattern of convection. Mountains formed and were eroded by weathering. At times, continental plates were joined in supercontinental structures. At others, they were more broadly dispersed. The juncture of India with Asia, for example, responsible for the formation of the Himalayas and the Tibetan Plateau, is a relatively recent occurrence: it took place about fifty-five million years ago. North and South America joined to form a composite unit as recently as a few million years before present (BP).

Tectonics, the internal dynamics of the earth, not only had an influence on the nature of landforms at the earth’s surface, but also almost certainly played a role in the origin and evolution of life. Life was an early arrival on the planetary scene. It developed at least 3.5 billion years ago, arguably earlier. The precise steps that led to the appearance of the first self-replicating organisms are unclear. Some believe that the action occurred in the atmosphere triggered by chemical reactions associated with lightning and ultraviolet solar radiation. Others contend that it arose first in the ocean, in the vicinity of hot springs emanating from regions where fresh material emerges from the interior to interact explosively with cold ocean waters of distinctly different chemical composition. Deep-sea vents, distributed along zones of sea-floor spreading, support a remarkable ecological system at present. Bacteria, drawing energy from oxidation of the sulfur contained in hot spring water, represent the base of a food chain supporting a dense population of worms and clams living in close proximity to the vents. Water emanating from the vents contains a variety of trace metals and other elements essential for life. Nitrate or nitrite formed from acids produced in the primitive atmosphere could have provided the oxidants for synthesis of the earliest forms of life.

The earliest forms of life consisted of simple organisms known as prokaryotes. Bacteria and blue-green algae represent examples of species that existed from the onset and that continue to function as important components of the diverse interactive web of life that characterizes our planet today. Bacteria play an important role in the decomposition of organic matter; they dispose of our garbage, transforming waste to useful matter. Blue-green algae have the remarkable ability to convert inert diatomic nitrogen to biologically available fixed nitrogen, rivaling the capabilities of the expensive energy-intensive fertilizer factories that accomplish the same task today. Prokaryotes dominated life for much of the early history of the earth. Several billion years elapsed before they were joined, roughly 1.5 billion years BP, by more complex life forms, the eukaryotes.

The cells of eukaryotic organisms were vastly more complicated than those of their prokaryotic antecedents. Lynn Margulis suggests that the eukaryotes may have evolved as a result of the fusion of cells of the preexisting prokaryotes.2 Cells of particular prokaryotes were invaded by cells of others, leading to the appearance of new life forms with greatly enhanced functionality. The development of the eukaryotic cell paved the way for the evolution of more complex multicellular organisms. Remarkably, almost a billion years elapsed before the appearance of the first multicellular animals, the so-called Ediacara fauna—flat, pancake-shaped, soft-bodied organisms named for the region in Australia where their fossil remains were first detected. The first hard-bodied (shelly) organisms, the Tommatians, named for the region in Russia where they were first discovered, appeared somewhat later, followed by the veritable profusion of life forms identified in the Burgess Shale, the paleontological Rosetta stone discovered high in the Canadian Rockies by C. D. Walcott in 1909.3

The diversity of life forms recorded in the Burgess Shale and the subsequent developments that led to the appearance of vascular plants (about 445 million years BP), amphibians (about 300 million years BP), and other life forms are truly remarkable. Life, for most of the early history of the earth, was confined to the ocean. Only later, at about 440 million years BP, did it spread to the land. Progenitors of all the modern phyla are present in the Burgess record, dated at about 550 million years BP, together with a host of other species that failed to survive. The factors that led to the evolutionary developments recorded in the Ediacaran, Tommatian, and Burgess deposits are not well understood. Recent work suggests, however, that a series of dramatic shifts in climate during the Neoproterozoic, between about 750 and 580 million years BP, may have had an influence. On at least four occasions over this period, the earth moved into a deep freeze, a condition referred to by Joel Kirschvink as a Snowball Earth.4 The evidence suggests that during these periods the earth was frozen over from equator to pole. The ocean was effectively isolated from the atmosphere. Paul Hoffman and his colleagues proposed that the Snowball Earth condition was triggered by a precipitous drop in the concentration of atmospheric CO2, prompted by a decrease in the release of CO2 associated with a decrease in global tectonic activity.5 Environmental changes, specifically changes in the chemistry of the ocean, accompanying these remarkable climate transitions could have provided the stimulus for the burst of evolutionary activity observed at the onset of the Cambrian. Changes in the environment may have been responsible also for the massive extinction events that punctuate the subsequent geologic record. The Cambrian expansion, for example, was followed a few hundred million years later, at about 225 million years BP, by what Gould termed the “granddaddy of all extinctions,” responsible for the elimination of as many as 96 percent of all the marine species alive at that time.6 A second major extinction took place 65 million years ago, at the boundary of the Cretaceous and Tertiary periods, and was associated with the demise of the dinosaurs. The later event, it is thought, was induced by a change in the environment triggered by the impact of a giant meteorite. The extinction at the Cretaceous-Tertiary boundary paved the way for large mammals and later for the evolution of hominids and our earliest human ancestors.

Mammals developed at the end of the Triassic, about 160 million years BP. As Gould remarks, they spent their first 100 million years as “small creatures living in the nooks and crannies of a dinosaur’s world.” He suggests that “their 60 million years of success following the demise of the dinosaurs has been somewhat of an afterthought.”7 If afterthought it was, we are the products of this circumstance. To quote Gould again: “in an entirely literal sense, we owe our existence, as large and reasoning animals, to our lucky stars.”

Our closest living relatives in the animal kingdom are the great apes (including the gorilla and the chimpanzee). Much of the evolutionary development that led to the eventual appearance of humans is thought to have taken place in Africa beginning about 4 million years ago. The details of the path to modern humans is unclear but is thought to have proceeded along a trajectory that involved, sequentially, Australopithecus africanus, Homo habilis, and Homo erectus. Homo erectus arrived on the scene about 1.7 million years ago and evolved later into Homo sapiens. Human history as we know it took off much more recently, about 50 thousand years ago, in what Jared Diamond termed the Great Leap Forward, with evidence for biologically and behaviorally modern humans in a variety of locations including East Africa, the Near East, and both southeastern and southwestern Europe.8

There is some dispute as to where our earliest human relatives originated. Early interpretations of human mitochondrial DNA suggest that we may have a common maternal ancestor, that she may have lived in Africa about 150 thousand years ago, and that her progeny may have migrated subsequently to the Middle East, Europe, Asia, and Australia, reaching the Americas as recently as twenty to thirty thousand years ago. Others favor a more distributed origin for humans. It is clear in any event that we are recent arrivals on the stage of planetary life. Never before, though, has the earth seen a species with a greater capacity to dominate its environment. As discussed by Diamond, our influence is far-reaching and not always benign.9

In the earliest period of their history, our ancestors had relatively little effect on their environment. For food and fiber, they relied on resources available in their immediate vicinity. They hunted wild animals and harvested wild plants for food. Human populations were relatively low, and supplies of food were adequate to meet the needs of these early nomads. With the passage of time, the hunter-gatherer life-style became increasingly more difficult. Depletion of wild animal stocks and sources of plants suitable for human consumption, exacerbated by increases in the human population, may have contributed to the difficulty, prompting the first great human social adjustment: the transition from the nomadic existence of the hunter-gatherers to the more sedentary life-style of the first agricultural communities. The advance that made this possible involved the domestication of plants and animals. Rather than searching in the wild for plants to eat or animals to slaughter, it was easier to cultivate the land in one place, sow and reap the most desirable crops, store crop surpluses, and tame available animals to serve needs for food, fiber, fertilizer, and labor. The transition to agriculture and animal husbandry occurred first, it appears, in southwest Asia about ten thousand years ago, in the region known as the Fertile Crescent occupied today by Jordan, Israel, Syria, Iraq, and parts of Turkey. It was accompanied by the evolution of new social structures, facilitated by the availability of food surpluses. No longer was it necessary for all members of a community to engage in an unending search for food. Human functions became more specialized. An artisan class developed, and later chiefs, philosophers, priests, warriors, and eventually nation-states, setting the scene for the evolution of science, religion, and other features of modern life.

These early social structures led to the first serious conflicts between man and nature. John Perlin recounts the problems encountered as a result of the unsustainable exploitation of locally available sources of timber. Wood, he points out, was the “foundation on which early societies were built.”10 It provided, among other functions, the fuel for fire and thus the means to convert clay to pottery and to extract metal from rocks, as well as the material to fabricate the implements of industry and agriculture and to construct ships, permitting societies to forage for resources far from native shores. Deforestation led to the decline and fall of the great civilizations that flourished five thousand years ago in Mesopotamia. Perlin attributes the demise of Sumerian civilization, for example, to a precipitous drop in agricultural production occasioned by excessive accumulation of salt in the previously rich alluvial soils of the region. The salt responsible for this problem originated in the salt-rich sedimentary rocks that formed the mountains to the north. The increase in salt carried by rivers draining these mountains and its accumulation in the alluvial plains was attributed to removal of the protective forest cover in the upstream region prompted by the inexhaustible demand for timber. Perlin argues that much of modern history, dating from Greek and Roman times but extending toward the present, can be attributed to actions taken by societies to ensure adequate sources of timber. Deforestation is not a recent phenomenon. It has existed from the beginning. It is spreading now to regions previously immune, such as the tropical rainforests, and it is this that draws our attention. Paradoxically, the development since the industrial revolution of economies based on fossil sources of energy rather than wood offers the opportunity to reverse the trend toward global deforestation.


We turn our attention now to problems of the present. To this point, we have sought to provide a broad context to define the place of humans in nature. It is difficult, however, to comprehend the significance of events that unfold on time scales measured in billions of years. It is instructive to recast the history of our planet on a more comprehensible time scale.

Assume for the moment that the 4.5-billion-year history of the earth is compressed into a single year. Formation of Earth from the primitive solar nebula begins in this case on January 1. The early prokaryotes are established by February 17. Almost seven months elapse before the eukaryotes appear in early September. The expansion of life recorded in the Burgess Shale takes place in mid-November. Mammals arrive on December 18, while dinosaurs meet their untimely demise on the evening of December 26. Humans make a late appearance at about 9 p.m. on the evening of December 31. The industrial revolution begins about two seconds before midnight on December 31. And we are grappling now with events that will unfold over the next few tenths of a second.

The industrial revolution marked a pivotal turning point in human history. It resulted in a host of inventions, including the heat pump, the steam engine, the internal combustion engine, the means to generate and distribute electricity, the railroad, the automobile, the airplane, the radio, the telephone, and the television. Advances in medical science extended life expectancies, resulting in a rapid growth of human populations. The population of the world in 1750 at the dawn of the industrial revolution was estimated at about 720 million. It had surpassed a billion by the end of the first quarter of the nineteenth century, rising to two billion by 1925, climbing above five billion by 1990.11 The benefits of the industrial revolution are not, however, evenly distributed. Disparities between rich and poor countries have increased, as has the gap between rich and poor within countries. Mechanization has reduced the demands for human labor required for the manufacture of new products: the contributions of the scientist, engineer, financier, politician, and manager are thus valued more highly than those of the laborer. To an increasing extent in an economically integrated world, rich countries turn to others less advantaged for cheap labor and for the natural resources required to supply the demands of their industry. Only now are we beginning to confront the consequences.

The industrial revolution was fueled initially by coal, replacing diminishing reserves of wood. Concentration of coal-fired factories and residences in cities had immediate and serious implications for local and regional air quality and public health. Criticism of these consequences was initially muted. For a long time the problems were accepted as an inevitable price of progress. Attitudes changed in the late 1940s and 1950s, when a series of air-pollution disasters in Donora, Pennsylvania, and London caused large numbers of people to get sick and thousands to die. It was relatively easy to deal with the problem of visibly dirty air. The solution was to burn cleaner fuels, to remove particles from smokestacks, or to build higher stacks and send the problem elsewhere. But the smogs of Donora and London were merely the harbingers of more serious problems to come—acid rain, photochemical smog, and now, most perplexing of all, the threat of global climate change.

There is a troubling pattern to our response to problems relating to the use of fossil fuels: the issues are often identified long after the technologies responsible for the problems have been widely employed. When we installed high smokestacks to disperse emissions from coal- and oil-fired factories, we were unaware of the phenomenon of acid rain. When we began our love affair with the automobile, we did not suspect that the interaction of sunlight with hydrocarbons and oxides of nitrogen could stimulate the production of ozone at levels harmful not only to humans but also to plants and animals. Given the enormous investment in infrastructure dependent on fossil fuels—roads, cities, industry—it is easier to look for piecemeal solutions, to search for technological fixes to specific problems rather than environmentally more friendly alternatives to our current, unfettered, use of fossil fuels. The potential for climate change associated with emissions of carbon dioxide, the end product of fossil-fuel combustion, brings the problem into even sharper focus.

Air-quality problems associated with the early use of fossil fuel were largely confined to regions where industrial activity was concentrated. Those responsible for the problems bore the brunt of the consequences and had an obvious self-interest in seeking improvement. Installation of high smokestacks spread the impact over a much larger region, requiring national and indeed international approaches to remediation. Problems, however, were still reasonably confined. A European initiative could address the problem of acid rain in Scandinavia arising as a consequence of emissions of sulfur and nitrogen oxides in Britain, Germany, and Poland. Likewise, a cooperative arrangement involving Mexico, the United States, and Canada could deal with the problem of emissions in North America. The climate issue, however, is global in scope and requires a global response.

Combustion of fossil fuels—coal, oil, and natural gas—accounts today for global emission of carbon dioxide equivalent to more than six billion tons of carbon per year (more than twenty billion tons of CO2). Deforestation, mainly in the tropics, contributes an additional source of about two billion tons of carbon per year, offset by an uptake of roughly comparable magnitude due to regrowth of vegetation at mid-latitudes of the northern hemisphere. Approximately half of the carbon added to the atmosphere since the beginning of the industrial revolution persists in the atmosphere today, with the balance incorporated in the ocean. Carbon dioxide is the largest single waste product associated with modern society. Emissions on a per capita basis amount to more than a ton of carbon per person per year. The developed world is largely to blame. The United States, with a little more than 5 percent of the world’s population, is responsible for close to 22 percent of global emissions. But the future will depend in large measure on what happens in developing countries such as China, India, Brazil, and Indonesia.

Emission of CO2 in such large quantities has resulted in a significant rise in the concentration of CO2 in the atmosphere. Carbon dioxide accounts for about 360 parts per million of the atmosphere today. It has increased by about 30 percent since the beginning of the industrial revolution and is expected to more than double if we continue to rely on fossil fuels for energy and if we fail to reverse current practices resulting in the destruction of tropical forests. The concentration of CO2 is higher now than it has been at any time over the past 450 thousand years (we know this from measurements of gases trapped in ancient ice preserved in Antarctica). Given current trends, it is likely soon to exceed levels not seen since dinosaurs roamed the earth 65 million years ago. And CO2 is not the only constituent of the atmosphere that is changing. Comparably large increases are observed for methane, produced by cattle and other ruminants and also as a by-product of rice cultivation and mining of fossil fuels, and nitrous oxide, emitted in conjunction with the decay of human and animal waste and the transformation of nitrogen-based fertilizers applied to stimulate agricultural production. Human activity has an undisputed effect on the composition of the atmosphere. The critical question concerns the details of the implications for the climate.

The climate system is extremely complex. A change in the radiative properties of the atmosphere associated with an increase in the concentration of greenhouse gases may be expected to trigger an initial adjustment in temperatures at the surface of the earth and in lower regions of the atmosphere, accompanied by changes in patterns of evaporation and precipitation, cloud cover, and the distribution of the primary greenhouse gas, water vapor. Variations in cloud cover and water vapor will lead to additional feedbacks resulting in both warming and cooling of the atmosphere, prompting changes in the circulation of the atmosphere and ocean with implications for vegetation and for snow and ice cover. The ultimate effect will depend on the composite effects of an interactive web of multifaceted disturbances. Diagnosing the implications for climate requires a realistic simulation of the coupled, interactive dynamics of the atmosphere, ocean, biosphere, soil, hydrosphere, and cryosphere (the ice world), a task of considerable complexity. There is no certain way to predict the future. The best we can do is to take the results of the most realistic computer models as a guide as to what might ensue and plan accordingly.

The evolving state of climate science has been reviewed over the past decade in a series of reports prepared under the auspices of the Intergovernmental Panel on Climate Change (IPCC). The IPCC was established in 1988 by the World Meteorological Organization (WMO) and by the United Nations Environment Programme (UNEP) to advise on the likelihood that human activities could lead to significant changes in climate, to evaluate the impacts of these changes, and to identify options for possible policy responses. In its first report, the IPCC concluded that “there is a natural greenhouse that keeps the Earth warmer than it would otherwise be,” that “emissions resulting from human activities are substantially increasing the concentrations of greenhouse gases,” and that “these increases will enhance the greenhouse effect, resulting in additional warming at the Earth’s surface.”12 Results from sixteen different computer models of future climate were reviewed in a second IPCC report published in 1996.13 Despite differences in detail, these models confirmed the conclusion of the earlier report: that emissions of greenhouse gases, should they continue at current rates, may be expected to result in significant warming of the earth with important if uncertain implications for regional climate. Results from a recent study by the United Kingdom Hadley Center provide an instructive indication of the changes that might ensue.

Assuming “business as usual”—that is to say, in the absence of steps to curtail emissions—the Hadley model suggests that the global average surface temperature will increase by about 2°C over the next fifty years. The increase in temperature expected over continental regions is almost twice as large: about 4°C by 2050, rising to 6°C by 2100. Increases in temperature are greatest for high latitudes in winter. Surprisingly, though, the model anticipates a significant change in climate also in the tropics, warming by as much as 4°C over Brazil by 2050, accompanied by a marked decrease in precipitation. A change of climate of this magnitude would signal the demise of the Brazilian rain forest, which would be replaced by savanna. Elsewhere, in India, Africa, and portions of North America, tropical grasslands would be transformed to either temperate grasslands or deserts. Results of the Hadley model should not be taken as definitive but may provide a wake-up call as to the gravity of the changes that are possible. They suggest that disturbances to ecosystems could be extreme and that implications for human societies, while difficult to quantify, could be serious, especially for populations lacking the economic resources required for an efficacious response.


The initial IPCC report influenced the deliberations of the Second World Climate Conference that convened a few months later in Geneva. It was responsible for the inclusion of the climate issue on the agenda for the United Nations Conference on Environment and Development that met two years later in Rio de Janeiro. This so-called Earth Summit attracted a remarkable twenty-five thousand delegates, including a large fraction of the world’s political leaders. The conclusions of the summit were summarized in a document formally titled “The United Nations Framework Convention on Climate Change.” The convention was “to enter into force on the ninetieth day after the date of deposit of the fiftieth instrument of ratification, acceptance, approval or accession.” This milestone was passed on March 21, 1994, after Portugal became the fiftieth country to register ratification on December 21, 1993. As of December 10, 1999, the convention had been ratified by 181 countries, including the United States.

The specific policy response of the international community to the climate issue was elaborated in a milestone protocol developed at the third Conference of the Parties to the Convention (COP-3) in Kyoto, Japan, in December of 1997. In advance of the conference, the European Union opted for a Europe-wide coordinated strategy to reduce emissions by 2008–2012 relative to 1990 by 16 percent. Under this arrangement, Germany and Britain agreed to assume the lion’s share of the European obligation, thus permitting less affluent members of the EU such as Greece and Spain to grow their emissions by modest amounts consistent with overall plans for economic development in the Union. This accommodation was possible as a consequence of events in Europe quite unrelated to the climate issue. Emissions in Germany declined precipitously in the early 1990s, reflecting elimination of economically inefficient highly polluting industries in the former German Democratic Republic following German reunification. Emissions in Britain decreased over the same period as a consequence of the politically motivated demise of the coal industry orchestrated by Margaret Thatcher and the replacement of coal by North Sea oil and gas as the fuel of choice for the British economy. In contrast, emissions in the United States had risen rapidly over the 1990s, by close to 10 percent, reflecting the ebullient state of the U.S. economy. It was judged impossible for the United States to meet the targets proposed by Europe, and President Clinton instructed U.S. representatives to negotiate for a target of zero growth rather than the 16 percent reduction proposed by Europe, arguing also for flexibility in means to achieve this objective. Largely as a result of a personal intervention by Vice President Gore at the end of the first week of the meeting in Kyoto, the parties arrived at a compromise: countries of the European Union agreed to reduce emissions by a collective 8 percent; the United States and Japan accepted reductions of 7 and 6 percent, respectively; the Russian Federation was allowed to maintain emissions at the level that applied in 1990; and emissions from Australia were permitted to grow by 8 percent. Overall, if implemented, the protocol would reduce emissions by a group of developed countries by 5 percent by 2008–2012 relative to emission levels that applied in 1990. Thus did COP-3 interpret the instruction of the Convention to define “common but differentiated responsibilities.”

The protocol was an extraordinarily complicated document. It sought to curb emissions of four gases (CO2, CH4, N2O, and SF6) and two classes of industrial compounds (hydrofluorocarbons and perfluorocarbons). It adopted an accounting scheme based on the potential of individual gases to alter the climate, placing all of these gases on a common carbon-equivalent scale. It incorporated a series of flexibility mechanisms included largely at the behest of the United States in response to President Clinton’s direction to the U.S. negotiators. These included an option allowing parties to claim credit for sinks, offsetting charges for sources of prescribed gases, and a provision by which Annex 1 parties could buy and sell rights to emissions, a so-called carbon-trading mechanism. It authorized a scheme by which Annex 1 parties could claim credit for reductions in emissions achieved by developing countries as a result of transfers of technology or financial resources from Annex 1 parties, an option known as the Clean Development Mechanism (CDM). The flexibility provisions are controversial, viewed by some as a device by which the United States could avoid politically difficult requirements to reduce its emissions by altering patterns of domestic consumption, an option to use economic muscle to shift the burden to others. To an extent, the criticism is valid. The carbon-trading provision offers an opportunity for parties having difficulty in meeting their obligations by domestic action to purchase relief by acquiring rights to emissions allowed but unused by the Russian Federation and other former Soviet republics. Given the economic problems of these countries, it is likely that a significant surplus of their emission rights will be available for trade. Such an arrangement, however, would result in no net reduction in Annex 1 emissions. It would constitute what the European Union has referred to as a license to trade “hot air.” The CDM option is similarly controversial. While the underlying objective in this case is laudable—to encourage the transfer of resources from developed to developing countries—it is difficult to see how it would function effectively in practice. The deal struck in Kyoto should not be considered, however, as the last word. It should be viewed rather as an initial step in a continuing process to deal with an issue of extraordinary complexity involving multifaceted dimensions of science, economics, and ethics, posing challenges that will require at least in some instances a subjugation of narrow national interest in favor of a larger if uncertain global good.

In advance of the meeting in Kyoto, the U.S. Senate passed a unanimous (though technically non-binding) resolution instructing U.S. negotiators (a) not to enter into an agreement that would adversely affect the economy of the United States and (b) not to enter into an agreement that would not involve a commitment by developing countries to reduce their emissions of greenhouse gases. The instruction flatly contradicted terms of the convention ratified earlier by the Senate, which decreed that “parties should protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities”; that “developed countries should take the lead in combating climate change and the adverse effects thereof”; and that a group of developed countries and countries from the former Soviet economic zone, identified collectively as Annex 1 parties, should take the initiative in addressing these objectives. Recognizing that the protocol negotiated in Kyoto could not be ratified by the required two-thirds majority of the U.S. Senate, the Clinton administration elected not to submit the agreement for ratification, passing the problem to its successors.

While suggesting that the underlying science might be more uncertain than was generally acknowledged, candidate Bush, in the 2000 U.S. presidential campaign, agreed that the climate issue was important and that it required a response. He proposed that it could be addressed, at least in part, using legislation embodied in the Clean Air Act to limit emissions of CO2. This suggestion later came back to haunt him as President when his newly appointed administrator of the Environmental Protection Agency, Christine Todd Whitman, referred to the campaign promise, assuring fellow environmental ministers at a meeting in Europe that the United States would act domestically to reduce emissions of CO2. In retrospect, it appears that the campaign commitment may have been based on a misunderstanding, a confusion of CO2 with CO: the latter is a pollutant regulated under the Clean Air Act; the Clean Air Act is mute as to emission of the former, though whether or not it could be covered under the broad definition of pollution encompassed by the Act is a matter of some controversy. In any event, Administrator Whitman’s widely publicized remarks led to an immediate clarification of the new administration’s views on Kyoto.

In a letter addressed to Senators Hagel, Helms, Craig, and Roberts on March 13, 2001, President Bush began by noting that “my Administration takes the issue of global climate change very seriously.” He went on to say, however, that “I oppose the Kyoto Protocol because it exempts 80 percent of the world, including major population centers such as China and India, from compliance, and would cause serious harm to the U.S. economy.” He referred to “the incomplete state of scientific knowledge of the causes of, and solutions to, global climate change and the lack of commercially available technologies for removing and storing carbon dioxide.” Paradoxically, he concluded that “we will continue to fully examine global climate change issues—including the science, technologies, market-based systems, and innovative options for addressing concentrations of greenhouse gases in the atmosphere,” and that he was “very optimistic that, with the proper focus and working with our friends and allies, we will be able to develop technologies, market incentives, and other creative ways to address global climate change.” The letter to the senators was greeted with dismay by the international community, interpreted as a signal that the Bush administration had elected to withdraw from the process initiated in Kyoto.

In a subsequent action, the administration requested what amounted to an independent review of the IPCC analyses by the U.S. National Academy of Sciences. The Academy report affirmed the general conclusions of the treatment of human-caused climate change presented in the IPCC Working Group I report while offering a somewhat more qualified assessment of uncertainties. President Bush, in a speech delivered in the Rose Garden of the White House on June 11, 2001, reiterated his opinion that “the Kyoto Protocol was fatally flawed in fundamental ways.” He acknowledged that the United States accounts “for almost 20 percent of the world’s man-made greenhouse emissions” but went on again to argue that developing countries, notably China and India, must also assume responsibility. He indicated that the targets defined by Kyoto “were arbitrary and not based upon science” and that “for America, complying with those mandates would have a negative economic impact, with layoffs of workers and price increases for consumers,” and that “when you evaluate all these flaws, most reasonable people will understand that [the Kyoto protocol] is not sound public policy.” On a more hopeful note, he stated that “America’s unwillingness to embrace a flawed treaty should not be read by our friends and allies as any abdication of responsibility,” that his administration “is committed to a leadership role on the issue of climate change,” that “we recognize our responsibility and will meet it—at home, in our hemisphere, and in the world.” The speech concluded with the enigmatic statement that “we will make commitments we can keep, and keep the commitments that we make.” As this essay goes to press, the nature of the Bush administration’s commitments to the climate challenge have yet to be defined pending the outcome of a comprehensive review currently underway under the leadership of the Secretary of Commerce.


It is instructive to note the extent to which the climate debate in the United States has been dominated by considerations of science and economics. Questions of ethics have been largely ignored. Despite the uncertainties noted by the National Academy of Sciences, the scientific facts are relatively clear. There is no doubt that we are changing the composition of the atmosphere on a global scale. While it is difficult to predict in detail the consequences for the climate, there is a reasonable expectation, as discussed above, that they will be serious and that the impact may be felt most severely by less advantaged members of the global community.

As discussed earlier, the concentration of atmospheric CO2 is greater now than at any time over the past 450,000 years, and given current practices it is likely to rise over the next few decades to levels not seen since the era of the dinosaurs. There is no dispute that consumption of coal, oil, and gas and the elimination of tropical rain forests are largely responsible for the increase in CO2. A variety of different human practices is implicated in the similarly unprecedented increases in CH4 and N2O. Destruction of tropical rain forests is responsible not only for significant emissions of CO2; it is a contributor also to the precipitous recent decline in planet-wide species diversity. A recent study by the United Nations suggests that as much as 25 percent of species living in tropical forests today may be doomed to extinction over the next few decades if current trends in deforestation are not reversed.

Do we have the right to change the composition of the atmosphere globally when we are unsure of the ultimate consequences, even though the best scientific studies suggest that they could be serious and persistent? The God of the Old Testament as recorded in the message of Genesis gave man “dominion over the fish of the sea and over the birds of the air and over every living thing that lives on the earth.” Nowhere, though, did he give man the right to destroy for no good reason. Dominion, for most biblical scholars, implies stewardship, not domination. No less an authority than Pope John Paul II is on record with a statement of the underlying principles. In a message delivered on January 1, 1990, referring specifically to the “depletion of the ozone layer and the related greenhouse effect [that] has now reached crisis proportions as a consequence of industrial growth, massive urban concentrations and vastly increased energy needs,” he stated that:

Theology, philosophy and science all speak of a harmonious universe, of a cosmos endowed with its own integrity, its own internal, dynamic nature. This order must be respected. The human race is called to explore this order, to examine it with due care and to make use of it while safeguarding its integrity.

How can this message be reconciled ethically with a decision to do nothing in response to the range of human-induced threats to the global life-support system discussed here? There is only one possible justification: a conviction that the problem is not real. But even the most recalcitrant skeptic must accept the possibility—I would say probability—that the threats are serious and conceivably even understated. We do not, I conclude, have the right to place the balance of the global life-support system at risk when there are sensible actions that can be taken at least to slow the pace of human-induced change. The answer to the question posed at the beginning of this paragraph, for me at least, is an unequivocal no.

How should we view the attitude expressed by the U.S. Senate, endorsed by President Bush, that the United States should not act to reduce its greenhouse gas emissions until such time as the large developing economies such as China and India are prepared to make a similar commitment? Energy consumption, measured on a per capita basis, in the developing world is more than ten times less than it is in the developed world. With approximately 5 percent of the world’s population, the United States is responsible for more than 20 percent of global emissions of CO2. Is there not an ethical imperative for the rich to take the first step? The New Testament extols the responsibility of the rich to help the poor. The Gospel of Mark teaches that “it is easier for a camel to pass through the eye of a needle than for a rich man to enter the kingdom of God” and indicates as the Second Great Commandment that “you shall love your neighbor as yourself.” Is it not appropriate, and indeed ethical, for we who have enjoyed for so long the benefits of unsustainable energy consumption to take the first steps? For me at least, the answer is yes. And there is also a practical reason to take the lead. A commitment on the part of the United States to reduce domestic emissions of CO2 could stimulate development of new energy-efficient technologies that would find applications not only in the developed world but also in countries of the developing world. It is clear that we could accomplish much of what we do today with less energy. Expanded use of hybrid vehicles, for example, could increase the efficiency of energy use in the transportation sector. Advances in fuel-cell technology offer promising opportunities to curtail demand for fossil fuels. Wind power is already competitive with fossil-fuel-generated electric power in some regions. With additional investment, solar energy could make a contribution, and, despite current difficulties, the potential for safe nuclear power in the future should not be ignored. The key is to provide incentives. These are largely lacking in an era when gasoline is cheaper than bottled water and the costs of waste disposal are invisible.


President Bush is correct in his general conclusion that the Kyoto protocol is unworkable in its present form. The response, however, should not be simply to walk away but to develop an alternate approach and to work with the international community to bring this into effect.

A primary difficulty with the existing protocol relates to the time line. It is unrealistic to expect countries such as the United States to meet their presently defined commitments by 2008–2012. Emissions in the United States are now more than 12 percent higher than they were in 1990. It would be helpful to extend the time horizon, to, say, 2030, while at the same time stiffening requirements. This would acknowledge the reality that it will take time to effect an economically efficient transition to a more sustainable industrial order. Large amounts of capital are invested today, especially in developed countries, in systems rooted in the past—in an age of cheap fossil energy. Rather than relegate productive investments of the past to a premature scrap heap, it would seem sensible that they be phased out gradually as they reach the end of their useful life, permitting a more orderly transition to a less carbon-intensive future. We need a long-range plan and incentives to encourage an effective transition.

The Bush administration has proposed an ambitious plan to address future energy needs of the United States. The plan includes incentives for conservation, for development of more efficient hybrid vehicles, for energy systems based on environmentally friendly fuel cells, for renewable sources of energy, and for a new generation of nuclear power plants. It recognizes the need for a strategy for safe disposal of nuclear wastes and proposes important investments in so-called clean coal technology. It would be useful if the plan could be integrated with the strategy currently under consideration to address the climate issue. By emphasizing the need to ensure the energy security of the United States while at the same time minimizing emission of undesirable pollutants, the administration could take an important step in the formulation of a comprehensive blueprint that would ensure not only the economic future of the United States but also a more sustainable future for the less advantaged citizens of the global society.

The choice of 1990 as a reference point in the Kyoto protocol against which to gauge targets for greenhouse gas reductions was arbitrary. As noted earlier, it works unduly to the advantage of the European Union in that events unrelated to the climate issue were responsible for an unusual decline in European emissions in the immediate post-1990 period. It would be useful to adjust the reference point to provide a more realistic representation of emissions by parties in the recent past. An alternative standard could be based on average levels of emissions for the decade of the 1990s.

In its present form, the protocol addresses the emissions of a suite of greenhouse gases. It might be preferable, initially at least, to focus on one, the major culprit, CO2. Our understanding of the factors responsible for the increase in the concentrations of a number of the other gases, notably CH4 and N2O, is deficient. Sources are related to a variety of disparate activities ranging from leaky gas lines to animal husbandry to waste disposal to rice cultivation. It is difficult to quantify emissions from any particular activity. In contrast, it is relatively easy to define the contributions to CO2.

President Bush is correct that a successful strategy to address the challenge of the climate issue will require a commitment not just by developed countries but also by the global community, specifically by the larger developing economies such as China, India, Brazil, and Indonesia. Inclusion of the latter two is important in that these countries host the bulk of the world’s dwindling reserve of tropical forests and a disproportionate share of the planet’s biological diversity. They are responsible also for major sources of CO2; emission of CO2 associated with tropical deforestation is estimated to contribute at present a source of CO2 equal to as much as 30 percent of that derived from worldwide combustion of fossil fuels. It is important, though, that developing countries be engaged in a manner consistent with the agreement defined by the Framework Convention, that “developed countries should take the lead.” Extension of the time line to 2030 would allow time for diplomatic initiatives to define an equable basis for participation by the developing world and for developed countries to demonstrate their bona fides.

Decisions should not simply be left to governments. Private foundations, nongovernmental organizations, businesses, academic institutions, and religious organizations all have important roles to play in advancing the goal of a sustainable, equitable, global society and in protecting the irreplaceable legacy of 4.5 billion years of planetary evolution. Private foundations are increasingly important players on the international stage, responding to priorities defined by socially conscious sponsors. Free of the political constraints limiting actions by governments, they have taken the lead in recent years, addressing a variety of socially important issues in the developing world ranging from immunization of children against infectious disease to the provision of small loans to encourage empowerment of women and other disadvantaged members of the global society. Nongovernmental organizations made their presence felt at the Earth Summit in Rio de Janeiro and more recently at meetings of the World Trade Organization and the International Monetary Fund, as well as at the gathering of the so-called G8, the leaders of the world’s most developed economies. Answering only to their members, these organizations are emerging as a powerful new force in international affairs. Investments and decisions by multinational corporations regulate flows of capital across borders, affecting the lives of countless millions of people around the world. Academic institutions, offering insights into nature and the human condition, also have an important role to play and can contribute to a more equitable global society by fostering a deeper understanding of human problems while at the same time identifying creative strategies for their solution. Religious institutions have a special responsibility. They can help set the ethical agenda. To be effective, though, they must be dynamic and must clearly enunciate their view of the place of humanity in nature. Where necessary, doctrines rooted in the past must be updated to incorporate insights from modern science.

We must appreciate that human society, like nature itself, is dynamic. We need a global vision to recognize that there is a unity to life on Earth, that we are part of nature, not independent, that we have the potential to change our environment but that we must exercise this power with discretion. We need a deeper appreciation for ourselves and for nature, drawing on insights not only from science but also from the intellectual heritage codified in the world’s great philosophical and religious traditions. This collection of essays represents an important step toward addressing this objective.


1 Thomas Berry, The Dream of the Earth (San Francisco: Sierra Club Books, 1988).

2 Lynn Margulis, Symbiosis in Cell Evolution (San Francisco: W. H. Freeman, 1981).

3 For an account of the Burgess discovery and a discussion of its implications, the reader is referred to a masterly, fascinating treatment of the subject by Stephen Jay Gould, Wonderful Life: The Burgess Shale and the Nature of History (New York: W. W. Norton and Company, Inc., 1989).

4 J. L. Kirschvink, “Late Proterozoic Low-Latitude Glaciation: The Snowball Earth,” in The Proterozoic Biosphere, ed. J. William Schopf and Cornelius Klein (Cambridge and New York: Cambridge University Press, 1992).

5 P. F. Hoffman, A. J. Kaufman, G. P. Halverson, and D. P. Schrag, “A Neo-proterozoic Snowball Earth,” Science 281 (1998): 1342–1346.

6 Gould, Wonderful Life: The Burgess Shale and the Nature of History.

7 Ibid.

8 Jared Diamond, Guns, Germs, and Steel (New York: W. W. Norton and Company, Inc., 1997).

9 Ibid.

10 John Perlin, A Forest Journey: The Role of Wood in the Development of Civilization (Cambridge, Mass.: Harvard University Press, 1989).

11 Joel E. Cohen, How Many People Can the Earth Support? (New York: W. W. Norton and Company, Inc., 1995).

12 Intergovernmental Panel on Climate Change (IPCC), Climate Change: The IPCC Scientific Assessment: Report prepared by Working Group 1 (New York: Cambridge University Press, 1990).


13 IPCC, Climate Change 1995: The Science of Climate Change. Contribution of Working Group 1 to the Second Assessment Report of the Intergovernmental Panel on Climate Change (New York: Cambridge University Press, 1996).