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4
Environmental Threats and Opportunities

The goals for a transition toward sustainability, as we set them out in Chapter 1, are to meet human needs over the next two generations while reducing hunger and poverty and preserving our environmental life support systems. The activities to approach this goal can only move ahead within the constraints set by resources and the environment. Many people have argued that, unless we make dramatic changes in our human enterprises, the development needed to meet future human needs risks damaging the life-support capabilities of the earth—which in turn would of course prevent society from meeting its goals. In this chapter, we therefore ask two related questions:

• What are the greatest threats that humanity will encounter as it attempts to navigate the transition to sustainability?

• What are the most promising opportunities for avoiding or circumventing these threats on the path to sustainability?

Our object is not to predict what environmental damages might be caused by development at particular times and places—a largely futile activity for all but the most specific and immediate development plans. Rather, it is to highlight some of the most serious environmental obstacles that might be met in plausible efforts to reach the goals outlined in Chapter 1 and along development paths such as those explored in Chapters 2 and 3, to take timely steps to avoid or circumvent these obstacles.1

This chapter begins with a brief discussion of the approaches and issues we considered in scouting the environmental hazards that societies may confront. We then turn to efforts to assess the relative severity of



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Page 185 4 Environmental Threats and Opportunities The goals for a transition toward sustainability, as we set them out in Chapter 1, are to meet human needs over the next two generations while reducing hunger and poverty and preserving our environmental life support systems. The activities to approach this goal can only move ahead within the constraints set by resources and the environment. Many people have argued that, unless we make dramatic changes in our human enterprises, the development needed to meet future human needs risks damaging the life-support capabilities of the earth—which in turn would of course prevent society from meeting its goals. In this chapter, we therefore ask two related questions: • What are the greatest threats that humanity will encounter as it attempts to navigate the transition to sustainability? • What are the most promising opportunities for avoiding or circumventing these threats on the path to sustainability? Our object is not to predict what environmental damages might be caused by development at particular times and places—a largely futile activity for all but the most specific and immediate development plans. Rather, it is to highlight some of the most serious environmental obstacles that might be met in plausible efforts to reach the goals outlined in Chapter 1 and along development paths such as those explored in Chapters 2 and 3, to take timely steps to avoid or circumvent these obstacles.1 This chapter begins with a brief discussion of the approaches and issues we considered in scouting the environmental hazards that societies may confront. We then turn to efforts to assess the relative severity of

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Page 186 these hazards for particular times and places. Following the lead of the Brundtland Commission, we next analyze how human activities in a number of crucial developmental sectors might pose important challenges and opportunities for navigating the transition toward sustainability. Finally, we turn to the question of interactions—how multiple developmental activities may interact with complex environmental systems to transform the very nature of the journey before us. Throughout our discussion, we not only seek to identify potential obstacles to a successful transition, but also to highlight the skills, knowledge, and materials that might be most useful in detecting and understanding the hazards, and in devising solutions or mid-course corrections to address them. We conclude that in any given place there are significant if often place-specific opportunities for societies to pursue goals of meeting human needs while sustaining earth's life support systems. Some of these opportunities are likely to be realized by individual actors—firms, organizations, and states—in the normal course of their self-interested activities. Others, however, will require integrative planning and management approaches. Conceptual Issues One of the most difficult challenges of the Board's exercise—and one that has bedeviled other attempts to evaluate the pitfalls to sustainable development—has been to determine which of the many potential problems are truly those that cannot be ignored. Perhaps the easiest approach might be to list as potential concerns for sustainable development every resource limitation or environmental response that can be imagined. Equally clear, however, is that a canoe-steering society that tries to focus public resources on avoiding every possible danger in a river at once will likely be looking the wrong way as it collides with the biggest rock. How can we distinguish those threats that, while not insignificant, are likely to be avoided or adapted to from those with a real potential for sinking the vessel? And how can we devise a system that encourages society to update its priorities among all hazards in light of new information and expertise? A further difficulty in the analysis arises because hazards have spatial and temporal dimensions and important interactions. However connected the world may be, and however global the transformations humans impose on it, the sustainability transition will be played out differently on a vast number of local stages. Neither population growth, nor climate change, nor water limitations will be the same in Japan as in the Sudan. The environmental hazards that nations and communities find most threatening and the response strategies they look to will continue to be

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Page 187 significantly different in different places in the world and at different times. Moreover, some components of the environmental system have impressive resiliency and ability to recover from human-caused or natural stress. Temporal dynamics and variations in the resiliency of systems confound clear illumination of critical hazards. Identification of hazards must also confront the difficulty of identifying, measuring, and predicting cumulative and interactive effects and discontinuous changes. Many of the activities that humans engage in occur at local scales, but as these activities are repeated around the world, their effects accumulate; collectively, local changes can lead to regional and global changes. Many of the worst and of the best-known environmental problems (e.g., stratospheric ozone depletion, anoxia in the Gulf of Mexico) resulted from the slow, day-by-day accumulation of small changes and dispersed activities. Such cumulative effects are only noticed after they have intensified over time, or when nonlinearities in the response of global or regional systems lead to dramatic and unforeseen events. Interactions of multiple changes also lead to surprise. Consequences that are deemed unlikely are often overlooked, yet rare events with extreme or large-scale consequences may influence the sustainability of the global system even more than cumulative effects. Clearly, uncertainty is rampant and surprise is inevitable. Recent environmental surprises have ranged from the emergence of "new" communicable diseases such as Legionnaires' disease, in a part of the developed world where such things were assumed to be hazards of the past; through the devastation of the developing-world town of Bhopal, India, in a very modern industrial accident; to the belated discovery that the nontoxic, noncorrosive CFCs that had displaced hazardous refrigerants and propellants turned out to have their own serious risks.2 More such surprises are likely as the earth system comes under increasing pressure from human activities. One difficulty lies in achieving a balance between falsely declaring certainty to engender action and the fatalistic resignation that societies can never know enough to know when or how to act. In dealing with these difficulties, the Board has attempted to develop a process for setting priorities and for identifying issues that require top concern. While our analysis builds on numerous national and international "stock-taking" efforts, we ultimately focus our attention on those issues that cut across sectors and that interact to simultaneously threaten human and ecosystem health, urban development, industrial advances, and sustained agricultural production. We conclude that integrative solutions-those aimed at interacting challenges across many sectors—will be key to successfully navigating the transition to sustainability. Perceptions of risk change with circumstances, as pressures increase, information is collected, technology advances, and surprises occur. The

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Page 188 environmental challenges that local places face as they navigate the transition to sustainability will also differ, because of inherent variations in resource bases and biophysical, social, and political environments. These variations include differences in geochemical and ecological vulnerability to pollution, social capital formation, and countless other details. Together, they make unsatisfactory any global-scale exercise to rank potential hazards. How do we then focus on challenges and opportunities that are relevant at the global scale yet meaningful locally? We conclude that the most serious threats are those that (1) affect the ability of multiple sectors of almost any society to move ahead toward our normative goals for sustainability; (2) have cumulative or delayed consequences, with effects felt over a long time; (3) are irreversible or difficult to change; and/or (4) have a notable potential to interact with each other to damage earth's support systems. To identify the problems that fit these criteria, we draw on several approaches. First, we use an environment-oriented analysis,3 in which hazards are ranked on the basis of the breadth of their consequences (e.g., having human health consequences, ecosystem consequences, and consequences for materials and productivity). Secondly, we use the framework of ''common challenges" to development in various sectors proposed by the 1987 Brundtland Commission as the basis for expert group analyses of threats and opportunities for the transition to sustainability. Finally, we identify the threats stemming from the interaction of sectoral activities. Environmental Perspectives Researchers4 drew on the UN Environment Program's The World Environment: 1972–1982, the U.S. Environmental Protection Agency's Unfinished Business and a range of other national and international environmental assessments that had been carried out worldwide, to develop a list of 28 potential environmental hazards that included most issues judged important in one or more of these studies. The hazards fell into five broad categories: land and water pollution, air pollution, contaminants of the human environment (e.g., indoor air pollution), resource losses, and natural disasters. Environmental data and explicit value judgments about the relative importance of present versus future impacts and of human health versus ecological impacts were then combined to generate comparative national rankings of the overall hazards list. From their analysis, it is apparent that the availability of high-quality freshwater is a priority concern in the United States, whether the most weight is given to human health, ecosystem, or materials concerns. Also, the more regional to global problems of stratospheric ozone depletion, climate change, acidification, and tropospheric ozone production and air pollution are common

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Page 189 and highly ranked issues of concern across the three areas. Such an approach provides the basis for assigning priorities to environmental threats. In support of this Board's activities, the list was modified5 and compared with eight other major efforts to assess environmental hazards, scoring each hazard on the basis of how important the various efforts found them to be (Table 4.1). Looking at Table 4.1 as a whole, some problems such as groundwater contamination and forest degradation stand out as being of nearly universal concern. Others, such as indoor air pollution and contamination, show up less frequently. Over time, there has been a shift from a focus on the depletion of natural resources and contamination of the environment to the loss of particular ecosystems (e.g., forests). In the individual assessments, the environmental threats identified as the most serious are often those most salient to a particular population. For example, the report on India devoted considerable attention to the health hazards of chemicals, both in the workplace and in accidental leakages, largely because at the time of the report the Bhopal disaster was still a major environmental event. Overall, these analyses suggest that, for most nations of the world, water and air pollution are the top priority issues; for most of the more industrialized nations, ozone depletion and climate change are also ranked highly; while for many of the less-industrialized countries, droughts or floods, disease epidemics, and the availability of local living resources are crucial. The scored hazards approach6 shows that sufficient data exist to make some relative hazard identifications for both today and the future. It also makes clear that relative hazard rankings—even of global environmental problems— are strongly dependent on the circumstances of the region assessed. One of the limitations of this approach is its failure to address interactions—for example, the fact that such issues as water quality, acidification, and climate change are intimately linked, and that change in one will have consequences for change in others. In addition, because the approach focuses on the problem rather than the cause, it is not a good pragmatic tool on its own. Solutions are difficult to develop without knowing causes. Development Perspectives For another type of perspective, we built on the work of the Brundtland Commission's report Our Common Future.7 In the interests of policy relevance, this effort broke with the tradition of analysis focused on environmental issues. Instead, analysis is directed to the "common challenges" to the environment arising from development activities within particular sectors: population and human resource development, cities,

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Page 190 Table 4.1 Assessments of the Importance of Environmental Hazards

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Page 191 Sources: UNCED (1992); World Bank (1992); WRI (1996); UNEP (1982) ; Easterbrook (1995); Centre for Science and Environment (1995); Council on Environmental Quality and Department of State (1982); Brown (1956).

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Page 192 agricultural production, industry, energy, and living resources. Using the Brundtland "common challenges" concept, we evaluated potential sector-specific resource and environmental impediments to reaching sustainability goals, along with the opportunities each sector offers to reduce, prevent, or mitigate the most serious threats. In addition, we evaluated progress over the last decade in achieving the measures identified by the Brundtland "challenges." Human Population and Well-Being In 1987, the Brundtland Commission framed the issue of human population growth in terms of both the balance between population and resources and the need for increased health, well-being, and human rights to self-determination. Today, these issues are strongly linked, and we recognize that the reduction in poverty, poor health, mortality, and the increase in educational and employment opportunities for all are the keys to slowing population growth and to the wise and sustainable use of resources. Thus, one of the most critical challenges for efforts to navigate a transition to sustainability will be to reduce population growth while simultaneously improving the health, education, and opportunities of the world's people. Population growth is an underlying threat to sustainability due to the increased consumption of energy and materials needed to provide for many more people, to crowding and competition for resources, to environmental degradation, and to the difficulties that added numbers pose in efforts to advance human development. Today, population growth has ended in most industrialized countries and rates of population growth are in decline everywhere except in parts of Africa (see Chapter 2); yet the population of 2050 is nonetheless predicted to reach about 9 billion. In a classic decomposition of future population growth in developing countries, a researcher examined the major sources of this continued growth: unwanted childbearing due to low availability of contraception, a still-large desired family size, and the large number of young people of reproductive age.8 Currently, 120 million married women (and many more unmarried women) report in surveys that they are not practicing contraception despite a desire for smaller families or for more time between births. Meeting their needs for contraception would reduce future population growth by nearly 2 billion. At the same time, such surveys also show that the desired family size in most developing countries is still above two children. An immediate reduction to the level of replacement (2.1) would reduce future growth by about 1 billion. The remainder of future population growth can be accounted for by so-called population momentum, which is due to the extraordinarily large number of young

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Page 193 people. This momentum ensures that population growth will persist for decades even if fertility were to drop to replacement level. Addressing each of these sources of future growth could reduce fertility and future population numbers further and faster than current trends would project. Opportunities include making contraception more readily available to those who desire it (Table 4.2), accelerating trends that lead to lower desired family size, and slowing the momentum of population growth arising from the large number of prospective parents that are alive today.9 Linking voluntary family planning with other reproductive and child health services can increase access to contraception for the many who want it. Improving the survival of children, their education, and the status of girls and women has been correlated with and may lead to a desire for smaller families. Increasing the age of childbearing, primarily by improving the secondary education and income-generating opportunities for adolescent girls, can slow the momentum of population growth. All of these opportunities, if exploited, could contribute directly to our societal goals for a transition to sustainability; at the same time, through these factors' influence on reducing the ultimate size of the population, they would increase the probability of meeting environmental goals. Threats to human-well being stem from many environmental sources. Environmental factors can affect human health directly—through exposure to air pollution, heavy metals, and synthetic chemicals—and indirectly through loss of natural biological controls over opportunistic agents and vectors of infectious disease. Because of human introductions nearly Table 4.2 Projections of the Population Size of the Developing World With and Without Unwanted Births Projection Projected population size (billions) in year     2050 2100 Standard* (with unwanted births) 8.6 10.2 Without unwanted births 7.5 8.3 Effect of unwanted fertility 1.1 1.9 *World Bank projection as quoted in Bos et al. Source: Bongaarts (1994). Courtesy of the American Association for the Advancement of Science.

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Page 194 50 years ago, the global environment now carries a number of synthetic chemicals that can interfere with human physiology, including the endocrine system, the immune system, and neurological function.10 Additionally, heavy metal deposition in the environment is rising and will continue to increase under development scenarios implicit in meeting our normative goals. Health effects of exposure to heavy metals may be substantial, and include long-term neurological effects on intelligence and behavior. Air pollution is a critical problem of urban systems in many regions of the world, and the increase in air pollution with a rapidly urbanizing world raises serious concerns for human health and the health of crops and natural ecosystems. As described in Chapter 2, over the past several decades, there has been an emergence, resurgence, and redistribution of infectious diseases. The potential eruption of diseases in an increasingly populated world is a serious threat to sustainability goals. These diseases threaten human health, water safety, food security, and ecosystem health. Fortunately, because of biological and other scientific revolutions and policy reform over the past decades, there are opportunities for addressing the health risks from exposure to environmental threats. Biotechnology holds great promise (for example, in the creation of new medicines and diagnostics, pest-resistant crop species, plants with low-water requirements, and biodegradable pesticides and herbicides). Policies that control the point sources of air pollution, deposition of heavy metals, and disposal of synthetic chemicals help resolve health-related problems for local and regional human populations and can have very significant and long-term payoffs for future generations. Also, the establishment of early warning systems and other predictive capabilities to identify conditions conducive to outbreaks and clusters of infectious disease could be useful for health institutions at all spatial scales. In addition, a number of opportunities arise via interactions of this human well-being sector with others. For example, reduction in industrial wastes through approaches using industrial ecology would have large advantages for human health, and also for the environment as it is affected by energy and water sectors, through the increased efficiency of these resources' use. Finally, the maintenance of natural ecosystems and the protection of their services can influence human health in many ways, including by providing natural enemies for disease vectors and natural water and air purification and supply systems. Cities Over the next half century, urban populations are likely to grow from the present 3 billion to perhaps 7 billion people, with most of the growth

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Page 195 occurring in non-OECD (see Chapter 2 and 3).11 Cities are engines of economic growth and wealth creation, of innovation and creativity, but they are also the sites of extremes of wealth and poverty, unequal access to drinking water and sanitation, pollution, and public health problems. As the Brundtland Commission noted, the growth of urban populations has often preceded development of the housing, infrastructure, and employment needed to sustain that population. In the 10 years from 1985 to 1995, a period during which the Brundtland report was published, the world saw the addition of the equivalent of 81 cities with populations of over a million people.12 There have been dramatic and successful efforts to improve water, air, and sanitation services in developing world urban centers during this period. But the number of city dwellers without adequate water and exposed to poor sanitation and air pollution has grown as urban population growth has outpaced investments.13 The health consequences of inadequate drinking water and poor sanitation services are felt most strongly by the poor. Among the major challenges of urban development is air pollution, produced largely by the interactions of hydrocarbons and nitrogen oxides produced in industrial and transportation processes as well as by heating and cooking.14 While investments in pollution control in industrialized countries have led to air pollutant reductions in many cities, air pollution is still a major problem in the developed world. In the United States, some 80 million people live in areas that do not meet air quality standards, and in many European cities air pollutant concentrations are also higher than the established standards.15 At the same time, air quality in the cities of the industrializing world has worsened. Worldwide, the World Health Organization estimates that 1.4 billion urban residents breathe air that fails to meet WHO air quality standards.16 Access to water and sanitation services also present enormous challenges to rapidly growing cities. Despite concerted efforts during the 1980s, designated the "International Drinking Water Supply and Sanitation Decade" by the World Health Organization, in 1990 about 200 million urban dwellers were without a safe water supply, and around 400 million were without adequate sanitation.17 In the largest cities of the industrializing world, the poorest populations in the slums and at the city margins tend to have the least access to safe water. For example, in Sao Paulo, nearly 20 percent of the city's population lived in slums (called favelas) in 1993; around 85 percent of the favelas had no sewerage service.18 Innovative technological opportunities—such as condominial sewers,19 improved ventilated pit latrines, various lower cost sewage treatments, and approaches to reuse of municipal wastewater—are available to provide flexible and cost-effective services and are being used with success in some regions, but have yet to be widely applied. Also, in some areas, such

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Page 222 Integrated Approaches in a Place-Based Context This chapter has illustrated the strong linkages and interactions that exist between resources and human activities across many different issues, sectors, and scales. Efforts to reach the goals we have sketched for a transition to sustainability cannot be expected to succeed if they are pursued within narrow disciplinary or sectoral frameworks that ignore these interactions. Rather, many of the greatest opportunities identified here for navigating that transition are integrative in defining the problems and seeking the solutions. As a result of this review of the environmental challenges and opportunities facing a sustainability transition, the Board believes that the most significant threats to it are likely to be the cumulative, interactive consequences of activities across a number of sectors. Society and its decision makers must recognize that agricultural, urban, industrial, and ecosystem processes interact with each other and must be evaluated as an integrated system. This conclusion is shared by other groups that have addressed analogous questions over a period extending back several years, but has been achieving renewed emphasis in recent years.90 Recognizing the importance of interactions among environmental problems, and of the need for integrated approaches to understand and manage these interactions, still leaves open some questions of appropriate spatial scale. In one sense, the answer is simple: because interactions occur at all scales, integrative research and management are needed at all scales. This is certainly correct as far as it goes. But it is not a particularly helpful observation in improving existing research and management systems. As a step toward developing such guidance, the Board drew on the history of efforts to develop and sustain improvements in agricultural productivity around the world. A major lesson of that experience has been the "location specific" character of useful knowledge and know-how that involves biological and social systems. In the agricultural realm, efforts simply to transfer understanding or technologies created in one part of the world across scales or places have generally not succeeded. Instead, as summarized by a major restrospective sponsored by the Rockefeller Foundation— The location-specific nature of biological technology meant that the prototype technologies developed at the international centers could become available to producers in the wide range of agroclimate regions and social and economic environments in which the commodities were being produced only if the capacity to modify, adapt, and reinvent the technology was available. It became clear that the challenge of constructing a global agricultural research system capable of sustaining growth in agricultural production required the development of research

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Page 223 capacity for each commodity of economic significance in each agroclimatic region.91 This Board's work suggests that the insights from experience with agricultural production systems have general applicability to the challenges of navigating a transition to sustainability. As the examples covered in the preceding section of this chapter suggest, many of the most successful integrated analyses of challenges to sustainability have focused on specific places. Like the earlier agricultural efforts, they have prospered to the extent that they have been able to integrate general principles and knowledge of global relationships with specific understanding of local environmental circumstances and social institutions. There is no magic scale for such effective integrations—they have ranged from the planetary work on ozone depletion, through continental assessments of acid rain and regional efforts to restore the Columbia Basin, to highly localized efforts to design sustainability strategies for particular communities. What effective integrative analyses do seem to have in common is the ability to take seriously questions of scale and linkages, and to shape research, development, and management strategies to discover the conceptualizations of "place" most relevant to the problem at hand. To emphasize our beliefs that attention to scale matters in efforts to promote a sustainability transition, but that no particular scale has a "natural" rightness for all the challenges likely to be faced, we have chosen to highlight here the need for "place-based" integrative analysis. As suggested in the Chapter 1 review of the progress towards sustainability reported at the 1997 Special Session of the UN General Assembly, selected leaders in government, industry, and advocacy groups have begun to recognize the need for such integrated, place-based assessments of the challenges and opportunities for a transition to sustainability. In Chapters 5 and 6, we turn to a consideration of the indicators, research, and institutions needed to realize the potential of these analyses. Conclusion This analysis shows that progress has been made toward identifying environmental hazards and toward a greater understanding of the challenges in each of the sectors identified 10 years ago by the Brundtland Commission. It has also identified some of the difficulties in overcoming these hazards, and the opportunities to address them. What has become evident in the past decade is the overwhelming degree to which there is increasing interaction among the sectors, and the degree to which the consequences of these interactions are cumulative, sometimes nonlinear, and subject to critical thresholds. Therefore, we conclude that most of

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Page 224 the individual environmental problems that have occupied most of the world's attention to date are unlikely in themselves to prevent substantial progress in a transition toward sustainability over the next two generations. Over longer time periods, unmitigated expansion of even these individual problems could certainly pose serious threats to people and the planet's life support systems. Even more troubling in the medium term, however, are the environmental threats arising from multiple, cumulative, and interactive stresses, driven by a variety of human activities. These stresses or syndromes, which result in severe environmental degradation, can be difficult to untangle from one another, and complex to manage. Though often aggravated by global changes, they are shaped by the physical, ecological, and social interactions at particular places, that is locales or regions. Developing an integrated and place-based understanding of such threats and the options for dealing with them is a central challenge for promoting a transition toward sustainability. References and Bibliography Aber, J.D., A. Magill, S.G. McNulty, R.D. Boone, K.J. Nadelhoffer, M. Downs, and R. Hallett. 1995. Forest biogeochemistry and primary production altered by nitrogen saturation. Water, Air and Soil Pollution 85, no. 3: 1665–1670. Aber, J.D., K.J. Nadelhoffer, P. Steudler, and J.M. Melillo. 1989. Nitrogen saturation in northern forest ecosystems. BioScience 39: 378–386. Allen, D.T., and N. Behmanesh. 1994. Wastes as raw materials. In The Greening of Industrial Ecosystems. National Academy of Engineering, B.R. Allenby, D.J. Richards, eds. Washington, D.C.: National Academy Press. Allen, D.T., and R. Jain. 1992. Special issue on industrial waste generation and management. Hazardous Waste and Hazardous Materials 9, no. 1: 1–111. Andreae, M.O. 1993. The influence of tropical biomass burning on climate and the atmospheric environment. In Biogeochemistry of global change: Radiatively active trace gases, ed. R.S. Oremland, 113-150. New York: Chapman and Hall. Ausubel, J.H. 1996. Can technology spare the earth? American Scientist 84: 166–178. Bell, David E., William C. Clark, and Vernon W. Ruttan. 1994. Global research systems for sustainable development: agriculture, health and environment. In Agriculture, environment and health: Sustainable development in the 21st Century, ed. Vernon W. Ruttan, 358–379. Minneapolis: University of Minnesota Press. Bender, William H. 1997. How much food will we need in the 21st Century? Environment 39, no. 2: 6–14. Berry, Brian J.L. 1990. Urbanization. In The earth as transformed by human action, ed. B.L. Turner II. W.C. Clark, R.W. Kates, J.F. Richards, J.T. Matthews, and W.B. Meyer. New York: Cambridge University Press. Bongaarts, J. 1994. Population policy options in the developing world. Science 263: 771–776. Bos, E., M.T. Vu, A. Levin, and R. Bulatao. World population projections 1992-93 Edition. Baltimore: Johns Hopkins University Press. Published for the World Bank. Botsford, L.W., J.C. Castilla, and C.H. Peterson. 1997. The management of fisheries and marine ecosystems. Science 277: 509–515. Brundtland Commission. See WCED, 1987.

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Page 231 13 World Bank (1992); WRI (1996). 14 NRC (1991a, 1997b). 15 WRI (1998). 16 WHO and UNEP (1992). 17 World Bank (1992). 18 Ibid. 19 The condominial sewerage system, which is used in northeast Brazil, has a shorter grid and shallower feeder sewers running through backyards, resulting in shallower connections to the main pipes, lower construction costs (20 to 30 percent lower than for conventional systems), and less pipe. 20 NRC (1995). 21 Berry (1990); UN (1996). 22 Bender (1997); Ruttan (1996); Daily et al. (1998); see Chapter 3. 23 Pinstrup-Anderson et al. (1997). 24 NRC (1991b); Pinstrup-Anderson and Pandya-Lorch (1996); Ruttan (1996); Strong (1998). 25 NRC (1991b); Ruttan (1996); Cassman et al. (1997). 26 Postal et al. (1996). 27 Matson et al. (1997); NRC (1991b). 28 Chameides et al. (1994). 29 Naylor and Ehrlich (1997); NRC (1991b). 30 NRC (1991b), (1992b); Ruttan (1996). 31 See Strong (1998). 32 Kendall et al. (1997); Conway (1997). 33 Matson et al. (1997); NRC (1991b, 1992b); Woomer and Swift (1994). 34 Postel (1992, 1993). 35 NRC (1992a). 36 NAE (1997). 37 NAE (1994a); NRC (1997a). 38 Industrial waste, Allen and Jain (1992); municipal solid wastes, EPA (1990). 39 Raskin et al. (1996). 40 E.g., selling the cleaning of the factory or office (''selling the factory") as opposed to selling cleaning products and tools. 41 Xerox (1997). 42 Product recycling, NAE (1994b); industrial ecology, NAE (1994a,b), and Socolow et al. (1994). 43 NAE (1994b). 44 NRC (1990,1991a). 45 NRC (1990,1998b). 46 PCAST (1997). 47 PCAST (1997,1999). 48 Daily (1997). 49 PCAST (1998). 50 Vitousek et al. (1997). 51 FAO (1997); Noble and Dirzo (1997). 52 Mangrove ecosystems, WRI (1996); oceans, Pauly and Christensen (1995). 53 Vitousek et al. (1997). 54 FAO (1994); NRC (1999a). 55 Botsford et al. (1997). 56 Lawton and May (1995); PCAST (1998). 57 E.g., Chichilnisky and Heal (1998).

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Page 232 58 Nabhan and Buchmann (1997). 59 Noble and Dirzo (1997); Vitousek et al. (1997); Matson et al. (1997). 60 See, e.g., IGBP (1994); IHDP (1998); DIVERSITAS (1998); and the NRC's "Pathways" report [NRC (1998a)]. 61 UNEP et al. (1998); World Bank (1998). 62 Vitousek et al. (1997). 63 Schimel (1994); IPCC (1996); NRC (1994). 64 NRC (1998a). 65 Gleick (1992). 66 Gleick (1998). 67 Nash (1993). 68 Smith et al. (1992). 69 Gleick (1998). 70 Chesapeake Bay, e.g., Costanza and Greer (1998); Columbia Basin, e.g., Lee (1993), and NRC (1996). 71 E.g., Mitchell and Hanemann (1994). 72 NRC (1991a). 73 Chameides and Cowling (1995). 74 Chameides et al. (1994). 75 IPCC (1995). 76 Graedel and Crutzen (1993); Andreae (1993); Rodhe and Herrera (1988). 77 Galloway et al. (1995); Vitousek et al. (1997). 78 Schimel (1994); Townsend et al. (1996). 79 Aber et al. (1989); Aber et al. (1995); Matson et al. (1999). 80 Chameides and Cowling (1995). 81 Hornung and Skeffington (1993). 82 Yagi and Minami (1990). 83 NRC (1992a). 84 Vitousek et al. (1997); Chapin et al. (1997). 85 Ausubel (1996); Waggoner (1994). 86 See chapter 2 NRC (1998a). 87 Daily (1997). 88 Risch et al. (1986); Pimental and Edwards (1982); Matson et al. (1997); Thies and Tscharntke (1999). 89 Matson et al. (1997); Crosson (1995). 90 Several decades, e.g., Odum (1994), Watt (1966), and Holling (1978); recent years, e.g., the World in Transition reports of the German Advisory Council on Global Change (WBGU 1993–1997); see also Chapter 6, Box 6.1. 91 Bell et al. (1994), p. 362; see also Schultz (1964).