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The Grand Challenges

For each grand challenge described in this chapter, the committee judges that major scientific and/or practical payoff is likely to result if there is a significant infusion of research support over the next decade or two. We begin the discussion of each challenge by identifying the scientific payoffs that appear most likely and practical payoffs that the expected scientific advances would make possible. We then identify recent scientific progress that makes major advances in the area of the challenge possible now. Next we list focused research areas within each challenge that are especially deserving of intensive development. These lists are not intended to be comprehensive; rather, they include only those areas we judge most exciting and likely to yield major break-throughs in the near future.

GRAND CHALLENGE 1: BIOGEOCHEMICAL CYCLES

The challenge is to understand how the Earth's major biogeochemical cycles are being perturbed by human activities; to be able to predict the impact of these perturbations on local, regional, and global scales; and to determine how these cycles may be restored to more natural states should such restoration be deemed desirable.

Practical Importance

Six nutrient elements—carbon, oxygen, hydrogen, nitrogen, sulfur, and phosphorus—make up 95 percent of the biospheric mass on the Earth and form the biochemical foundation for life (Schlesinger 1997). The cycling of these



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Grand Challenges in Environmental Sciences 2 The Grand Challenges For each grand challenge described in this chapter, the committee judges that major scientific and/or practical payoff is likely to result if there is a significant infusion of research support over the next decade or two. We begin the discussion of each challenge by identifying the scientific payoffs that appear most likely and practical payoffs that the expected scientific advances would make possible. We then identify recent scientific progress that makes major advances in the area of the challenge possible now. Next we list focused research areas within each challenge that are especially deserving of intensive development. These lists are not intended to be comprehensive; rather, they include only those areas we judge most exciting and likely to yield major break-throughs in the near future. GRAND CHALLENGE 1: BIOGEOCHEMICAL CYCLES The challenge is to understand how the Earth's major biogeochemical cycles are being perturbed by human activities; to be able to predict the impact of these perturbations on local, regional, and global scales; and to determine how these cycles may be restored to more natural states should such restoration be deemed desirable. Practical Importance Six nutrient elements—carbon, oxygen, hydrogen, nitrogen, sulfur, and phosphorus—make up 95 percent of the biospheric mass on the Earth and form the biochemical foundation for life (Schlesinger 1997). The cycling of these

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Grand Challenges in Environmental Sciences elements through the Earth system in their biological, geological, and chemical forms constitutes the biogeochemical cycles. Also included under the rubric of biogeochemical cycling can be elements such as potassium, calcium, molybdenum, iron, and zinc, which are needed as physiological regulators or cofactors for enzymes. Imbalance in the availability or utilization of these elements has both direct and indirect influences on the distribution and viability of many organisms. Research during the last several decades has provided many insights into the importance of biogeochemical cycles. It is now recognized that the evolution of photosynthetic organisms more than 2 billion years ago transformed the Earth's atmosphere from strongly reducing to its current oxygen-rich state. The interrelationship between greenhouse gases and climate was identified more than a century ago (Arrhenius 1896). Today we understand that carbon dioxide (CO2)-induced ocean warming was sufficient to trigger the large-scale destabilization of methane hydrates (Norris and Rohl 1999). This positive feedback with global effects occurred at the Paleocene/Eocene transition, and was associated with high-latitude warming and changes in terrestrial and marine biota. The concentrations of many greenhouse gases (e.g., CO2, nitrous oxide [N2O], and methane [CH4]) have risen over the last 100 years at rates unprecedented in the geologic record. It is clear that these rapid rises in concentrations are being driven by global changes in the Earth's biogeochemical cycles. What is less clear is how long these changes in biogeochemical cycles will continue, what effects they are having on the climate system, how these effects will reverberate throughout the Earth system, and how positive and negative feedbacks within the system will interact to accelerate or ameliorate these effects. Human actions strongly influence changes in the Earth's biogeochemical cycles, with potentially devastating effects. Combustion of fossil fuels and conversion of forested land to agriculture have redistributed carbon from plant, soil, and mineral pools into the atmosphere, where greatly increased CO2 has the potential to alter climate, affect the photosynthetic efficiency of vegetation, and change large-scale ecosystem dynamics (Amthor 1995). The combustion of fossil fuels and the manufacture and use of nitrogen fertilizers have approximately doubled the annual supply of fixed nitrogen to the soil relative to preindustrial times, a circumstance that has the potential to alleviate nitrogen limitation of productivity in terrestrial ecosystems and may thus contribute to enhanced terrestrial carbon uptake (Holland et al. 1997). Similarly, ore smelting and coal combustion have roughly doubled annual emissions of sulfur gases to the atmosphere, with implications for both acid rain and global climate change (Galloway 1995). Anthropogenic perturbation of the cycle of phosphorus, a limiting nutrient for many plants, has been less studied, but is thought to be significant at least at a regional scale. It is clear that these human-induced stresses to the biosphere interact, but the net effect of the multiple perturbations remains uncertain. Increased tropospher

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Grand Challenges in Environmental Sciences ic CO2 and widespread nitrogen deposition both act to fertilize plant growth, but other factors—such as soil acidification, high tropospheric ozone levels, loss of soil fertility through base cation loss, and their interactions with plant diseases and pests—all reduce plant productivity and have other effects on the biosphere. The net effect of these factors on crop productivity and the biosphere's ability to consume the carbon emitted through fossil fuel combustion needs to be understood. This is but a single example. We also know, for instance, that the current changes to the nitrogen cycle have had profound impacts on freshwater and perhaps oceanic resources and fisheries. Human influences on the biogeochemical cycles are not all increasing so dramatically. Recent restrictions on sulfur dioxide (SO2) emissions in some countries have resulted in reduced inputs of acid rain to surface waters and ecosystems. The production and emissions of chlorofluorocarbons (CFCs) have also been reduced. Despite these scientifically informed policies, however, the abundance of N2O, CH4, and sulfate aerosols, all biogeochemically important compounds, will interact with the changing climate to influence the rate of recovery of the ozone layer. Yet while the biogeochemical cycles of the nutrient elements constitute crucial constraints on the Earth 's physiology, they remain poorly understood. This lack of understanding strongly limits our perspective on the many facets of global change. During the next century, continuing expansion of the influence of urbanization, industry, and agriculture on already perturbed biogeochemical cycles is likely. Increased scientific understanding of these cycles and the activities that are perturbing them is vital to formulating plausible political and social solutions to these important environmental perturbations. Scientific Importance The goal of biogeochemistry is to quantify the rates of transfer of relevant compounds and their accumulation or depletion in storage reservoirs. Knowing the residence time of compounds in each type of reservoir is central to predicting their changes over time. For example, during the last decade, research on the global carbon cycle has established that fossil fuel combustion has released an average of 5.5 (+/−0.5) gigatons (Gt) of carbon in CO2 into the atmosphere each year, and land-use changes have contributed an additional 1.6 (+/−1.0) Gt, for a total of 7.1 (+/−1.1) Gt (Schimel et al. 1995). Only 3.3 Gt of carbon is actually stored in the atmosphere. Ocean uptake of 2.0 (+/−0.8) Gt leaves an additional 1.8 Gt to be accounted—for the so-called “missing sink” of carbon. The remaining carbon is probably stored on land, and the locations and mechanisms of this carbon storage continue to be the subject of discussion and research (Tans et al. 1990, Nabuurs et al. 1997, Fan et al. 1998, National Research Council 2000a, Schimel et al. 2000). The likely mechanisms are CO2 or nitrogen fertilization of

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Grand Challenges in Environmental Sciences the biosphere; reforestration, resulting in carbon storage in wood; and interactions with climate and its interannual variability. Yet the lack of a complete understanding of the current carbon budget hampers efforts to understand past geologic changes and to predict future changes in CO2 concentrations. The magnitude, global scale, and potential destructiveness of some cycle perturbations make research on these cycles particularly urgent and timely. As indicated by its very name, biogeochemistry links scientific specialties. New discoveries have emerged as specialists in any number of areas have recognized that they must collaborate with scientists from other disciplines to solve their problems. Limnologists and oceanographers recognize that atmospheric chemists and ecosystem ecologists may be their best sources of information on future rates of nitrogen fixation. Researchers around the world are using the output of climate models to understand the internal dynamics of the ecosystems they study. Modelers, foresters, and botanists are beginning to appreciate how increases in nitrogen deposition may enhance carbon storage, for example, or how carbon uptake may be limited in other areas that are nitrogen-saturated (Townsend et al. 1996). Bringing these different perspectives together is important, but it poses a challenge for scientists and managers seeking to build workable structures that can support the needed science. The ecosystem implications of the biogeochemical cycles come into focus most sharply when variations in space and time are taken into account. Ecosystems vary widely from place to place and over time for many reasons, and globally averaged cycle information relates only weakly to those unique situations. As the broad outlines of the biogeochemical cycles become better delineated, spatial distributions and temporal trends in the parameters of interest will link the cycles in increasingly useful ways to topics of interest within other grand challenges. Scientific Readiness The growth of the field of biogeochemistry during the past 10 to 15 years has led to significant theoretical and experimental developments that can serve as the base for future research, and the study of carbon and nitrogen cycles has greatly benefited from recent technological advances. Of particular note are analytical techniques for isotope analysis of 13C, 18O, 15N, deuterium, and 14C, as well as the measurement of an increasing array of atmospheric trace gases, including reactive oxides of nitrogen, sulfur gases, OH, and O2. Direct flux measurements of energy, momentum, and CO2 and H2O vapor exchanges, not possible a decade ago, today have become a cornerstone of both the U.S. and European field experiment programs (Brasseur et al. 1996). Remote measurements of ocean and land surfaces and the atmosphere made possible by recent satellite launches (such as the National Aeronautics and Space Administration's [NASA]

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Grand Challenges in Environmental Sciences TOMS instrument and Terra satellites) have and will continue to enable great advances in understanding. They will also fill gaps in the global information database, including the understanding of land-cover change argued for under Grand Challenge 7. Models have progressed dramatically, and are beginning to provide realistic simulations of the complex interactions among atmospheric, oceanic, and terrestrial systems (American Meteorological Society 1998). The existence of long-term measurements made possible by funding from a number of federal agencies has been essential to progress in the field. These datasets include the global trace gas measurements made by the Climate Monitoting and Diagnostics Laboratory (1996-1997), funded by the National Oceanic and Atmospheric Administration, which have provided insights into the carbon cycle and carbon cycle models. NASA's archiving of Landsat satellite images has enabled quantification of large-scale land-use change (Skole and Tucker 1993). The Environmental Protection Agency's surface observations of pollutants and the development of emission inventories have helped test our understanding of atmospheric chemistry (Guenther et al. 1994, Benkovitz et al. 1996). The National Atmospheric Deposition Program/National Trends Network Program and the National Dry Deposition Network have provided long-term measurements (1978-present and 1990-present, respectively) of wet and dry deposition that enable regional and national evaluations of acid rain inputs, nitrogen deposition (Holland et al. 1997), base cations inputs (Driscoll et al. 1998), and surface water resources. The Department of Energy 's funding of the Carbon Dioxide Information and Analysis Center has provided a much-needed synthesis of CO2 data at a critical time. Maintaining these long-term data programs is seldom easy, but is crucial to deriving increased insight. The above are but a few key examples of successes in the field. We are now poised to place our understanding of biogeochemical cycles on a much firmer theoretical and empirical base than now exists. In the coming decade, it will be possible to gain a solid quantitative understanding of the cycles and budgets of the key biogeochemical constituents. In fact, a well-developed strategy (the U.S. Carbon Cycle Science Plan) already exists for understanding the cycling of CO2. Continuing major commitments of financial and human resources by multiple agencies are needed to bring this plan to fruition. An ultimate goal is to make reliable predictions of future changes in these cycles and the resulting effects on planetary functioning. Progress toward this goal will depend on continued research on biogeochemical processes and on human activities that drive these processes. (The extent to which this approach spans disciplinary areas is indicated by the fact that the use of the nutrient elements and of land, water, and various natural materials is addressed in Grand Challenge 7, Grand Challenge 4, and Grand Challenge 8, respectively.) In a policy context, predictive biogeochemical models could help guide decisions about such matters as fossil fuel use, energy production, agricultural and industrial practices, and mitigation of climate change.

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Grand Challenges in Environmental Sciences Important Areas for Research Improve the quantification of sources and sinks of the nutrient elements, and gain a better understanding of the biological, chemical, and physical factors regulating transformations of nutrient reservoirs. Greatly improved estimates of the sizes of nutrient reservoirs on regional and global scales and their rates and causes of transformation are essential for identifying those reservoirs and transformations most influenced by human activity and predicting the impact of the transformations on ecosystem health; global climate; and human needs, such as food supplies and clean air. Studies of the Earth's history can reveal the significance of biogeochemical cycles in altering climate and the distribution, abundance, and diversity of organisms, and aid in understanding positive and negative feedbacks within the global system. Improve understanding of the interactions among the various biogeochemical cycles. Nitrogen, phosphorus, and essential trace nutrients such as iron alter the productivity of terrestrial and oceanic plants and the transfer of carbon from the atmosphere to living organisms. Likewise, decomposition and remineralization of organic matter transform nutrients captured by organisms back into inorganic form. All of the cycles of essential nutrients interact with each other, and the positive and negative feedbacks among them are at present poorly quantified and understood. In addition, the biogeochemical cycles are strongly influenced by the terrestrial hydrologic cycle. An understanding of these synergisms and their impacts is necessary if changes in any one cycle are to be predicted. Assess the impacts of anthropogenic perturbations of biogeochemical cycles on ecosystem functioning and atmospheric and oceanic chemistry, and develop a scientific basis for societal decisions about managing these cycles. Greatly improved projections of future concentrations of CO2, CH4, nitrous oxides, and aqueous and atmospheric pollutants, as well as understanding of the responses of natural and managed ecosystems to these and other atmospheric components, are required to make wise management decisions regarding human activities. Better projections will depend on research to improve understanding of the drivers of human actions that perturb the cycles and to enhance models of biogeochemical processes and their ecological effects. An understanding of the impacts of past and current land-use and agricultural, industrial, and domestic practices and policies on nutrient cycles would facilitate the development of models for fully assessing those impacts. In addition, the cycles of non-nutrient elements, addressed in Grand Challenge 8, Reinventing the Use of Materials, are important to ecosystem functioning. Thus a longer-term goal is to integrate the environmental implications of the nutrient and non-nutrient elements. Research on the effects of changes in biogeochemical cycles on human societies and economic activities is also an essential part of the scientific basis for societal decisions.

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Grand Challenges in Environmental Sciences Explore prospects for mitigating these perturbations. There is a need for extensive research regarding the feasibility and effectiveness of a variety of both technical approaches (e.g., precision agriculture, creation of carbon sinks, technologies for more efficient uses of nutrient elements) and institutional approaches (e.g., financial incentives for resource conservation, creation of emissions markets) for achieving sustainability of the essential nutrient cycles. This research priority has obvious overlap with Grand Challenge 6 on institutions and resource use. The research priorities for biogeochemistry are clearly related to those for a number of the other grand challenges in addition to the overlaps noted above. Significant changes in biogeochemical cycles are often driven by extreme weather events, such as those outlined in Grand Challenge 3 on climate variability. Moreover, it is clear that interannual variation in climate drives interannual changes in carbon and possibly nitrogen cycling (Braswell et al. 1997, Erickson 1999). Understanding the linkages between micronutrient and nutrient cycles, as well as transforming that understanding into meaningful policy, will also require information and insights gleaned from Grand Challenge 3. Vitousek et al. (1997b) have shown how acceleration of the nitrogen cycle can affect biodiversity and species composition in terrestrial and aquatic ecosystems, effects that have obvious overlap with Grand Challenge 2 on biological diversity and ecosystem functioning. In addition, acceleration of the nitrogen cycle is implicated in the widespread hypoxia in the Gulf of Mexico, in freshwater pollution following the North Carolina floods of 1998 and 1999, and in the Pfiesteria outbreaks along the Eastern Coast of the United States, addressed by Grand Challenge 5 and Grand Challenge 6 on infectious disease and institutions, respectively. And changes in land-use dynamics (Grand Challenge 7) have driven large-scale changes in the carbon and nitrogen cycles. GRAND CHALLENGE 2: BIOLOGICAL DIVERSITY AND ECOSYSTEM FUNCTIONING The challenge is to understand the regulation and functional consequences of biological diversity, and to develop approaches for sustaining this diversity and the ecosystem functioning that depends on it. Practical Importance Human impacts on the land and oceans are pervasive and profound. The human enterprise has appropriated nearly half of the Earth's primary productivity, more than doubting the global cycling of nitrogen (Vitousek et al. 1997a,b). Humans harvest much of the oceans' production as well, drill petroleum from continental shelves, and are poised to begin using the deeper ocean floors for both mining and waste disposal and petroleum recovery.

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Grand Challenges in Environmental Sciences Human use of an area has generally meant its severe degradation as a natural habitat. Ecosystems and their functioning are threatened. As a result, the rate of species extinction is higher now than at almost any time in the Earth's history (National Research Council 1995). Today, indeed, we face the risk of a great mass extinction, one of only a handful in the history of the Earth. The permanence of extinction makes it qualitatively different from other kinds of environmental change. Many societies around the world support the protection of species diversity, often explicitly, on ethical, moral, cultural, and aesthetic grounds. Many U.S. federal and state laws support the maintenance of species diversity. For example, the U.S. Endangered Species Act of 1973 states that it is “the policy of Congress that all Federal departments and agencies shall seek to conserve endangered species and threatened species. . . .” (Section 2 {b[c]}). Thus an anthropogenically driven mass extinction would be a great societal as well as biological loss. Such a loss would also be risky. Humans depend crucially on nature for many things, from food, fiber, and medicines to recycling of nutrients and regulation of air quality, water quality, and climate (Daily 1997, National Research Council 1999f). Environmental scientists do not yet fully understand the sensitivity of these things to changes in the diversity of organisms and ecosystems. At present, we have a limited appreciation of what is really at risk, of the time scale for losses, and of the environmental consequences of simplifying and mixing the Earth's biota. Nonetheless, a major loss of biological diversity clearly threatens the capacity of the Earth to support human societies. To predict the impacts of human activities on the diversity of genotypes, species, and ecosystems, we need a thorough understanding of the fundamental natural controls on biological diversity. We also need to make a major investment in discovering to what extent ecosystems with altered diversity can provide the services humanity depends on. Further, progress made in understanding the genesis and regulation of biological diversity needs to be applied in developing the capacity for preserving that diversity. Given the already pervasive impacts of human activity, high priority must be placed on the formulation of strategies for integrating conservation with human uses. Threats to biological diversity on the land and in the oceans are generally unintended consequences of the development of human societies, growth in human populations, and efforts to improve standards of living. Practical efforts to protect species and ecosystems must reconcile ecological objectives with human needs. Scientific Importance Throughout its history, the field of ecology has focused on understanding the factors that produce and control biological diversity (e.g., von Humboldt 1807, Preston 1948, Hutchinson 1959, Rosenzweig 1999). Success would be a

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Grand Challenges in Environmental Sciences substantial intellectual prize. It would represent a pinnacle of knowledge of the Earth's riving systems—comparable to the goal of cosmology to discover the events and processes that determine and guide the development of the physical universe. The practical value of such understanding would appear to be inestimable. Since the early 19th century, observers have noted striking variations in patterns of species diversity with latitude, productivity, climate, and area (e.g., von Humboldt 1807). Area and isolation are fundamentally important, reflecting control of local and regional diversity on shorter time scales by the balance between migration and local extinction. Understanding of the relationship between species diversity and area —known as a species-area curve—is a powerful tool. At longer time scales, speciation also becomes important as the factor generating species diversity. Although considerable understanding of the processes that lead to new species and those that destroy established ones has been achieved (e.g., National Research Council 1995), we do not yet know how to fuse that understanding into a quantitative theory capable of predicting changes in continent-scale or even local species-area patterns. It is not yet known whether a local extinction in one group will cause extinctions in others or whether species introductions, which are such an important part of the modern biological landscape, always lead to compensating or amplified losses in the diversity of native species. Without quantitative theories, we have only limited ability to predict rates of change or specific losses and gains that will follow a perturbation in the environment. However, current theories can be applied successfully to rank species diversities both within and among scales (MacArthur and Wilson 1967, Rosenzweig and Ziv 1999). Thus, a concerted effort during the coming decade could bring substantial advances. Meanwhile, recent deep-sea research has taught us that the planet 's deep ocean floor—most of the Earth's surface—harbors many more species than was previously believed. Thus, many of the species of the deep sea and their patterns of diversity remain to be discovered. At present, we do not know even the major features of the biogeography of the deep sea. The technology needed to obtain this information now exists. But the vastness and severe habitat of both the abyss and the edges of the continental shelves make sampling expensive and have restricted such activities. At present, deep-sea habitats remain wildernesses, and as such they allow the study of diversity in an environment relatively unaffected by human activities. Soon they may be affected by petroleum drilling, mining, waste disposal, and fishing. An infusion of major support is therefore needed to take advantage of the current window of opportunity. Diversity in terrestrial soils is poorly characterized as well. Although soils are easier to study in many ways than the deep sea, what their diversity means for microbes is not well understood. Because microbes are such an old and large fraction of the Earth's biota, improving this understanding is of great scientific and practical interest.

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Grand Challenges in Environmental Sciences It is also important to understand diversity at scales larger and smaller than that of the species. Past changes in the number and distribution of the major terrestrial biotic communities, or biomes, are important keys to understanding the history of the Earth. Understanding the limits on the number and distribution of biomes becomes more critical as human-caused climate change creates pressures for biome shifts and perhaps for the disappearance of some biomes and the emergence of others. Dynamic global vegetation models (International Geosphere-Biosphere Programme 1997) are a recent attempt to simulate the number, diversity, and distribution of biomes, based on competition among plants representing the major functional types. Unfortunately, our understanding of the factors that control this competition is still limited, and the results of these models are therefore tentative. The study of the relationship between biological diversity and ecosystem structure and functioning is in its infancy. Early studies have produced many examples but few general principles (Tilman 1999, Wardle et al. 2000, Naeem 2000). Obviously, at the lower limit (only one or very few species), loss of species diversity must affect ecosystem functioning, but there is no general principle concerning the impact of decreasing biological diversity on the risk of widespread loss of ecosystem functioning. It is clear that not all species are equally important, but little is known about the general extent to which ecologically similar species can substitute for each other in providing ecosystem services. A dedicated effort combining experiments with long-term studies, opportunistic observations, and synthesis would greatly advance understanding of the relationships between diversity and functioning. Although we cannot predict the results of these studies, almost any result would be of great value. Whether there is a general relationship, no relationship, or—most likely—different relationships under various circumstances, the knowledge will be essential for understanding and preserving biological diversity and ecosystem services. For much of the 20th century, researchers in population genetics and population biology sought to understand the factors that regulate a third scale of biological diversity—the genetic diversity within species and populations. Biologists succeeded in many particular cases. But they lack a comprehensive theory linking genetic diversity with other factors, including environmental stresses and diversity at the level of species or ecosystems. While it is clear that genetic diversity is a powerful influence on ecological success and hence on the persistence of species, we cannot yet quantify this relationship, although many examples illustrate the vulnerability of low-diversity agricultural systems to attack by pests. Even total understanding of the laws of diversity would be inadequate by itself to conserve diversity in the face of the changes humans make in the environment. Research is also necessary on the needs of specific species and ecosystems that have been truncated by human activities. Moreover, as noted above, practical efforts to protect species and ecosystems must be based on a balance

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Grand Challenges in Environmental Sciences between conservation needs and human needs. Achieving such a balance will entail answering many scientific questions related to three major strategies for protecting biological diversity—reservation, restoration, and reconciliation: Reservation is the setting aside of natural and near-natural areas for non-human biota. This strategy, exemplified by the establishment of national parks, has grown into a U.S. and worldwide program. It has reduced species losses, but it has not and cannot by itself eliminate them because so much natural habitat has been altered by human activities. Nonetheless, research is important to improve the design and implementation of biological reserves. Restoration ecology—only now beginning to see large-scale scientific application—attempts to return degraded sites to some degree of natural structure and functioning (see, e.g., National Research Council 1992). Restoration has much to offer for protecting biological diversity but is challenging, largely because of incomplete knowledge of which aspects of an ecosystem must be restored to protect an endangered species and to what degree of functioning. For example, Zedler (1996) describes how an apparently successful restoration of the vegetation in a coastal wetland did not support endangered clapper rails because the cordgrass was not tall enough to support their nesting. Similarly, red-cockaded woodpeckers do not depend simply on the presence of long-leaf pines, but require nest-holes in living trees (McWhite et al. 1993). And natterjack toads need more than early successional stages of sandy heathlands; they must have ponds warm enough to support early breeding so their tadpoles can escape predation by tadpoles of the common toad (Denton et al. 1997). Reconciliation ecology is beginning to emerge as a scientific discipline. Reconciliation is based on the premise that there are ways to design and manage habitats for productive human use and the maintenance of natural biota. Given continued human dominance of most terrestrial ecosystems, successful conservation of biological resources will depend on continued advances in our understanding of reservation, restoration, and especially the relatively new field of reconciliation ecology. Scientific Readiness The following conditions make a scientific initiative on biological diversity and ecosystem functioning particularly timely. Advances in understanding biogeography, speciation, and extinction. Species-area patterns are now known to exist at four scales, each of which has been associated with a set of processes ranging from sampling artifacts, to co-evolution, to speciation-extinction dynamics. Many details of these relationships and of their mechanisms of action are beginning to emerge, creating the

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Grand Challenges in Environmental Sciences change continues to contribute significantly to anthropogenic releases of CO2 to the atmosphere, changes in hydrologic dynamics and nitrogen cycling, and alterations in habitat for almost all terrestrial species. Land-use changes can also interfere with the migration of some species and facilitate the spread of disease vectors (Meyer and Turner 1992). And through their impacts on ecological services, land-use and land-cover changes affect the ability of biological systems to yield enough food, fiber, and fuel to meet human needs (Vitousek et al. 1997a). Thus, land-use and land-cover dynamics and their spatial patterns play a significant role not only as drivers of environmental change, but also as factors increasing the vulnerability of places and people to environmental perturbations of all kinds. Improved information on and understanding of land-use and land-cover dynamics are therefore essential for society to respond effectively to environmental changes and to manage human impacts on environmental systems. Scientific Importance The basis for a science of land-use dynamics is beginning to emerge (e.g., Skole and Tucker 1993). However, regional and global-level stocks of most land covers and uses, including such essential categories as forest and grassland cover, agricultural uses, and urban and suburban settlement, are still poorly documented and monitored. Theory and assessment models used to address land dynamics are mainly static, economic sector-based, and nonspatial, and do not account for neighboring uses; the roles of institutions that manage land and resources; or biophysical changes and feedbacks in land use and cover, including climate change and anthropogenic changes in terrestrial ecosystems. Such inadequacies must be redressed if we are to achieve a robust understanding of these phenomena and provide the kinds of projections required to conduct environmental planning and to ensure the sustainability of critical ecosystem functions. In particular, it is necessary to improve understanding of which land units change, how, where, and why. A growing interdisciplinary research community stands poised to document, develop theory, and provide robust regional models of land-use/cover change. Research efforts are under way worldwide to address almost all land covers and uses. Certain types of changes have been identified as especially critical and should be the focus of immediate concern: deforestation and its opposite, afforestation; pasture creation; grassland degradation; intensification of agriculture; and urban-industrial spread, including suburbanization. Of the first four, three types of change focus on the spatial magnitude of terrestrial land covers, while the intensification of agriculture deals primarily with increased water and chemical inputs to cultivation. Urban-industrial spread is important even though it involves only a small percentage of the total land surface under human management; for example, from 1982 to 1992, a relatively modest 25,800 km2 of agricultural land in the United States was converted to urban or built-up uses (Vester

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Grand Challenges in Environmental Sciences by et al. 1997). The changed parcels, however, often constitute prime lands for cultivation with concomitant cropping infrastructures, as in the case of the spread of megacity complexes worldwide. Urban development affects hydrologic processes as well (e.g., effects of paving on runoff and of urban heat islands on storms). Close inspection by the research community has begun to illuminate the nuances of land-cover dynamics and to challenge the conventional wisdom on a number of fronts. For example, studies of deforestation in Amazonia reveal that as much as 31 percent of formerly cut forest is in various stages of regrowth (Alves and Skole 1996), with significant implications for estimates of carbon emissions and of annual rates of change in the forested areas of the tropical world. Similarly, studies of land changes in the humid savannas of West Africa indicate that woody biomass has been increasing and continues to do so in areas claimed by some observers to be experiencing desertification (Bassett and Koli 2000). Inventories of ecosystems in the United States during the 1980s demonstrate an accumulation of carbon, largely through afforestation, equivalent to between 10 and 30 percent of U.S. fossil fuel emissions (Houghton et al. 1999). And changes in land use and cover affect local and regional climates; in South Florida, for instance, a drier, warmer interior during the months of July and August has followed the expansion of agriculture (Pielke et al. 1999). Documentation and monitoring of these and other trends provide an observational base for efforts to improve understanding of the dynamics of land change, projections of climate change (by better specifying the contribution of land cover), and estimates of the full range of impacts of various land-cover “swaps” intended to reduce CO2 emissions (e.g., trading energy units from power plants in temperate industrialized countries for afforestation in the tropics). The international, interdisciplinary research community has begun to address the explanatory power of relative location (the effects of surrounding land uses on the potential for a unit of land to change), path dependency (the role of previous conditions and trajectories of change in constraining options for future change), biophysical feedbacks (e.g., effects of nutrient depletion with cropping), land and resource institutions (e.g., land tenure), and induced innovation (the capacity of agents and society to innovate internally as conditions change). Understanding the interrelations among these factors is often key to explaining land-use change and its environmental and social effects. For example, the highest recorded emissions of the greenhouse gas nitrous oxide and the ozone-affecting gas nitric oxide from soils have been linked to policy-influenced cropping procedures in northern Mexico's irrigated “wheatbasket” (Matson et al. 1988). Likewise, different tenure institutions controlling land uses and stocking strategies in Rajasthan, India, have led to significant differences in grassland quality and presence of trees (Robbins 1998). Researchers are also beginning to demonstrate the value of spatially explicit analytical approaches as compared with nonspatial measures of the magnitude of change (Lambin 1994, Turner 1990). For example, by including the spatial

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Grand Challenges in Environmental Sciences heterogeneity of the landscape and modeling interactions between land users and other decision makers, recent economic models of suburbanization in the Patuxent watershed of Maryland have improved the explanation of land use and its change over what could be achieved with traditional nonspatial and noninteractive models (Bockstael 1996). As a result of such advances, the research community is now poised to develop at least four types of spatially explicit, integrative, explanatory land-change models: (a) those based on behavioral and/or structural theory linked to specific geographic locations, (b) those drawn from changes registered in remotely sensed imagery, (c) hybrids of these two types, and (d) dynamic spatial simulations (DSSs) that offer projections under different sets of assumptions (Frederick and Rosenberg 1994, Liverman et al. 1998). Theory- and imagery-based models are used to explore explanations of change and to provide near-term (5-10 years) projections under differing sets of assumptions. They permit tests of the applicability of various theories for different areas and conditions and the coupling of local-, regional-, and global-scale models by land cover or use type. An example is the fit of the Yucatan Peninsula to local versus pantropical models of tropical deforestation. DSSs, on the other hand, address scenarios over the longer term (more than 10 years) by making the agents, structures, and environment interactive and dynamic. For example, a DSS can examine how changes in the structures governing land access change agents' decisions about use, and in turn, the environmental qualities of the land feed back to agents and institutions governing land access. Scientific Readiness In addressing this challenge, new research would characterize regional variations in the pace, spatial scale, and magnitude of change in critical land uses and covers. It would identify the ways in which individual, household, and institutional actors and structures affect these changes and, in turn, respond to their biophysical consequences. The research would also develop increasingly robust models for addressing these dynamics in spatially explicit ways at different spatial scales and in relation to multiple sectors of human activity. Several recent developments make the area ripe for further advances, promising to transform land-use/cover change science. Improved databases on land cover and land use. Key organizations and agencies are improving their databases on land in a manner consistent with the needs of global change science. For example, the Food and Agriculture Organization is leading an effort to create an international land-use typology and to employ this typology in its country-wide compilations of land conditions. The new Landsat 7 satellite will provide frequent worldwide imagery of land cover from the Thematic Mapper system at costs affordable to the community of land researchers.

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Grand Challenges in Environmental Sciences Advances in imagery analysis and geographic information science. These developments are providing the tools and analytical capacity needed to address land-use/cover dynamics spatially and to link social science and biophysical data. These capabilities and the emergence of other kinds of spatially explicit data have triggered interest in land use among new communities of researchers, such as demographers and economists (National Research Council 1998), and have inspired researchers to develop various modes of spatially explicit, multisectoral land-change models that begin to integrate statistical, diagnostic, and prognostic approaches at the regional level. Advances in the analysis of spatial data. Advances are being made toward solving some major methodological problems involved in the analysis of spatial data. For example, spatial autocorrelation, the tendency for two points in close proximity on the Earth's surface to have similar properties, invalidates the use of statistical tests that assume independence among observations. Methods are being developed to account for spatial autocorrelation and explore its properties (e.g., Bailey and Gatrell 1995) and to analyze variables as functions of spatial location (e.g., Goovaerts 1997). Progress is also being made in finding ways to improve the drawing of inferences from large-area data—often the only data available —to small-scale processes (e.g., King 1997) and in understanding how the results of spatially aggregated data analysis depend on the basis of aggregation (Openshaw 1983). Increased inter- and multidisciplinary interest in the science of land-use/ cover change. Stimulated by various international and national research programs, formerly diverse sets of researchers worldwide are engaged in collaborative ventures to create integrative approaches to the study of land-use/cover change. In the United States alone, 25 such teams have been formed by NASA's Land-Cover and Land Use Change program, with strong linkages to several of the centers of excellence sponsored by NSF. This figure is substantially larger at the international level. Additionally, the U.S. Geological Survey, working with the Environmental Protection Agency, is supporting research projects on land-cover trends and on urban dynamics, and NSF sponsors a small Human-Environment Regional Observatory project. These federal initiatives are an important beginning, but still lack the coordination, scope, and focus on integrated land-change models called for under this challenge. Important Areas for Research Develop long-term, regional databases for land uses, land covers, and related social information. These databases should emphasize the critical land uses/covers of forest, grasslands, agriculture, and urban-industrial settlement and should include complementary demographic, economic, and institutional information. Work on developing useful land-cover data must include efforts to

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Grand Challenges in Environmental Sciences improve the accuracy and reduce the uncertainty of vegetation classification from remote observation platforms. The research community has identified regional data observatories and archives as essential. They are, however, extremely difficult to establish and sustain, and few if any interdisciplinary exemplars exist. Increased temporal resolution of high-spatial-resolution, space-based imagery is needed, along with reduced costs of such data for individual researchers. The issue of the confidentiality of social data also requires attention. Formulate spatially explicit and multisectoral land-change theory. Research in this area should address the causal roles in land dynamics of relative location, past uses (path dependency), land and resource institutions, and biophysical changes and feedbacks (e.g., climate change, nutrient depletion), and should determine the significance of regional variations in these relationships. Until now, land-change theory has been crafted in relatively simple terms and focused on specific economic or land sectors or products (e.g., agriculture or timber production). Understanding the causes and implications of land-use/cover change requires the development of theory that can account simultaneously for changes in multiple uses and covers by accounting better for the complexity of interactions that stimulate these changes. To achieve this aim, improved understanding of how agents and social structures behave or operate over space is required, along with better statistical methods that permit hypothesis testing and model validation. It is also important to understand the ecological consequences of land-use change and how ecological changes can influence land use. Link land-change theory to space-based imagery. Space-based imagery offers one of the few ways to scale analysis up spatially beyond the local level. Research in this area would push the boundaries of land-cover change detection from space and develop and test imagery-led models of change that could be coupled or merged with models based on theory (actors and/or structures). The research would also press imagery analysis to detect variables or develop proxy measures important to the human science of land change. The potential of this line of research will expand as new remote platforms offer observations at increasingly finer scales, suitable for detecting human activities not previously observable from space. Develop innovative applications of dynamic spatial simulation tech niques. Research in this area would exploit recent gains in computing resources and techniques. It would (a) extend dynamic spatial simulation techniques to model the distinct temporal and spatial patterns of land-use and land-cover change; (b) connect these models to extant and pending theoretical frameworks that accommodate the complexity of, and relationships among, socioeconomic and environmental factors (see research area 2 above); (c) establish common validation and replication protocols necessary for determining the robustness of model outcomes under different assessment scenarios; (d) consider the value of

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Grand Challenges in Environmental Sciences information and the role of uncertainty in determining model outputs; and (e) examine the utility of dynamic spatial simulation models for land managers and government decision makers. GRAND CHALLENGE 8: REINVENTING THE USE OF MATERIALS The challenge is to develop a quantitative understanding of the global budgets and cycles of key materials 2 used by humanity and of how the life cycles of these materials may be modified. Among the materials of particular interest for this grand challenge are those with documented or potential environmental impacts, those whose long-term availability is in some question, and those with a high potential for recycling and reuse. Examples include copper, silver, and zinc (reusable metals); cadmium, mercury, and lead (hazardous metals); plastics and alloys (reusable substances); and CFCs, pesticides, and many organic solvents (environmentally hazardous substances). Practical Importance The extraction, use, and dissipation of technology-related materials affect humans and natural ecosystems in a myriad of important ways. First, toxic elements such as cadmium, mercury, and lead accumulating in the environment can have important negative impacts on human health (see, e.g., Thomas and Spiro 1994). An understanding of the flows of these elements and of the technological and cultural factors that drive those flows is required to mitigate these harmful effects and reduce exposure levels over the long term. Second, recovery and recycling of valuable elements such as platinum or copper can be accomplished at only 10-20 percent of the energy cost of refining these elements from natural sources (Schuckert 1997). Finally, understanding where these elements are lost during manufacturing processes and where in the environment they ultimately come to reside is necessary in considering whether to recover them. With the changes brought about by population growth, rapidly evolving technology, more intensive agriculture, and increasing energy usage, global use of technological materials is expected to grow by as much as a factor of four 2   “Materials” includes elements, compounds, alloys, and other substances created or mobilized by human activities, except it specifically excludes the elements that constitute the grand nutrient cycles—carbon, nitrogen, sulfur, and phosphorus. (The cycles of these elements have historically been dominated by natural processes, though human activities are now important perturbers; these cycles are the subject of Grand Challenge 1, Biogeochemical Cycles. Because of their association with human uses, the discussion that follows often refers to the materials of interest as “technological” or “technology-related.”)

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Grand Challenges in Environmental Sciences during the next several decades. The cycles of many important materials are in rapid fluctuation, with existing reservoirs changing in size and new ones being added, and timely analysis is needed to understand some of these changes. For example, we are approaching local toxicity thresholds for some materials (Environmental Protection Agency 1998), and the availability (at reasonable cost) of certain materials essential to manufacturing is becoming threatened (Kesler 1994). New compounds and other substances are constantly being incorporated into modern technology and hence into the environment, with insufficient thought being given to the implications of these actions. All of these issues assume added importance in urban areas, which concentrate flows of resources, generation of residues, and environmental impacts within spatially constrained areas. From a policy standpoint, reliable predictive models of material cycles could be invaluable in guiding decisions about issues related to fossil fuel use, energy production, agricultural practices, and a wide range of other topics relating to human-environment interactions (Allenby 1999). This grand challenge centrally encompasses questions about societal-level consumption patterns, since consumption is the primary force driving human perturbations of material cycles. Social scientists are exploring many questions about consumption patterns that are relevant to the issue of material cycles, such as the reasons for the large variations in consumption of resources among different cultures (National Research Council 1997); the factors that drive changes in consumption patterns over time (Organization for Economic Cooperation and Development 1997); whether policy initiatives influence these patterns; and if so, which policies are most effective for any given situation. These questions relate also to Grand Challenge 6, Institutions and Resource Use. Scientific Importance The basic framework for understanding the flows of materials is the “budget,” in which short- and long-term reservoirs are identified, and the flows between the reservoirs are quantified (e.g., Graedel and Allenby 1995). No overall pictures of generation, use, and fate have yet been produced for materials whose cycles are dominated by technology; our understanding of the budgets and cycles of nutrient compounds of carbon, nitrogen, sulfur, and phosphorus (addressed by Grand Challenge 1, Biogeochemical Cycles) is far more advanced. The construction of budgets for technological materials would be a natural outgrowth of the interaction of environmental science and the emerging discipline of industrial ecology, and would follow directly from the theoretical and analytic approaches developed for the major biogeochemical cycles (e.g., Bolin and Cook 1983). In fact, part of the scientific excitement generated by these questions is that they can be adequately addressed only through close collaboration among specialists in the natural sciences, the social sciences, and a variety of engineering disciplines to achieve the following:

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Grand Challenges in Environmental Sciences Understanding the operation of the natural cycle of an element, compound, or other material (if it occurs in nature) Identifying the ways in which human activities define, perturb, or dominate material cycles (and establishing the magnitudes, trends, and causes of resource flows within an anthropogenically dominated system) Determining the environmental and resource supply implications of these perturbations Once this information is in hand, focused, practical implications can be addressed: to mitigate undesirable environmental consequences related to human activities, we must have an accurate understanding of those activities and of how they might be changed. One form of change is largely technological, and involves the redesign of products and processes such that the use of materials is optimized; the environmental implications of manufacture, delivery, and customer use are minimized; and the eventual recovery and reuse of resources are enhanced. A second form of change is behavioral, and involves economic producers and consumers and the forces that determine their adoption of technologies that alter the use of materials. A useful perspective on the intellectual challenges presented by technological material cycles is provided by activities related to the biogeochemical cycles of Grand Challenge 1. For those cycles, natural and perturbed, the research activities are centered on identifying the complete suite of sources, sinks, and feedback loops; assessing how these variables have evolved over time; and predicting how they are likely to evolve in the future. Complicating factors include missing or poorly quantified information, incomplete understanding of human activities that shape the budgets, substantial spatial variation, and uncertainty about the behavior of the sources and sinks under altered physical and chemical conditions. Many of these difficulties are present as well for the budgets controlled largely by anthropogenic activity. While sources are often rather well established, both in kind and magnitude, sinks and feedback loops are not, and the forms and magnitudes of storage in various reservoirs (formal and informal stockpiles, landfills, environmental receptor basins) are generally quite uncertain. In addition, the human activities that shape the budgets are not well documented or understood. In many cases, proxy data, inference, and archeomaterials research will be necessary to complete the picture. In this connection, the most ambitious portion of this grand challenge activity is likely to be the acquisition, comprehension, and integration of data sets and other information from the environmental, economic, and social spheres, and the development of robust ways of utilizing those results in predictive exercises. The achievement of data harmony, consistency, and rigor across this interdisciplinary landscape will be a major effort and will provide the necessary basis for a scientific understanding of material cycles.

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Grand Challenges in Environmental Sciences An understanding of the use of materials and its implications is a prerequisite for many of the predictive exercises encompassed by the other grand challenges. As one example, Grand Challenge 5, Infectious Disease and the Environment, identifies chemical selection pressure from the environment on pathogens as a priority research area. This area could make use of data on contemporaneous rates of heavy metal and pesticide loss to ecosystems of interest, as well as informed projections of how those flows might be expected to change over space and time. A second example relates to Grand Challenge 4, Hydrologic Forecasting. Informed projections derived from analysis of material use would be directly applicable to predictions of water availability and quality. Scientific Readiness This grand challenge is timely for both scientific and policy reasons. From a scientific standpoint, work has begun on devising regional and global budgets for several of the toxic trace metals (e.g., Jolly 1992, Jasinski 1995). These and related studies have started identifying data sources related to extraction, processing, use, and disposal, and provide a framework for more general research related to the budgets of key materials used by humanity. Moreover, the sophisticated techniques and considerable scientific expertise developed to investigate nutrient cycles are directly applicable to questions about material cycles, and thus can be used to initiate research efforts in this area. In addition, as part of the Industrial Transformations project of the International Human Dimensions Programme (1999), social science and policy research has begun to address changes in production and consumption patterns. This effort is developing an international and interdisciplinary research community that is addressing fundamental questions about consumption trends and their causes that must be addressed to predict future trends in material cycles and the environmental effects of these changes. Historical changes in material mobilization, use, and dissipation are beginning to be understood, for example, by constructing histories of fossil fuel consumption or trace metal deposition on polar ice or lake sediments. In addition to providing historical information on material utilization and dispersal, these data contribute to understanding of the historical intensity of interactions between human activities and the environment. Such efforts need to be expanded to include a wide range of materials and locales, with the ultimate goal of constructing gridded budgets integrated over the time period since the Industrial Revolution. International collaborative efforts should be encouraged, since material cycles do not respect national boundaries. In a more practical vein, engineers in industry and academia are beginning to devote significant effort to “design for environment, ” in which the selection, processing, and use of materials play central roles. This technology-oriented research is key to the implementation of insights gained from an understanding

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Grand Challenges in Environmental Sciences of reservoir contents and flows, and could lead to reinvention of the ways in which materials are acquired and used by modern technology. One could envision, for example, that the results would stimulate the development of policy instruments designed to encourage the recovery, reprocessing, and reuse of a variety of selected materials, along with the development of technologies that would make these policy instruments implementable in efficient and effective ways. Such new approaches to material utilization would be informed by research in the environmental sciences in general and materials-environment interactions in particular, and enabled by modern engineering tools such as life-cycle assessment, computer-aided design and manufacturing, and performance analysis. Important Areas for Research Develop spatially explicit budgets for selected key materials. This research would involve quantifying reservoir contents and flows for the materials in question; constructing spatially resolved maps of these stocks and flows; and combining these results with other environmental, economic, and social data sets to learn more about the causes and consequences of changes in material cycles. As has been demonstrated by budgets for naturally cycling compounds of carbon and nitrogen, budgets constructed with a high degree of spatial resolution are much more useful than those that provide only aggregate, global information. The budgets thus developed would include analyses of anthropogenic flows by type of activity (e.g., mining, manufacturing, household use) and by technology, as well as by spatial location. They would require as well comprehensive integration with data on natural flows of the same materials. The generation of location-specific information would provide links between anthropogenic material cycles and their human causes and potential environmental impacts. Develop methods for more complete cycling of technological materials. Addressing this topic would involve pursuing life-cycle design of products; lengthening the useful life of products by modular design; and advancing research on the utilization of residue streams, the recovery of discarded materials, and the transformation of patterns of consumption. The work might also involve the use of more easily recycled and reused materials, perhaps including benign new materials such as biological products and composites. This is largely an engineering activity, but one whose priorities are established by contemporary budgets and future budget scenarios. Determine how best to utilize materials that have uniquely useful industrial applications but are potentially deleterious to the environment. This research would include describing the spectrum of uses for these materials, identifying points of loss of the materials to the environment and methods by which such loss might be reduced, developing substitutes for these materials, and investigating reengineering activities that could be used to cycle the materials

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Grand Challenges in Environmental Sciences more completely. As with other types of material use, but especially in this case, dematerialization (accomplishing a given design goal with a substantially smaller amount of material) could contribute substantially. Develop an understanding of the patterns and driving forces of human consumption of resources. This research would involve studying material consumption patterns across time, in different countries, and at different levels of economic activity, with the aim of understanding how differences develop, why the patterns change, and what changes might be anticipated in the next several decades. The results would aid in understanding current patterns of material flows and provide a basis for anticipating societal drivers of those flows in the future. Formulate models for possible global scenarios of future industrial development and associated environmental implications. This research would draw on contemporary material budgets, predictions of technological developments, studies of consumption patterns, and assessments of industry structure and environmental law and policy to predict how specific circumstances or policy options might strongly influence industry-environment interactions in the next several decades. Thus, this research constitutes the equivalent for impacts of resource and material use of scenario exercises such as those of the Intergovernmental Panel on Climate Change (1996).