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--> OVERVIEW AND PERSPECTIVES Peter C. Schulze, Robert A. Frosch, and Paul G. Risser The expectations placed on engineers shift with the cultural evolution of the societies in which they practice. An important shift has occurred with the growth of human impacts on the planet (Kates et al., 1990; Vitousek et al., 1986). When the cumulative impact of humans was small, the environmental implications of engineering designs were of less concern. Now that the impact of humans has reached a global scale, there is growing concern about the environmental implications of engineering designs. A new set of constraints has become important to engineers—ecological constraints. Engineers are accustomed to contending with a variety of design constraints, from the most rigid thermodynamic laws to budgetary constraints to issues of social justice. Ecological constraints add one more set of considerations to the list. Engineering designs are now expected to result in products or management plans whose use or implementation will not endanger important ecological conditions and processes. This would be a tall order if the requirements in particular instances were precisely known. It is made all the more challenging by our only partial understanding of the set of important ecological conditions and processes, and what those conditions and processes require to persist. One conclusion seems clear. Engineers and ecologists will need to work together more often than they have in the past. Progress in both engineering design and ecological understanding will be necessary if humans hope to keep (or bring) their impacts within the limits imposed by the desire for "sustainability."1 Ecologists and other environmental scientists need to collaborate with engineers to describe the requirements of important ecological conditions and processes in terms that can be incorporated into engineering design considerations, and con-
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--> tinue to work together to develop suitable engineering plans. Engineers and ecologists certainly can not solve these problems alone, but they do have important responsibilities in efforts to keep human environmental impacts within acceptable bounds. With the exception of selected subdisciplines (Mitsch, in this volume), there is so little dialog between engineers and ecologists that it is hard to know where to start. What would it mean to engineer within ecological constraints? What are the ecological constraints? Which constraints are most important? Can some be ignored? How would one distinguish satisfactory and unsatisfactory designs? What does it mean to keep human environmental impacts within "acceptable" limits? Four related topics arise frequently during discussion of these broad questions: problem definition, uncertainty, lessons from environmental control efforts, and the difficulty of finding short-term solutions that do not aggravate long-term problems. We summarize key themes regarding these four issues below. Problem Definition "Everything should be made as simple as possible, but no simpler." —attributed to Albert Einstein A plan is not likely to be successful if the problem that it is intended to solve is not accurately defined. Whether ecological constraints are met will depend upon whether the definition of the problem included those constraints. Moreover, when substantial consequences of a project, product, or management plan are not appreciated at the design stage, costly problems may arise later. For example, almost as soon as the Kissimmee River channelization project was completed, the severe ecological consequences became apparent and much more expensive work was begun to reverse the damage (Shen, in this volume; Wodraska and yon Haam, in this volume). Other examples could be cited, including the impacts of dams and forestry practices upon salmon and other fish, the tendency of pesticides to kill a pest's natural predators and lead to pesticide-resistant pests, transportation of exotic species by ships and airplanes, impacts of chlorofluorocarbons (CFC) on stratospheric ozone, and even the impact of carbon dioxide emissions on the global atmosphere. This is not to suggest that the activities that led to these problems should not have occurred, merely that had these consequences been appreciated and taken into consideration from the outset, it might have been possible to reduce or eliminate impacts through design or management modifications. As the problem-definition stage of engineering efforts continues to expand in response to environmental concerns, and as our dependence on ecosystem "services" becomes better understood (Cairns, in this volume), these sorts of problems should become less frequent. To this end, several general criteria and
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--> guidelines have been offered. Schaeffer (in this volume) suggests that engineers adopt the medical oath to "do no harm," in this case to the environment. Norton (in this volume) suggests that engineers adopt the Pareto welfare criterion of economics, in which case an engineering design would be considered satisfactory if its effects were positive for some individuals and neutral for all others. Holling (1992) argues that efforts to identify ecological constraints may benefit from a focus in which the environment and its many components (including humans) are systematically viewed as a hierarchy of systems within systems. Daly and his colleagues (Costanza et al., 1991; Daly, 1990) have suggested acceptable boundaries for human environmental impacts. Rates of extraction of renewable resources should not exceed regeneration rates. Rates of waste emission should not exceed the assimilative capacity of the environment.2 Rates of extraction of nonrenewable resources should not exceed the rates at which substitutes are found and developed. These guidelines imply a variety of long-term performance standards. For example: pumping from aquifers should not exceed recharge rates; pollutant concentrations should not increase; soil depth should not decline; harvesting should not cause reductions in population sizes. These guidelines can be useful for identifying unsatisfactory circumstances, but it remains to be seen whether they will be elaborated in ways that will make them directly useful to engineers struggling to satisfy particular ecological constraints in the context of particular engineering problems. Available evidence suggests that when ecological constraints are clearly defined, engineers can develop designs or management plans with the potential for meeting them. Shen (in this volume) describes two such examples. On the Niobrara River the challenge was to release water from a dam such that the downstream reaches of the river would maintain the broad shallow morphology that is required by migrating whooping cranes. In south Florida the challenge was to restore the Kissimmee River such that flood waters would inundate the floodplain frequently and return to the river channel slowly. In both cases seemingly satisfactory water management plans were developed. Lindstedt-Siva et al. (in this volume) describe another example from ARCO's experience of exploring for oil in tropical rain forests. Roads built into remote rain forest regions facilitate human immigration and subsequent forest destruction. Lindstedt-Siva and her colleagues were determined to explore for oil without building roads. They took their lead from offshore exploration operations, and used helicopters rather than trucks to move equipment. These examples suggest potential for fruitful collaboration between ecologists and engineers. In all three examples, recognition of important ecological processes led to the identification of key ecological constraints, and engineers used those constraints to develop designs that appeared capable of satisfying them. Plans for the proposed dam on the Niobrara River were canceled because of budgetary constraints, and it is too soon to assess the success of the other designs. In addition, satisfaction of particular ecological constraints is not neces-
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--> sarily the same as satisfaction of all important ecological constraints. Nevertheless, these examples are encouraging. Because natural systems are complex, it will not always be easy to identify key ecological constraints. The examples discussed by Shen and Lindstedt-Siva et al. are relatively simple. In other situations the challenge for designers will be greater, either because the ecological constraints are poorly understood, or because the connections between design options and ecological processes are indirect. Nevertheless, past efforts to identify key variables in ecological systems give some cause for optimism. For instance, the condition of a grassland can be predicted from five parameters: species composition, primary productivity, species diversity, organic material content of the soil, and nitrogen content of the plants (Risser, 1995). Likewise, the condition of river ecosystems can be assessed on the basis of a relatively small set of variables (Karr, in this volume). Once such key variables are identified, studies can begin to examine the types and magnitudes of impacts that environments can absorb without being unacceptably altered. Other situations are even more complex. What are the ecological implications of the design of, for example, a radio? The answer to this question depends on a variety of factors, such as the methods of raw material acquisition, the ecological effects of manufacturing wastes, and the way the radios will be discarded (Allenby, 1994). When the ecological implications of an engineering design are obscure, it may be most productive to adopt the general approach of ''life-cycle analysis'' or "design for environment" in which there is a conscious effort to consider systematically the environmental implications of all aspects of engineering designs (Allenby and Richards, 1994). Such efforts may be assisted by Holling's systems perspective and by an identity recently suggested by Herman Daly (personal communication): A = (B)(C)(D)(E) where: A = economic services gained/environmental services sacrificed B = economic services gained/economic stock consumed C = economic stock consumed/environmental throughput D = environmental throughput/environmental stock exploited E = environmental stock exploited/environmental services sacrificed The above examples suggest that when specific constraints are identified and agreed on, suitable designs or management plans can be developed. The challenge for engineers and ecologists is to work together to identify key constraints and develop plans that satisfy those considerations. In many cases it will also be necessary to work together to convince others that the desirable environmental properties of those resulting designs warrant the necessary investment (Wurth, in this volume).
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--> Uncertainty "And then what?" —Hardin (1993:16) Because ecosystems are complex, the environmental consequences of human activities are uncertain (Brooks, 1986; Costanza, 1993; Holling, 1993; Ludwig et al., 1993). Thus, uncertainties are an important consideration in engineering designs and management plans. It can be useful to distinguish three types of uncertainty. "Risks" refer to situations where probabilities may be ascribed to various potential consequences. "Unknowns" refer to situations where the range of possible consequences is thought to be reasonably well understood, but the probabilities of the various consequences are unknown. "Unknown unknowns'' are phenomena that one is not even aware one fails to expect or understand. Even though new technologies are often environmentally preferable to those they replace, their large-scale adoption often results in unanticipated undesirable environmental impacts (Gray, 1989).3 Hindsight suggests there is room for improvement in our ability to anticipate these impacts. Myers (1995) notes that neither global warming nor acid rain were major concerns at the 1972 United Nations conference on the environment in Stockholm, even though Arrhenius had warned of global warming 100 years earlier and biologists were aware that massive quantities of sulfur dioxide and nitrous oxides were being emitted into the atmosphere. Perhaps some unknowns would be better described as unappreciated knowns or ignored knowns. Whole cadres of environmental scientists, policy analysts, and others work on risk assessment, but few are studying approaches to anticipating that Which would otherwise come as a surprise. Differences in approaches to uncertainty have major implications for environmental policy (Costanza, 1993). Approaches that focus on risks use quantitative models in attempts to identify most likely scenarios, and then use the results as the basis of policy recommendations (Committee on Science, Engineering, and Public Policy, 1992; Nordhaus, 1992). An alternative approach, focused on unknowns, attempts to identify the policy option that minimizes the likelihood of a catastrophic outcome. This approach, which is embodied in the precautionary principle, does not attempt to ascribe probabilities to alternative possible outcomes (Cameron and Abouchar, 1991; Costanza, 1989, in this volume; Daily et al., 1991). At the extremes neither approach is perfect. Policies based on a most likely scenario will be unfortunate, if not catastrophic, if the eventual outcome is not the one that was deemed most likely. Conversely, reliance on the precautionary principle begs the question, "How much precaution?" Environmental impacts are but one of many important consequences of new technologies. An excess of precaution could reduce innovation and its associated benefits. In addition, even though a new technology may have unanticipated effects, its aggregate environmental impacts may be preferable to those of the older technology that it replaces.
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--> Finally, there is an issue of opportunity costs. An excess of precaution directed toward one concern may reduce the potential effort available for investment in other concerns. Thus, opportunities to address ecological constraints could be harmed by being too cautious. Good policy requires explicit consideration of risks, unknowns, and unknown unknowns. Approaches to dealing with uncertainty are particularly relevant to discussions among engineers and ecologists since both casual experience and the literature suggest that members of these two communities tend to have different expectations regarding the future consequences of human environmental impacts (Nordhaus, 1994; Schaeffer, in this volume). Differences in expectations may lead to differences in priorities and disagreements about appropriate actions. For example, Schaeffer (in this volume) describes the virtual stalemate between the Corps of Engineers and the representatives of various resource management agencies and environmental groups regarding studies to assess the ecological effects of increased barge traffic on the upper Mississippi River. If there are indeed systematic differences in the expectations of engineers and ecologists, disagreements might not depend as much upon the particulars of the case in question as upon differences in fundamental disciplinary perspectives or assumptions, such as the time frames of consideration or expectations regarding future technological developments. Perhaps engineers who are accustomed to choosing design alternatives involving fairly well Understood phenomena may naturally tend to focus on risks while ecologists, who are not so accustomed to making precise predictions, are naturally inclined to focus on unknowns and the possibility of unknown unknowns. An effort to get at the roots of these differences in perspective and focus, if they are real, might lead to improved understanding all around and better mutual appreciation of ecologists for engineering perspectives and vice versa. Engineers deal with uncertainty regularly in their design efforts. Safety factors are routinely used to minimize the risk of hazards due to variables outside the designer's control. In essence, safety factors represent one way to try to insure against catastrophe. This is not unlike conventional approaches to many everyday sources of uncertainty, where substantial sums are invested to protect against the consequences of potentially catastrophic but uncertain events such as personal illness, automobile accidents, or military aggression (Daily et al., 1991). One goal for collaborating engineers and ecologists could be to develop new ways to think about "safety factors" and other means to incorporate the possible effects of uncertainties into considerations of human environmental impacts. Approaches To Environmental Control: Lessons From Resource Management Efforts There is no consensus regarding the precision with which humans can expect to manage ecosystems. Some feel that we can not expect to control the environ-
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--> ment on scales larger than individual agricultural fields, whereas others are optimistic about regional control strategies, and still others are optimistic about the potential for control on global scales. Regardless of the ultimate potential of human control, analyses of past resource management efforts provide important lessons regarding pitfalls to avoid in control efforts. Like conventional engineering, resource management faces substantial challenges with regard to uncertainties, problem definition, and the need to maintain the flexibility to shift course if necessary. Holling (1986, in this volume) describes the insights from a review of efforts to manage forest insects, forest fires, fisheries, and arid rangelands. Managers typically enjoyed initial success in efforts to constrain one variable within narrow bounds, but this success led to economic developments that depended on perpetuating those management strategies. These dependencies increased the pressure to maximize the productivity of particular components of the managed systems and made it difficult to modify management practices. Agencies shifted their focus toward increasing their efficiency in maintaining the initial programs, and in some cases larger socioeconomic objectives were neglected. As a consequence, systems became simpler and less resilient to perturbations. Disturbances that previously would have had little effect on the ecosystems began to have significant impacts on the simpler systems. Holling and his colleagues conclude that a loss of resilience is a consequence of the imposition of stability upon one component of a naturally dynamic system. Wodraska and von Haam (in this volume) argue that managers must continually monitor the effects of their efforts and enjoy the flexibility to modify strategies when necessary. They note that Congress dictated particular water flow rates into the Everglades, but the timing and magnitude of the prescribed flows exaggerated natural extremes and exacerbated existing environmental problems. Wodraska and yon Haam would have preferred an incremental approach that was flexible enough to make adjustments in response to new information. Holling (in this volume) notes that the rigid control approaches used in the 22 cases he reviewed differ from natural ecological controls, which tend to be "soft" and overlapping. A variety of different controls tend to keep natural systems within loose boundaries. Though bounded, the systems are dynamic and resilient to disturbances. For example, temperature regulation in endotherms (loosely speaking, "warm-blooded" animals) is managed by at least five separate, mechanistically distinct sets of controls, evaporative cooling, metabolic heat generation, regulation of blood flow, insulation, and habitat selection. Endotherms have flourished even though their normal body temperatures are very near their lethal body temperatures. Is it necessarily the case that control of one key variable leads to fragility of the larger system? Can management objectives be achieved without destroying the resilience of the system being managed? To what extent could future engineering and management efforts simply facilitate natural processes so that those
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--> processes serve the purposes (e.g., flood control) that have traditionally been served by single-variable control-based engineering efforts (Mitsch, in this volume)? It seems likely that significant progress toward answering these sorts of questions will require extensive, regular collaboration among engineers and ecologists. Short-Term Solutions That Aggravate Long-Term Problems The resource management programs reviewed by Holling represent situations where short-term solutions aggravated long-term problems. The same situation is probably the essence of most environmental problems. Inappropriate short-term actions sometimes appear sensible because their long-term consequences are either not recognized or not appreciated. Engineering within ecological constraints must anticipate when short-term solutions will exacerbate long-terms problems (Cairns, in this volume; Norton, in this volume). Wodraska and yon Haam's description (in this volume) of the California water supply system provides an example of the tension between short-and long-term goals. To supply water to 16,000,000 residents of southern California, earlier managers of the water system stretched tentacles out to water sources in northern California and to other western states. Water flows through pipes as large as 6 meters in diameter in an area prone to earthquakes. This has solved the problem of providing water to the residents of the region, but it has led to a system whose operation depends on the integrity of a plethora of components, including long aqueducts and pumps that lift water more than 500 meters. The problem of supplying water has been solved for the time being, but the solution has made the water distribution system brittle in the sense that it is sensitive to earthquakes and other disturbances. In addition, adequate present supplies relax immediate constraints on human immigration, which will lead to a larger regional population and concomitantly greater dependence on the water distribution system. (The present managers are now attempting to increase the system's resilience by building in redundancy of function through conservation and wastewater reclamation, rather than simply increasing capacity by obtaining new supplies.) Herman (in this volume) refers to several other examples where short-term solutions aggravate long-term problems. His examples include highway "bypass" routes that attract development and thus result in greater traffic congestion, and pest control efforts that lead to the evolution of pesticide-resistant pests. These situations have been described as cases of "revenge" by the system and discussed under the rubric of "revenge theory" by Tenner (1991). In other cases the conflict is not between the society's short- and long-term interests, but between the individual's interests and the society's interests, as in the case of CFC-based air-conditioning systems. Costanza (in this volume) refers to situations where short-term incentives conflict with long-term goals as social
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--> traps. He argues that our tendency to fall into social traps results from the speed of cultural evolution: societies change so rapidly that it is difficult to incorporate long-term considerations into day-to-day decisions. He argues that in order to eliminate social traps, short-term incentives must be brought into correspondence with long-term incentives. Norton (in this volume) argues that decisions with long-term or widespread implications should be based on different criteria than decisions whose implications are only local or ephemeral. He contrasts the individual's roles as a consumer and as a member of a constitutional convention. Norton argues that while the consumer makes economic decisions based on individual utility in the relatively short run, the delegate to a constitutional convention must make decisions on the basis of the long-term best interests of the nation whose constitution is being drafted. In other words, different priorities must serve as the basis for decisions that have the potential for long-term effects, whether the issue is a nation's constitution or its environment. This is not to suggest that the short-term problems discussed above should not have been "solved," merely that those searching for solutions should recognize the potential for "revenge" on the part of the system. As Garrett Hardin (1993:16) suggests, when contemplating the effect of a particular solution, one should ask, "And then what?" We believe that the following papers will help as engineers and ecologists consider Hardin's question in the course of future attempts to engineer within ecological constraints. Acknowledgments These remarks are based on discussions and presentations during an April 1994 National Academy of Engineering meeting on engineering within ecological constraints. George Diggs, Alexander Flax, Hugh MacIsaac, Deanna Richards and three anonymous reviewers provided valuable comments on earlier drafts. Credit for any insights should be attributed to the meeting participants. Notes 1. Many definitions of sustainability have been proposed or implied. We use the term to refer to situations where the environmental impacts of present human activities do not reduce the potential for the environment to support future human activities. The laws of thermodynamics preclude truly infinite sustainability, but we consider this unimportant. With so many systems so far from sustainability at present, the concept is most useful as a guide in efforts to shift actions onto paths that appear to be more sustainable. Costanza (in this volume) elaborates on our conventional if loose definition by defining sustainability in terms of the expected life span of a system. Under his definition, if a system attained its expected life span, then it was sustainable. A species has a longer expected life span than a population, which has a longer expected life span than an individual, which has a longer expected life span than a cell. 2. Assimilative capacity is the rate at which the environment can render wastes innocuous. 3. New technologies could conceivably also have unanticipated desirable consequences.
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--> References Allenby, B. R. 1994. Integrating environment and technology: Design for environment. Pp. 137-148 in The Greening of Industrial Ecosystems, B. R. Allenby and D. J. Richards, eds. Washington, D.C.: National Academy Press. Allenby, B. R., and D. J. Richards, eds. 1994. The Greening of Industrial Ecosystems. Washington, D.C.: National Academy Press. Brooks, H. B. 1986. The typology of surprises in technology, institutions, and development. Pp. 325-350 in Sustainable Development of the Biosphere, W. C. Clark and R. E. Munn, eds. Cambridge, England: Cambridge University Press. Cameron, J., and J. Abouchar. 1991. The precautionary principle: A fundamental principle of law and policy for the protection of the global environment. Boston College International and Comparative Law Review 14:1-27. Committee on Science, Engineering, and Public Policy. 1992. Policy Implications of Greenhouse Warming. Washington, D.C.: National Academy Press. Costanza, R. 1989. What is ecological economics? Ecological Economics 1:1-7. Costanza, R. 1993. Developing ecological research that is relevant for achieving sustainability. Ecological Applications 3:579-581. Costanza, R., H. E. Daly, and J. A. Bartholomew. 1991. Goals, agenda, and policy recommendations for ecological economics. Pp. 1-20 in Ecological Economics: The Science and Management of Sustainability, R. Costanza, ed. New York: Columbia University Press. Daily, G. C., P. R. Ehrlich, H. A. Mooney, and A. H. Ehrlich. 1991. Greenhouse economics: Learn before you leap. Ecological Economics 4:1-10. Daly, H.E. 1990. Toward some operational principles of sustainable development. Ecological Economics 2:1-6. Gray, P. E. 1989. The paradox of technological development. Pp. 192-204 in Technology and Environment, J. H. Ausubel and H. E. Sladovich, eds. Washington, D.C.: National Academy Press. Hardin, G. 1993. Living Within Limits. New York: Oxford University Press. Holling, C. S. 1986. Resilience of ecosystems: Local surprise and global change. Pp. 292-317 in Sustainable Development of the Biosphere, W. C. Clark and R. E. Munn, eds. Cambridge, England: Cambridge University Press. Holling, C. S. 1992. Cross-scale morphology, geometry and dynamics of ecosystems. Ecological Monographs 62(4):447-502. Holling, C. S. 1993. Investing in research for sustainability. Ecological Applications 3:552-555. Kates, R. W., B. L. Turner II, and W. C. Clark. 1990. The great transformation. Pp. 1-17 in The Earth as Transformed by Human Action, B. L. Turner II, W. C. Clark, R. W. Kates, J. F. Richards, J. T. Matthews, and W. B. Meyer, eds. Cambridge, England: Cambridge University Press. Ludwig, D., R. Hilborn, and C. Waters. 1993. Uncertainty, resource exploitation, and conservation: Lessons from history. Science 260:17,36. Myers, N. 1995. Environmental unknowns. Science 269:358-360. Nordhaus, W.D. 1992. An optimal transition path for controlling greenhouse gases. Science 258:1315-1319. Nordhaus, W. D. 1994. Expert opinion on climatic change. American Scientist 82:45-51. Risser, P. G. 1995. Indication of grassland sustainability: A first approximation. Pp. 309-319 in Defining and Measuring Sustainability: The Biogeophysical Foundations, M. Munasinghe and W. Shearer, eds. Washington, D.C.: The United Nations University. Tenner, E. 1991. Revenge theory. Princeton Alumni Weekly, October 23. Vitousek, P. M., P. R. Ehrlich, A. H. Ehrlich, and P. A. Matson. 1986. Human appropriation of the products of photosynthesis. BioScience 34:368-373.
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