Walter Isard’s Contributions to Environmental Economics and Ecological Economics

Abstract

This article summarizes Walter Isard’s important contributions to environmental economics and ecological economics. The former is the traditional field that incorporates some limited aspects of the environment into neoclassical economic theory, while the latter is a more comprehensive integration of economic and ecological principles in a set of eclectic frameworks. Walter’s contributions include pioneering research, primarily in a spatial context, and the mentoring of prominent researchers in these fields during the period of 1965–75. We examine these contributions in the context of the state of the art of knowledge in these fields at the time and today. We also discuss Walter’s influence in Europe in these areas. We conclude with a discussion of some promising new directions, with an emphasis on regional science dimensions.

Keywords

Walter Isard ecological economics environmental economics ecological–economic systems material balance model input–output framework environmental capacity pollution control plant location

Introduction

Walter Isard is well known as the father of Regional Science and almost as well known more recently as the father of Peace Science. Walter was trained as an economist, and his pioneering work on the formal incorporation of space and location into neoclassical theory is held in high esteem by the profession, though his insistence on creating a separate and broader field of Regional Science to build on this work alienated him somewhat from his original colleagues. Walter is also claimed by geographers and planners as a major contributor to their discipline.

Less well appreciated are Walter’s important contributions to environmental economics and ecological economics. The former is the traditional field that incorporates some limited aspects of the environment into primarily (neoclassical) economic theory, dating back to the 1960s, while the latter is a more comprehensive integration of economic and ecological principles in a set of eclectic frameworks, dating back to the early 1980s. That is, environmental economics views environmental preservation as a typical economic allocation problem with strong emphasis on the substitution between man-made consumption goods and nature, and between man-made capital and natural capital (Siebert 2008). Ecological economics, on the other, hand views the economy as a subsystem of the ecological system and emphasizes preserving natural consumption goods and natural capital in the first place, rather than trading them off for man-made consumption goods and capital (van den Bergh 2001). In addition and in contrast to environmental economics, it is transdisciplinary. Interestingly, and perhaps not surprisingly, an increasing number of environmental economists have ventured into ecological economics over the years.

Walter’s contributions include pioneering research, primarily in a spatial context, and the mentoring of prominent researchers in these fields during the period of 1965–75. His primary attention to Regional Science at the beginning of this period and then his shift of emphasis to Peace Science at its end limited the time he had to interact in a major way with leaders in the environmental economics field. Nevertheless, his work on ecological economics was ten years ahead of its time, and thus the interest of others in his research began long after Walter’s direct involvement had waned. The research seminars organized by him at Penn and other universities during and after this fertile period were often a refreshing mix of analytical contributions to Regional Science, ecological and resource studies, and Peace Science, and served as a further inspiration to others.

This essay will summarize Walter Isard’s contributions in the following ways. The second section will discuss Walter’s research in environmental and ecological economics and the third section his mentoring of students in the United States. The fourth section will focus attention on Walter’s influence in Europe in these areas. The fifth section will present some promising new directions in these fields, with an emphasis on regional science dimensions of environmental economics and ecological economics and ecological economics.

Isard’s Intellectual Contributions

In this section, we provide a discussion of Walter Isard’s broad conceptual ecological economics framework first, and then relate it to more focused aspects of environmental economics and regional science. Walter’s own empirical work relates to this broader framework, but the more specialized work in areas like the environment and location, environmental policy instruments, and the regional economic impacts of pollution control were undertaken primarily by his students, as discussed in the following section.

Isard’s Ecological–Economics Framework

It is remarkable that Walter not only laid the foundation for regional science but also for spatial environmental and ecological economics. Already in 1969—at the dawning of the age of the environmental awareness instigated by the environmental movement and studies of economy–environment interactions such as that of the Club of Rome (e.g., Meadows et al. 1972) and writings of a small, though prominent, number of economists (Boulding 1966; Ayres and Kneese 1969; and Leontief 1970)—Walter (1969) wrote an important contribution on the linkage of ecologic and economic systems, a contribution that was clearly inspired by his interdisciplinary methodological interest. His major opus on the spatial analysis of ecologic–economic systems, Ecologic–Economic Analysis for Regional Development, was published by the Free Press¹ in 1972 (Isard et al. 1972). This book contained a wealth of new methodological insights and empirical contributions. It provided a conceptual framework for the integration of these two disciplines. It was mainly based on a generalized activity analysis model for ecologic–economic systems as well as on various elements of materials balance models. Analogous to Walter’s pure interregional model (Isard 1951), this framework had four main quadrants, with the “intra” quadrants of the economy and ecosystem on the main diagonal, and interaction quadrants on the off-diagonals:

E₁₁	E₁₂
E₂₁	E₂₂

The economy-to-economy interactions (E₁₁) were couched in terms of a standard input–output model. The effects of the economy on the environment (E₁₂) were specified in terms of fixed “pollution coefficients.” The inputs of the environment to the economy (E₂₁) were specified by the primarily nonmarket details of the resource base, again as fixed coefficients of inputs per unit of output. The ecosystem quadrant (E₂₂) was the most novel aspect, as it represented food chains and some biogeochemical cycles as individual activities, and the broader environmental system as this matrix partition.

Walter’s broad ecological–economic framework is related to the material balance model (see, e.g., Kneese, Ayres, and d’Arge 1970; Ayres 1972), which traces the most important flows and technical processes in a technical–economic system.² For instance, raw materials obtained by extractive processes are converted within the productive sector to consumer goods, which flow into the household sector. However, not all material inputs are fully used in the relevant consumer goods; there are often residuals (in this case, pollution components) in each production process. In the end, most materials contained in consumer goods are also broken down to waste matter and/or residuals. Ultimately, on the basis of the Law of Conservation of Matter and Energy, and because consumers do not actually exhaust the material ingredients of goods but only consume their services, matter is not lost in the process but rather transformed into temporary nutrient storage and waste. In fact, the sum total of all waste products equals the sum total of all the inputs into the production process, thereby giving an indication of the huge magnitude of the potential pollution problem (Kneese, Ayres, and d’Arge 1970). In this light, Boulding’s (1966) well-known characterization of the “spaceship earth” is explicable: the earth is generating an increasing stream of waste matter, while it has only finite resources and absorptive/storage capacity for its voyage. The pollution input–output analysis framework has been extended to the resource and energy sector, as has been shown by Isard and others, including extension to computable general equilibrium models at the regional, national, and international levels (Rose 2009; Global Trade Analysis Project [GTAP] 2011).

Walter’s 1972 volume also empirically specified the model in a careful case study of the introduction of a boating marina into an ecosystem. It was somewhat unfortunate that the empirical application—the major part of his book—focused on a small-scale marine problem, which gives the impression that his analysis was mainly addressing micro-ecologic issues. The methodological scope of this opus was much wider and richer. It probably failed to capture much attention, in part because its case study application was thought so trivial by many. However, Walter is to be commended for choosing an application of manageable scope for a detailed and thorough activity analysis of ecological systems and their integration into an input–output economic framework.

Although not typically cited by ecological economists,³ this work did in actuality or de facto serve as a template for leading research in this new field beginning a decade later and carried through to this day, although with more sophisticated models on both sides—dynamic models of ecological reproduction and computable general equilibrium models integrating ecological and economic processes (see, e.g., Finnoff and Tschirhart 2007).

Walter’s 1972 book was a culmination of some earlier work, primarily in collaboration with John Cumberland published in the Papers of the Regional Science Association (see, e.g., Isard and Cumberland 1969), that sketched out the framework. This included the concept of the pollution coefficient, or a fixed output of pollution per unit of output of economic activity in each sector, which was also put for the by engineers around the same time, and has been in widespread use ever since. This work predated Nobel laureate Wassily Leontief’s more widely known papers on the subject a few years later (e.g., Leontief 1970). In a similar vein, Walter encouraged the work of Eli Romanoff (Isard & Romanoff, 1969) in developing a set of sectoral water use coefficients, while later on Walter also directly addressed broader resource and energy issues (see the following subsection).

The methodology employed by Walter Isard to understand and map out complex ecological and resource interactions found its origin mainly in the toolbox that was developed by him for Regional Science. So, this analytical toolkit forms his seminal contributions to various disciplines.

Ecological Economic and Environmental Economic Analysis for Regional Science

It is interesting to seek early traces of Walter Isard’s interest in environmental and resource matters. His interest in these matters was not an abrupt change, but marked a gradual transition. In his major opus on Location and Space-Economy (Isard 1956), the author refers on page 1 to “changes in environmental features, such as soil erosion or silt agglomeration at mouths of rivers.” In the same book, he pays extensive attention to the spatial dimensions of natural resources and agricultural land use. Moreover, the roots of Isard’s concern for environmental issues can already be found in his earlier work on regional development. In subsequent years, he used his analytical techniques geared toward advanced regional science research as a solid foundation for regional–ecological investigations. His contributions to multiregional input–output models, including environmental and pollution sectors and his later work on spatial–ecological systems analysis, are illustrative of his deep involvement in the importance of the physical surroundings for regional welfare. Thus, already in Isard’s earlier work, we can observe an undercurrent of interest in environmental matters, which are also at the nexus of Regional Science and Peace Science.

This interest was later clearly expressed, from yet another vantage point, in Isard’s Introductory Word in Nijkamp’s monograph on Theory and Applications of Environmental Economics (1977), where he interpreted environmental issues from the perspective of conflict analysis: “. . . these chapters expose conflict problems which range over all social sciences and beyond—problems centuries old, but which to this day are still with us in a major way” (p. vii). This statement already marks the gradual transition in Isard’s interest from regional science methodologies to environmental and resource issues and then to conflict management.

A major focal point of early environmental science was pollution of air, water, or soil. From a technical point of view, pollution can be regarded as a by-product of most physical–economic activity. Almost every activity (either as production or as consumption) which absorbs material resources (e.g., productive inputs, consumer goods) also leads, after a transformation process, to residuals which can pollute the physical environment. Examples of such residuals are carbon monoxide, carbon dioxide, sulfur dioxide, hydrocarbons, hydrogen fluoride, lead, particulates, and so on. The technical processes through which inputs (e.g., materials, consumer goods) are transformed into outputs and residuals can be described by means of a transformation function. A simplified, but nevertheless very useful (and frequently used) assumption concerning the production function is the Leontief hypothesis: a constant linear relation between the level of production and necessary amount of input. This relationship can be applied to the economic process of pollution abatement as well. Analogous to classical input–output analysis, the integrated relationship between production, pollution, and abatement can be described in a systematic way in a pollution abatement input–output model by means of the following framework composed of four matrix partitions (see Leontief 1970):

A₁₁	A₁₂
A₂₁	A₂₂

This is a subset of the more general framework presented in the previous subsection. There is no ecological domain here, nor is there an explicit role for ecological inputs into the economy. What the model does reveal is the interconnectedness of remedial environmental policy and economic activity. The entries of matrix A₁₁ are the normal input–output coefficients, which indicate the necessary input of a certain good per unit of output of anther good. A₂₁ contains the direct pollution output coefficient, that is, the emission of a certain pollutant per unit of output of a certain good. The matrix A₁₂ represents the input structure of pollution abatement activities: each entry represents the input of a certain good needed for the elimination of a unit of a certain pollutant. Finally, A₂₂ contains the pollution output coefficients of pollution abatement activities: each element represents the emission of a certain pollutant per unit of eliminated pollutant, indicating that abatement does not typically “destroy” the waste products but simply alters their form (see the further discussion below). In this way, a manageable and quantifiable model for the complicated structure of production and pollution can be constructed. Clearly, not only the production sector but also the consumption sector contributes to environment pollution, and hence the above model can be extended with analogous pollution–consumption coefficients, which indicate the relation between pollution and consumption. As will be discussed in more detail in the following section, much of the work that Walter encouraged and supported in the late 1960s and early 1970s provided the empirical basis for this framework (e.g., Isard & Romanoff 1969; Rose 1974). His own work and that of his team helped extend it spatially. This includes his explicit treatment of the environment as a location factor (Isard et al. 1975) and the paper by Manas Chatterji (1975), published in the first issue of this journal, that provides a framework for demonstrating that the production of one region is to a great extent influenced by the demands for its products by another region. This theme of how countries “export their pollution problems” continues to be a major issue today in relation to climate change (Intergovernmental Panel on Climate Change [IPCC] 2007). Moreover, the issue of the fair sharing of the burden of climate change among countries has been the major stumbling block in the formation of a truly international treaty on the reduction of greenhouse gases (Kverndokk and Rose 2007).

One of Walter’s other research efforts dealt with the broader public policy issue of “environmental capacity” and the spatial distribution of economic activity, and hence pollution. Walter conjectured that areas with little prior economic development would be prime targets of an increase in economic activity because they had excess environmental capacity in relation to industrialized, and especially urban, areas, for which he anticipated that environmental regulations would be relatively more stringent. Interestingly, there arose a fear that this situation would lead to a homogenization of air quality across the United States and the elimination of pristine areas. The US Environmental Protection Agency (EPA) chose to protect these areas through a “no significant deterioration (of air quality)” position, which made regulation of the environment equally strong across the United States, thereby limiting spatial and environmental arbitraging.

Walter summarized much of his early work in Environmental Economics in a survey published as the inaugural article in the International Regional Science Review (Isard and van Zele 1975). He emphasized the importance of practical models that can be implemented with real data. Particularly, he introduced spatial planning as a policy instrument to control externalities. Although various instruments to correct for socially undesirable outcomes caused by externalities, like air and water pollution, had existed in the literature for many decades, notably taxes (Pigou 1920) and the allocation of property rights (Coase 1960), Walter’s proposed policy handle was an innovation. It directly followed from the spatial dimension that he considered as fundamental a characteristic of socioeconomic phenomena and development as is time.⁴

Walter’s research on the environment and location has preceded and initiated a substantial literature that is still growing. On one hand, there is the basic question how important environmental quality is as a location factor. This issue is critical in inter alia environmental, urban, and regional economics, geography demography, planning, and management science. This topic is relevant in the context of migration research (see, e.g., Greenwood 2006). The main outcome is that environmental amenities are a strong pull factor. On the other hand, there is the question of how environmental regulation impacts plant location decisions (Jaffe et al. 1995; Jeppesen and Folmer 2001; Jeppesen, List, and Folmer 2002). In this case, the outcome is less clear-cut. The reason is that costs related to environmental policy are one element in a complex set of location factors including quality of the labor market, relocation costs, accessibility, reputation, and so on. In addition, the polluter has the option of abating pollution at whatever location is chosen. (Jeppesen and Folmer 2001). From this perspective, space matters in environmental social studies.

It is thus clear that Walter has played a pioneering role in the development of ecological and resource science in tandem with Regional Science (see also Isard 1974). The spirit of his mind can also be traced to one of the first comprehensive monographs on environmental economics by Nijkamp (1977), as well as to subsequent research on the topic by other regional scientists such as Karen Polenske, William Miernyk, Frank Giarratani, Shelby Gerking, Kieran Donaghy, and ZhongXiang Zhang, and the other authors of this article. Regional scientists that have integrated the spatial and environmental dimensions include Michael Greenwood, Gary Hunt, J. Vernon Henderson, and Matt Kahn (see Gerking and List 2001).

Walter’s Mentoring

Walter received some of the first major grants from the US EPA in the early 1970s. He supported research by graduate students from these grants, whose work has become well known. His first major student in this area was W. David Montgomery, on whose Harvard Economic Department dissertation committee Walter served, along with Kenneth Arrow and Herbert Scarf, while he was a visiting professor there in the late 1960s and early 1970s. A major portion of Montgomery’s (1972a) dissertation was proving the existence of a general equilibrium in the presence of externalities, which was published in the Journal of Economic Theory in 1972b. This is a major contribution not only because of its existence proof but also because this provided a way to value the externality, which served as the basis for creating a market for it in the context of what was originally called “emission permit trading” and is now referred to as “cap and trade.” Montgomery’s paper has received more than 2,000 citations since it was published, placing it among the most oft-cited in the environmental economics profession. It also received the Association of Environmental and Resource Economists (AERE) Award as a “Publication of Enduring Quality.”

Walter also funded research in environmental economics by several students at the University of Pennsylvania and while serving as a visiting professor at Cornell University beginning in the early 1970s. The senior author of this article was Walter’s first graduate student research assistant in Cornell’s Economics Department in 1972 and his first PhD graduate at Cornell in 1974. His research was funded by Walter’s grant on “Marginal Pollution Analysis for Long-Range Forecasting.” This project included analysis of environmental policy at the small area level in a case study in Watertown, New York. However, the major research involved the conceptual formulation and construction of a linked linear programming/input–output model of pollution abatement. The empirical work was based on the first major air pollution emissions inventory, consisting of data on emission characteristics and pollution control equipment characteristics for more than 20,000 point sources in Upstate New York.⁵ The linear programming model was developed to choose the least-cost combination of pollution control technologies to meet a given target in each industry, while the I–O component estimated its direct and indirect economic impact on the state’s economy.⁶ The dissertation was published in the Cornell Regional Science Series (Rose 1974), and a more extensive policy application was published in the Journal of Regional Science (Rose 1977). Continued work in this area also led to a JRS paper that assessed a decade of literature on input–output analyses of the economic impacts of pollution abatement and offered a comprehensive framework for future work (Rose1983), laying the basis for computable general equilibrium analysis of the issue (see Rose 2009).

Walter also supported the dissertation research in the environmental field of Phyllis Kaniss (1981) at Cornell and Roger Van Zele (1977) at Penn. He also mentored Frank Cesario, who first served as a postdoc and Walter’s right-hand man at the Cornell Center for Urban Development Research, and then served for several years as an assistant professor in the Department of Civil Engineering (see, e.g., Cesario 1976). Walter also influenced several faculty members in Cornell’s Regional Science Group working on environmental topics during the 1970s, before he joined Cornell’s faculty on a permanent basis. The Group included the aforementioned students, as well as faculty such as Stan Czamanski, William Goldsmith, and Courtney Riordan, Sid Saltzman, Richard Schuler, as well as faculty from neighboring universities such as Manas Chatterji from SUNY-Binghamton.

Walter continued his tradition of working side by side with his students and giving freely of his time during the decade of his major interest in environmental topics. He had students accompany him on visits to major companies and government agencies. These road trips became an opportunity to know the man on a personal basis and to understand his primary interests in both his scholarship and his family, and to learn about the history of the Regional Science Association International (RSAI) and its relation to other disciplines. Walter was also a patient mentor and spent long hours going over every word of drafts of his students’ dissertation chapters. In addition to his brilliance, Walter’s kindness will be long remembered.

Walter Isard was not only generous in sharing his insights with his colleagues and students. He was also keen to invite young scientists for a short visiting period. The last mentioned author of this essay remembers vividly the intellectual debates with Walter at the University of Pennsylvania on energy efficiency and spatial distribution of economic activity.

Walter Isard also had a great role in disseminating his views and findings on resource and environmental issues and their spatial implications throughout the world but especially in Europe, both through his writings and many presentations at conferences. As a result, environmental issues have an important place in Regional Science and Regional Economics curricula and research programs at European universities including the Free University Amsterdam, Groningen University and Umeå University.

Future Directions

Walter Isard has laid the foundation for various new research directions connecting different disciplines. This is an important inheritance for the future. We will offer a few perspectives here on the ecological domain.

Ecologic–economic analysis—as an interdisciplinary methodology—should not only be based on the two constituent disciplines of ecology and economics but also on a broader set of disciplinary perspectives. And therefore, ecologic–economic science comprises at least the following disciplinary dimensions:

regional science as a cross-cutting approach to analyze regional and urban issues from a transdisciplinary angle; economics as a discipline addressing valuation issues of goods under scarcity (including externalities); ecology dealing with the biotic and abiotic environment and its resource base including interactions between species);

physics and chemistry focusing on materials balances and life-cycle analysis (including entropy principles);

social psychology as a discipline addressing awareness of environmental goods, including social choice mechanisms;

mathematics and operations research dealing with decision models and equilibrium/disequilibrium models (e.g., chaos models, network analysis);

geography focusing on the spatial–physical base of environmental concerns (including contributions from geoscience);

political science, planning and law addressing property rights and/or “polluter pays” principles;

peace science focusing on equity and justice regarding the distribution of impacts of resource use, pollution and pollution control across socioeconomic groups and regions.

Interestingly, all these disciplines are incorporated in Walter Isard’s pathbreaking contributions to ecological science in a spatial context. All these dimensions have to be considered in developing operational ecologic–economic policy principles in regions and cities. Various seminal contributions on the integration of various perspectives from multiple disciplines can be found in Isard (1979). These contributions have definitely been instrumental in developing systematic tools for environmental impact analysis (see also Lakshmanan and Nijkamp 1980).

Clearly, many years have passed since Isard wrote his pathbreaking work on the integration of space and ecology. The discipline of environmental and resource science, including economics, has certainly reached a stage of maturity. It has moved on from early modeling attempts—as witnessed in systems dynamics models of the Club of Rome type—to broader and more social science oriented sustainability analyses—as witnessed in the Brundtland Report (WNCED 1978) type of analysis—and more recently to integrated regional–global climate models—as witnessed in the post-Kyoto types of analysis. This development over the past decades has also seen the introduction of complementary analytical tools. In a recent toolkit book on natural resource and environmental economics, Batabyal and Nijkamp (2011) distinguish various new strands of research, in particular:

material balance and industrial ecology models

dynamic natural resource use and management models (including stochastic and game-theoretic analyses)

empirical policy support tools (including environmental evaluation models, hedonic price models, sum-of-specific damages approaches, econometric estimation and simulation models, or computable general equilibrium (CGE) models.

new interdisciplinary toolboxes (including ecological–economic models, GIS and spatial data analysis techniques, evolutionary modeling).

Despite the increased sophistication of the analytical apparatus, it is fair to say that the seeds of many contemporary research methodologies can be found in Isard’s works, which spanned almost half a century. Clearly, the scientific inheritance of Isard is rich and has left his descendants with many intriguing research issues at the interface of regional science and ecology. The region is essentially the action space of the economy, while the realization of economic activities prompts the emergence of various environmental externalities. The spatial analysis of such (both positive and negative) external effects calls for an appropriate analytical apparatus, including statistical models on resources and local environmental quality, equilibrium models on regional dynamics and natural resource use, policy studies on nonmarket distortions and spatial governance mechanisms, spatial mapping of externalities using geoscience methods, and multiregional response models for climate mitigation effects.

Walter was not only a creative but also a critical mind. As observed in another contribution to this special issue, Walter was concerned about the prominent role of economics, especially neoclassical economics, in the Regional Science curriculum at Cornell. Hence, he would undoubtedly have shared the criticisms of traditional neoclassical economics as too narrow a framework for the analysis of social and economic behavior, including environmental and resource economics. To provide just two examples, the famous theoretician Morishima Michio Morishima abandoned the field of economics because it produces “ . . . on a large scale “aeroplanes” which have no engine” (Morishima 1984). He considered the disciplines of sociology, anthropology, and history better conditioned to explain economic behavior than economics (Folmer 2009). Furthermore, Paul Krugman (2009), in an editorial in the New York Times in 2009 entitled “How did economists get it so wrong” exclaimed: “The fact that an economist offers a theoretical analysis does not and should not automatically command respect. What is needed is some assurance that the analysis is actually relevant.” and “As I see it, the economics profession went astray because economists, as a group, mistook beauty, clad in impressive-looking mathematics, for truth.”

Morishima’s and Krugman’s criticisms should also be most seriously considered in environmental and resource economics (Folmer and Johansson-Stenmann 2011). The theoretical frameworks, methodologies, and techniques that are criticized in other fields of economics are also applied in this subdiscipline, in many cases routinely and at a large scale. Unfortunately, there is little critical debate in the field; the culture in environmental and resource economics is live and let live. Moreover, there is little interaction with other disciplines, notwithstanding the fact that economic behavior is social behavior and economics is a social science. Associations like RSAI and EAERE are the institution par excellence to stimulate logical duels and interaction with other disciplines. By doing so, it could transform environmental and resource economics from an uncritical follower of mainstream economics to a leader. Because of his sharp intellect and critical mind, Walter would undoubtedly have played a major role in this debate, since most of his work has been in the tradition of comprehensive analysis of human behavior.

Conclusion

Given Walter’s brilliance and proven track record, he could have made even greater contributions to Environmental Economics and Ecological Economics than he did. The major reason, as those who knew Walter clearly understand, was that his inquisitive mind and commitments outpaced his seemingly boundless energy. While holding down the chairmanship of the Regional Science Department at Penn, he typically held two visiting positions (first Harvard/Cornell and then Northwestern/Cornell during the 1970s), in his remaining time he worked on regional economic development, his Regional Science textbook, his General Theory volume, and even on the relationship of regional science and the theory of relativity. Walter was invited to present a paper on environmental policy at the American Economic Association Meetings in 1972, along with Robert Dorfman and Michael Evans, and scrambled to put this article together. You will not find the paper in the May 1973 AER Proceedings volume as usually would be the case because Walter, to his credit, did not deem the rushed work up to his usual standards. Those who know Walter would often note how he had the energy and accomplishments of three people. Had it been four, it is likely he would have been a giant in Environmental Economics and Ecological Economics as well.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Notes

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