Sustainable economic development

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1. Introduction 2. Changing views on environmental problems 3. Viewpoints on sustainable development 4.An overview of the literature on sustainable development 5. Regional approaches to sustainable development 6.Economic-ecological modeiling for sustainable development References 1.

INTR0DUCT10N.
In this paper the origins and the elements of the notion of sustainable development are examined.Two specific dimensions of research receive special attention, namely the regional scale and the use of dynamic models.First, a short historical background is provided, which is foliowed by a discussion of the new elements that sustainable development conveys.Furthermore, a concise account is given of the already large body of diverse literature on sustainable development Next it is argued that a regional approach of sustainable development is needed.This will especially faciiitate economic-ecological integration on an operational level, which is argued to be important for a successful approach in studying sustainable development.Such integration can be based on the use of dynamic integrated economic-ecological models.The advantage of dynamic models and several criteria for their structure in the context of sustainable development are discussed.On an abstract theoretical level these models are tools for aiding our thinking about sustainable development, for analyzing dynamic cnaracteristics of long term economic-environmental interactions and evaluating intergenerational distributional consequences of specific development paths.In addition they are valuable on an operational level for studying sustainable development of national and sub-national regions, for which purpose interactions between economie and environmental phenomena have to be considered.

2.
CHANGING VIEWS ON ENVIRONMENTAL PROBLEMS.
The relationship between the natural environment and economie activity and development has never been denied by economists1 .However, the ideas on this relationship have changed over time (see Barbier, 1989).Since the time of the origin of economics in the 18th century, the role of the environment for the economy has been regarded as one of direct supply of water and land, while agriculture was seen as the sector that directiy interacted with the environment.After the industrial revolution attention was also pakJ to physical limits of renewable (e.g., timber/forests) and non-renewable resource (e.g., coat) availabllity.The conscious notice of specific types of interactions has always artsen from a simultaneous occurrence of both manifestation and hurnan or political awareness of specific environmental problems.For instance, degradation of natural ecosystems as a result of various types of poiiution and disruption was perceived much later than problems of city poiiution and congestion.Scarcity and sensitMty of fish resources was considered Important only after several disturbances in certain world fisheries had occurred.And the importance of amenlties generated by natural systems was recognized only after development had reached the level to fulfil most material needs and many additional wants.Especially in the past decades the Interest in environmental problems has drastically changed character.Concern for resource scarcity, attention for poiiution problems, bio-physical and ecological views, elements of social, cultural and economie development, and ethica!considerations have all entered the environmental economics sphere.Genuine and ingenious integration of all these different perspectives in theoretical or operational analyses however has not been accomplished yet, and to stnVe for that may even be over-ambitious.Still, a step towards this direction is necessary if one wants to contribute to a better understanding of structural and long term economic-environmentaJ issues.
The first wave of profound environmental concern since 1960 nas mainly focussed the attention on negative externalitles (i.e., social costs) emerging from the industrial stnicture of our economies in the form of air and water poliution (see e.g., Mishan, 1967;Kneese and Bower, 1968;OECD, 1976) and the long term consequences of resource depletion (e.g., energy resources, minerals, fisheries).Following this, the attention was also pointed towards the disruptive impacts of various specific production processes, technologies used, and various forms of consumption (e.g., recreation, mobility behaviour, see Shechter and Lucas, 1978).
The discussion in Barbier (1989) mentions some drawbacks of the conventional theoretical approaches towards interactions between economy and environment A partial view is chosen in which the focus is on either material scarclty, and environmental damage, or preservation versus development.No ecological elements are Introduced, so that irreversible paths, qualitative changes and collapse of natura!systems are not taken into account Furthermore, relative rather than absolute scarclty is emphasized, motivated by reference to resource price adjustments, substitution between resources, backstop substitutes and technological progress.Also the material balance model approaches (starting with Kneese et al, 1969) take a limited view, as the focus is on the correlation between the quantities of material inputs to and outputs of economie (producttve) systems.These approaches do not consider amenity services of natural environmental systems giving rise to direct utility, they omit other causes of environmental damage such as disturbance by noise or encroachment by land-use, and they exclude the consequences of environmental damages for the economie system.Redclift (1988) states that social science -and thus also economies -nas treated the environment in an unproblematic, unsystematic and a-historical way.The approach having had most supportwhich he calls 'environmental managerialism' te criticized on several points.It takes the environmental probiem as the starting point; k is not hoiistic (in the sense of allowing for interrelationships between environmental variables In the analysis); It does not include international dependencies, provkJes for ad hoc piecemeal solutions; it is positive In the sense of reliance on finding technical solutions; it does not consider distributional issues in relation to environmental ones; and it places environment after development As a consequence, economie and ecological factors receive unequal weights or attention in the objective function (see Redclift, 1988). 2  in the past decade a shift nas occurred from studying relatively partial cause-effect relationships and short-term consequences of economie activities towards a more integrated approach in dealing with environmental problems.This is made expiicit by the consideration of interdependencies of different production or consumption processes which are related to specific environmental problems and were often studied in teolation before.Also the perception of various environmental damages as a consequence of one economie actMty or one type of resource use is indicative for this.Further integration is accompiished through simultaneous consideration of economie and ecological phenomena.A third change in focus concerns the growing attention for interdependencies between regional or national phenomena.These types of integration are indispensable stages in dealing with long term issues of development and environment.Thus trade flows, trade barrière, unequal growth, international competition, North- South relationships, global environmental media and phenomena have all acquired a more central posltion in the environmental debate.The two global environmental problems most alluded to are the rise in carbon dioxide concentration in the atmosphere leading to a rise in temperature (the so-calied 'greenhouse effect'), changing weather and climatological patterns, and possibly a rise in seawater levels around the wortd, and the ozone depletion which may have consequences with respect to nealth of living organisms as a result of more intense and/or different radiation reaching the surface of the earth (for instance, skin cancer, erop damage, genetic mutatlons).As a third global issue may be regarded the exploitation of the common seas, in terms of exploitation of fisheries as well as dumping of waste and pollution.
The concept of sustainable development arose as a difference between a perceived and a desired state of the wortd' (de Vries, 1989, p.3).To accomplish a reconciliation between these two states, the need for the above mentioned types of integration was recognized.Although in the seventies attempts have been made to study long term relationships between development and environment these have emphasized mainly the limits posed by the avallability of nonrenewable resources (e.g., the Forrester-Meadows type of models).The new dimension in sustainable development is the inclusion of all kinds of ecological processes -natura!growth, regeneration, assimilation, ecosystem evolution, geochemicaJ cycles, etc. -and the resulting dynamlcs of and feedback mecnanisms between global and workl-wide economie and ecological systems.Thus the environment Is now seen not only as providing potential limitations and opportunities for development but also especially as changing over time, and a pool of intrinsically dynamic processes, providing dynamic opportunities and constraints.
The implications of integration for research are inter alia an explicit consideration of spatial dimensions and dynamic relationships (feedback and time-delays), and an orientation towards multidisciplinary studies.It is increasingly recognized that an integrated approach is needed in solving environmental problems, arising frorn e.g.land use, urban development, use of common property resources, multiple use of natural resources, spatial patterns of activity, and economie development.For both theory and operational analysis, this involves a fusion of resource and environmental economics, of economics and ecology, and of development and spatial interactions.
In terms of genera!poJicy considerations, sustainable development Implies that environmental concerns must be integrated in decistonmaking at all levels, that the relationship between various environmental problems is recognized so that they are not treated as if they were independent, or that conflicting environmental questions can be answered through tradeoffs or compromises.
In the context of sustainable development especially the spatial dimension nas not been considered very often.The importance of the spatial element arises trom a reclprocal relationship: (1) local trends cause global impacts, and (2) global trends giving rise to iocal effects.For example, the loss of ecosystems In some regions may have large -and very uncertain -impacts on global climatological conditions and geochemical cycles.In other cases, over-grazing and deforestation may lead to large-scale sol erosion, downstream sedimentation, flooding and salinization.A destruction of the ozone layer, acid rain, erosion, desertification, eutrofication, ocean pollution and use of extracted resources are taking place at a world-wide scale, but their impacts can clearly be observed at a iocal or regional scale.
The political formulation of the idea of sustainable development is most pronouncedly reflected in the publication of the World Commlssion on Environment and Development (1987), called 'Our Common Future' (the so-calied Brundtland Report).This report strongly supports the notion of 'ecoJogically sustainable economie development' (further on referred to as 'sustainable development', abbreviated sometimes as SD), meaning 'a process of change in which the exploitation of resources, the direction of investments, the orientation of technological development and institutional changes are made consistent with future as well as present needs' (WCED, p.46).Thus it is evident that the issue of SD te essentially much broader than that of environmental protection 3 .SD in this broad cultural, political and international context, presupposes a radical change of priority setting and agenda formation within the socio-economic and environmental policy Institutions.It also needs a planning structure for sectoral and Inter-sectoral deveiopment, and -given the global impacts of regional environmental issues -an international alignment of policy.The notion of SD calls also for a more coherent (instead of a partial) and a more long-term (instead of a short-term) oriented policy perspective.Most Importantly, there shoukJ be woridwide political support for attaining a sustainabie deveiopment One cannot expect this to exist in a worid of poverty, and hence SD requires a policy oriented toward spatial (inciuding intragenerational) as well as intergenerational equity.An adequate use of this political wül presupposes also a greater extent of democracy In international decision-making.Finally it is important to mention the idea of the Brundtland Commission that sustainabie deveiopment is not a fixed state of harmony but rather a balanced, adaptive process of change.
Some confusion about the meaning of sustainabie deveiopment nas to do with the various interpretations of the term 'sustainabie' 4 .The most frequent use of it in economic-ecoiogical settings nas been in combination with use or utüization.Sustainabie use (utilization) is a resource management practice that applies to renewable natura!resources and is -in the strict sense -based on the rationale of keeping the stock leveJ constant Often, sustainability and sustainabie deveiopment are used interchangeably, although we prefer the second terminology, which is more explicit about what should be sustainabie and points at the relevance of change, whiie the first term may be taken in a more static sense.'Sustainabie deveiopment' consists of two words which both can have either a narrow or a wide interpretation.'Sustainabie' may refer to social, financial or natural bases of deveiopment, but is taken here to apply oniy to the natural environment.Deveiopment is restricted here to economie deveiopment which leaves broader sociai-cultural phenomena out of the discussion.Thus sustainabie deveiopment is used here as a shorter way of saying ecoiogically sustainabie economie deveiopment and incorporates the idea of maintaining the ecoiogicaJ base of economie processes (see Opschoor, 1987).In addition to sustainabie deveiopment, sometimes the notion of sustainabie growth is used (for instance, Archibugi and Nijkamp, 1989, andPezzey, 1989), sometimes in an equivalent way and sometimes in a neoclassJcal growth view of sustainabie increase of a onedimensional indicator of growth such as GNP or man-made capital.Sustainabie deveiopment can be regarded as a means of expioring the Interface between (environmental) economics, (human) ecoiogy and (intergenerational) ethics (see Turner and Pearce, 1990).Economics deals with the allocation, production and valuation of scarce resources, goods and services.Ethics is seriousiy bwoh/ed as soon as future generations or the approach vis-a-vis other species enter the discussion.Ecoiogy enriches our understanding of the dynamics of potentials and constraints posed by the environment on economie activity For instance, the WCED merrtione the reiattonship between deveiopment, environment and safety (war and peace).
In the English language one can find many eynonyme and words with similar meanings for the verb to sustain'.The following list of verba is illustrative: abide, aooommodate, aki, assist, attend to, base, bear, board, brace, care for, carry (on), conserve, continue, curüvat», defend, endure, feed, foeter, found, fuel, further, gird, go, ground, harbor, heed, help, hold (up), house, huaband, Insist, keep (for, up), keep into being, keep elevated/ flowing/ functioning/ going/ operating/ performing/ rolling/ running/ streaming/ working, last, linger (on), lodge, maintain, make last/ endure, mind, nouriah, nurse, nurture, obey, outlast, outtive, perpetuate, peraevere, persist, preserve, prevent, proceed, proiong, protect, provide for, remain, repair, rescue, retain, reserve, respect, root, safeguard, sanction, save, secure, serve, set aside, shelter, shiekJ, shoulder, spare, stay, store, suffer, support (the IKe of), survive, tend, tolerate, undergo, underpin, uphold, wtthstand.in general.Consequently, as a basis for agreement on sustainable development consensus on the following issues is necessary (see also Repetto, 1966): (1) sdentific knowledge, (2) real world data, (3) ethical princlples, (4) satisfaction of human needs and wants.Scientiftc knowledge consists of theoretical, experimental and empirical proofs of the existence and validity of social, environmental and economie phenomena.The main obstade here is that much understanding of the many processes is not yet availabie -tf It will ever be.Another difficulty arises when scientists do not agree with one another.Especially in the economie and ecological sciences severe limits are posed on finding exact relevant statements.To a certain extent, this is the consequence of the limited avaüabiiity of information on processes in and present states of the economy and the environment Furthermore, ff certain Information is availabie, it may not be accessible to everyone, or not to the same extent and of even quality.Next, acceptance of certain ethical prindples is unavoidable in discussing sustainable development, and this may pertain to conskJeration of justice (or more limited equity 5 ) between generations and concern for non-human life.The last important Issue is the understanding of our needs and wants, which, to a certain degree, is also a matter of ethical choices.It involves two questions: should everyone's needs be satisfied first before we turn to wants; and, is maximizing the realization (and creation?) of wants a desirable goal.Disagreement on one or more of these issues may resuit in different opinions about the goal and contents of SD.Of course assuming that preferences are dynamic, that they can be manipulated, and are changed as a resuit of various social processes will iead to extra complications.For instance, a question of maximizing the realization of wants is not so simple then, but involves considerations of a combination of changing and satisfying them (see Daly about 'ultimate ends' and 'reJatfve wants* 6 ).
If we take an anthropocentric starting poirtt, which is usually done, and strive for intergenerational equity, then we must focus on welfare over time and present and future generations.This means that we have to study the relationship between welfare, the environment and economie development So, in general, for darifying and defining ecoJogically sustainable economie development the following questions have to be answered: ( 1 So sustainable development impiies management of the mix of human, physical, financial and natura!assets to increase long term wealth and weil-being.It involves the ultimate recognition that the environment is not static, but dynamicaliy reacting to inputs and outputs from an economie system.It may be liuminating to think of 'sustainable' as a constraint and not as an optimality criterion.Severai futures may be sustainable; only one may be optimally sustainabie • In the sense of some intergeneraüonal criterion.The constraint will be derived from a combination of ethical and physteal-ecoioglcal considerations. 8 9Sometimes, sustainable development is regarded identJcal with preventing irreversible changes.Environmental changes may be irreversible for physical, btologlcal, ecoiogicai or economie reasons.But cautioun is needed here, as many long term indigenous ecoiogicai phenomena and socio-economic changes are irreversible in this sense as weil.It may therefore be too restraining to state such a rigorous constraint a priori.It seems preferable to judge irreversible changes in their total -economie, technical and environmental -context and in relation to their impact on opportunities for present and future generations. The use of the notion of sustainable development can be regarded as the result of a need to solve a potential or actual conflict between growth and conservation, or between comucopian and extreme preservationist standpoints.With regard to the notion of sustainable growth the following question deserves more attention: are the objectives of economie growth and environmental improvement (or non-degradation) mutually consistent in the long term in both a global and a national-regional context?(for the project level, see Van Pelt et al., 1990).Conservation arises from anthropocentric goals, which may include concern for one's own future or that of one's descendants.It is not as strong as preservationist's opinions arising from for instance 'Deep Ecoiogy* (see Devall and Sessions, 1984) which attribute intrinsic (existential) values and rights to non-human species.Preservation of certain natural areas and in general genetic diversity of plant and animai species can be mottvated by reference to speculative use values of future potential services, especlally for medicine and agriculture (food, genetic varieties, pest control, restoration of ecosystems) (see for instance WCN/ IUCN, 1980;and Turner, 1988).Conservation and preservation as management objectives on microlevels may thus both be integrated with macro-deveiopment As Norgaard (1988) states, 'to a large extent the cali for sustainable development is a call to tap bito the sun for energy through constructive management of organisms, ecosystems and environmental systems'.
One central element of conservation is the maintenance of the quality and quantity of the stock(s) of natural resources, sometimes expressed as 'consumption of flows instead of capital'.If 'stock 1 is regarded as an abstract concept we may link it to multifunctionality of natural resources.The conservation objective then applies to the formation of useful materials, storage and assimiiation of waste and pollution, and the generation of amenity services.Keeping stocks intact or even increasing them may be rationa!when the optimal stock is higher than the present one.Other reasons for this objective originate from risk aversion in the face of uncertainty and potential irreversibUity of decreases or quaiitatfve changes in the stock.Constancy may apply to physical measures, the economie value or productMty, or it may be expressed via a constant price over time.Pezzey (1989)  project' principle (see KJaassen and Botterweg, 1976).The notion of stock constancy nas different impiications when applied to an aggregate stock inciuding all natural resources, or single stocks of natural resources, renewable and non-renewable (see Pearce, 1988;James et al., 1989;and Opschoor and Reijnders, 1990).
Maintenance of renewable resources is usually regarded as being equivalent to sustainable resource use.However, the iatter terminology has mainly been empioyed to indicate only the extraction of renewable resources (see Clark, 1976Clark, ,1985)), and is not related to damage effects arising from other than extraction actMties such as for example pollution, land use and recreation.For renewable resources separately stock conservation means that extraction rates must be smaller than the natural or manlpulated regeneration rate, and that the stock itself is not injured through pollution or physical impacts otherwise, or that these are compensated for.O'Riordan (1988) mentions a whoie list of assumptions underlying this notion, related to independence, homeostasis, confinement of the resource ecosystem, and exclusion of other functions.Holling (1978) and Waltere (1986) express the idea of 'adaptive leaming through management experiments with the resource' as an altemative strategy to the conservation of a renewable resource through sustainable use.These ideas arise from the recognition that each natural resource system is unique and subject to environmental variability, and cannot be trusted to act like all other similar systems under all circumstances.The advantage of the Iatter approach is that ft allows for development of potential benefits and recovery from historical depletion.To deal with some of the drawbacks of the sustainable use concept mentioned above, Siebert (1982) and Opschoor (1987) suggest the concept of a resource regenerative system which can be seen as an intermediate between a simple resource and a complex ecosystem approach.This approach allows for dealing with an integrated analysis of resource extraction, pollution and other physical impacts.
Keeping non-renewabie resources constant and using them at the same time seems contradictory at first sight.However, also here we must ask the question what exactly should be kept constant, for instance, the so-calied effective resource base, or the price levels.Extraction may be counterbalanced by a oombination of recycling, efficiënt use, increases in technological efficiency, compensation (e.g., for fossl fuels) with knowiedge (nuclear fusion), expioration, or other non-renewabie resources (ff we consider one specific type of nonrenewable resource).However, neither of these will completely undo the effective decrease of the non-renewable resource stock.
A first implication of the objective of constancy of the total of renewable and non-renewables resources is the constraint that the regeneration rate of renewable resources must compensate for extraction of both renewables and non-renewables as well as physical damage otherwise to renewables (see Barbier, 1989, chapter 8).A second implication is the substitution of renewable for non-renewable resources (so that a non-renewable in this context, or the total of both, is a quasi-renewable stock; see Daly, 1990).A third implication is that renewable resources combined with man-made capital (e.g., wind and windmills with a capacity equal to that of lost reserves) may compensate for non-renewable resource use.In the Iatter case manmade capital is explicitiy included because it coukJ become a large -and increasing -part of the total expenses to maintain the production that is based on the original resource, for instance, in the case of energy production with altemative sources.The two Iatter options have been addressed to in the literature with 'compensation (prpjects)' (see for instance Pezzey, 1989) and 'shadow projects' 10 (see KJaassen and Botterweg, 1976, and the end of this section).
We nota here that compensation and realizatJon of ahadow project» can ba undarstood in a very general way, namaly to include substitution of renewable for non-renewable resources, substitution of one renewable for another one and sJmilarty for non-renewables, and subslHuUon of a oombination of taohnology or man-made capital with a natural resource to raplace another natural resource.Because of these different types of compensation, this idea is expre8sed at various stages in the main texL Furthsrrnore, perfect compensation ki raality will not be simple to acoompli8h because K involves the understanding of eoonomic and finanoia!oonsequenoes, and time and spatial patterns of effects, in addition to natural environmental effects.And these are all surrounded with much uncertainty, especially when they have to comply with long time horizon*.
if we take economie (man-made) and natural stocks of capita!together, then the notion of stock constancy may be interpreted even more broadly than in the foregoing situations.One proposal is formulated as the steady state economy which -In addition to a constant stock of naturel capital -includes a stabüized population level and stock of man-made capital, while it aims for minimizing or limiting the growth of throughput (see DaJy, 1977).However, a less rigld interpretation of stock constancy in such a worid allows for substitution over time between man-made capital and naturel capital, as long as the constraint of a constant sum of both is not violated.However, what it means to have a constant sum is just as difficult to answer as it is for the total of different types of naturel resources.Furthermore, by comparing the manmade and naturel stocks of capital we discover differences with respect to productMty, energy efficiency, multrfunctionality, Independence, irreverslbility of depletion, and uniqueness and substitutabiltty of goods and services stemming from the stock.The most profound distinctions are multifunctionality and substitutability.While most naturel resources are multifunctional, most man-made stocks perform only a single function.Man-made and naturel capital are substitutes sometimes but non-substitutabüity in terms of characteristics of functions is crucial 11 .The stocks may be indicated by some aggregate measure that is close to either material, financial, or utility/welfare units.If one of the latter two is chosen, the aggregate measure should include not only services derived from the stock now but in all future times as well.
The most direct link between Justice and sustainable development is through the category of intergenerational justice.Why are we, or should we be interested in future generations?This is a very basic question which we will not address in depth here.One may regard sustainable development as a concept arising from the application of the anthropocentric objective of intergenerational justice to the development of economies in a dynamic naturel environment.But the concept of justice may also call attention for the socially disadvantaged in the existing generation, or for 'Nature' and especially living nature (see Pearce et al., 1988).In the latter case, an ecocentric perspective (indicated by various labels, such as 'Deep Ecology 1 , 'Bioethics', 'Ecocentrism' or just 'PreservattonSsm') is chosen as an altemative to the anthropocentric notion of intergenerational justice.It shows a deep concern for Intrinsic or existence values in nature and is usually associated with the objective of preserving diversity of species and ecosystems.
Such an ecocentric approach can be criticized for being obstructive towards development, and therefore possibiy socially costly, and for not taking passable notice of problems In developing countries.It may be argued that some human problems are so pressing that they deserve more sympathy than bioethical considerattons.Besides, the need for preserving genetic diversity -both of ecosystems and of species -and a stable environments] quality can nonetheless be supported on the basis of concern for future generations and optional economie values (see World Conservatton Strategy, WCN/IUCN, 1980 12 ).However, the ecocentric standpoint covers all ecosystems and species while an economie perspective is more limited and focuses on ecosystems and species reiated to specific economie sectors (agriculture, medicine, etc.) instead of, for instance, on rare species.In addition, taking both Moraovar, natural atocks ara tha ultimate phyaioal-nialarial basis of man-mada stocks, induding the primary life support function for tha 'stook' of population.See also tha (daas of Qaorgaaou-Ftoagan (1971) on the different» between stocks and ftows, and batwaan tha two necessary typas inputs of production, namely the resources (natural materials and energy) and tha actors (labour and maohinas).Tha krteresting ralationship between the two types of stocks in such a context is reiated to tha materials ganerativa function of the first The natural stocks provide for materials that ara transformed through tha producten prooess by acttons of tha man-mada stocks.R means that spaoies axtinotion should be preverrted, that aa many variaties as possibie should ba preserved of all domesticated anlmeJa, otherwise eoonomioaHy valuable spaoies and thair wUd ralativas, togather wMh their habitate (these include orop and foraga planta, Amber traas, livestook, animals for aquaouKura, microbes and other); and that unique and raprasentative ecosystems should ba protactad.So an Important motivation for preserving genetic diversity is the existence of potential economie benefits.
existence and anthropocentric values into conslderatton wil -as long as It Is not conflictingcommand a careful and risk-averse approach towards the reiationship between development and nature 13 .
Finally, it is clear that intergenerational equity implies a long term horizon, although the exact choice is arbitrary.However, either endless increases of entropy or a ciose-by supernova will make its value finite.So we do not have to take care of all future generations.If one wants to include future generations in a meaningful way, then one shoukJ aim for a period at least as long to include (part of) the next generation after the present one nas disappeared.If, for instance, we reckon people above the age of 16 to the present generation, wish to depict 20 years of the next generation, and assume a maximum person's life time of 80 years, then the time horizon is at least 80-16+20=84 years.
The baslc confiicts that one tries to solve are between the present and future generations, between the long and the short term objectives, between environment and economy, and between the multiple functkxis of the environment As a result of its focus on future generations, sustainabie development incorporates a long term horizon.The conflict between the present and future generations is characterized by the non-presence of the later ones and the uncertainty surrounding the future.Although confiicts may arise simply because some of our actions cause irreversible changes, care for our future setves and our descendants, as well as prevention of certain regeneratie and reversible economie and natural processes, will diminish the potential degree of conflict When long term issues are studied, usually the assumption is made -in any case implicitly • that in reaching long term goals no extra compiications will arise as a result of short term processes.However, there may be a conflict between controlling environmental degradation in the long run and gukJing economie actMty in the short run.For instance, it is assumed that overcoming instabiirty caused by business cycie processes is not conflicting with fulfilling long term objectives of sustainabie development And tf growth is inevttably related to stable economie development (as a condition or a result), then we face a real dilemma in finding a sustainabie development Simultaneous consideration of fulfilling long term goals and short term goals, or of fulfilling long term goals and accounting for short term constraints and infSexibilrties, is rarely touched upon in environment-economic studies.Economie approaches towards sustainabie development seem most suited to deal with this issue, because environmental-ecologica! viewpoints do certainly not include conskJerations of choosing Instruments and institutions to harmonize short term and long temt objectives.
To a certain extent a trade-off has to be made between the multiple type of functions of natural resources, materials' generation, providing productive conditions, waste storage and assimilation, and providing amenity and recreational services.However, much scope for tradeoff is usually not available as these qualitatrveiy different functions are interdependent via the relationships in the ecoiogical system.
In general, ecosystems, populations and resources may provide services for both natural and economie activities.An example is a species functioning both as a prey for a natural and a human predator (e.g., the fishery sector).In this case the services provided to the different users are of the same nature.But the services may also be very different, like a forest that provides timber, recreational services, a stable flora and fauna, regulation of precipitation and evaporation of water, assimilation, diminishing pdlutant Sevels, etc.In using or affecting a resource base, economie activities and natural processes may be independent, one-way dependent, competitive (in several degrees, like the extreme case of exclusiveness), complementary or commutative.Finally, the important question of whether a conflict exists between growth in the scale of an economy and maintenance of the scale of the natural environment has been addressed before.
See Opschoor (1989) for a general -historica!, aooial-ethical and ecooomic -anarysis of the reiationship between man and his natural environment, and Ka impact upon the manHeetation of environmental problems.
The concepts of sustainabie profit from resource use, maximum sustainabie yield, harvest, extraction and pumping stem all directiy from sustainabie use of resources, and may all be elements of resource management Sustainabie deveiopment might also be portrayed as resource management, but then on a high aggregation level.Sustainabie growth translated to the resource level would imply growth of harvest under the condition of sustainabie use, whlch is clearly imposslble.It is hard to translate deveiopment to the level of one resource without losing much of the inherent character of deveiopment It may in any case involve the requirement that the scale of an economy, determined by the population level and economie activity per capita, must be within the carTying capacity of the region, so that the population level can be maintained without natura!capita!consumption (Daly, 1990).
Sustainabie deveiopment can be regarded as extended resource management by taking one or a combination of two possible routes: (1) Imposing aggregate constraints that are satisfied by the application of regulations (standards and property rights) and economie incentives (subsidies, taxes, monetary policy).Additionally, resources should not be consldered separately (see also second route), as this would be too restrictive and iead to inefficiency; (2) Intergenerational compensation projects, through compensating negative impacts of main projects by performing (executlng or financing) one or more secondary or 'shadow' projects such that the sum of the indMdual project damages is zero.This can be regarded as an alternatrve -and improvement -to valuation of environmental damage and monetary compensation.The main characteristic is that it deals explicitly with correcting, diminishing or compensating the direct (dynamic) physical Impacts of the project, while the cost of the alternate project(s) allow(s) for corrections upon the cost-benefit analysis of the original project 'Shadow' projects may either replace lost environmental values or avoid the environmental degradation and disturbance caused by the original project, where the last option is favoured.A main advantage of such an approach is that the dHficult cardinal valuation is preceded by an easier to perform ordinal valuation of suitable 'shadow 1 projects (see Klaassen and Botterweg, 1976).
The idea usually expressed here is that current decisions should not impair the prospects for maintaining or improving future living standards (see, for instance, WCED, 1987).When faced with the choice to invest, save or consume now and impact thereby upon the future, we have to deelde how to evaluate the various altematives.Distribution of a fixed amount of something over time is already a difficult probiem.When we add to this the dynamics of investment, saving, technology, resource depietion and pollution accumuiation we are confronted with a more complex choice probiem.Further compllcatlons arise from uncertainty and controllabillty of the economic-environmental system.Do we conslder the distribution of welfare 14 or do we highlight the opportunities for attaining certain welfare leveis?One may start by stating conditions to the minimum or maximum leveis of time paths for certain variables, for instance to ensure survival.At the other end is the search for optima!sustainabie deveiopment paths based on a speciflc intergenerational welfare function.In between these extremes on may search for monotonous changes.Pezzey (1989) makes a distinction between the characteristics of deveiopment paths of welfare over time into optimality, sustainability and survivability, which he regards as independent criteria.Sustainability is then taken in terms of non-decreasing time paths of welfare (see MSIer and Bojö, 1989).It is noted that concern for future generations in terms of opportunities impiies that in addition to endowments of natura!assets also man-made capita!, technology and knowiedge should be consldered.Finally, Welfare of a generation is a vague oonoapt BaskJas tha usual problems of aggregation of individual Utilities addWonal ones arise In a dynamic setting.The flrst question is whathar we have to think of tha welfare of a generation in terms of a valua at ona point in tima, or to approaoh It oontinuoualy.In the latter case one may explicitly take into account the fact that a generation exists for a oartaJn period.This idea can be expressed by way of a function which explicitly aggregates the ftow of welfare over a generation's lifëtlme into an indicator which should act as an index of compariaon between generations (see Rfley, 1880; Nljkamp and Rouwendal, 1988).Furthermore, one may include the notion of overlapping generations.establishing intragenerationai equity is part of the solution to attaining intergenerational equity, as fewer poor now means fewer, or fewer poor descendants of the present poor.In this respect, it is worthwhBe to note that one may support the conviction that we should solve present problems of poverty before tuming ourselves to future generations.One may add hera that inharant to etake all external, environmental, optional an only be reaiized if the market system te perr? the transltional initial period.

Iite development is the opinton that market mechanisms fail to •&:•'. values into aooount ao that sustalnable development can
i «ïrrected.This means that the conflict wil! not be solved after the knowiedge on exact scarcity, precise environmental impacts, and present/future values is surrounded with much uncertainty.Difficulties arise here for instance because of ambiguity in the valuation of environmental amenity services and the defictency of future markets.
Another obstacle to sustainabie development concerns the regional differences and competition that may hinder international cooperation, provkje for the wrong incentives, and cause global inefficiency.
Finally, a very genera!deficiency is our stiil limited knowiedge for solving the complicated problems that we face.So, if circumscribing the goal of sustainabie development is difficult, 'accomplishing it is a matter of trial and error, and conducting experiments with reality is the only way to test our ideas', to use a phrase of Norgaard (1988).In general, the reactions to this report have been very positivo, malniy because of lts politica!effect and stimulus for scientific research.However, some authors mention the possibility of inconsistency between its objective of growth and regard for ecoiogical limits (see Daly, 1990;and Hueting, 1990).According to the Brundtland report growth In LDC's is necessary to overcome poverty and at the same time -because it is one of its causes -environmental degradation.Also it is argued (and in the opinion of the critics to a certain extent assumed) that growth in developed countries is beneflclal to development of LDC's because financiai support is easier and demand for their products will increase.AskJe from the criticism that is possible on this specific argumentation (Hueting criticlzes the Brundtland report conclusions more explicitly), a general crftlque is possible.This is most cleariy expressed in the many writings by Daly (see especiaily Daly, 1977 and1980).The idea is that continuous growth in the physical size of an economy -and usually going along with a rise in GNP -for a general economy is not compatible with maintaining a non-decreasing environmental quality, generation of resource inputs, and assimilation of wastes.However, when instead of a general economy the specific reiationships -between and different characteristics and needs'*] 13~+( '~U%* and developed countries are taken into conskJeration such a goal may be conflicting with solving problems of poverty.A simple compromise solution might be: the global environment may not be able to sustain global continuous growth; if growth in the South is regarded as necessary to solve problems of poverty it should be compensated by a decline in the size of the economies of the Norm so that the physical scale of the world economy is not increasing.Of course, this is politically even less acceptable man the steady-state concept of Daly applied to each national economy, and from an international economical viewpoint also very risky.

AN OVERVIEW OF THE UTERATURE
Much of the literature related to sustainable development nas a strong bias towards developing countries (see Bartelmus, 1986;Redclift, 1987, Repetto, 1986;Toiba, 1987;and Simonis, 1990).Some authors prefer a more historica!or theoretical economie argument to end with proposals on sustainable development (Daly, 1977;Barbier, 1989;Collard et al., 1988;Pearce, 1988;Pezzey, 1989;NAVF, 1990).Other approaches show a variation of issues related to sustainable development and deal with scarcity of specific resources, decreasing environmental damage through technical soiutions, and relate more to developed countries or avoid such a choice.Also they discuss techniques to be used for studying sustainable development (Turner, 1988;Archibugi and Nijkamp, 1989).Still other approaches do stress the ecoiogical factors, and propose a more Integrated approach between economie and ecoiogical studies pasman et al., 1973;Holling, 1978;Clark and Murtn, 1986).A critica! study of the social and psychoJogical need for (further) growth and development along the lines of western economie development nas been undertaken by various authors (Galbraith, 1959;Mishan, 1967Mishan, , 1977;;Scitovsky, 1976;Daly, 1977;Hirsch, 1977).They accentuate the existence of social and psychoiogical limits to growth, the inequality in access to and use of resources, the need to maintain a balance between material and spiritual values, and -in comparison with the other studies mentioned -they focus on 'uitimate ends' instead of 'uitimate means' (except Daly, who addresses both these concepts).Finally, some books contain very personal or environmentalistic statements (for example, Commoner, 1971;Schumacher, 1973;Lovelock, 1985).Definitions of sustainable development and related concepts abound, and some attempts have been made to a systematic approach towards a definlüon (for instance, Brown et al., 1987) or collect those expressing very different positions (see the appendix in Pezzey, 1989).
Finally, we mention Dutch studies dealing with sustainable development.Hueting (1974/1982) provJdes for a conceptual Hnk between economie growth and the loss of environmental functions.He proposes to valuate the latter and correct for mem in the GNP figure (see also Hueting, 1990).Opschoor (1987) gives an overview of the general discussion and issues invoh/ed.He supports the idea of a resource regeneratlon system as an intermediate level of observation and analysis to the ecosystem and resource approaches.He advocates the ecocentiic approach llnked to the preservation of species and ecosystem diversity.Soeteman (1988)

5.
REGIONAL APPROACHES TO SUSTAINABLE DEVELOPMENT.
In this section we will argue that the study of sustainable development in the regional system is a logical phase in the approach towards the implementation of ecologically sustainable economie development Various considerations are relevant in that respect (see table 1): Global developments do not uniformly and smootNy impact on all regions.Global warming of the atmosphere, for example, may have positive effects on the total of organic production in the worid, but will certainly result in socio-economic and ecological disasters in parts (regions) of the worid.Second, the finiteness of naturel resources on a global scale may have important different consequences at a regional scale.These consequences can be understood better by recognition of several relationships between global and regional leveis.Third, many global environmentai problems are caused by the total of a graat many small-scale and meso level activities.The fact that the level of economie processes is moving towards a global scale, with more interactions between nations, adds to these phenomena, Fourth, the effects of many global environmentai problems are visible at the meso level.
Global processes can be seen as consistlng of interregional processes.The study of interactions between subsystems of a global system adds to the understanding of many global processes.in order to pursue such a study, the global system has to be decomposed into a set of open systems.All processes In a global or closed system are internally determined, while for the development in a regional system many factors are determined outside (e.g., international prices of resources, competitkxi and demand for exported goods, imported pollution, and ciimatic conditions).Such a (mutti-)regionaI approach has several advantages: lts analysis will become less abstract and more operational; certain issues (e.g., linked to crossboundary flows) as well as development paths are more easHy traceable; furthermore, it may even be a necessary step in obtaining any operaÜonaJIy useful resuits.Finaliy, on a multiregional level of analysis and poiicy there is much scope for various trade-offs: interregional, global-regional and intertemporal.
While the study of a global system often necessitates the assumption of homogeneous space and processes and (implicitiy) equal distributions, a multi-regional setting allows one to study heterogeneous patterns and distributional issues within the total system.Regions differ with respect to, for Instance, the Standard of living, type of environmentai problems and potential solutions avaHabie, rate of population growth, and autonomy.Heterogeneous patterns allow for compensation between regions.An example is compensation in terms of resourcesthe reserves of which may be unevenly distributed over regions -by interregional flows of resources and substitution of one type of resource by another.However, such compensations will only be possible if there exists a wkJe diversity among regions and if the resources or resource-using activities are mobile.In the case of land (an immobHe resource), the interrelation of regions may ease the moblity of human activities when the pressure on this resource becomes too high.Qeariy, from a management and poiicy point of view, a regional system is more suitable for contra!and transformation than the global system.This follows from the non-homogeneous character of poiicy systems and goals in countries around the worid, which gfves rise to conflicting priorities in socio-economic objectives and govemmental measures.Of course, regional poiicies should also be based on international communication and be in coherence wrth supra-national poiicies.In addition, a regional scale allows one to choose reliable and measurable indicators, while scenarios, concrete poiicy objectives, and strategies can be Wenttfied and anaiyzed.Thus, by focussing on regions, k is possible to operationalize the sustainable development concept While sustainable development nas been extensfveTy discussed in genera!and for a global scale (see the foregoing section), the regional approach has not been adequately addressed.Consequently, it is worthwhile to provide for a conceptual4heoretical treatment of ecologically sustainable development in open economies (before operationalizing).This may complement the empirical regional and natkxial studies on interactions between economies and environment that are already being performed.A theoretical baste for the study of regional sustainable development includes at least the foilowing elements: defining the basic concepts; general characteristics of development of regions; difference between global and regional sustainable development; and a step-wise procedure for operattonal analysis of regional sustainable development The use of indicators, data, economic-ecoiogical models, and scenario-analysis in the study of sustainable development can be more easily accompiished on a meso than a global level.The choice of indicators is derived from the specific regional dynamics, constraints and objectives, many of which differ between regions and therefore either cannot be aggregated into an indicator on a global scale, or can be aggregated, only with a significant loss of Information.For the study of SD on a regional scale with models specific dynamic economicecoiogical models are needed.In order to be able to kitegrate potential economie and ecological submodels -i.e., provide for an Interactive module -they should be consistent with one another in terms of geographical coverage and level of aggregation.The level of aggregation in a model should be consistent with the objectives of using that model.In the context of (global) SD two important objectives are that processes modelled on a chosen level of aggregation should be linked to those on the highest O-e., global) level of aggregation and that the model is able to generate long term pattems (see next section).Hence, to provide for the consistency mentioned above, not too much compiexity must be strived for.The complexity of models for SD wiil tend to be high if one aims at three distinct features in the design: (1) integration of three main modules (economie, ecological and interaction); (2) a high level of completeness o A R / U A S+' iption of each module; (3) much disaggregation of descriptions.Therefore, the choice of a regional scale seems to be a logica!compromise in order not to further increase the complexity.
The design of scenarios may include relevant policy options and use of Instruments, local desires, specific regional pattems, and details and (in)formai Information on planned developments.A global scale wHI not allow for such an amount of detail and a direct link between policy Instruments and effects.It only makes sense to link policy Instruments with effects on a global scale when those poücies can be implemented actually, which is not always evident.With a scheme of interactions between regional processes one may study the a link between the use of policy Instruments and global effects systematicaliy.Furthermore, by concentrating on cross-boundary fiows and extemaJ determinants of interna!processes the open character of a region can be expticltly used In scenarios.
In conclusion, there seem to be many reasons for conskJering the regional impacts and implication of SD.And hence it is evident that the objective of SD may be achieved more easily, if the processes of socio-economic development and environmental change at a regional scale are cleariy understood and properiy managed (cf.Kairiukstis, 1989).
An analysis of sustainable development of regions (RSD) is therefore necessary.Figure 1 shows the most essential elements to be considered in such an analysis, namely the economie and ecological systems, the welfare derived on the basis of their performances, the fiows between the economie and ecological systems, and the cross-boundary economie and ecological fiows.Furthermore, one must consider for RSD the development of a regional system in relation to interactions with other regions and their respective developments, and, where relevant, the extemaJ determinants of interna!economie and environmental processes.Regional sustainable development is thus reiated to the sustainable provision of natura!resources in the region and the sustainable import of resources, goeds and services, thereby taking cross-boundary fiows of pollution Mo account

ECOLOGICAL-SYSTEM
FIGURE 1: A scheme of regional economic-ecological interactions.

ECONOMIC-ECOLOGICAL MODELUNG FOR SUSTAINABLE DEVELOPMENT.
One of the elements in the discussions around sustainable development is the integration of economics and ecology.These are not mereiy different objects of study, but also separate disciplines.This means that many of their theoretical concepts and methods are differenL Also, the technlques used to operationalize theoretical concepts, or to perform empirical studies, and test hypotheses are dissimilar.However, some similarities can be found as weil, for instance, between the sub-disciplines dealing with a rather aggregate treatment of the subjects, namely macro-economics and synecology, in both of which the method of deduction nas dominated (see Van der Ploeg, 1974).Furthermore, although experimenting is limited in both fields, ecology possesses more opportunities for this than economics.A rational approach to integration is me use of formal models, in which processes of both fields are described as far as they are reiated to one another.Methodological differences are circumvented to a certain extent in this way, whiie the specific accumulated disciplinary knowledge is used to estabiish the structure of the model, select the elements and spectfy their reiationships (see Braat en van Uerop, 1986).
It was mentioned before that sustainable development entails the simultaneous consideration of (seemingly independent) environmental probiems or economicenvironmental interactions.Formal models again seem most adequate to deal with this.
We will argue subsequently that dynamic descriptive or analytical models, in combination with dynamic simulation technlques, scenario analysis, evaluation procedures or optimlzation objectives, are most suitable for dealing with sustainable development issues.It is possibie to deal in such frameworks with the goals of development, and the interactions between economie and ecological-environmental systems.As an exampie, we can visualise this in terms of an optima!controi model (see Kamien and Schwarz, 1982) distributions of utility/wetfare that searches for the optimal value of (usually) an additive utllity or maximin criteria function.To make these analytical models suitable for dealing with sustainable development we may add constraints to limit extreme values or time-path structures, or to include ideas of various types of stock maintenance -such as those mentioned in section 3 (see Pezzey, 1989;andBarbier, 1989, 1990 Conceivabie limitations on substitution In production and utBity functions should be built in; furthermore, interdependencies between substitution of production factors, investments and techndogical progress have to be conskjered simultaneously.In addition, model assumptions should not conflict with thermodynamic laws, while material baiances can be induded explicitly.These considerations point out that the dynamic element is essential.Therefore, we will focus our attention on dynamic models.They can deal with the transformation of short term processes Snto long term processes.They can indude 'strange dynamics' assoclated with non-linear, feedback, stochastic and multiple interacting processes.For instance, it is necessary to describe the inherent dynamics of the fundamental chain --extraction-processing-consumptionwaste generation-emisston-in one framework and in a manner consistent with material balance principles.Furthermore, basic evaluation techniques such as cost benefit analyses assume that the dynamic path of the costs and benefits is known, and just this can exactly be the output of a dynamic model. A second important ImpSication of the above considerations is the need for incorporating environmental-ecdoglcal and economie processes In these models.The terminoiogy 'economic-ecological' has been used to denote models that implement very different concepts of integration.It has been employed for economie process models which Include environmental variables (e.g., waste emisslon or resource extraction) and ecologlcal process models with economie variables (e.g., stress factors).The considerations above indteate that a stronger concept is necessary to deal with sustainable development, namely one that integrates economie and environmental-ecological processes rather than a process and a variable.
Of course, the use of models nas some drawbacks.First, there are always a lot of subjecth/e decisions invotved when one establishes the crucial elements and relationships in the observed system.In addftion, developing formal mathematica!descriptions is one step which has to be compiemented by quantifying these.Very important in building a complete and representatie picture of the economicecological interactions is that it requires the specificatton of many relationships.Consequently, rf as a resuft of lack of knowiedge and data each of them is surrounded by uncertainty, this will severely impact on the reliability of the whole model in a negative way.Simpie dynamic analytical models are more abstract in nature so that this drawback has less relevance there.However, to be analytically soluble they require that the form, complextty and slze of the representation of the Interactive economie and ecological systems, possibly supplemented by a formulation of an objective, is kept wfthin certain boundaries (particulariy reiated to the number of state variables and nonlinear speerfteations).
As alternative approaches for dealing with human-environment intaractionsRedclift mentions sociobiology, Neo-MaKhusianism, and an acocentric approach.SootobtoJogy (WUaon, 1975) highlights the biotogical basis for social action and behaviour.Neo-Malthusianism statas that populaüon cannot exceed resource-determined carrying capacity levels, as natural check» are counterbalandng population growth.Against this view ertticisms have been put forth, such as failure of the mechanism in the case of oommon property resources (Hardin, 1968), and failing institutional and polltical feedback» (e.g., Commoner, 1972).Rnally, the ecocentric approach (O'Riordan, 1981) is concemed with the ends to which resources are put, and considera both the objectivee and means of development.H makes a strict distincüon between structural factors In LOC's and devetoped countries.LDC's have distorted development processes and the period before ookmiallzation is regarded of great importance, while developing countries are in a 'post-industriaT stage with a focus on high-teoh produetion, services, leisure and culture (see Redclift, 1988).
) is there an ultimate end?; (2) what determines It directly?; (3) what is affecting change of this determinant 7 ?; and, (4) what is constraining lts change?Simplified answers without details corresponding with this numbering may men be: (1) Intergenerational equity in terms of social welfare (a given time pattem, a constraint conceming lts time-structure, or a dynamic optimizing objective); (2) economie and environmental services and goods; (3) dynamic processes in the economy and environment and economic-environmental interactions; (4) the limited potential of the environment to generate and accept materials, and undergo physical non-material infiuences.
mentions maintenance of the effective resource base in terms of a constant real price index for virgin materials (derived from Page, 1977) or a constant economie productMty of the whoie resource base by balancing resource depletion with capital accumulation and technical progress (from Howe, 1979).The total economie value over time may be used in combination with the compensation/ 'shadow Proposals have been made for incluaion of such constraints in Standard economie avaluation methods such as cost-benefrt anarysis (CBA), so that a constrained optimization problem has to be soived.For instance, placing constraints on depletion and degradation of stocks of natural capital combined with CBA (Pearce et al, 1988), or applying safe minimum Standard» in combination with CBA (Goodïand and Ledec, 1987). 9Some possible oombinations of objectives and constraints for sustainabie development are the following.Maximizing a preference-based function subject to a physloaity/eootogicaMy-baaed constraint; maximizing a preference-based function subject to an ethically-bassd constraint; or, maximizing a function based on private preferences subject to a constraint based on sooial preferences.Which of these is considered most relevant depends for instance on whether one sees the requirement of ecoiogicai sustainabiüty as a sooial preference.
It is very difficult to describe accurately the characteristics of sustalnable development paths.Partly, this is caused by the ethica!choices involved.However, to a large extent one's belief in economie and eooJogical flexibüity, and the subjective estimation of the risks Involved are determining different positions.And where an exact description is difficult, an 'anti-description' may sometimes be iiluminating and inciting.We have come up with the following general examples of antklescriptions of sustalnable developmentand export of specific resources; at the cost of the environment and the population in Is and population levels in a region that cannot be like water and food in the short or medium term by the gton; r via economie or environmental media; ater, air and living creatures; ^mental degradation in one part of the world as a result nother because of too impoverished living conditions; in or encroachment of ecosystems essential to the wironment, for Instance by decreasing species diversity ier 'mtior» in the atmosphere, when the possible JSI fhreatening, and surrounded with much uncertalnty, •&\ with the impediments to sustalnable development, of st important one seems to be that economie systems dbiurbing their performance (efficiency) and stability.i Ighties have strengthened the conventional, and ~mm poiicy agencies that free market mechanisms are x» economie system.On the other hand, the call for m to discussions on govemmental policies with regard ie economie actMties of production and consumption f Ms iatter view is especiaily related to a transltional ges in the economy before a sustainable development Ï corrected market system, It still leads to a conflict -periy resources where a lot of polluting or extracting, some of these cases no instrument will guarantee an tracts and mutual confidence.Km market mechanisms aiming at so-called 'right land positive) effects, are difficult to realize because ON SUSTA1NABLE DEVELOPMENT.Attention for the environment -as providing constraints or incentives for economie change -in long term processes has been rare, although an outstanding classical exception is found in the work of Malthus, who envisioned inescapable limitations to continuous population growth.In a more recent contribution Wilkinson (1973) argues that economie changes have aiways been preceded by an ecological disequiiibrium of a society, causing scarcity, and acth/ating processes of cultural and technological change.Other approaches to an integration of long term development and environmental processes can be found in the work of Daly (1977), who supports the oid idea of a steady or stationary state, with a stable level of population and capital -already discussed by Ricardo as the inevitabie flnal outcome of the social and economie transition process, and by MUI as a desirabie state in which more attention could be paid to the conditions of weil-being than to accumuiation and economie competition.The ideas of Boulding (1978) also include an integration of development and natura!environment, in a way similar to the fameus work of the French anthropoiogist Theilhard de Chardin, namely by stressing the similarities of the processes of change in different systems -physical, biological, ecological, economie, and soclal/cultural -which can all be considered as evolutionary.Finally, the inconsistency of continuous growth and the existence of ultimate limits has been addressed most noticeabiy by Georgescu-Roegen (1971), who has criticlzed the urge for growth by referring to the second iaw of thermodynamics, which implies increasing entropy, disorder and irreversibility.The other weil-known critique has been expressed in the 'Club of Rome' report (Meadows et al., 1972), In which the physical limits of resource availability, food production potential, and assimilative capacities of natura!systems as well as population pressure and congestion are emphasized.Since the eighties, sustainabie development is a central concept in investigations of environment and development reiationships.Some important events and statements in the past decades that have paved the way to the emergence of the concept of sustainabie development are the Stockholm Conference on the Human Environment and the establishment of the UNEP in 1972, The limits to growth' debate (Meadows et al., 1972; and 1982 for a overview of aJternative models and reactions)studied the relationship between environment and development, with regard to both industriallzed and developing countries, and concern for international, global economie and global ecological phenomena.The central message was: the worid resources are sufficiënt to meet long-term human needs; they are unevenly spread; and they are wrongly used, namely inefficientiy, inequitably and irraüonally.In other words, it stresses the needs of the worid's poor and the environment's abüity to meet present and future needs, if basic changes would occur in the fieids of resource use, investment, technotogy and institutions.
proposes a conceptual model of economic-ecological relationships for dealing with sustainable development This includes three leveis, namely a physical (causality, effectiveness, efficiency), a subjective (temporal and spatial dimensions) and an ethical (indicators, critica!variables).This conceptual model is used for looking at land use in relation to the agricultural sector for the Netherlands in more detail.De Vries (1989) examines the role of formal models for defining and applying the concept of sustainable development and thereby emphasizes the concepts analog, isomorphism and metaphor to compare formal and natura!(real-world) systems, and shows several operational studies of energy analysis.A research report of the Dutch Councfl for Environmentai and Nature Research (RMNO; de Wit, 1990) collects a set of papers showing perspectives from various disciplines, including semeiology, ethics, systems ecoiogy, environmentai economics, socioiogy and psychology.
. In genera!It nas four main elements: (a) The inltiai conditlons representing the economie capitaJ and natura!resources or ecosystems; (b) A dynamic very simpiifying description of naturel and economie processes; the representations of naturel processes may include functions for short term regeneration and assimiiation or changes of parameters that indicate long term changes; the economie processes described in such a framework can range from short and medium processes of extraction, recycling and emission, medium term process of investment and capital accumiiation, and long term processes of technological progress and structural changes indicated by parameter changes; (c) A description of a (generation's or IndMduaJ's) utlity or welfare function which may be based on consumption flows and naturel resource stocks to represent naturel environmental amenities.(d) An ethica!view on intergenerational justice via an evaluation of intergenerational ; and chapters 4 to 7).Furthermore, comparative static and dynamic analyses are relevant in the context of SD, as they deal with parameter changes which may resuit in the long term, for instance changes in tastes reflected by other parameter values in the welfare function, or evolution in the environmental sphere by changing parameters in the ecological description.If descriptive models are used one can include uncertainty by iinking probability distributions to descriptions of processes or events.Furthermore, It is then possible to add slow and fast dynamics, seasonal pattems, and economie, ecological and spatial disaggregation.Especially for dealing with the regional scale larger descriptive models are useful, because a detailed description can often be supported by avaiiabie and reüabie data, and regkxvspecific concrete policies, strategies, and scenarios (see the foregoing section).In addltton, It is possible to include systematically the various economie, ecological, and Interactive processes in a larger descriptive model without being limited by analytical requlrements.Of course, simplrfying where possible is aiways desirable in order to keep the overview, limit the data requlrements and uncertainty, periorm more formal analyses (e.g., optimization), or derive simplified models.The type of model that is relevant for gaining insight into sustainable development issues, or for tracing sustainable development paths shoukJ be checked with the following set of criteria:(1) Does the model take a complete or genera!-in contrast to a partial -approach.The latter is likeiy to become less relevant when long term horizons are conskJered.The entire economie structure with both productive and nonproducth/e uses of the environment shoukJ be included.The description of the naturel environment should be compatible with t in the long run.(2) Are the impacts included of economie productive and consumptive activities upon the naturel environment, in terms of materials extraction, waste emission and pollutlon, and non-material disturbances.In more detail one nas to pay attention to (I) extraction of non-renewabie and biotic and abiotic renewable resources, (ii) agricuitural activities affecting groundwater and sous like fertilizing, use of pesticides, irrigatlon, drainage, ploughing, (iii) the use of terrestrial and aquatic ecosystems for recreational purposes, 0v) land use, and the pattems and infrestructure involved, and (v) poHution and waste disposal, with a special view on for toxines, reactiveness, dlsperskxi, degradabMity, and also specific types such as thermal, radiation and noise pollution.(3)Is a mechanlsm induded to describe the feedback from the ecology to the economy.This Indudes various elements related to for instance recreation and tourism, landscape values, quiet and annoyance.Inclusion of feedbacks of ecological impacts of general economie activity to the economie system is essential for an adequate description of long term processes in economie systems.For instance, feedback to dedsionmaking with respect to productive actMties may be induded among other things via perception of resource scarcity, and pollution levels, or environmental damage in general.(4) Not only material or priced services shoukJ be induded, but also, as much as possibie other services, such as for instance productive conditions (eg., soil quality) and amenlty services.The latter may be Induded in the evaluation or welfare function, but equally by way of behavioural feedback mechanisms.Furthermore, multifunctionality of ecosystems, and resource systems (as opposed to single one-dimenstonal resources) can be dealt with in a systems description.(5)Concern for future generations must be induded.First, this may imply that a judgement criterion is chosen for the evaluation of Intergenerational distributions.Also, various conditions may be imposed on natural capital, pollution or economie capital to ensure an equitabie intergenerational distribution.if the repercussions of intergenerational concern are taken in a behavioural rather than an evaluative or constraining sense it implies that behavioural or pdicy feedbacks aiming at intergenerational equity are endogenous.(6) A long time horizon is a logica!consequence of the foregoing point.it means that short term processes are left out where possibie to simplify the picture.Also, it implies that linear models will not be adequate for a description of every process, and that risk or scenario analyses may be used for dealing with various uncertainties.(7) It must be possibie to describe qualitative (structural) change, either implicitly or explicitly.This means that one has to attow for a description of irreversible processes, threshokis, nonlinear structures and time-delays.This options may be suppiemented by risk analysis (e.g., with Monte-Cario experiments) to deal in various ways explicitly with uncertainty.(8) The model assumptions should not conflict with physical constraints.