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Potentialities, Problems, Policies and Progress in Modelling Sustainable Development: A Dynamic, Hierarchical Approach

Posted on: Friday, 16 June 2006, 06:00 CDT

By Moffatt, Ian

Key words: Sustainable development, sustainable corridors, dynamic, hierarchical modelling

SUMMARY

This paper discusses some of the potentials, problems, policies and progress in modelling sustainable development. After briefly describing ten approaches to modelling sustainable development, some of the methodological problems still to be resolved are addressed. It is then suggested that policies to promote sustainable development should operate at six different spatial levels connecting global, multinational, national, regional, local and individual. Attempting to model sustainable development in such a hierarchical manner is exceedingly difficult. One way of modelling sustainable development is to develop the concept of a sustainable corridor, combining ecological, economic and equity considerations in a hierarchical fashion and through space-time. A preliminary dynamic, hierarchical model is described connecting global and national patterns of development. Using global and national data for Scotland, the calibrated model, running under the business-as-usual scenario, shows that current development paths are unsustainable. It is shown that, by implementing a judicious choice of policies, a sustainable corridor for a global and a national system can be achieved. The ways in which this preliminary model can be developed to connect all six hierarchical levels are discussed.

INTRODUCTION

Despite the plethora of definitions, sustainable development can be broadly defined as a complex process integrating ecological, economic, equity and ethical considerations for current and future generations of people, and other living creatures, without endangering the life-support systems of the planet upon which, ultimately, all life depends. This approach is often referred to as the four Es (ecology, economy, equity and ethics) (Ekins and Max- Neef 1992) and it is the integration of these four Es which represents a major challenge for modelling sustainable development. Whilst we may argue over the various nuances about definitions of sustainable development, it is clear that there is an emerging consensus amongst researchers and some enlightened policy-makers that we need to actively pursue this process to make it a reality in the early years of this century. This strategy has been approved in principle by the various heads of government, at the various Earth Summits in Stockholm (1972), Rio de Janeiro (1992) and the World Sustainable Development Summit at Johannesburg (2002). It is clear that we need to develop policies and put them into action to make development sustainable, and modelling can make a key contribution to this process.

Obviously, none of us are gifted with God-like qualities of being all-knowing, so that we can see all possible futures and steer societies to a predetermined outcome, but we can, at a more modest level, offer different possible futures as a guide to make development sustainable. In fact, there have been numerous attempts to suggest different ways of making development sustainable and some of the potentials that modelling can play are outlined below. Despite the limited experience in modelling sustainable development, it is possible to identify some of the problems that any modelling effort will have to overcome. If we imagine that we have an agreed model, or set of models, of sustainable development and different types of future scenarios, then we would still face the problems of ensuring that our efforts can contribute significantly to democratic policy-making. Having briefly outlined the potentials, problems and policies underpinning sustainable development, we turn to progress in modelling. We begin by outlining a theory of sustainable corridors influenced by the work of Gorshkov (1995). We will then present a simple hierarchical dynamic model of sustainable development as ONE approach to the current research agenda, and comment on progress in this approach to modelling sustainable development.

POTENTIALITIES

In 1964, Kaplan remarked that 'Models are undeniably beautiful, and a man may justly be proud to be seen in their company. But they have their hidden vices. The question is, after all, not only whether they are good to look at, but whether we can live happily with them' (Kaplan 1964: 288). Despite the sexism of the sixties, Kaplan is correct to note how we can live happily with modelling, especially when we are dealing with a complex set of issues (the 4Es) implicit in sustainable development. Over the last 40 years, modelling methods and computing power have increased enormously to tackle problems, especially interdisciplinary cross-cutting research, which could only be dreamed of but not made operational 40 years ago. Unlike the 1960s, we now have an embarrassment of riches of modelling approaches. Table 1 presents a partial and incomplete approach to modelling sustainable development and lists ten ways in which modelling can assist in both understanding and contributing to the necessary changes which are required to move the world onto a sustainable path rather than continue on the present unsustainable trajectory we are now locked into. It should be noted that these diverse approaches to modelling sustainable development all offer an enormous potential for modelling sustainable development. It should also be noted that it is essential that we break the mould of the current trajectory, but this will require good models, sound data, judicious policy-making and social support across the planet.

Database approaches are becoming increasingly important in sustainable development modelling, based in part on increasingly good data. They tend to lack dynamics and often lack any underpinning theory. Econometric and input-output approaches are similar to database modelling in that they use only data in their model structure, but they tend to be based on neo-classical economic theory and research is currently aimed at making some of these models dynamic. More complex modelling using entropy maximising methods are available, but these have not been used for sustainable development modelling, although in principle they could be (Wilson 1981). More recent research exploring the use of cellular automata and self-organising structures is also being developed but, again, use in modelling sustainable development is at present limited. For short-term policy-driven work, optimisation techniques and decision- support systems are useful. It should be noted that decision- support systems (including expert systems) are not a substitute for accountable decision making (Moffatt 1990). Generally, these models require good data and are rarely used for non-linear and dynamic systems. Geographical information systems (GIS), based on relational databases and optimisation tools, are becoming increasingly popular for environmental management projects. At present, they are static rather than dynamic but some research is ongoing to make four- dimensional GIS models and, when developed, these would have an important role to play in sustainable development research and policy. Given the longer term needs of sustainable development, dynamic models are a fundamentally important tool for understanding the processes leading to the current unsustainable situation and for exploring different possible future scenarios. All of the models mentioned in Table 1 use statistical analysis for parameter sensitivity testing, as well as for verifying the model output. All these different modelling approaches can be employed in sustainable development research and policy. My current research favours an integration of dynamic modelling and GIS.

Table 1 A classification of modelling approaches to sustainable development, with advantages and limitations

PROBLEMS

Any attempt to model sustainable development will encounter problems. These problems can be divided into three categories, namely methodological, data and risk.

A question of method for a matter of survival

As noted above, there are a host of methods used in modelling studies (Table 1) and some of these have been applied to modelling sustainable development. Whilst we all agree that models are a a simplification of the real world, it is less well accepted that a model should be based on some sound theory. This immediately raises a problem in developing a theoretical framework when dealing with sustainable development conceptualised as the integration of ecology, economy, equity and ethics. No doubt the development of such a theory will be intellectually demanding and difficult. There may even be a temptation to retreat into pure empiricism or to develop language games as in post-modern studies. Neither of these retreats would encourage the development of theory or offer the help to people, other living organisms and the well-being of the planet that is urgently required.

At the heart of the methodological debate is the need to address fundamental questions about the type of epistemologies required to address vital issues such as a question of method for a matter of survival (Harvey 1973, 1985). This debate needs to be undertaken from all perspectives so that we can at least appreciate the concerns and worries of \those under-represented at the world table, such as the G8 summit meetings. What is lacking is a clear statement of theory which can simultaneously capture the complex processes needed to restructure the economic, social, environmental and political life of the contemporary period to make future development sustainable. O'Riordan sees the need for a new theory of development based on the concept of sustainability. This he suggests will open up 'refreshingly different approaches to project appraisal, where costs and benefits are not just treated as economic commodities but as assets and liabilities with social and environmental meaning' (O'Riordan 1989: 412). We will return to this fundamentally important aspect of theory development later.

Of course, not everyone will subscribe to the project of making development sustainable. Some sceptics see no need to spend money on dampening global climate or changing current paths of resource exploitation and distribution (Lomborg 2001). These environmental sceptics are, however, living in a world where the harsh realities of climate changes, lack of water, food, health care and social justice are not recognised - or are merely noted as improving. Alternatively, some other sceptics recognise the problems but see these as simple manifestations of market failures which will be solved by another dose of neo-classical economics (Beckerman 1995). Needless to say, most scientists, environmentalists and the increasing number of the world's poor are not convinced by these arguments (Brydensholt 2002)!

Data and indicators

Inevitably, the model community is always needing more data of good quality, being made available quickly and covering comparable geographical areas on an internationally agreed set of standard measurements. Clearly, the ideals of obtaining good quality data are rarely met, but it is clear that there have been significant improvements in the collection, storage and retrieval of data in recent years. The public availability of data and information from the Genome project, for example, is one area where data are freely available to all. It would be good to see the development of meta- databases and this would be useful for modelling sustainable development. Ideally, these data should be freely available to all interested people. If data are to be priced, then one thing that politicians must seek to avoid is making the data too costly. In the UK there are signs of this happening with access to some financial data. This pricing of data is similar to going back to Medieval times, where books were once the preserve of organisations and public access was generally denied. Policy-makers in Europe and elsewhere should ensure that access to data is freely available.

There has been a virtual explosion of interest in the development of indicators of sustainable development based on the pressure- state-response framework. Some organisations suggest we use a combination of over 130 indicators. Other groups suggest combining these single indicators into a smaller set of headline indicators (DEFRA 2004) and yet other groups suggest we need to use both single and combined indicators to help describe progress towards making development sustainable. Arguably, the best way forward would be to have a set of agreed indicators which are arranged in a lexical order from weak to strong - few indicators actually achieve this. Meadows (1990) once suggested that if such an ideal indicator was developed then it could be broadcast in the mass media (in newspapers, radio, TV and over the Internet) showing how an area/ country is performing with regard to making development sustainable. Again, this is technically possible but few researchers believe we have yet achieved this goal. From a modelling perspective, what would be useful is to have an agreed set of indicators integrated into a model so that the simulation of both actual conditions and the impact of policies could be monitored.

Risk and uncertainty

Risks and uncertainty are part of contemporary life. In modern society, however, the quest for profits has exposed people and the environment to unnecessary risk (Beck 1994). The use of nuclear power, the threat of planting GM crops, as well as the over- consumption of non-renewable and renewable resources are all threatening life-support systems of the planet. We must confront some of these technologically developed risks and ask the ediical question about the suitability of developing some of these products for excessive profits and not for the long-term benefit of current and future generations on the planet. Of course, the greatest risk to life on the planet is that we sit around and do little but we must, as model builders, recognise the uncertainty in our models and in our data. Table 2 offers some suggestions for improving our diverse approaches to modelling and monitoring sustainable development.

POLICIES

Policy-making can be defined as an expression of intent to achieve certain objectives through the conscious choice of means and usually within a specified time period. In liberal democracies, public policy is distinctive in so far as it is normally open to public scrutiny and debate; it must proceed through formal channels of the constitutional process and is often codified through the sanction of law (Moffatt 2004: 26). In the sustainable development debate there have been various internationally agreed views on the intention to make development sustainable. At the national level, some countries, for example the Welsh Assembly, have formally adopted a written constitution making sustainable development one of its objectives. The attempts to promote Local Agenda 21 in Europe (O'Riordan and Voisey 1998) and elsewhere are encouraging, although they still have a long way to go to make development sustainable in the early years of this century.

Table 2 Suggestions for improving modelling and monitoring of sustainable development

In Table 3 a partial list of the complex interlocking of geographical scales, policies and indicators for promoting sustainable development is presented. It will be observed that policy-making works simultaneously on different levels. The Table outlines some of the typical issues, policy responses and indicators used in attempts to promote sustainable development. The Table does not attempt to be comprehensive but it illustrates three points of concern for the public policy-makers as well as for modelling sustainable development. First, there are some fears that the integration of interlocked policies from top to bottom can lead to the development of a tyranny of technological surveillance. Second, short-term policy options, by definition, tend to exclude long-term strategies. Yet it can be argued that several of the problems confronting society, such as global warming, require long-term commitment to resolve them. Furthermore, short-term 'solutions' often do not encourage the envisaging of alternative futures which is vital if we are to move onto a trajectory of sustainable development. Third, there is a fear that if we are committed to making development sustainable, then we cannot afford to do so.

It is now 20 years beyond George Orwell's fateful year 1984 (Orwell 1949). Over the past 20 years there has been growing concern with systems modelling, stemming from the fear that it could lead to the terror of a police state and a society of surveillance. There is evidence of this in the UK and elsewhere, with the widespread use of closed circuit television (CCTV) and other techniques of 'spying' on citizens. Underlying these techniques of surveillance are questions over ideology, social control and justice. Gregory (1978, 1980), for example, has expressed concerns about systems modelling and the ideology of control. In one sense it is true that systems modelling, which had its roots in the development of missiles, was designed to hit very specific targets. Later, after World War II, cybernetics was applied to many aspects of life. Other researchers from a post- modernist perspective are very wary of the idea of the application of modelling to sustainable development. They fear the further development of GIS and remote sensing as 'big brother' watching over us in a fashion similar to the Orwellian novel or the Foucault panopticon (Foucault 1980). Whilst these concerns and fears are recognised by many model makers most post-modernists offer no alternative strategies to the present predicament of unsustainable development. Lyotard (1979) notes that the computerization of society could lead to the use of terror, with the 'dream' (or Orwellian nightmare) of using system models for controlling market performance and citizens. But he also notes, naively, that there is a radical alternative which gives public free access to databanks and leads to a politics that would respect justice and the desire for a better but unknown future. It must always be remembered that models can be likened to sharp tools and in unskilled hands they can be used incorrectly and for good or bad purposes.

Some of these alternative futures have been described in publications on modelling since the 1970s. The infamous Limits to Growth models, for example, noted that if present trends continue, then in the near future the Earth would face a rapid and unmanageable collapse in the demographic, economic and environmental systems (Meadows et al. 1974). Sixteen years later, the same model was used to argue that we need to develop a more sustainable future based on changing our attitudes and behaviour (Meadows et al. 1992). A similar conclusion is being developed by other system dynamicists using an essentially neo-Malthusian model (Frey and Lam 2000). One criticism of the early Limits to Growth models is that they lacked good data to calibrate and then independently validate the models and that they lacked any consideration of market mechanisms. It could be argued t\hat this led to other researchers attempting a more empirically-orientated approach. In 2000 Hall et al., for example, examined development in Costa Rica and, unsurprisingly, showed that current trends there put that nation onto an unsustainable path. Surprisingly, alternative scenarios to the business-as-usual were not explored - which was a pity and points to the major limitations of purely empirically-based modelling and evidence-based policy approaches (Hall 2000). Other researchers have developed different approaches to modelling and have come up with a host of alternative scenarios (King 1985). The database POLESTAR studies, for example, have developed a flexible, user-friendly framework for mounting economic, resource and environmental information for exploring alternative development scenarios (Raskin et al. 1996). Similarly, the four scenarios derived for the GEO3 study have explored four very different scenarios, namely the market approach, policy-dominated, security and sustainability first options. Each of these different scenarios has differential and different impacts on the world's ecosystems (UNEP 2002). Imaginatively, Costanza (2000) has examined different visions of alternative and unpredictable futures and their use in policy making. He explores a two by two payoff matrix with technological optimism and scepticism versus individual optimism and sceptical positions. This leads to four alternatives called Mad Max, Ecotopia, Star Trek and Big Government - all except the Mad Max scenario are possible sustainable futures. His preliminary work shows that if we adopt a cooperative, precautionary policy set that assumes limited resources, then this is shown to be the most rational and resilient course of policy action in the face of fundamental uncertainty about the limits of technology and the future. He also notes, following Sen (1995), that value formation through public discussion is the essence of democracy.

It is clear that sustainable development is part of a political agenda; it is also clear that systems modelling has a role to play in the emancipation of people from hunger, lack of water and tyranny, and in protection of the biodiversity of the planet. The implications of making development sustainable are fundamental to the development of a good quality of life for all which, at present, some 80% of the world's population do not share. To implement changes to address the catalogue of environmental, social and economic ills is tremendous, yet we must prioritise the ways in which we can move towards the development of trajectories which are sustainable. The costs of doing this are achievable. Henderson (1996), for example, suggests that if the world's national governments actually spent less than 25% of the annual arms budget on promoting sustainable development, then it is achievable. A similar suggestion of an armaments tax of 1% on military spending would have yielded US$800 million dollars per year in 1995. A tax to be set at a higher rate than other trade was also proposed in the Brandt Report (1980), and this could have gone to aid sustainable development and the eradication of poverty. Obviously, implementing such modest proposals requires both political will and open accountability to effect changes. It should also be noted that in the European Union auditors have refused to sign off the annual accounts for the last few years due to financial malpractice. Clearly, this is an area of concern for all people in the enlarged, democratically run European Union. Similarly, a global tax on armaments to be hypothecated for promoting sustainable development would need to be carefully accounted.

Table 3 A partial list of the complex interlocking of geographical scales, policies and indicators for promoting sustainable development

PROGRESS

Clearly, there are a host of different and sometimes ideologically competing models which are currently vying for attention in the marketplace of academic thought and political practice. Given this plethora of approaches, it may be useful to cut the Gordian knot of complexity by suggesting one way of making some progress in modelling sustainable development. One way of achieving this goal is to develop a dynamic, hierarchical model.

A theoretical framework

Models can be loosely defined as theoretical or a-theoretical. An a-theoretical model makes a simplified representation of the real world system in order to understand the ways in which the system functions. A theoretically-based model, however, is also a simplified view of the real world that is used to explain the processes involved and is based on a solid theoretical base. As we are dealing with fundamentally important issues affecting all life on the planet, it is important that we develop robust models based on rigorous theory rather than theoretically deficient models. It is also essential that the theoretical framework used can lead to a consistent set of measurements and indicators of sustainable development. It is rare to see both of these criteria being met in the literature (Moffatt 1996).

This immediately raises major problems for modelling sustainable development as we have to try, somehow, to model environmental, economic and equity issues within the one theoretical framework. Pearce and Atkinson (1993) suggested a 'weak' sustainable development framework, based on the idea of perfect substitution of environmental and economic capital. The advantage of this approach is that it unites the environment (ecology) and economics in the one framework based on neo-classical theory. Another advantage of this approach is that it is able to put all ecological and economic aspects into a common, monetary measure (e.g. pounds, dollars, euros). In this weak measure, a nation is sustainable if the Pearce- Atkinson measure is positive; it is unsustainable if it is negative. As a starting point for measuring sustainability it is useful as it combines both aspects of economics and ecology into one framework and it is noted that if nations cannot pass the 'weak' test, they are unlikely to pass a sterner test. The two main disadvantages of this framework are that some fundamental aspects of the environmental life-support systems cannot be substituted, for example the upper ozone layer which protects life on Earth. Next, even in areas where economic evaluation of environmental goods and services is possible - through contingent valuation or similar techniques - the error bars on the estimates are often very large, which makes policy choices difficult. Furthermore, the problems of equity are eschewed.

An alternative 'strong' framework, which puts the protection of the Earth's life-support systems above that of human capital, can be developed as a theory of sustainable corridors. A strong indicator of sustainable development recognises the primacy of ecology over economic welfare. The best example of this approach is the Barometer of Sustainability (Prescott-Allen 2001) which attempts to integrate ecology and economic well-being into one indicator. The basic argument underpinning his empirical work is that sustainable development must safeguard the life-support systems of the planet from which economic development can emerge. The barometer of sustainability makes ecological well-being the independent variable and economic development dependent. The latter processes must stay within ecological constraints. This would satisfy Jacobs' (1991) criteria for development which is sustainable. At present this imaginative approach lacks theoretical justification and this lack of theoretical underpinning also applies to ecological footprinting (Wackernagel and Rees 1996, Haberl, Wackernagel and Wrbka 2004; Mather and Moffatt 2004).

It is, however, possible to present a theoretical basis for a strong approach to sustainable development. Such an approach recognises that we must live well within the ecological constraints of the planet and not try to live beyond our ecological resources (Jacobs 1991). Many rich nations are already attempting to do this. The idea of protecting the life-support systems of the planet was first produced in detail by Gorshkov and colleagues (1994) and is similar too, but different from, Lovelock's (1989) Gaia theory. Gorshkov (1995), in a detailed exposition, has shown how human activities are impacting the Earth and that there are ecological constraints that we will have to live within if we are to leave the planet and its potentially renewable resources intact for current and future generations.

It is widely acknowledged that the Earth is a set of complex interacting systems (lithosphere, hydrosphere, pedosphere, atmosphere, biosphere and arguably the noo-sphere). Hence, to portray all these control parameters affecting the ecosphere would be difficult. Fortunately, Gorshkov (1995) has shown that only a few critical control parameters are required to gain some understanding of the ecological constraints which determine life in all its manifestations on Earth. Unfortunately, it is also recognised, belatedly, that we are already altering these parameters in such a way as to threaten life on Earth. The production of greenhouse gases above the assimilation capacity of the receiving environment is one example from many of the ways in which some societies are trying to live beyond the ecologically possible. In effect, the irresponsible actions of a few major nations are driving the Earth to destruction. Similarly, if we re-examine the level of food production for the Earth's ecosystems expressed as Net Primary Production (NPP), then we find that human appropriation of NPP is already consuming over 40% of the total. If the human demographic expansion of the globe continues, from its current 6 billion people, to double, then we will have destroyed most of the NPP for all living organisms (Vitousek et al. 1986). Those people who continue to argue that the Earth does \not have some real biophysical limits to continued human population growth and resource consumption appear unaware of these biological realities (Lomborg 2001). Is it then possible to prevent eco-catastrophes from happening? One way of preventing eco- catastrophes is to imagine that we could live in a sustainable corridor well within the ecological constraints of the planet, and then try to locate such a corridor(s) to support all life on Earth.

Figure 1 Sustainable corridor and future scenarios (see text for explanation)

A sustainable corridor is a trajectory of population and resource use which varies through time and geographical space. This sustainable corridor remains beneath the maximum value that the global and local ecology can support and remains above the minimum pattern of consumption of other resources which are essential prerequisites for life on Earth. For human societies, a sustainable corridor also has the property that production must be equal to or greater than consumption and that both activities are contained within the upper bounds of the ecologically possible and above the minimum nutritional level required for human survival.

Whilst sustainable corridors are conceptually simple to define, they are very difficult to measure in such a way that they can help strategic decision-makers to ensure that human activities stay well within the bounds of the ecologically imposed constraints. These constraints, over time, are not constants but they do vary within limits and trying to exceed these limits can only bring universal ruin to human societies. Figure 1 shows in a very simplified manner the concept underlying a global sustainable corridor within which all peoples and other living organisms have to live together in the confines of the Earth's life-support systems. Figure 1 shows a three- dimensional conceptualisation of sustainable corridors. The X-axis represents ecological well-being and this is measured, as in Prescott-Allen's (2001) work, on a scale of ecological well-being from poor to good quality. The Y-axis illustrates human economic well-being. Again, this scale of measurement ranges from poor to good quality. As in the Barometer of Sustainability (Prescot-Allen 2001), ecological well-being has precedence over economic well- being because, ultimately, all economies depend on the ecology of the planet. The third, Z- axis, represents the temporal dimension measured in years.

The sustainable corridor can be conceptualised as a tube, where different societies live well within the boundary of sustainability (see A on Figure 1). It will be noted that in the past all the diverse societies lived in a relatively good ecology but at a modest to poor level of economic well-being. Importantly, local and global ecological constraints were not breached. In the past, different societies were able to have economic development well within stable local ecosystem thresholds for hundreds of years but others did not survive (Diamond 2005). Economic development dependent on foraging and fishing, followed by domestication of plants and animals have increased the use of energy derived from the human appropriation of Net Primary Productivity (HANPP). By 1740, alterations to the natural environment by energy-intensive farming under colonialism saw the land-based biota decrease in stability. The introduction of fossil fuel-based industrialisation and the development of wage labour was associated with a decline in the stability of the atmospheric systems after 1790 (Gorshkov 1995). In general terms, what we have witnessed in the evolution of human activity across the globe is increasing economic development at the expense of the ecosystems on which all life ultimately depends. This is shown by the rapid growth and development of the economies for diverse societies at the expense of the life-support systems (atmosphere, hydrosphere, ecosystems) of the planet (see Figure 1 A to B). It will also be observed that some societies have achieved greater dominance over the planet's resources and over other people and these latter groups have fared less well.

In the past 50 years there has been a growing inequality between developing and developed countries (and growing patterns of relative poverty within these diverse nations) (WCED 1987). This rapid expansion of economic wealth has been bought at the expense of exploitation of both the natural capital and labour. It will be observed (see Figure 1 C) that the wealth of some nations has been achieved at the expense of the Earth's life-support systems. The current situation is due to the past 200 years of development of capitalism and, more recently, globalisation has witnessed acceleration in the growth of human population, resource consumption and the global spread of different pollutants in the atmospheric, terrestrial and ocean systems. These developments of economic growth under free market globalisation are heavily subsidised by the use of carbon-based fossil fuels and have resulted in an increasingly high standard of living for an affluent minority. It has been noted that these spectacular changes in wealth for the minority have been bought at the expense of further immiserization for a large proportion of the world's human population, especially, but not exclusively, in the so-called developing world (WCED 1987). The price for this apparent affluence has been paid, in part, by destroying the natural biota. The extermination of the natural biota as recorded by the Living Planet Index (LPI) (Loh 2002), Ecological Footprinting as well as HANPP results in major and possibly irreversible changes to the environment (Mather and Moffatt 2004).

The details of the lower and upper ecological limits within which all economic activity must remain - at least if it is to be sustainable - have been described in detail elsewhere (Moffatt et al. 2001:153-83). The theory of sustainable development corridors depends heavily upon the detailed calculations provided by Gorshkov and his co-workers (Gorshkov et al. 1994). In brief, Gorshkov (1995) has demonstrated that with regard to energy consumption and ecological stability, human activity has already crossed the threshold of ecological stability. Human activity is also appropriating NPP, altering the Earth's carbon cycles, reducing the organic stores of the land and sea and altering the world's climate to regions beyond human historical experience. Continuation of these trends (as seen in Figure 1) will result in unsustainable development and ecological collapse of regional and, eventually, global life-support systems. These trends are already perceptible in the data and many people are being made aware of these changes by the mass media. There are, then, sound theoretical reasons to question the current patterns of exploitation of the environment and the reliable empirical indicators do show that current resource and population trends are unsustainable. What then of alternative scenarios?

Several research groups and enlightened politicians have noted that we are currently facing economic development which is unsustainable (see C in Figure 1). The early Limits to Growth Models argued that this would happen (see above). More recent research has described a transition to a sustainable economy (Frey and Lam 2000; Michnowski 2004). Even more orthodox modelling using neo-classical economic theory has shown that even with the use of renewable resources we are locked onto an unsustainable path if present trends continue (Bartosczuk 2004). These 'doomsday' views are shown as D in Figure 1, where a poor economy and poor ecology results in a very impoverished world - the Mad Max scenario (Costanza 2000). Pathway D envisages a very poor world ecology and poverty-ridden economy, in a word, it is unsustainable.

Alternative sustainable paths of development, which provide the vision of a better economy for most people and a good ecology, are shown as E in Figure 1. It should be noted that every nation is located within this tunnel or sustainable corridor. This does not mean that individual nations are all at the same level of development; they will have cultural differences. The actual pathway or trajectory a country pursues depends on internal policy options and individuals' actions, as well as the influence of external natural and economic forces. It should also be recognised that there will also be economic differences between and within nations, but the overall effect is a reduction in the obscene levels of wealth between rich and poor within all nations. Furthermore, it should be noted that the sustainable corridor implies that some rich OECD nations will have to reduce resource consumption and that the developing world will have to address human population growth. For some other developing countries the corridor concept holds out the hope of moving some societies from their wretched situation towards a sustainable level of living (Gray et al. 1993). The pathway from C to E in Figure 1 represents an important point of transition to a sustainable world. If we can identify one or more sustainable development corridor(s) then it behoves us to try and model the complex processes comprising all humanity with its natural environment and locate these corridors in the space-time framework. Needless to say, this is a huge task.

If, then, we are seriously concerned about making development sustainable for current and future generations, we need to identify possible corridors of sustainability. Such corridors would lie on or, more preferably, above the minimum levels of human resource consumption and stay well within the ecological constraints. Individuals and nations would, of course, show some variation in preferred life styles within these constraints. Similarly, ideas of a just distribution of resource use would also have to be addressed, rather than relying solely on market mechanisms. The latter are efficient bu\t they are not necessarily just (Atkinson 1983). One way of exploring possible sustainable development scenarios is by constructing a simple dynamic, hierarchical model of the Earth system.

A dynamic hierarchical global/national model

One of the outcomes of the criticism of the Limits to Growth types of models was that if we are to consider sustainability then we have to simultaneously model development both globally (to determine the constraints) and locally (i.e. at a subglobal scale). Obviously, individuals and individual nations can rarely stop major environmental changes although some nations do contribute much more to damaging the world's ecosystems than others. Similarly, as several researchers have noted, it may be possible that one nation can achieve sustainable development but such 'sustainability' may be at the expense of other people (Pezzey 1996). Clearly, from an ethical perspective, this is unacceptable as it raises issues over a just distribution of resources jusdy arranged (Rawls 1971). Allowing 'free trade' to be the sole arbiter of such key resource allocation and ethical questions is like leaving a fox in charge of the chicken coop. It will be immediately apparent that any model of sustainable development will be a very simple structure compared to the complexity of the real world. Hence, if we are to avoid self- delusion by oversimplifying our analysis then it is vital that any realistic model of the transition to a sustainable world needs to examine the global resource constraints within which all living creatures, including human societies, must operate.

Whilst numerous studies have attempted to model the ecosphere, very few have recognised the differences between the rich and poor countries within their model structure. There are some exceptions, the Bariloche group in Latin America have attempted to include social justice into their model. Similarly, the regionally-based global model developed by Mesarovic and Pestel (1975) also included a regional dimension. Apart from these early studies, generally, however, modellers have failed to see the links between poor and rich nations in the context of modelling. The clearest study of these inter-relationships is presented by McMichael (1993) in his investigation of global environmental change and the health of the human species. In his study of planetary overload he suggested a model of the context, causes and consequences of ecological and social disruption in the rich and poor countries. His descriptive model is not operational but represents a point of departure for the current attempt to model global/ national interactions to form a model of sustainable development based on the theory of sustainable corridors.

We appear to be living at a turning point in human development, where our actions are having increasingly major impacts on the Earth's ecosystems. In a sense, we are at a bifurcation point (see C in Figure 1) and we can either collectively make a transition to a sustainable set of societies or not. Scenario D (Figure 1) shows the folly of pursuing the latter course of action - all nations suffering both poor economic and ecological well-being. As noted earlier, there has been a whole host of alternative future scenarios describing possible sustainable futures. Scenario E shows all people living in a good ecology within a decent economy (Figure 1) or, alternatively, risking life on Earth by recklessly pursuing the chimera of unbridled economic growth in a finite world. This latter course would be an extreme high-risk win or lose strategy in a risk society (Beck 1994). In the dynamic, hierarchical model it is presumed that if current patterns continue then we will usher in a global economic and ecological crisis. This crisis could take one of two forms; either we would witness the sudden and uncontrollable collapse to a poor environment and weakened economic system or, alternatively, we can make transition to an ecologically stable and economically sound, socially just future for current and future generations. A point of bifurcation occurs in the model (Figurel at C) when a sudden collapse leads to impoverished ecology and economy. It will be noted that, in both limbs, beyond the bifurcation point individual national economies may be different but more equal with regard to resource consumption production. Given this stark choice of alternatives, can we locate a sustainable corridor to ensure that current and future generations have a sustainable future?

It is possible to develop a global/national hierarchical dynamic model of sustainable development by integrating the ideas of sustainable corridors with a simplified model of planetary overload. In Figure 2 the structure of a hierarchical, dynamic global/ national model of sustainable development is presented. At the upper level of the hierarchy are two feedback loops (one positive and the other negative). The negative feedback loop connects population with NPP. As the population increases, then the NPP declines, resulting, ultimately, in a declining human population. Population also links with non-renewable resources, pollution and NPP as a positive feedback loop. If the positive loop dominates, then an increase in population causes a reduction in non-renewable resources which, in turn, increases pollution which impacts on NPP. The interactions of these two loops can give rise to ecological stability - a condition of ecological dynamic equilibrium.

At the lower level of the hierarchy each nation is modelled in a simple way to represent the interactions within a nation and with the rest of the global economy and ecology. Unlike the global model, two major changes are included in the model's structure. First, the fluctuating pattern of world trade has to be included as all nations are involved in such transactions (at the global scale there is no trade with other planets!). Next, the pattern of international human migration has also to be included. Again, this is absent from the global model for obvious reasons.

The simple global/national hierarchical model is predicated upon several causal hypotheses. The first hypothesis states that there is an inverse relationship between rising material consumption and falling birth rates. Obviously, many other factors influence birth rates but, in this simple model, it is suggested that this hypothesis is a first approximation to real demographic change. Next, the second hypothesis links anthropogenic emissions of carbon dioxide and other greenhouse gases as a non-linear function of material consumption. Third, the rate of consumption or appropriation of the Net Primary Product is increasing and is unsustainable. Empirical work by Vitousek et al. (1986) indicates that some 40% of NPP is used by human population directly or indirectly. Obviously, as NPP represents a stock of the basic food supply for all organisms, then this cannot exceed 100%. The base run of the model permits only 50% of NPP to be appropriated by humanity. The fourth hypothesis states that international trade is responsible for the unequal distribution of material goods entering the world market and is observed in the unequal consumption of resources per capita. Currently, disagreements over the role of world trade are important environmentally, socially, economically and politically. In the model, a parameter (epsilon) is used as a measure of unequal trade between rich and poor nations. By altering epsilon to 0.5, then an equal amount of resources (measured in tonnes) can be used to simulate a more equal allocation of resources across the globe. It should be noted that a more equal distribution of resources can still lead to a massive difference in the per capita consumption patterns, which depend on both the wealth and the number of people doing the consuming. The fifth hypothesis assumes that there is a direct relationship between employment opportunities and the pattern of international migration. The sixth hypothesis states that when food resources cannot be met by national agriculture and fishing, then imports of foodstuffs are essential. This is represented as a change in the 'balance of trade' in the model. Unlike the earlier Limits to Growth models, this model uses a modified Cobb-Douglas production function as a broadly Keynesian mechanism to represent the global and national economies.

Figure 2 A hierarchical, dynamic global-national model for sustainable development (note only two levels out of six in the hierarchy are represented)

The entire model was written as a set of difference equations. All the levels or stocks in the model were initialised for the year 1950 and the model was calibrated for the period 1950-1990 and run as a business-as-usual scenario for the next 300 simulated years. The solution time for the equations was set at one year. The model was programmed in STELLA and runs on an IBM PC (full details of the model are described in Moffatt et al. 2001). The results of this preliminary simulation model are described below.

A dynamic, hierarchical case study

Any complex, dynamic model has to overcome the problems of calibration and validation. At the global scale, this is difficult as we often only have one dataset, e.g. global estimates of CO2 concentrations or global population. Similarly, in national studies the data for physical parameters are often associated with error bars around the measurement of the data - but, typically, economic data do not come with associated error bars. Given the nature of the data in many studies, then, the practice is to use the best estimates of the state variables to initialise the model and, again, to use the best estimates of the numerical parameters gleaned from the literature. This was undertaken for the model (1950-2000) and then the model was run to simulate 300 years of development from 1950-2250. It should be noted that, to prevent a circularity of argument, it is importan\t that the model reveals some testable predictions (new discoveries) so that it has an extra content than merely replicating historical patterns.

The problems associated with validation are also daunting. The major problem is that of obtaining a good fit between the actual data for several observed variables and the simulated variables. Often, in complex models optimum performance, as measured by the goodness of fit statistical criterion, does not perform well on all variables. This means that one variable could be a good fit with the relevant data but other variables are not performing well. One solution to this problem is to obtain an overall goodness of fit criterion, but this may mean that no one simulated variable is statistically close to the real data. The approach adopted here was to combine various estimated parameters and then, by using successive simulations, attempt to capture the best fit between individual state variables rather than adopting an average fit between all variables. It should be noted that calibration can only be used to compare the simulated data with the observed datasets. Once forecasting extends the simulated data into the future, then only different scenarios can be explored. The choice of scenarios depends, in part, on how good a fit the model performs with historical data. It is also obvious that any scenario reflects the implicit value judgements of the model maker and decision-makers. It should, of course, be realised that each future scenario, if chosen as the basis for policy, has both potentially important positive and negative impacts. Clearly, the methodological problems associated with calibration and validating dynamic, hierarchical models are still in their infancy.

The base run of the dynamic simulation model assumes no major changes to the structure of the world economy or policies to alter world trade, so it represents a business-as-usual scenario. The total population continues to rise from 2.5 billion in 1950 to 14.1 billion by 2150. By that time, the simulated human population will have consumed all renewable resources as represented by NPP and the human race becomes extinct within the year. The rich population grows from 752 million in 1950 to 4.2 billion, whereas the poor population rises from 1.76 billion to 9.9 billion. It should be noted that the Earth's population is slightly over 6 billion at present and the model indicates that increasing the population to 14 billion is unsustainable. The CO2 level increases from 275 ppmv and reaches a maximum of 633 ppmv. The environmental index (I) - using the Ehrlich and Holdren (1971) equation (I = P*A*T), where P is population, A is affluence (consumption) and T is technology, rises from 2 in 1950 to a maximum of 3.3 (Figure 3).

Global World Product (GWP) measured in US$ trillions rises from 5.47 through to a maximum of 53.6 before the collapse. Interestingly, the economic value of the world's ecosystem estimated at $2.52 trillions in 1950 also increases to a level of $55 trillion. Estimates of the latter are notoriously difficult to obtain as the ecological services are essential to the life-support of the planet and cannot be simply viewed as market transactions. Nevertheless, Costanza et al. (1997) have attempted to provide a dollar estimate of these indispensable ecological services. Their estimate for 1990 is between $16 trillion and $54 trillion and the model forecasts $19 trillion for the same year.

The national model is set up to represent potentially any nation. In the study, only a highly simplified model of the ecology and economy of Scotland was produced. Again, the levels were initialised for 1950 and the model run for 300 simulated years. By 2160, the global population collapses and, unsurprisingly, so does the Scottish population. The Scottish population does, however, remain more or less stable at 5.3 million people throughout the simulation. Despite the constant population, the Scottish Gross Domestic Product (GDP) grows from approximately 18 billion to 23 billions. Real Scottish wealth (i.e. the values of the ecosystems) rises from 25 billion through to 29 billion over the period 1950-2150 before the collapse. The environmental index also rises from 2 to almost 3 over the same period (Figure 4). It should be noted that the preliminary model is a very simplified structure of the real world but does indicate that we can in both theory and practice combine ecological and economic systems within the same dynamic, hierarchical framework. More research needs to be undertaken to develop this approach to modelling. In particular, the need to include every nation into the simulation model is required. A summary of the calibrated base run for the globe and a nation (Scotland) (1950- 1990) is given in Table 4.

Figure 3 The base run simulation - unsustainable (business-as- usual) at the global level

Figure 4 Current pattern of national development in also unsustainable

It will be observed that, on the basis of the data, the global / national model performs reasonably well. The gloomy forecasts are based on a business-as-usual scenario and, as in many simulation models, it is possible to introduce policy options to enquire into the way in which the models of the system may behave if politically and ethically sound environmental policies are pursued. Several simulation experiments were performed with the model and one sustainable corridor for the world and the national economy was located (Figure 5).

Table 4 Summary of the global (upper) and national state (Scotland) (lower) output of the calibrated variables for the hierarchical model, 1950-1990

Figure 5 A corridor of sustainable development (only global level shown)

The sustainable corridor whereby demographic and economic systems live within the world's ecological carrying capacity was located by a judicious choice of policies and parameter changes. This corridor required several policies to be introduced simultaneously: (1) constraining the world population to approximately 10 billion; (2) assuming equal distribution of material resources, i.e. altering current world trade patterns; (3) reducing resource consumption and associated CO2 pollutants; and (4) investing heavily in renewable technologies, especially with regard to maintaining the natural capital of the Earth: only then is it possible to achieve a sustainable future. Simultaneously, at the national scale, population migration will have to be controlled and altering taxation by introducing eco-taxation also aids the sustainability of the national economy and ecology. The results of these changes are to ensure - at least in the model - a sustainable future for both the globe and one nation (Figure 5).

Obviously, further research including all nations rather than just one country (Scotland) is required. It would be very useful to integrate our models of sustainable development with models of climate change. Current research has made a link between global climate change and regional and local impacts (Moffatt and Parnell 2003) but much more detailed work integrating ecological-economic interactions at a local level is required. It would, therefore, be useful to exchange concepts and codes with other modelling groups such as the GUMBO group in Vermont (Anon, undated) and climate change modellers in Europe (Schellnhuber and Wenzel 1998). Once the model is further refined and developed then the mediodological and political implications of some of the futures would need to be examined and discussed. If the next generation of dynamic, hierarchical modelling, linking global to local processes, proves its mettle, then the arduous task of moving from a simulated work to activating policies in the real world must begin. These problems are part of the process of making development sustainable identified in the Brundtland Report (WCED 1987).

At present it would appear that the vast economic machinery of the global economy has brought untold wealth to a rich minority; it has also increased the living conditions of many of the people living in the developing world. It should be noted that the price of this pattern of economic development has been extracted from both ecology and the rest of society. The current patterns of economic development have been inequitable and a growing number of people are now left in absolute poverty and in squalid living conditions in an impoverished environment. This pattern of exploitation of people and their environment is part of a continuing historical process - it need not continue. Concerted efforts by many individuals and groups are urgently required so that the global economy can be redirected to improve the lot of all people now and in the future within the constraints of ecological systems. Given sufficient political will and action, the patterns of sustainable development can be achieved although, in the light of recent political negotiations at Kyoto, Bonn and Genoa in 2001, the political will to re-direct and manage the global economy is not as strong as it could be.

CONCLUSIONS

This paper has described the potentials, problems, policies and progress in modelling sustainable development as a dynamic, hierarchical model. Sustainable development is a complex process embracing ecological, economic, ethical and equity issues, often ranging from the local to the global. We have suggested that there are several ways of contributing to this process using different modelling methods. The potential of the different types of models is, as yet, untapped and it would be useful if researchers were able to pool their resources to address the real world problem of making development sustainable. None of the modelling methodologies are trouble-free. In fact, we have identified three main problems of modelling sustainable development, namely epistemological issues, the availability of data and indicators and the aspects of risk and uncertainty in \any modelling enterprise. We have noted that to make development sustainable we have to introduce a raft of policies at different spatial scales and aimed at different organisations. Again, the task of implementing policies in the real world, as distinct from a model of that world, is surrounded by difficulties.

Despite the magnitude of the problems that confront us in modelling sustainable development, some progress in this area of research has been made. It has been argued that we need to develop theoretically sound models of sustainable development. It has also been argued that sustainable corridors offer a theoretically sound way of developing dynamic, hierarchical models of sustainable development. A relatively uncomplicated dynamic model linking global and national processes has been outlined. This simple model captures some of the important processes involved in making development sustainable. It should be stressed that much more detailed work with other model builders would enrich the efforts towards modelling sustainable development. It has been demonstrated that it is feasible to develop a set of models that capture the essence of sustainable development. This means trying to combine ecological and economic systems into a coherent whole whilst simultaneously permitting different future scenarios to be explored. The latter are based on a planning system that is socially just, transparent and democratically accountable (Daly 1977, 1992). The model described in this paper integrates global and national economic-ecological interactions and explores, albeit at a crude level of aggregation, Scodand as part of the nation within a global system of nations. Further research in linking the hierarchical model to multinational and regional/local studies has still to be accomplished. Some progress in making the links between global climatic processes and local responses has been made (Moffatt and Parnell 2003) but much more detailed work needs to be undertaken.

In summary we have outlined the potentials and problems in modelling sustainable development and suggested some ways of making progress in this fundamentally important area of research and policy relevance. Development of models can be seductive but we must be ever vigilant about their limitations. The world is not a clean slate on which we can write in whatever imagery is currently in vogue, but it is possible to use scenarios for the future as an informed and systematic basis from which to make choices. Obviously, we have much to do to ensure that the progress we are making can reach and inform both the public and the policy-makers. It is suggested that if researchers can pool their resources in an organised, systematic manner, then it may be possible to develop a set of integrated approaches which can help us and future generations to an economically sound, socially just and environmentally stable future.

REFERENCES

Anon. The Global Unified Model of the BiOsphere (GUMBO). Gund Institute for Ecological Economics, University of Vermont, http:// www.uvm. edu/giee; accessed 30 May 2004

Atkinson AB. The Economics of Inequality. New York and Oxford: Oxford University Press; 1983

Bartoszczuk P. Model of Economic Growth and Environmental Policy in System Dynamics. Paper presented to the System Dynamics meeting, Oxford University, Oxford; 2004

Beck U. Risk Society: Towards a new Modernity. London: Sage; 1994

Beckerman W. Small is Stupid: Blowing the Whistle on the Greens. London: Duckworth; 1995

Brydensholt HH. Decision regarding complaints against Bjorn Lomborg. Danish Committees on Scientific Dishonesty (in Danish ) (http://www.forsk.dk/ uwuudtaldebat/b1_decisio.thml; accessed 13 January 2003

Costanza R, D'Arge R, de Groot R and Faber S. The value of the world's ecosystem and services and natural capital. Nature 1997;387:253-60

Costanza R. Visions of alternative (unpredictable) futures and their use in policy analysis. Conservation Ecology 2000;4(1):5 http:/ /www.consewcol.org/ vol4/iss/art5

Daly HE. Steady-state economics: The economics of Biophysical and Moral Growth. San Francisco: WH Freeman; 1977

Daly HE. Allocation, distribution and scale: towards an economics that is efficient, just and sustainable. Ecological Economics 1992;6:185-93

DEFRA. Sustainable Development - the UK government's approach. The Sustainable Development Unit, DEFRA, London, http:// www.sustainabledevelopment.gov.uk/contect.htrn; accessed on 31 May 2004

Diamond J. Collapse: How societies choose to fail or survive. London: Allen Lane; 2005

Ehrlich P and Holdren J. Impact of population growth. Science 1971;171:1212-17

Ekins P and Max-Neef M. Real-life economics: Understanding wealth creation. London: Routledge; 1992

Frey WR and Lam ACW. The bridge to Humanity's future. http:// www.ecocosmdynamics.org/Pubs/EDLNe wsletterVol1.htr, accessed 31 May 2004

Foucault M. Power/Knowledge: Selected interviews and other writings. Gordon C (ed.). Brighton: Harvester Press; 1980

Gorshkov VG. Physical and Biological Bases of Life Stability. Berlin: Springer Verlag; 1995

Gorshkov VG, Kondratyev K, Ya K and Losev KS. The natural biological regulation of the environment. Journal of Ecological Chemistry 1994;3(2):85-90

Gray R, Bebbington J and Walters D. Accounting for the Environment London: Paul Chapman; 1993

Gregory D. Ideology, Science and Human Geography. London: Hutchinson University Library; 1978

Gregory D. The ideology of control: Systems theory and geography. TESG 1980;1xxx1327-62

Haberl H, Wackernagel M and Wrbka T. Land Use and Sustainability Indicators: An Introduction. In Mather A and Moffatt I (eds), Special Issue of Land Use Policy 2004;21(3):193-8

Hall CAS (ed.). Quantifying Sustainable Development. San Diego: Academic Press; 2000

Harvey D. A question of method for a matter of survival economics. Geographical Papers GP32, University of Reading; 1973

Harvey D. The geopolitics of capitalism. In Gregory D and Urry J (eds), Social Relations and Spatial Structures. London: Macmillan; 1985:128-63

Henderson H. Building a win-win world: life beyond global economic warfare. San Francisc

Source: International Journal of Sustainable Development and World Ecology

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