What is sustainability?
A tricky conceptNowadays the concept of “sustainability” is a staple of any public debate and is used in an inflationary way. Playing on the positive connotations of the word “sustainability” – much like “peace”, “justice” and “conservation” – people tend to use it in every possible context. Industry talks about “sustainable production” and financial services providers offer “sustainable performance”. Consumers are urged to “eat and drink sustainably”; music classes support “sustainable child development” and even a warm-water bathing day for senior citizens at a public pool is advertised as “sustainable”. Everybody understands “sustainability” to mean something slightly different.
- 1.1 > The concept of “sustainable” silviculture was introduced in 1713 by the Saxonian chief mining official Hans Carl von Carlowitz in his treatise Sylvicultura oeconomica, in which he advocated prudent management of forest resources.
- The concept tends to be more confusing than clarifying. Depending on the given definition, project or context it takes on a different meaning. But the current inflationary use of the term is not solely to blame for this baffling ambiguity; the fact is, the concept is indeed a blend of different factors. Sustainability is a complex matter. Economic development models, the world food supply, nature conservation, poverty reduction or distributive justice – all these aspects play a part in the sustainability debate. Looking back into the past, however, it is evident that the individual themes were often considered in isolation from one another and studied separately. Depending on the historical situation, certain questions took precedence, and others were put on hold until they in turn had become urgent.
Experts today endeavour to frame plausible theories and models in order to enhance the understanding of all the elements that comprise sustainability. The main challenge for the future is to put the broadly accepted insights of sustainability theorists into practice in concrete societal, political or economic models.
Fear of timber scarcityThe expression “sustainable” or “sustainability” came into use in German silvicultural theory in the 18th century. Back in 1713 the chief mining official Hans Carl von Carlowitz, from Freiberg in what was then the Principality of Saxony, published the forestry treatise Sylvicultura oeconomica, in which the principle of “continuously enduring and sustainable use” was discussed for the first time. Von Carlowitz coined the term at a time when many parts of Europe were in need of vast quantities of wood for mining and ore-smelting. Gradually the environs of many mining towns were becoming deforested. Wood shortages were an imminent threat. Even at the start of the 18th century, wood was having to be shipped from far away by river. Von Carlowitz warned that, without wood, people would “suffer great hardship”. In his Sylvicultura oeconomica he called for the forests to be conserved. People, he wrote, should save wood, conserve forests by sowing and planting trees, and seek “surrogata” or alternatives to wood. All in all, people should only harvest as much wood as could regrow.
The aim of forest management was to achieve the greatest possible wood harvest sustainably – in other words, consistently over time – without overexploiting the forest. Thus, 300 years ago, von Carlowitz was voicing demands which are still crucial to the current sustainability debate. Then, however, the focus was on economic considerations rather than nature and forest conservation per se. That was equally apparent from the composition of the forests, and what was considered sustainable at the time: they tended to be monocultures of tree species of interest to the wood industry rather than near-natural forests. Since the concept of sustainability was originally clearly and narrowly defined, it provided a basis for deriving binding rules. For every tree species, prescribed felling rates were defined, i.e. annual maximum quantities of wood that were permissible to cut in a section of forest.
Too many people – too little foodNot just in Germany but throughout Europe, scholars in the eighteenth century were getting to grips with the finite nature of natural resources, although in this context – unlike in the work of von Carlowitz – there was no discussion of sustainability. An important aspect was how to supply foodstuffs to the growing population. Today it is estimated that the population of Europe as a whole grew from 140 million to 266 million between 1750 and 1850. In England alone, the number of inhabitants swelled from around 7 to 20 million people during the same period.
- 1.2 > Silviculturists in the state of Minnesota, USA at the end of the 19th century. Wood was in particular demand as a raw material at the time, and vast quantities of it were required for housebuilding in the growing towns.
- The British economist Thomas Robert Malthus warned that food production would not be able to keep pace with population growth in future. And if the plight of the poor improved, he wrote, this would lead to further population growth – and hence to a food crisis. Ultimately, the result would be a worsening of overall poverty. One solution, Malthus and others seemed to think, would be to maintain the population figure at a constant level. A few years earlier, scholars like the North German lawyer, Justus Möser, had already argued against smallpox vaccination on population policy grounds. The vaccination, Möser warned, would reduce child mortality so greatly that “the world would become too small for all the progeny of mankind”.
The doom-laden fears of scholars like Malthus and Möser did not come to pass. Before population growth in Europe could lead to a large-scale food shortage, the problem was solved by a natural scientist: in the mid-19th century, the German chemist Justus Liebig developed artificial fertilizer, paving the way for a huge increase in the productivity of arable farmland. Just as his precursor von Carlowitz did for forestry, Liebig strove to achieve persistently high yields in agriculture whilst endeavouring not to deplete soil fertility.
1.3 > Back in 1892 the richly forested Adirondack Park in New York State was designated a National Park by the US authorities. With an area of 24 000 km2 it is almost as large as the island of Sicily.
Environmental degradation caused by the Industrial RevolutionThanks to Liebig’s invention, the kind of food shortage that Malthus had prophesied for the future never came to pass. On the contrary, the topic that captured the attention of thinkers and scientists was degradation of the natural environment because, in the late eighteenth and the first half of the nineteenth centuries, Europe was overtaken by the Industrial Revolution: the slow and deep-seated transformation of an agricultural into an industrial society. The world was radically transformed by coal mining, metal smelting, the growth of towns and the construction of barrage dams, highways and railways.
One who criticized the devastating impacts of this industrial growth was the US statesman and scholar George Perkins Marsh, who toured Europe in the 1850s and was ambassador at the Italian court in Rome between 1861 and 1882. In many of the locations he visited, he observed how humans were changing and to some extent destroying nature. In 1874 he published his most important work, Man and Nature: The Earth as Modified by Human Action, in which he described his observations. Marsh’s ideal was the village community which conserves nature in the long term and uses its resources mindfully. He warned that humans were in the process of rendering the Earth, the home of humankind, unfit for habitation. People needed to protect nature out of “enlightened self-interest”, he argued. But Marsh also emphasized that it was possible to use natural resources rationally. People have a right to use nature’s assets, he stated, but not to abuse them.
- 1.4 > The US scholar George Perkins Marsh is acknowledged as one of the forefathers of the environmental movement. In the mid-19th century on a tour of Europe he experienced how nature was being destroyed. His drastic descriptions of this overexploitation contributed to the introduction of sustainable forest management in the USA.
- Marsh’s theories and his drastic descriptions of environmental degradation in Europe had the most momentous impact in his country of birth, the USA. In order to prevent deforestation on a European scale, the decision was made to conserve forests. Initially, protection was given just to some areas in isolation. The year 1892, for example, – 10 years after Marsh’s death – saw the founding of the richly forested Adirondack Park in the state of New York. Covering an area of 24 000 km², this National Park, the largest in the USA today, is almost as large as the island of Sicily. At the beginning of the twentieth century, the authorities finally came round to safeguarding forests throughout the country from overexploitation. It was in 1905 that the United States Forest Service was founded, a forest authority whose first Chief was Gifford Pinchot. Pinchot, a forest scientist and politician, was inspired by Marsh’s teachings. He established sustainable forest use in the USA, just as had been advocated by von Carlowitz almost 200 years previously.
Prosperity rather than sustainability?Apart from a few positive examples, however, the idea of making prudent use of nature stubbornly failed to take off. For one thing, periods of severe deprivation during two World Wars led policymakers in Western industrialized countries to pursue one goal above all else in the mid-20th century: to generate prosperity for all and, through constant economic growth, to overcome absolute poverty and alleviate class disparities. Thus, the dualism of economic growth and sustainability was preordained.
At the beginning of the 1960s, however, there was mounting criticism of this naïve faith in growth and progress. The damage caused by unchecked economic growth took on increasingly vast dimensions. Soils and rivers were being poisoned. Smog was forming in many urban centres from the emissions of cars, factories and power plants. Children in particular suffered from respiratory illnesses. Sulphur dioxide emissions from power plants and car engines led to the phenomenon of “acid rain”, which caused trees and entire swathes of forest to die off. Environmental conservationists talked about “forest death”.
In the 1970s, the concept of “sustainability” then underwent a renaissance. It was now defined more broadly than before. Advocates of sustainability criticized the established economic models which insisted that economic growth was an ongoing necessity. In 1972 the Club of Rome published its highly respected study, The Limits to Growth, which mentioned a “sustainable global system” for the first time. In its report, the Club of Rome warned against the consequences of overexploitation. It developed a theory which stated that every phase of strong economic growth would inevitably be followed by a major collapse of the system. Resource scarcity and environmental pollution would turn into severe crises and reduce people to living in the most basic conditions well before the year 2100.
- 1.5 > In 1966 Essen was the first city in Germany to introduce driving prohibitions in order to reduce the pollution caused by smog. But only when power stations and industrial plants were fitted with emissions filters in the 1980s did air quality improve noticeably.
- Club of Rome The Club of Rome is an international non-governmental organization and expert body which was founded in 1968 by leading industrialists, engineers, business experts and academics in order to analyse the negative consequences of economic growth and to develop solutions.
- Today opponents of this gloomy vision of the future continually point out that there was no shortage of non-renewable resources after all, because new sources of raw materials have constantly been discovered and exploited. On the other hand, many experts today warn about supply bottlenecks for certain metals either because they only exist in small quantities or because individual states have a monopoly over them. Moreover, they say, resource extraction continues to cause the destruction of natural areas. In their view, the Club of Rome’s forebodings are perfectly justified.
The Club of Rome’s assumption that environmental pollution would definitely increase in line with economic growth has been considered by some critics to have been refuted in the meantime. Some economists asserted that growing prosperity would be accompanied by greater investment in environmental protection. Many European countries and other industrialized countries around the world did indeed succeed in considerably reducing environmental pollution by means of technical measures like sewage treatment plants and filters in power stations and cars – despite the continuation of economic growth. In the light of environmental pollution and degradation on a massive scale in emerging economies like Brazil, China and India, today the warnings of the Club of Rome take on renewed importance. Contemporary China in particular is a textbook example of the environmental destruction and ecological costs that go hand in hand with unrestrained economic growth. The debate between the critics and proponents of growth continues to this day.
Same rules for all?From the 1960s onwards, the “underdevelopment” of the so-called Third World was another much-discussed topic. On the one hand there were economists who saw the economic growth and business model of the industrialized nations as an example worth emulating. In their view the national economies of the Third World countries should match, as rapidly as possible, the industrialized countries’ standard of development through “catch-up” industrialization and modernization. Support should be provided to them in the form of development assistance. For this, the prototype was the U.S. aid for reconstruction in Western Europe in the immediate post-war period, which had been organized under the Marshall Plan. But this policy did not work well everywhere. Moreover, it did not guarantee universal development or that the entire population of a country would share in the resulting prosperity. Therefore, alongside these more capitalist Western models, other models of development emerged. These were overtly aimed at greater ownership by developing countries of their development processes, and at a more socialist policy of redistribution from the top down, for instance by means of land reforms. The aim of development in such models was not primarily higher consumption of goods but was rather oriented towards aspects like education, health or public participation in policy-making processes.
One milestone was the “eco-development” approach of the Dag Hammarskjöld Foundation in the 1970s. This Foundation was named after the Swedish diplomat and United Nations Secretary-General Dag Hammarskjöld, who had lost his life in a plane crash in 1961. The Foundation has its headquarters in the Swedish city of Uppsala and has continued to organize international conferences and seminars at which experts debate themes of policy such as security, democracy and development. At that time the Dag Hammarskjöld Foundation proposed guidelines on the future of developing countries, which comprised the following aspects:
- Satisfaction of basic needs largely on the basis of own resources;
- Not a copy of the Western lifestyle and pattern of consumption;
- Conservation of the environment;
- Respect for cultural difference and local traditions;
- Solidarity with future generations;
- Use of technologies adapted to local conditions;
- Participation of all population groups and particularly of women in societal and political decisions;
- Family planning;
- Some decoupling from the global market and development of local markets;
- Orientation to religious and cultural traditions;
- No admittance to the military power blocks of NATO (North Atlantic Treaty Organization) and the Warsaw Pact.
Far more than silviculture and pollution controlWhile sustainability was originally applied to forestry alone, this was later joined by aspects like population growth, food, and environmental protection. Since the 1970s, aspects of society have increasingly come under the spotlight of the sustainability debate – for instance, the question of how different stakeholder groups can participate in societal and political decisions, or to what extent people today are responsible for the well-being of future generations. Against this backdrop, in 1980 the United Nations (UN) convened the World Commission on Environment and Development (WCED). It was tasked with finding ways to achieve several major objectives simultaneously, namely:
- to fight poverty in developing countries;
- to support developing countries in development in keeping with their traditions;
- to master environmental challenges;
- to level out the contrast between Western market economics and state socialism.
The Commission chose the phrasing “sustainable development” at least partly in an effort to pull together the different and in some cases competing objectives of environmental protection, poverty reduction and economic growth. Its use of this definition was an attempt to integrate some of the divergent ideas on the pathways that developing countries might take in future. The phrasing “sustainable development” was intended to help:
- to take account of the idea of the developing countries’ ownership of processes without veering too far towards socialist ideals;
- to draw attention to the ecological limits to growth;
- not to lose sight of the old UN objective of fighting poverty;
- not to fundamentally challenge Western lifestyles;
- to address the challenge of population growth.
- All in all, the Commission wished to define the lowest common denominator of sustainability that all its members could accept. The result was a compromise formula. A further aim of the WCED report was to bring the theme of sustainability into the public sphere. That was accomplished. The report was quite catalytic in sparking a new debate about the meaning of sustainability. What it did not provide were concrete directions for political intervention. The problem with the concept of “sustainable development” and the entire WCED report is that the wording of the definition was a compromise solution which left it open to completely different interpretations by different stakeholder groups, by politicians or by industry. Hence, the WCED report contains no systematic conception of sustainability. This is a key reason why the sustainability concept has remained so vague in the political discourse until now.
Following the publication of the WCED report, many countries embraced the idea that sustainability could be achieved by striving for the objectives framed by the Commission – poverty reduction, equitable economic growth and environmental protection – in equal measure. Taking that as a basis, theorists derived what is known as the “three pillars” model. According to this model, sustainability rests evenly on the three pillars of the environment, the economy and society, all three of which rank equally in stature. However no clear verdict is given as to whether this equal ranking is the case already, or whether it first has to be accomplished. Critics also object that the sustainability concept incorporates a normative dimension. In their view, sustainability is more than a philosophical theoretical model because ultimately, such a theory ought to make it possible to derive clear directions for action and to implement appropriate measures.
Responsibility for posterityMaking mindful use of resources over the long term to ensure that they will still be available in future is one of the pivotal ideas of sustainability. So sustainability ties in very closely with the responsibility of generations living today for the future. How far this responsibility extends has long been a matter of contention. In the 1970s, a few scientists defended the view that the generation living in the present day had absolutely no responsibility for those born later. The argument was as follows: unborn persons do not exist, are not therefore legal entities and thus cannot have rights of any kind whatsoever. On that basis, the living have no obligations towards the unborn. Today, however, this extreme perspective has few if any adherents. The very fact that future persons will have rights, the critics contend, is sufficient to permit obligations to be derived for people alive today. These obligations would not relate to particular unborn individuals but in a general way to generations of human beings living in the future. It follows that intergenerational distributive justice is an essential component of sustainable development. What legacy, or how much present-day humankind should leave for posterity, is nevertheless a debatable issue.
Auf der Suche nach dem gerechten StandardThere are many possible answers to the question of what obligations people living today have towards generations yet to come – depending on the chosen reference standard. For example, scientists make a distinction between the comparative versus the absolute standard. According to the comparative-standard model, people of future generations should be no worse off overall than the people alive today. But that immediately raises the question of whose living standards will be used for comparison – those of people in the industrialized countries or in developing countries? People’s living standards can differ substantially even within the industrialized countries or emerging economies themselves. So defining a single global comparative standard is very difficult, as every basis for comparison seems arbitrary.
The absolute standard, on the other hand, stipulates minimum requirements which are fundamental elements of a life in human dignity. This absolute standard should be valid for all human beings without distinction; that includes those still to be born. Nevertheless, an absolute standard that only requires basic needs to be met is quite a low standard.
Today’s reality is that a plausible absolute standard for all does not yet exist. After all, millions of people worldwide are still living in conditions of severe hardship, lacking food, clean drinking water or access to education. This realization can cause an over-emphasis on combating poverty through economic growth in emerging economies and developing countries, which detracts from the importance of conserving natural resources over the long term as a policy of sustainability would demand.
- 1.7 > A slum in Dhaka, the capital of Bangladesh. Millions of people in the world live without clean water, sanitation or access to education.
- Today the prevailing opinion among sustainability theorists is that neither the comparative nor the absolute standard alone is sufficient as a yardstick for sustainability models, for in reality living conditions around the world are just too disparate at the moment. Nor do the experts see any reason to believe that in the medium term it will be possible to raise living standards in poor developing countries, such as Bangladesh for instance, to the same level as rich industrialized nations like Switzerland. It is therefore more pragmatic, they say, to define regionally differentiated standards. Thus, it would make sense to work towards one good, absolute standard for the developing countries and emerging economies, on the one hand; over and above this, on the other hand, different comparative standards are practicable for more highly developed regions and may vary from country to country or region to region.
This does not in any way mean that living conditions in the given regions are expected to stay the same forever. Modern sustainability models are very much geared towards reducing absolute and extreme poverty, as well as tackling the extreme disparities between the rich and the poor. A distinction needs to be made between these two goals. For as the example of China shows, it is possible for poverty in a country to lessen generally even though major disparities in income and wealth exist. Poverty in China’s rural regions is receding whilst at the same time a prosperous middle class is emerging in the metropolitan centres with significantly higher incomes than the rural population.
Sustainability theorists advocate reducing absolute poverty first and foremost, arguing that that is the paramount goal. They accept that some responsibility must be taken for the future, but responsibility for the present is their most immediate concern. To concentrate on the future while ignoring present-day hardship, they say, is to set the wrong priorities. So far, theorists are still at odds over the extent to which economic inequality can be permitted to exist at all.
The great goal: a life worth livingAs an answer to the question of what constitutes a life of human dignity, the “basic needs” approach has been cited since the 1980s. However, this comprises only the absolute essentials of survival, particularly food, clothing and shelter. Far more ambitious is the capabilities approach which was developed around ten years ago by the US philosopher Martha Nussbaum. This contains a list of capabilities which are said to enable anybody to live a life according to their own ideas. The list relates both to the people alive today and to future generations, and proposes that every person should be capable of
- being able to live to the end of a normal human lifespan and not having to die prematurely;
- being able to have adequate nourishment, shelter and good health, and being able freely to express their sexuality;
- being able to live without unnecessary pain and suffering;
- being able freely to exercise imagination, thought and logic and to practise a religion;
- being able to maintain attachments to things and people and to experience and cherish interpersonal values like love, care, gratitude but also longing and grief;
- being able to form their own conception of a good life and plan their own life;
- being able to engage in social interaction and to experience recognition, community, friendship and professional life;
- being able to live well in relation to animals, plants and the world of nature;
- to be able to laugh, engage in recreation and experience enjoyment;
- being able to participate politically, freely carry on an occupation under fair working conditions, and acquire property.
- This list includes aspects which go far beyond the definition of an absolute material living standard. In fact, it comprises all those capabilities which universally characterize quality of life and human dignity. Naturally, the capabilities approach is first and foremost a theory-of-justice model that was developed by philosophers. Ultimately it is the responsibility of countries to ensure that their citizens can develop and exercise all of the capabilities. Looking at the living conditions in developing countries, however, fulfilment of this standard for all people still seems a very remote prospect. This is not a complaint against the capabilities approach, though, but much more against the political and economic circumstances. One strength of the approach is that it contains a list of aspects which are transferable to all cultures. Over time, the capabilities approach has been taken into account in many UN documents. It has thus established itself as an important basis for the political discourse about the responsibility of those alive today towards the people of the future.
- 1.8 > A hillside vineyard in Radebeul near Dresden. Economists assign vineyards to the category of cultivated natural capital.
- If we follow the capabilities approach, the question is which things people alive today should bequeath to future generations to ensure that the people of the future can likewise attain the 10 capabilities and live fulfilled lives. Experts talk about this in terms of a “fair bequest package”. For a good education, people need libraries, for the transportation of goods they need roads, for food production they need fertile farmland, for clean air they need forests. Beyond this, the fair bequest package also includes natural landscapes, which are all the more important because people can only develop the capability to enjoy nature by experiencing these landscapes themselves. This capability is in no way a luxury for human life but is accepted as one of the basic ideas of a good life.
Capabilities like the capacity to enjoy nature may appear abstract. But they are all linked to a concrete resource. The capability to engage in recreation, for example, presupposes that there are forests to walk through, beaches for bathing, and urban green spaces where people can relax. Economists refer to such resources as different types of “capital”:
- real capital (machines, factories, infrastructure);
- natural capital (forests, oceans, rivers, coasts);
- cultivated natural capital (commercial forests, livestock herds, vineyards, agricultural land, aquacultures);
- social capital (political institutions, social cohesion, sources of social solidarity);
- human capital (skills, education);
- knowledge capital (libraries, universities).
- In the sustainability debate, the natural forms of capital are of greatest importance. These are characterized specifically as follows:
- renewable or self-regenerating resources (for example, plants and animals) and non-renewable resources (for example, metal ores, petroleum);
- original natural capital (unregulated rivers, primary forests) and cultivated natural capital reshaped by human activity;
- sources (for example, minerals from the mountains), sinks (for example, the ocean as a carbon dioxide reservoir) and stocks (for example, animal populations).
Weak versus strong sustainabilityTo what extent certain forms of capital, particularly natural capital, should be conserved for posterity has long been a contentiously debated issue. Since the 1970s, the debate has circled around the following two contrasting models: the model of weak sustainability and the model of strong sustainability.
According to the weak sustainability model, only the sum total of a society’s capital stocks needs to be held constant. By that standard, it is possible for capital resources that have been consumed to be replaced with different types. In principle, then, there is unlimited scope for substituting natural capital with real and human capital. Under the weak sustainability model, these substitution processes are permissible almost without restriction. Even destroyed elements of natural capital, such as rivers that are biologically dead due to pollution, can be replaced under this model. The recreational function of river bathing, for example, can be substituted by constructing open-air or indoor swimming pools; obtaining drinking water not purely from groundwater but alternatively from desalinated seawater; or replacing the aesthetic quality of natural landscapes with artificial, virtual worlds. According to the model of weak sustainability, all that matters is to satisfy the sum total of people’s needs – irrespective of which type of capital is utilized.
Particularly in the 1970s, a period of great environmental degradation, many economists believed in the idea of weak sustainability. Some of its proponents note that critical natural capital stocks – i.e. stocks that are very difficult to substitute – are indeed worth conserving. When a form of natural capital should be classified as critical is often a matter of dispute, however.
- 1.9 > The Golden Horn, one of Croatia’s most popular beaches. Not just the Adriatic but every sea in the world has so many different functions that it can never be substituted in full. The recreational function is one of these.
Strong sustainability for environmental qualityWhile some economists still stick with the model of weak sustainability, scholars in other scientific disciplines consider it a write-off: today it is generally accepted that not every form of natural capital is indiscriminately substitutable. If we consider the scale and the consequences of the destruction of natural capital today, the limits of substitutability become very much clearer than in economic models. This is particularly true of multifunctional natural capital, i.e. forms of capital which fulfil several functions simultaneously. Oceans, for example, supply food, are an income source for fishers or aquaculturists and a recreational zone for millions of tourists. Completely replacing the multifunctional habitat of the ocean is impossible – hence, the idea of substitutability is obsolete. A similar argument is valid for forests with their many functions.
Over the last few years, therefore, the “strong sustainability” model has gradually gained ground in sustainability theory, and is becoming increasingly widespread in the political sphere. The aim of strong sustainability is to conserve natural capital, regardless of whether and to what extent it is substitutable or how other capital stocks such as real capital (for example, in the form of industrial and consumer goods) might develop. In keeping with strong sustainability, natural capital has to be conserved because of its many different functions – not only because of its material values, but also its cultural values, for example. So the question is not just whether natural capital can be substituted but, more importantly, whether humankind actually desires a permanent substitution now and in future. The generation living today cannot judge what needs and cultural value ideals future generations will have, and whether those yet to be born are in agreement with the substitutions we make today. Substitution of natural capital, in other words ultimately the loss of natural habitats and the decline of biodiversity, is irreversible and scarcely justifiable. If natural capital is consumed today, it no longer remains available as an option to the people as yet unborn. In that case, generations to come no longer have the choice between natural capital and the substitute, but have to live with the substitute.
- Since the strong sustainability model decrees that present-day amounts of natural capital should be held constant, it means that the destruction of natural habitats and degradation of environmental systems must be halted.
Modern sustainability models try to reconcile the economic use of natural capital with its conservation. To make this possible, however, a few rules are necessary. One example is known as the Constant Natural Capital Rule (CNCR) which requires maintaining the sum total of natural capital. This in no way implies a kind of museum-style nature conservation which totally prohibits any modification of near-natural areas. In fact, the CNCR’s aim is the conscious use of natural capital and, above all, the substitution of consumed natural capital with other natural capital of equivalent value.
It is important to emphasize that according to the CNCR there is not just one way to replace natural capital. Strong sustainability does not force any ideal path upon policymakers from which they must never stray. Rather, the CNCR requires people to be creative in seeking good solutions for any substitution of natural capital. Thus, a harvested tree might be replaced with a tree of a different species. It is even conceivable that a certain forest biotope might be substituted with another. In some cases, near-naturally managed forests could fulfil the functions of destroyed virgin forests. It may also make sense to build up natural capital in the form of plantations if virgin forests elsewhere might be protected as a result.
The CNCR represents a modern, flexible and practicable rule of strong sustainability which can be used to resolve conflicts over use. The major difference from weak sustainability is that according to the CNCR, consumed natural capital must be replaced by equivalent natural capital. The CNCR approach does not allow substitution with real capital, nor exclusively technical solutions, as in the substitution of clean river water by water from seawater desalination plants.