Towards a sustainability indicator for production systems

0959-6526(95)00064-X

J. Cleaner Prod., Vol. 3, No. 1-2, pp. 123--129, 1995 Copyright © 1995 Elsevier Science Ltd

Printed in Great Britain. All rights reserved 0959-6526/95 $10.00 + 0.00

Towards a sustainability indicator for production systems

A . M . J . Ragas, M.J . K n a p e n , P.J .M. van de Heuve l , R .G.F .T .M. E i j k e n b o o m , C.L. Buise and B.J. van de Laar

Department of Environmental Studies, Catholic University of Nijmegen, Toernooiveld 1, 6525 EL) Nijmegen, The Netherlands

An important goal of (inter)national environmental policy is to realize a sustainable development. However, the implications of sustainability for society are not yet fully understood. This paper contributes to the interpretation and elaboration of the concept of sustainability. It outlines a procedure to measure the sustainability of production systems. The method presented in this paper is not an instant recipe to measure sustainability. However, it indicates the social and scientific barriers that are to be overcome in order to understand, elaborate and measure sustainability.

Keywords: sustainability indicator; production system; environmental policy

Introduction

Sustainable development has been the most important aim of international environmental policy since the report Our Common Future of the World Commission on Environment and Development 1. The Dutch government has endorsed this aim in its National Environmental Policy Plans (NEPPs) 2,3. Sustainable development is a process of change in which the exploitation of resources, the direction of investments, the orientation of technological development and the institutional change are in harmony and increase the present, as well as the future, possibility to accommodate human needs. The relation between society and its physical environment should be such that a natural carrying capacity is ensured for future generations 4.

To realize a sustainable society it is necessary to obtain insight into the sustainability of production and consumption processes. This insight can be obtained by determining whether the production and consumption of certain products meet with the concept of sustainability. With this information, the actors within a production system (government, producers and consumers) can adjust the system. The government can use sustainability indicators as a tool to make political decisions. For example, when a production system appears not to be sustainable, measures can be taken. For producers, the indicator can offer a long-term perspective and more legal security. The consumer will gain an understanding of which products are produced within the preconditions of sustainability.

A sustainability indicator is defined as an absolute environmental measuring tool which, on the basis of a comparison of the present and the sustainable situation, shows to what extent the aims of sustainability are met. Various indicators that meet this definition already exist 5. These indicators differ from the indicator presented in this paper because they are developed to measure the environmental quality or because they only take into consideration a few forms of environmental pressure. However, to assess the sustainability of production systems, all forms of environmental pressure should be taken into account.

A production system includes every process necessary for the functioning of the product, from the cradle to the grave 6. At this point the method presented is comparable with methods for life cycle assessment (LCA) of products 7. It differs from LCA methods by its absolute character. The method presented leads to a conclusion concerning the extent of sustainability of a production system, while an LCA leads to a conclusion concerning the extent of environmental pressure in comparison to other comparable production systems 8.

The procedure outlined in this paper shows the steps along which a sustainability indicator for production systems can be developed. It is by no means an instant recipe to measure sustainability. The procedure is developed in order to indicate the scientific and social barriers that are encountered when elaborating the concept of sustainability and measuring the sustainability of production systems.

J. Cleaner Prod. Volume 3 Number 1-2 123

Sustainability indicator for production systems: A.M.J. Ragas et al.

Sustainability

The first step in the development of an indicator to measure the sustainability of production systems is a description of the concept of sustainability. For this purpose, a schematic reproduction of the relation between man and his physical environment is used: the environmental impact chain (Figure 1). This chain describes the way environmental problems can be traced back to their source, and consists of four links: human activities, environmental pressure, environmental quality and unacceptable harmful impacts 9. Assuming that unacceptable harmful impacts should not happen in a sustainable situation, the implications of sustainability can be determined for each link in the chain by following the chain in the opposite direction. This leads to a description of the concepts of sustainable environmental quality, sustainable environmental pressure (environmental space) and sustainable human activities (Figure 1) . Sustainable environmental quality covers the physical, chemical and biological conditions which do not lead to unacceptable harmful impacts. This quality has to correspond with the target levels for the diversity of species, the abundance and quality of ecosystems, the concen- trations of pollutants and the extent of disruption of natural processes and cycles. In a sustainable situation, the physical environment can be used within the limits of these target levels. This environmental pressure is called 'environmental space' and is defined as: 'the use of the physical environment by social factors which does not impair the sustainable environmental quality. By definition, environmental use within these limits is sustainable '1°.

This description of sustainability elucidates what is meant by a sustainable relation between man and his physical environment: this is the case when sustainable

environmental quality is present and the actual use of the physical environment does not exceed the sustainable level. Human activities, the first link in the chain, can be considered sustainable as long as they take place within the borders of the environmental space.

Method

Now the demands which sustainability makes upon society in terms of environmental pressure have been described, it becomes possible to develop a method to measure the sustainability of production systems. A production system is sustainable whenever the environmental pressure it causes is smaller than or equal to the part of the environmental space that is allocated to this production system. To compare the actual use of the physical environment by the production system with the allocated enviroamental space, six steps have to be taken (Figure 2). These steps will be explained below.

I. Classification of environmental problems

A production system causes various forms of environmental pressure. The sustainability indicator should take all forms of environmental pressure caused by a production system into consideration, weighing the impact of the environmental problem as well as the contribution to this problem. This calls for a classification of environmental problems. In this study the different environmental problems are classified in themes that are extracted from the NEPPs of The Netherlands (Table 1, column 1). Two environmental problems which are considered to be threatening for a sustainable society are absent in this classification. These are the extinction of biological species and the

Hunlan activities

The environmental impact chain

Environmental I I Environmental

pressure I - I quality

Description of sustainability

I Unacceptable harmful

- [ impacts

Sustainable human

activities

Human activities which do not exceed

the maximum sustainable

environmental pressure

Sustainable environmental

use

Use of the environment at

which the sustainable quality

is not affco.cd

Sustainable environmental

quality

All physical, chemical and biological

conditions at which one can speak of

sustainability

Sustainability

No unacceptable harmful impacts for

humans, plants animals and goods occur either now or in the future

Figure 1 Description of the concept of sustainability on the basis of a schematic reproduction of the environmental impact chain

124 J. Cleaner Prod. Volume 3 Number 1-2


Table l Survey of the (sub)themes with accompanying geographical scales, units, sustainable environmental quality and national environmental space. The sustainable environmental quality and the environmental space are filled in tentatively

Theme Subtheme Unit Geographical Sustainable Environmental scale environmental space on

quality national scale

Climatic change greenhouse effect Ceq a global 460 ppmg 15 depletion of the ozone Oeq b global 0.24 ppb h 22 layer

Squandering squandering of biotic Beq" global in = out 425 k resources exhaustion of energy Eeq d global not applicable 0.85 k carriers exhaustion of non- resource specific global not applicable resource specific renewable resources

Acidification acidification Aeq e continental 500 Aeq/ha 1.69 - - - - - 109" ̀Eutrophication eutrophication EUeq r regional in = out 95" Pollution pollution ? global-local ? ? Disposal disposal of waste ? regional ? ? Desiccation desiccation ? regional ? ? Disturbance nuisance ? local ? ?

extinction of species ? global ? ? deterioration of nature ? regional-local 9 ? safety risks ? continental-local ? ?

alCeq = 1 CO2 equivalent = 1 megaton CO2/year blOeq = 1 ozone equivalent = 1 ton CFK-11/year c1 Beq = 1 biotic squandering equivalent = 1 megaton organic material from the primary production al Eeq = 1 energy exhaustion equivalent = 1 exajoule/year el Aeq = 1 acidification equivalent = 1 mol potential H+/ha year rl EUeq = 1 eutrophication equivalent = 1 kiloton P/year gFrom ref. 11 hDeduced from ref. 11 kFor background information refer to ref. 12 "From ref. 13 "From ref. 14 not applicable, it is impossible to determine the sustainable environmental quality for these subthemes ?, not determined yet

Classification of environmental 1 problems into themes and

subthemes 1 T

Determination of the ] environmental space for

each (sub) theme 2 T

Determination of the ] Determination of the reall environmental space for I environmental use of a one production system 3 production system 4

T T Calculation of the section

indicators 5

t Integration to one overall sustainability indicator 6

2 The six steps for the development of a sustainability indicator for production systems

de t e r io ra t i on of na tu re by the use of space for bui ld ing and inf ras t ruc ture . Because these p r o b l e m s lead , to a cer ta in extent , to the d i s tu rbance of ecosys tems , they are classified as sub themes unde r the t h e m e ' d i s tu rbance ' . F o r this r ea son , this t h e m e is subd iv ided into four sub themes . Because bo th o f the t hemes 'c l imat ic change ' and ' s q u a n d e r i n g ' cover m o r e envi ronmen ta l p r o b l e m s , t hey a re also subd iv ided into subthemes (Table 1, co lumn 2). To c o m p a r e p roduc t ion

systems with r ega rd to the i r con t r ibu t ion to an env i ronmen ta l p r o b l e m , the e nv i ronme n ta l p ressure for each ( sub ) theme has to be expressed in c o m p a r a b l e units. The weighed con t r ibu t ion to the g loba l warming process , for ins tance , is expressed in CO2 equivalents : one CO2 equ iva len t equals the effect of the emiss ion of 1 m e g a t o n of CO2 in one year . The chosen units for each ( sub ) theme are p r e s e n t e d in Table 1 (co lumn 3) 12 .

2. Environmental space

The env i ronmen ta l space is d e t e r m i n e d for each ( sub) theme . Because the re a re large gaps in concep tua l knowledge , the d e t e r m i n a t i o n of the env i ronmen ta l space is m a r k e d by n u m e r o u s scientific uncer ta in t ies .

The geograph ica l scale at which the env i ronmen ta l space is d e t e r m i n e d d e p e n d s on the geograph ica l scale at which the env i ronmen ta l p r o b l e m manifes ts itself. F o r the t h e m e 'c l imat ic change ' , for example , the env i ronmen ta l space is d e t e r m i n e d at a g loba l scale, whereas for the t h e m e ' e u t r o p h i c a t i o n ' the envi ronmen ta l space is d e t e r m i n e d at a reg iona l scale. The geograph ica l scales for each ( sub ) the me are p r e s e n t e d in Table 1 (co lumn 4).

The e nv i ronme n ta l space is d e t e r m i n e d on the basis of two pr inciples . The first p r inc ip le is ' input =



output'. This principle is applied for those cases in which it is possible to determine a sustainable environmental quality. At the limit beyond which unacceptable harmful impacts arise, any input of contaminant or substance should not exceed the output. Box I illustrates the deduction of environmental space for the greenhouse effect, according to this principle. For reasons of practicality, it is assumed that the actual environmental quality is sustainable. Because this is a false assumption, in reality the environmental space should be limited for some time, so that the environmental quality can recover. Starting from the present environmental quality and the Dutch aim to realize a sustainable environmental quality by the year 20102,3, this limitation leads to a negative environmental space for greenhouse gases. This indicates that under the present circumstances the Dutch aim will not be achieved even with zero-emission of greenhouse gases up to the year 2010.

When calculating the environmental space for greenhouse gases it was assumed that the environmental space has a fixed volume in time. This assumption is not entirely correct 16. Aforestation may, for example, lead to a greater binding capacity of COE and consequently allow the emission of greater quantities of COE. Further studies might lead to adjustment of the assessed environmental space.

The principle of 'input = output' cannot be used for environmental problems which lead to depletion. In those cases a substitution approach is followed 17A8. The environmental space is determined for each resource and depends on the stock that is available and the time that is needed to develop an alternative for this resource. In Box 2 the deduction of the environmental space for copper is illustrated.

3. The distribution problem

The next step in the development of a sustainability indicator is the distribution of the available environmental space among different production systems. To accomplish this, the environmental space should be brought to one geographical scale. When translating environmental space to higher or lower geographical scales, one is confronted with gaps in conceptual knowledge.

In this paper the national scale is chosen for integration. For each (sub)theme the environmental

Box 1 Environmental space greenhouse effect

The environmental space concerning the greenhouse effect is deduced according to the principle 'input = output'. The sustainable environmental quality is 460 ppm CO2 (ref. 11). The natural background concentration is 380 ppm. This background is raised with 17% (80 ppm) for human activities. The output of CO2 is about 1.3% of the present quantity a year. So, for one year the environmental space is 1 ppm CO2 (1.3% of 80 ppm). This equals an absolute quantity of 6.1 x 10 a CO2 equivalents.

Box 2 The environmental space for copper within the subtheme 'squandering of non-renewable resources '13

The environmental space for non-renewable resources is deduced according to the substitution approach. According to this approach the environmental use is sustainable if there is enough time to develop substitutes. For all the elements the minimal term of substitution is arbitrarily equal to 50 years. If the stock is squandered within 50 years, the situation is not sustainable. Use has then to be restricted to the level at which the term of squandering is 50 years.

The global stock of copper is 306 kilotons. Of this, 10% (30.6 ktons) is reserved for applications that are specific for the element. This 10% has to be available for more than 50 years. The other 90% (275.4 ktons) can be used in 50 years. The environmental space is then -+5.5 kton/year. The present use is about 10.6 ktordyear (in 1985).

space for The Netherlands is determined. This choice corresponds to the existing administrative structures, and there is a relatively large amount of information available at this geographical scale. But it also involves a major limitation. A production system is usually situated in different countries, international dispersion being more common than exceptional. Environmental pressure which is caused in a particular country should be compared with the environmental space which is allocated to that country. This makes it extremely complex to examine the sustainability of an international production system. To avoid this problem, one can imagine the production system taking place in the studied country. Using the method in this way will lead to an answer to the question of whether sustainable production and consumption of a certain amount of product are possible within the boundaries of the country.

The translation of environmental space from the highest geographical scales (global, continental and fluvial) to the national scale can take place in many ways. Distribution keys for global environmental problems can, for example, be based on the level of development of a country (less developed countries obtain relatively more environmental space for further development), population index, surface area, production capacity or gross national product. The choice for a specific distribution key has to be made on a global political level. For problems on a continental and fluvial scale, a distribution based on surface area is the best solution. A homogeneous dispersion of environmental pressure avoids effects on a regional scale, or effects caused by concentrated emissions in boundary areas.

At lower geographical scales (regional and local scales), the translation of environmental space to the national scale could, for example, be made by summation on the basis of surface area. This, however, brings the risk of averaging environmental problems: the actual environmental pressure at a national scale might be within the limits of the environmental space,

126 J. Cleaner Prod. Volume 3 Number 1-2


while at a local or regional level problems do occur. This averaging effect makes the indicator less valuable for environmental problems at a lower geographical level. For example, the averaging effect for a national sustainability indicator for noise pollution is so great that the indicative value will be close to zero. For this reason the nuisance theme is not considered further in this paper. The averaging effect applies also for (sub)themes on a regional scale, such as desiccation. As desiccation concerns only a limited number of regions, the averaging effect is smaller. Therefore the regional (sub)themes are maintained in the indicator with the remark that the environmental pressure within the borders of the national environmental space does not automatically mean that no problems will occur on a regional level.

When the national environmental space is determined for each (sub)theme, it has to be distributed among the different production systems in The Nether- lands. This distribution is a matter for the government. The following considerations can play a part:

1. The fulfilment of the necessities of life. The allocations of environmental space for primary, secondary and tertiary necessities decrease in amount.

2. The share of the production system in the gross national product of The Netherlands. The extent of this share determines the size of environmental space to be assigned.

3. The specific aspects of the production system. The paper industries use a relatively large amount of water but produce relatively small amounts of acidifying agents, in contrast to the business of intensive cattle farming.

4. Issue of transferable emission rights. Environmental rights give the owner the right to a certain amount of environmental use. A share can only be sold within the geographical scale of the specific (sub)theme.

Many other distribution keys and combinations of distribution keys are possible. These are not elaborated in this study. For drafting new distribution keys, further research is recommended.

4. Actual environmental use

The environmental space assigned to a specific production system has to be compared with the actual environmental use of the system. This can be done by using elements of the method of life cycle assessment of Heijungs et al. 6. This method examines the environmental aspects of products from 'the cradle to the grave'. It consists of five steps: goal definition, inventory, classification, valuation and improvement analysis.

The first two steps are used to determine the actual environmental use. During the first step - the goal definition - the demarcation of the production system takes place: the 'functional unit' is determined. After

this, in the second step - the inventory - a survey of different forms of environmental pressure is made. Problems can occur in assessing the boundaries between related processes, and at the quantification of items that are not related to one production system 6,19. Finally the inventory results in a survey table which categorizes all kinds of environmental use into (sub)themes.

5. Section indicators

A section indicator is related to a (sub)theme. It is the ratio between the actual environmental use of a certain production system at a specific amount of production, and the environmental space assigned to this production system. When the environmental use is larger than the assigned environmental space, the ratio is larger than 1, i.e. the situation is not sustainable.

The values of section indicators which consist of more than one subindicator (this is, for example, the case in the theme 'pollution' and the subtheme 'exhaustion of non-renewable sources') are, while weighing factors are not yet determined, calculated by averaging the subindicators. However, averaging of subindicators that are not sustainable (X > 1) against sustainable subindicators (X - 1) can occur. The average of a subindicator values at 0.7 and a subindicator valued at 1.2 is 0.95. This is not a sustainable situation. To avoid this kind of averaging effect, the minimum value of a subindicator is set at 1.0.

6. Overall sustainability indicator

The values of the section indicators can be integrated into one overall sustainability indicator. The usefulness of this overall indicator is that the sustainability of a production system is indicated by only one number. An overall sustainability indicator is comparable with other indicators such as the gross national product. The overall sustainability indicator can, for example, be used to compare the degree of sustainability of different production systems in a simplified way. A disadvantage of an overall sustainability indicator is that much information is lost during the integration.

The overall sustainability indicator is calculated by multiplying the section indicators with a weighting factor, summing them and taking the average value. The weighting of heterogeneous environmental effects is a complex scientific and political problem that needs further research.

There are two aspects related to the weighting: the conceptual aspect and the aspect concerning the process. The conceptual question concentrates on methods which can be used to weight heterogeneous kinds of environmental pressure, as much as possible based on objective scientific information. The second aspect is related to the procedure that has to be followed to reach consensus in society about the subjective aspects of the weighting 15. In this paper it is assumed that problems on a higher geographical scale are more severe than problems on a lower



Table 2 Survey of the weighting factors for the different (sub)themes when calculating the overall sustainability indicator

Theme Subtheme Arbitrarily chosen weighting factor

Climatic change greenhouse effect 5 ozone layer depletion 5

Squandering biotic resources 5 energy carriers 5 non-renewable resources 5

Acidification acidification 4 Eutrophication eutrophication 2 Pollution pollution 1-5 Disposal disposal 2 Desiccation desiccation 2 Disturbance extinction of species 5

deterioration of nature 1-2 safety risks 1-4

geographical scale (Table 2). If (sub)themes concern different geographical scales, the weighting factor depends on the situation. An alternative way of assigning the weighting factors is by the judgement of independent experts who determine the severity of the environmental effects described by a (sub)theme 22.

When calculating the overall sustainability indicator, the minimum value of the section indicators is set at 1 to avoid averaging of non-sustainable section indicators. The value of the overall sustainability indicator is therefore equal to or larger than 1. A value of 1 indicates a sustainable situation of a production system at a specific amount of production.

Presentation of results

The results are presented in a radargraph. This figure is derived from the so-called A M O E B E approach described by Ten Brink et al. 2° and Udo de Haes et al. 22. The section indicators are presented in a circle. The distance from the circle to the centre indicates the sustainable situation. When a section indicator exceeds the circle, the situation is not sustainable. In this way the relation between the section indicators and the sustainable situation is clear at a single glance. The value of the overall sustainability indicator is indicated at the bottom of the radargraph. The results for an imaginary production system are illustrated in Figure 3.

Conclusion

The method presented in this paper is an initial impetus to develop a sustainability indicator which takes into consideration all forms of environmental pressure during the life cycle of a product. A large number of social and scientific problems have to be solved before the method can be made applicable. More attention has to be paid to the interpretation of the environmental space, particularly considering the quantification of scientific uncertainties, the variation in time of the environmental space and the occurrence of synergistic effects. Besides, additional research is necessary to determine suitable units and the environmental space for the themes pollution, disposal, desiccation and disturbance. It is necessary to develop distribution keys for distribution from higher to lower scales, and vice versa, that have a firm scientific foundation and are socially acceptable, This is also the

Acidification

Extinction of species \

Deterioration of nature

Safety

Greenhouse effect

Depletion of the ozone layer

/

Pollution

Eutrophication

~ / Exhaustion of non renewable resources

Exhaustion of energy carriers

Squandering of biotic resources

Desiccation /

/ \

Disposal

The value of the overall sustainability indicator is 3.4

Figure 3 Presentation of a fictitious sustainability indicator

128 J. Cleaner Prod. Volume 3 Number I-2


case for the d i s t r ibu t ion of the na t iona l env i ronmen ta l

space a m o n g d i f ferent p roduc t i on systems. A d d i t i o n a l conceptua l knowledge is necessa ry to solve the bot t le -

necks tha t occur as a resul t of the in t e rna t iona l d i spers ion of p roduc t i on systems. The def ini t ion of p roduc t ion sys tems and the quant i f ica t ion of par t s that are not r e l a t ed to one p roduc t ion sys tem also d e m a n d fur ther research . P r o b a b l y the larges t scientific and social bo t t l eneck is the d e v e l o p m e n t of me thods to weight unl ike forms of env i ronmen ta l p ressure . The absence of sui table weight ing factors gives rise to the impress ion tha t apples a re be ing c o m p a r e d to oranges . This may compl ica te the social accep tance of susta inabi l i ty indicators .

H o w e v e r , solving these n u m e r o u s bo t t l enecks may lead to a power fu l pol icy ins t rument , which can, for example , be used to out l ine p roduc t i on scenar ios . The sect ion ind ica tors show the d i f ferent sorts of env i ronmen ta l p ressure of a p roduc t ion system. This offers poss ibi l i t ies to r educe the env i ronmen ta l pressure, for examp le by technologica l improvemen t s ,

decreas ing the a m o u n t of p roduc t ion , deve lop ing p roduc t a l t e rna t ives or rep lac ing the p roduc t ion . The overa l l sus ta inabi l i ty ind ica to r can be a helpful tool to c om pa re p roduc t i on sys tems concern ing susta inabi l i ty .

The m e t h o d p r e s e n t e d here is a theore t ica l f rame- work for a sus ta inabi l i ty ind ica tor for p roduc t ion systems and indica tes the out l ine of a sus ta inabi l i ty indicator . Sus ta inabi l i ty ind ica tors a re n e e d e d because they are an abso lu te e n v i r o n m e n t a l measur ing tool which can he lp the g o v e r n m e n t , p roduce r s and consumers on the i r way to sus ta inabi l i ty . F u r t h e r research into deve lop ing the concep t of sus ta inab le d e v e l o p m e n t in measu rab l e a ims and the deve lop ing accompany ing

indicators is necessary .

Acknowledgements

The authors wish to acknowledge Dr R.S.E.W. Leuven and Dr M.W.H. Th6rig for their useful comments on the manuscript.

References and notes 1 World Commission on Environment and Development. 'Our

Common Future', Oxford University Press, Oxford/New York, 1987

2 Dutch Ministry of Housing, Physical Planning and Environ- ment (VROM). 'National Environmental Policy Plan' (in Dutch), Second Chamber, 21137, no. 1-2, 1988-1989

3 Dutch Ministry of Housing, Physical Planning and Environ- ment (VROM). 'National Environmental Policy Plan 2' (in Dutch), Second Chamber, 23560, no. 1-2, 1993-1994

4 Opschoor, J.B. and Van der Ploeg, S.W.F. in 'The Environ- ment: ideas for the 21st century' Dutch Committee for Long- Term Environmental Policy, Kerckebosch, Zeist, 1990, pp. 81-127 (in Dutch)

5 Van de Meer 17 developed two sustainability indicators for non-renewable resources; one on the basis of exhaustion and term of substitution and one on the basis of economic aspects. Van Egmond et al. 18 developed a sustainability indicator for the use of copper and aluminium, based on exhaustion and a term of substitution. Van Dijk et al. 13 described the development of a sustainability indicator for the deposition which leads to eutrophication in The Netherlands, and Udo de Haes et al. 22 developed a method to construct an indicator for the sustainable quality of the environment

6 Heijungs, R., Guin6e, J.B., Huppes, G., Lankreijer, R.M., Udo de Haes H.A., Wegener Sleeswijk, A., Ansems, A.A.M., Eggels, P.G., Van Duin, R. and De Goede, H.P. 'Environmental Life Cycle Analysis of Products - Guide and Backgrounds', Centre of Environmental Science, Leiden University, 1992

7 Fraanje, P.J. and Lindijer, E.W. Milieu 1993, 4, 257-261 (in Dutch)

8 It is very possible that the environmental pressure of a product or a production process is low in comparison to other products or production processes, while it does not meet the demands of sustainability. For example, it :s not clear if the car with the least environmental pressure is suitable within a sustainable concept of traffic and transport. A sustainability indicator can elucidate this and suggest measures to be taken

9 Udo de Haes, H.A. and Van der Voet, E. 'Guidelines for the ammonia emission of intense cattle farming business: an example of deduced ecological quality standards', Landschap, theme number Ecological Quality Standards, 1987 (in Dutch)

10 Advisory Council for Research on Nature and Environment. 'Vision Through the Years, 1992. Programme of Research on Nature and Environment for Sustainable Development', Publication RMNO no. 70, Rijswijk, 1992 (in Dutch)

11 Maas, R.J.M. 'National environmental outlook 2 1990-2010', National Institute of Public Health and Environmental Protection (RIVM), Bilthoven, 1991

12 Eijkenboom, R.G.F.T.M. and Van den Heuvel, P.J.M. 'A method to develop a sustainability indicator for production systems', Report of the Department of Environmental Studies no. 67, University of Nijmegen, 1993 (in Dutch)

13 Van Dijk, I., De Graaf, N., Van Hecke, A. and Tiemessen, I. Mil ieu 1994, 4, 124-127 (in Dutch)

14 Adriaanse, A. 'Environmental Policy Performance Indi- cators', Environment of the Dutch Ministry of Housing, Physical Planning and Environment (VROM), SDU Pub- lishers, Den Haag, 1992

15 Weterings, R. 'Indicators for a Sustainable Development. An Exploration of Dutch Research', Advisory Council for Research on Nature and Environment, Report 86, 1993 (in Dutch)

16 Musters, C.J.M., De Graaf, H.J. and Ter Keurs, W.J. 'Environmental Space. How can we determine the boundaries. Part 1: Theory', Environmental biologics report no. 93-2, University of Leiden, 1993 (in Dutch)

17 Van der Meer, G.J. Milieu 1990, 5, 133-137 (in Dutch) 18 Van Egmond, P., Graafland, F., Hanekamp, E., Petit, A.,

Raad, J., Van Sark, Y., Spanbroek N. and Vlak, J. 'Copper and Aluminium Measured. A Research on Sustainability Indicators for the Use of Metals', Report of the project of groupe 5, Environmental Studies, University of Amsterdam, 1991 (in Dutch)

19 Lambert, A.J.D. Mil ieu 1994, 1, 12-22 (in Dutch) 20 Ten Brink, B.J.E., Hosper, S.H. and Colijn, F. Marine

Pol lut ion Bullet in 1991, 23, 265-270 21 Clarenburg, L.A. Mil ieu 1993, 1, 33-36 (in Dutch) 22 Udo de Haes, H.A., Nip, M. and Klijn, F. 'In Search of

Indicators of Sustainable Development', Kluwer Academic Publishers, Dordrecht/Boston/London, 1991, pp. 89-105


Documents

Towards a sustainability indicator for production systems