Investigations into the Club of Rome's World3 model : lessons for understanding complicated models Citation for published version (APA): Thissen, W. A. H. (1978). Investigations into the Club of Rome's World3 model : lessons for understanding complicated models. Technische Hogeschool Eindhoven. https://doi.org/10.6100/IR79372 DOI: 10.6100/IR79372 Document status and date: Published: 01/01/1978 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 05. Oct. 2021 INVESTIGATIONS INTO THE CLUB OF ROME'S WORLD3 MODEL LESSONS FOR UNDERSTANDING COMPLICATED MODELS Wil Thissen INVESTIGATIONS INTO THE CLUB OF ROME'S WORLD3 MODEL LESSONS FOR UNDERSTANDING COMPLICATED MODELS P R 0 E F S C H R I F T ter verkrijging van de graad van doctor in de technische wetenschappen aan de Technische Hogeschool Eindhoven, op gezag van de rector magnificus, prof.dr. P. van der Leeden, voor een konnnissie aangewezen door het college van dekanen in het openbaar te verdedigen op vrijdag 5 mei 1978 te 16.00 uur door Willem Antonius Helena Thissen geboren te Ougree (Belgie) Dit proefschrift is goedgekeurd door de promotoren Prof.ir. O. Rademaker en Prof.dr.ir. P.M.E.M. van der Grinten Part of this thesis is based on material originally appearing in IEEE Transactions on Systems, Man, and Cybernetics, Vol. SMC-6, No. 7, pp. 455-466 (1976), and Vol. SMC-8, No. 3 (1978). Printed by Krips Repro, Meppel. gutta cavat Zapidem, non vi, sed saepe cadendo CONTENTS SUMMARY Olapter GENERAL INTRODUCTION 3 1. 1 Background of the study 3 1.2 Motivation of the study 5 1.3 More about this thesis 5 Olapter 2 AN ANALYSIS OF WORLD3 8 2.1 Outline of the model 8 2.2 Subsystem analyses 10 2.2.1 Decomposition for standard-run conditions 10 2.2.2 Capital and resources 13 2.2.3 Agriculture 29 2.2.4 Persistent pollution 46 2.2.5 Population 50 2.3 Study of the model as a whole 68 2.3.1 Standard-run conditions - Interplay of submodels 68 2.3.2 Non-standard conditions 70 2.3.3 Analysis by means of total linearisation 75 2.3.4 Equilibrium analysis 80 2.4 Policies derived from the model 86 2.4.1 Introduction 86 2.4.2 General considerations 87 2.4.3 A resource-conservation and birth-control policy 88 2.5 Conclusions 91 2.5.1 Model behaviour and properties 91 2.5.2 Policy conclusions 93 Olapter 3 METI-IOD'JLOGICAL EVALUATION 96 3. 1 Introduction 96 3.2 The importance of model understanding 97 3.3 An approach to understanding corrrplicated models 101 3.3.1 General considerations 101 3. 3. 2 Attitudes 102 3.3.3 Strategies 103 3.3.4 Techniques 108 3.3.5 Classification 121 3.4 Concluding remarks 125 Olapter 4 EPILOGUE 127 LIST OF SYMBOLS 131 REFERENCES 135 SUMMARY This thesis presents the main results of a study that aimed at uncovering the inner workings of Meadows' World3 model, not to criticise the underlying assumptions, but to be able to understand and explain precisely why the model behaves the way it does, under a variety of assumptions. The model's so-called standard-run properties are studied sector by sector, and at different levels of detail. Standard-run behaviour appears to be mainly determined by the assumptions on capital growth and resource availability in the model. The capital and resource submodel impresses its behaviour of growth, followed by decline, upon all other sectors. The implication is that policies aiming at modification of this behaviour cannot be effective unless they affect capital growth and resource usage in the model. Population growth in World3 tends to continue until stopped by starvation. A5 a result, policies designed to create and maintain acceptable and sustainable living conditions in World3 have to include a population policy in addition to a resource conservation policy. The policies need not to be as abrupt and radical as those advocated by the Meadows team. The main reason for the difference is that, as the :Meadows team failed to recognise the more or less hierarchical structure of the model, their study of policies had to be conducted along a trial-and-error type of approach. Model understanding is a crucial, but underdeveloped part of model-based systems analysis and policy formulation. Therefore, the World3 excercise was reconsidered from a methodological point of view. A proposal for a general approach to model understanding is the result. In addition, an extensive list of techniques, sone of which have been developed in the context of the World3 analyses, is given. The major methodological conclusion is that, in contrast to current practice - in which sensitivity analysis is considered to be about the only technique - great flexibility is desirable, and a wide variety of techniques may have to be used to properly understand a complicated model. The integrated approach presented here offers a general framework for discussion and a variety of suggestions and ideas to those confronted with the problem of constructing, understanding and exploiting a complicated model. C h a p t e r o n e GENERAL INTRODUCTION 1. 1 BACKGROUND OF THE STUDY In the late sixties, a number of businessmen, scientists, and others who were alarmed at what they considered to be rrankind's self-destructive tendencies formed an international group that was to become known as the ''Club of Rome", according to the location of their first meeting. The subject of concern was called the ''World Problematique", or "the Predicarrent of Mankind". The Club was looking for a unifying approach for study and communication at the time Professor J.W.Forrester attended one of its meetings. Forrester had developed a particular method of dynamic modelling and computer siilUllation (called "System Dynamics" by himself and his associates), and had applied it already to industrial management and urban planning problems /7,8/. He proposed to use the System Dynamics method for the study of the world-wide problems the Club was worrying about. To demonstrate the utility of his approach he quickly designed a diagram "on the back of an envelope". This diagram is said to be called ''World1". Within a few weeks, Forrester elaborated the diagram and developed a simulation model called "World2". That model describes the global developments in the fields of economy, resource availability, demography, food production and pollution in a rough and highly aggregated manner. After a presentation of World2, the Club decided to adopt Forrester's method because it seemed to ireet many of the requirements of the approach the Club was looking for: a synthesis of many isolated components into a more comprehensive picture, and an attempt to analyse the system as a whole rather than just its parts. In order to examine Forrester's assumptions and conclusions in greater depth and to rethink and refine the components of his model, a more extensive study was initiated under the leadership of D.L.Meadows, The outcome was a new model, called ''World.3", which, since, the publications of "The Limits to Grcwth" in 1972 /15/, has been a subject of 3 intense debate for several years. In the rreantirre, Forrester1 s model had been published in a book called "World Dynamics" /9/. The book received world-wide attention, probably more because of its far-reaching conclusions and recommendations concerning the future of mankind than because of its scientific " contents. Among those who got interested in the problematique were a number of systems and control engineers in the Netherlands. The staterrents put forward by Forrester were intriguing, and, on the assumption that the problems were real problems indeed,a clarification of the debate would be relevant to the future of mankind. In addition, the rrethod employed was very familiar to systems and control engineers who had been working with matheootical models of dynamic systems for oony years, and had build up a broad ioothodological knowledge and experience in the field. Little of this had been utilised in Forrester's and M=adows' stu::lies.