CONFERENCES WITH DENNIS L. MEADOWS, PUGH-ROBERTS, AND JAY W. FORRESTER REGARDING SYSTEMS DYNAMICS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP82M00531R000400120022-8
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 33
• Document Creation Date: December 16, 2016
• Document Release Date: March 9, 2005
• Sequence Number: 22
• Publication Date: August 3, 1973
• Content Type: MFR

t/ DCl/IC-73d~S~
lease 2005103/ 3 0 : CIA-RDP82 Mb0531 Z00120022-8
P, :M31 NDUM FOR THE RvECORI)
SUP>7; Cr: Conferences with Dennis L. Meadows, Pugh-Roberts,
and Jay W. Forrester regarding Systems Dynamics
Dennis L. Meadows
Associate Professor of Business and Engineering, Thayer School
of Engineering, Dartmouth College, Hanover, N.H. 03755
I I and I met Professor Meadows at his office at
Murdoug enter at Dartmouth about noon on 31 July 1973, went to
lunch with him, and then continued our conference at his office. He
was very cooperative and forthcoming throughout the 2 1/2 hour period --
a dynamic and enthusiastic individual, obviously highly motivated
toward achievement, practical and realistic.
Although he is not very familiar with intelligence he believes the
systems dynamics methodology has much to offer since it is uniquely
suited to analysis when precise relationship, and accurate, objective
measurements are not available or can't be determined. He discussed
four kinds of analyses: philosophical - in which there is little
restraint on the framework; communications - in which the objective
is to describe various notions or relationships; projective - in which
greater structure is provided and more factual or assumed data is
employed; and predictive - typified by physical and engineering
equations in which the relationships are know with great precision
and the dynamic or time related behavior of a system can be confidently
predicted. Systems dynamics is effective in the communication/
projective areas -- it does provide structure and an insight into the
dynamic characteristics of systems which is difficult or impossible to
achieve otherwise.
Based^on his experience as a teacher, and as an organizer and
lecturer of seminars in the systems dynamics methodology, he felt that
the three week introductory course in systems dye! ariics which we are
considering was about right for our purposes, i.e. providing sufficient
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STAT
working Iaowledge to analysts and others with little or no mathematical
or computer background to make an intelligent assessment of the potential
usefulness of applying the systems dynamics methodology to their problems.
Meadows reconni nded that several changes in content and sequence be
considered to male the course more effective. Ile believes it is very
important to quickly iir:merse the student in real problems instead of
trying to complete the development of the theory before getting into
applications.
I purchased a pre-publication copy of The I,m.amics of Growth in a
Finite 1 orld (the detail studies related to Limits to Groait _ isThi chi can
reused as a source for illustrative problems and. applications in,systems
dynamics,,, and a set of lecture notes and exercises, "Principles of
Dynamic Systems" which Meadows used in the introductory systems dynamics
course at the Sloan School during the spring term, 1.972. (Vuegraphs and
other related instructional material can be obtained) When they arrive
from Copenhagen, Meadows will forward a copy of the 300 page outline/
notes lie used. in conducting a 2-week seminar for a group of European
industrialists last month. He provided copies of several reprints and
monographs which he thought might be useful.
Prof. Meadows has been very active, and the tempo may be increasing.
He noted that lie was MIT's only PhD graduate in systems dynamics. (I
believe he said-his other major fields were RV management, operations
research, and management information systems.) In addition to having
taught at MIT he headed the Club of Rome project which resulted in three
publications thus far: Limits to Groi-,th, Towsrard Global Equilibrium,
and The ri.cs of Growth in a Finite ti orlcl. He helped conduct a
systems dynamics tutorial se, ina or a.M'VI'O group (sponsored through
the IN~NFO science activity) and will conduct a two week seminar in
systems dynamics at Dartmouth this Fall. for senior government officials.
During his 14 months at Dartmouth he has initiated the establishment of
a Research Center which will emphasize systems dynamics applications,
not further theory development. He noted that the methodology now
available is quite adequate, but that there was one area which was
troublesome, i.e., introducing (mapping) opinion, intuition, or
subjective judgments into the systems dynamics model in a systematic
manner. He is currently working along Delphi lines, but thinks Delphi
so slow and cumbersome that it is di.ffucult to maintain participant
interest.
Prof. Meadows described a number of current activities reflecting
the growing interest and application of systems dynamics methodology.
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In addition to the teaching, the Research Center, and the seminars
previously mentioned, Meadow's group is developing a regional model
for Vermont (the Vermont government is apparently very receptive and
an interested sponsor is supporting the work), and P. more extensive
study is being outlined dealing with the total U.S. energy resource
problem (some partial studies have been done in the past, e.g.
"The Discovery Life Cycle of a Finite Resource: A Case Study of
U.S. Natural Gass," by Roger F. Naill (who is currently with Meadows
at Darn mouth) in 'i'ow,ward Global Equilibrium). An International
Conference (seminar?) in systems dynamics is being organized to
be held at Dartmouth this year. Broad interest and attendance is
anticipated.
Others briefly contacted at Dartmouth were Roger Naill and
Prof. Meadow's secretary, Donna Brown.
Pugh-Roberts Associates
Pugh-Roberts Associates, Inc. 5 Lee Street, Boston, Mass.
a
This consulting firm was established ten years ago by two of
Professor Forrestex's MIT colleagues: Alexander L. Pugh III, who
developed the DYIND,I1:O program generally used in systems dynamics, and
Dr. Edward B. Roberts, an early student of Forrester's who remains,
like Pugh, on the MIT faculty.
Our discussions about Pugh-Roberts capabilities were with
Henry B. Well, Vice President, and Gary B. Hirsch, Senior Consultant.
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Although the fir-in is small (about six full-time professional
staff) the Qualifications of the staff is excellent--probably unique--
with respect to systems dynamics background and practical application
experience.
Pugh-Roberts is clearly opposed to undertaking work in which they
take over a problem, design and test a ai odel, and crank out comparisons
of alternative policies. I'lley see their role as limited to first
assuring a working level of competence in systems dynamics in the
organization they are assisting, and thereafter providing advice and
assistance to the organization as it develops its representation,
or model, of their problem. They feel that this approach best exploits
their expertise in systems dynamics and the expertise and experience
of the organization in identifying the important parameters and
relationships in the problem to be studied.
They have conducted one week seminars in systems dynamics to
provide a rudimentary knowledge of the methodology, and they have
worked on a wide variety of economic, social, regional, etc., model
development programs. They have done extensive work in extending
DYNAMO, e.g. developed proprietary enhancements of DYNAI\IO, developed
a gaming simulation language, and developed a FORMAN' precompiler for
DYNAMO.
They provided brochures describing the company's past experience
in detail, resume-s of the staff members experience, and ball-park
estimates of consulting and CPFF fees for assisting in the conduct
of courses or model development.
Jay W. Forrester
Jay W. Forrester, Professor of Management, Sloan School of
Management Massachusetts Institute of Technology, Boston, Mass. 02139,
Prof. Forrester was most
cordial, willing to assist, enjoyed passing along his philosophical
concerns with his technical opinions, and gave no indication of
wanting to terminate our visit until he had to leave to attend another
meeting. Tea and cookies appeared after about an hour of discussion.*
Prof.. Forrester is the inventor and principal developer of the
systems dynamics methodology. With him throughout our discussions
was Naren K. Patni who Forrester introduced as, "MMMy colleague." I
believe that Patni is President of Wright-flllen Press, the publisher
of most of Forrester's books, and he is also identified with the
Forrester Consulting Group, Inc.
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Prof. Forrester reviewed the tentative course outline and suggested
a feti; revisions. In particular, Forrester feels that it is important
to instill early in the course the notion that the systems dynamics
methodology leads to new perspectives toward systems that cannot be
achieved through conventional approaches. lie gave some examples of the
slow, but eventual, acceptance of the methodology by various people and
groups with which he has dealt. He reconunended that efforts be made to
instill the notion of the new perspective concurrent with the develop-
ment of illustrative applications during the conduct of the course.
In regard to assistance in the conduct of a course, or later
consulting assistance, Forrester pointed out that the requests for
such assistance are now heavy, and becommi.ng more so--there just aren't
enough good people with e e ence to o around. He suggested that
we might like to consider
Forrester was especially interested in the need of the Agency
for long range outlooks--say, 10, 20, or 30 years-- His long
experience has convinced him of the necessity for paying more attention
to the longer range h-pact of present policy decisions. He said,
for example, that the notion that political leaders and depressed
minorities would consistently opt for the short term gain over the
long term consequences just ti,=asn't true--that, in fact, these groups
generally turned out to be the most enthusiastic supporters of the
realism provided in systems dynamics analyses--even though the
methodology wasn't understood very well.
Professor Forrester is concerned about the need, therefore, for
an institute dedicated to training Congressional staffers, senior
civil service, and other goverment managers and executives in the
possible uses of systems dynamics. We mentioned the Federal Executive
Institute as one possibility that he might like to consider as a
source of-support for such work.
At the present time Professor Forrester is heading a group
developing a comprehensive, detailed model of U.S. economic growth
with particular emphasis on inflation. The work has been supported
by the Rockerfellow Fund (Foundation?) and should be in the initial
test phase by this Fall. Forrester described the model as having
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about 30 to 40 times the detail of the world dynamics model.--and this
gives him concern. He said that even the world dynamics model with
its high level of aggregation was still too complex for many to grasp,
and consequently he believes that the U. S. model will reach only a
limited audience. Of special irmporta nce, the model is designed to be
generally applicable to any country providing the necessary parametric
adjustments are made.
In response to a question about the development of universal,
or generalized, models, Forrester stated. that he thought such
developments could be very useful in comparing different national
economies, etc. since the use of corar,on models would serve to focus
attention on the basic elements responsible for the differences in
economic growth, performance, etc.
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Toward a Science of Social Forecasting
Reprinted from the Proceedings of The Notional Academy of Sciences
Vol. 69, No. 12, pp. 3828-31331, December, 1972.
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Toward a Science of Social Forecasting*
rroduction
,)day the United States is searching for improved policies
is energy production, population growth, rural developnent,
t ;orne distribution, foreign relations, and other important
ycial areas. It will take decades to work out such policies and
r implement then, and decades more to assess completely
icir consequences. Should the policies prove ineffective or
udesirable, the process of revision will require still more years.
In spite of these delays, the political and economic in-
itutions that make most social choices are structured to give
I. tie weight to the consequences of their actions more than
few years into the future. Politicians at-2 mainly concerned
ith those outcomes of their decisions that may appear before
ie next election. The normative and descriptive models of
it economy generally disregard the delayed, nonlinear, and
reversible nature of the consequences that may derive front a
alicy. As a result, most of our society's actions are based
L;;.plicitly upon a concern for only the next 5-10 years.
This myopia is reflected in the lack of any systematic
fort to develop a comprehensive view of our society's long
rm evolution. The Council on Environmental Quality re-
fitly conducted an informal survey of forecasting efforts by
>vernment agencies (1). The survey found that some agencies,
ch as the Council of Economic Advisors, make no attempt
comprehensive projections of social and economic changes
rare than 5 years into the future. Interestingly, the Soviets
Eve assigned an economist to make comprehensive forecasts
the United States' society in the year 2000. However, this
3taomist complained recently that he is the only specialist
his institute who has been unable to find a counterpart ill
c United States.
If an ocean liner takes 5 miles- or more to change course,
to cannot successfully steer it on the basis of information
dy about obstacles a fear hundred yards ahead of it.. In-
cad, radar or some other mechanism must be used to pro-
c.t the course and the speed of the ship well ahead of its
ininiun maneuvering distance. Because it may take 30
1'his disco=lion i.-;abstracted from a presentation on forecasting
ethodulogies 1)(-fore the Cununitlcc nn Science .Ind Public Policy
the Natinnal AI:;!d(mv of tieiclicc's.
years or more to alter the course of economic, social, and po-
litical institutions, society also needs some form of projective
process which will indicate necessary changes well in advance
of 'the time they must actually be effective. We need to de-
velop a social radar function that encompasses the full set of
important interactions and whose time horizons are commen-
surate with the inertia of our institutions.
During the past 2 years I have directed a group of scientists
and students at M.I.T. in a preliminary- forecast of the long-
term consequences of global population growth and economic
development. Drawing on that experience, I want today to:
(i) Describe the cause for concern over the lack of adequate
long range social forecasting methods.
iii) Indicate several minimum requirements for the new
forecasting techniques we need.
(iii) Point to some of the unanswered questions about the
mechanics and the ethics of the process through which formal
models of social systems are used to influence the develop-
ment of social policy.
I hope I will leave you with the impression that the develop-
ment of improved methods for long-range social forecasting is
a legitimate and urgent area of scientific investigation.
Three characteristics of the global system
The resuu.s of our research on current growth patterns are
summarized elsewhere (2). The basis for our conclusions can
be found in three dynamic characteristics of the human
socioeconomic system. These characteristics emerge most
clearly when the globe is viewed as a whole, but they are also
true for each individual nation.
First, most physical attributes of the global system are
characterized by exponential growth. Population, mineral
resource consumption, pollution generation, and food prodrtc-
tion are all examples of major global elements that are cur-
rently growing exponentially at rates unprecedented in
human history. Current rates of growth would lead the world's
population atld food production to double in about 31) years;
annual rates of resource consumption grid pollution generation
would double ill 17 and 13 year.,, respectively (3). Of course,
(IU?reut grnlvth may nut continue at. such rates. Nevertheless,
it remains true that numerous social institutions promote and
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 -prof !,by physical growth, and it is unlikely that global growth the chemical declined linearly to zero by the year 2000, levels
rates-will change very rlpklly. of DDT in marine fish would continue to rise for about 10
Secon(l, the earths nniteA 64e 4 rnvt'RZeidAe 19005/03/3rbbteGIAtRMfr3$12M{?i6}&3)$RPcQQIU IAQQ2 ?1 1995, arul
i
capac
ty of the ecosystem to absorb material emissions place.
some limits to material growth. Should the unabated growth
of any plhy-su (d quafltity p-ess on one of these limits, it could
impose tuincceptable costs on the global society. The concept
)f a limit to material growth is imprecise, for the nature of
my limit depends in a complex fashion on the available
I echnology, and on the magnitude, composition, and geo-
;raphical distribution of the existing material flows. ' ever-
heless, most people accept as axiomatic the motion that no
Material quaitity can continue to grow indefinitely on a finite
,lanet. Any' sustained material growth trend will eventually-
leplete a finite resource stock or precipitate the collapse of
ogle important natural ecosystem.
To state as an axiom that material growth must stop is not,
?f course, to suggest that human progress must stop or even to
apply that global economic production must eventually
tagnate. Ilunian activities include many functions that are
of material intensive. Education, basic research, athletics,
ocial development, and cultural activities of all kinds can
ontinue to expand more or less indefinitely, even of ter the
se of materials comes into balance with the finite environ-
rent.
Third, there is typically a very long delay in the effective
~sponse of society to any problem associated with material
aid population growth. The delay arises in several ways:
(i) It may take many years for the growing quantity to
Toss a threshold above which its costs begin to outweigh its
enefits.
(ii) Because our information about the functioning of coin-
iex systems is incomplete, several years may elapse before
e cause of the increasing costs is perceived.
(iii) Since there are both costs and benefits associated with
oast activities, and since different individuals, institutions,
nations generally receive the costs and benefits unequally,
will often take many years to obtain agreement on the need
respond to some problem.
(iv) Once action is agreed upon it may take years to de-
rlop alternative technologies or to make the economic in-
+stments and institutional changes needed to reduce the
agnitude of a material flow.
(v) Finally, the physical and biological processes of the
,)be have a certain inertia. The response of the environment
a change in man's materials use is not immediate.
The global response to DDT u-age illustrates the nature
t:l the magnitude of these delays. The global use of DDT as
insecticide was initiated in 1940. It took several years for
is level of use to rise to the point where observable biological
Wage began to occur to species other than the target pests.
rt until about 1960 was significant public attention focused
possible harmful consequences of widespread DDT use.
en in the Unitcd States, where economic and technical
-tors favor the use of alternative pest control methods, it
taken until 1972 to ban DDT from most uses. Poorer
i ntries are -,till very far from adopting similar harms. Finally,
nr when DDT usage begins to decline, its levels in the
rifle elivironnlent will continue to rise for several years
?ause of the delays in transmission and degradation of the
would still be present in significant amounts in the year 2020
(4).
Similar delays exist in most other sectors of our global
system. For example, after more than 20 years of strenuous
development, fission power sources still provide only a frac-
tion of 1% of the total United States power deeds. Even after
the average family size declines to replacement level, about
two children per family, it will take the population 70 years to
stabilize.
These three dynamic characteristics of social systems a
rapid rate of physical growth, limits to physical growth, and
long delays in social response to changing conditions, have
serious implications. Any engineer would recognize those
three conditions as sufficient to introduce a pronounced ten-
dency toward system instability. A growing system charac-
terized by these three conditions will tend to expand beyond
its ultimate limits, in-a behavior mode we call "overshoot,"
and eventually fall back to a sustainable level. If, during the
period of overshoot, the overloaded resource base'is consumed,
eroded, or otherwise degraded, the final sustainable level may
be greatly decreased.
Possible ways to reduce instability
The above analysis indicates three possible ways of decreas-
ing the instability of our growing socioeconomic system,
one directed toward each of the three dynamic characteristics
that produce the potential for instability.
One approach is to raise the effective limits to population
and economic growth through technologies that allow more
efficient use of resources or create less harmful impact on the
environment. Such technologies can easily- be envisioned and
some have been developed, although historically technologies
have usually been developed to meet other goals and have
tended to be environmentally destructive. Raising effective
limits by technological advance does not make the system
inherently more stable; in fact, it may ultimately make the
magnitude and the consequences of an overshoot more severe.
Hoil ever, technologies - that conserve materials would pro-
vide time to make more permanent system adjustments;
therefore, such technologies are to be encouraged.
A second approach to system stability would be to decrease
the rate of physical growth, through deliberate social and
economic flanges. The goal of such a process would be a
stable population and an economy based on a constant flow of
energy and materials. Ultimately, ending growth is the only
viable policy on a finite planet, but it is an extremely long-
term policy, which can only be planned and implemented on a
time scale of 50-100 years. Thus, while this approach should
be adopted, it must be augmented.
A third way to decrease the probability and magnitude of
a physical overshoot is to reduce the length of system delays.
This approach has only a limited range of application, since
many physical and biological delays are fixed--for example,
the time it takes for populations to age, pollutants to he
degraded, or radioactive materials to decay are essentially
outside of cur control.
Ilowever, many social delays-could be circumvented if
?mical. One study suggests that if we were to begin de- policies could he based on anticipation of me ial needs, rattier
asing the use of DDT today so that global application of than on responses to them. Today, we typically- evaluate a
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 policy by examining the costs and benefits it has yielded in Interdisciplinary factor., are not constant and cannot be
the past. Were we to shift from historical analysis to projec- excluded frorn~,, 1l' t y, the vocabu-
tive plarutilr? we would Ap dved ibutl llF ESt~I #E 'tItQ3/30 l,1r*l 8IT1 l a a tc:il0ru we s0 !one profession
could be expected 20 or more years from now if a new policy are generally not shared by others. Interdisciplinary re?earch
were implemented. With the availability of suitable projective has often faker the form of one person acquiring information
techniques for evaluating the future costs arid benefits of a from many others, then attempting to distill out everything
decision, the projective approach would serve to decrease relevant to a particular problem, and finally incorporatin ; the
many of the social respon c delays in the system, accumulated informations into an analytical methodology
Of course tentative efforts are already being made to de- from his own field. The inescapable preconceptions and value:
velop inlpinved forecasting methods. There is a significant inherent in any one professional's outlook on the world make
difference between the "try it and see" attitude implicit in the that approach far less than an optimal procedure. We need
decision to use DDT back in 1940 and environmental inn- general methodologies that can be understood and used by
pact statements we now require before certifying new pesti- people from many different professions.
tides. Unfortunately, in spite of recent efforts, most areas of Third, we require a philosophy of systeni structure that
social decision making still use no formal long range assess- acknowledges the complexity, the nonlinearities, the delays,
merit techniques in choosing among alternative policies. This and the tenuous causal relationships that determine the be-
is true, at least in part, because we have no generally ac- havior of real-world systems. Associated with that philosophy
cepted techniques for projecting the social consequences of should be analytical techniques that can accommodate such
our policies. Therefore, given the fact that our policies do mathematically difficult relationships.
have important, long-term implications for our social, Finally, we need a new theory of inference and a set of
economic, and ecological system, we should assign a high formal techniques that will permit analysts to assess the con-
priority to developing the appropriate forecasting method- fidence that may be assigned to conclusions derived from
ologies. complex, nonlinear, imderidentified, simulation models. At
Requirements for a new forecasting methodology the moment, we have well-developed procedures for asses-
sing confidence intervals only for the results of a limited
To be useful, new social forecasting methods must have several set of models based on some rigid mathematical prerequisites.
features. First, they must be able to integrate into one con- These procedures cannot be applied to the nonlinear and conn-
ceptual framework information that ranges in precision plea models needed to represent the total behavior of large
from intuitive perceptions to controlled measurements of social systems.
physical systems. There already exists a great amount of in- In the absence of formal validation techniques, we rely on
formation about the determinants of long term societal evolu- the qualitative and subjective interpretation of sensitivity
tion. However, our confidence in the-vations pieces of that analyses to determine whether the results of a model study are
information varies widely, perhaps by several orders of maglti_ insensitive to error. When it is found that no member of a
tude. 'Many of our current analytical methods require data reasonable set of changes in underlying assumptions leads to
that are more numerous or more precise than those typically different conclusions, then it is declared that more confidence
available. These methods are thus unable to deal with many can be placed in the model. This is not a satisfying mode of
of the more important long-term problems. validation for someone who has come from a background in
If we wish to understand the behavior of total systems, we the physical sciences, and it is a poor basis for social choice.
cannot ignore several relevant areas simply because the data The validation techniques we need are probably some com-
are in a form that cannot be handled by our particular methods bination of formal control engineering methods with the
of analysis. Social changes come through the interaction of statistical formalisms that have been developed in the field of
demographic, economic, technical, cultural, and other factors. econometrics.
When we ignore elements in one or more of these areas, we It is important to recognize that methods which will meet
may overlook the fundamental cause of the problem. Instead, the above requirements are not simple extensions of tech-
we should incorporate into our studies the best information niques Currently used in the natural sciences. The natural
available, whatever its form or precision. Of course, care must sciences have advanced through reductioliisln by isolation
also be taken to test the potential impact of errors in the data of individual elements of a system, control of exogenous
on the conclusions derived from the analysis. influences on their behavior, and then systematic variation of
Second, the analytical frameworks we need should provide a few "independent" variables to measure their influence.
a neutral vocabulary that permits professionals from many- There are very few truly "independent." variables in social
different fields to cooperate directly in pooling their knowledge, systems, and the problems of interest often come from the si-
No demographer, no economist, no political scientist, no multancous interaction of all the parts. The techniques we
Dnirineer can snake by himself the forecasts we need. The be- require must be holistic-based on the recognition that social
havior of social. systems conies from the interactions among change does not depend on the attributes of a single factor,
variables that are included within the bounderies of many but on the interaction of many.
Iiffercnt traditional disciplines. To study short-run phenoni-
'lla, profess ill:lls ill one discipline often call usefully Coll- Models and the process of social choice
icier most of the influences from factors outside their dis- Even when we have developed modelling nnethods with the
ipline to be exogenous or constant, and then they can restrict above characteristics, we will riot have provided society with
heir study only to the fac?tor; within their area of specialty. an effective social radar. Tine'nahtrc or huni:u- and social
.)ver the longer ran, however, the interaction., of real systems decision making will prevent, any form of formal model from
ail to conrfirn? tllenn.elves to aim's artificial boundaries. directly making decisions, Policies '16C set 1 ecisiorts are
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 made tltruualt the interaction of many individuals as they Estimating model coefficients
assess the possible consequences of alternative actions and (10) How can we improve the process through which
compare the expected co:pPg ,defstpr4 d#2 sLOidWS/03/3Drttl [ -R[#IRB2MOOSt3i11R6(lG4i00:1120&ur8rneuts out the
outcome. Fornt:Wnlodels can only assist in the first half of
that decision process, establishing what could be. Deciding
what should he-i.e., exercising social values-will remain the
perogative of individual-, and the institutions that represent
them. Thus, we must view the nature of social decision mak-
ing, even with vastly better models than are available today,
as a process through which the formal model of the system
analyst complements the value system and verbal models of
the decision maker. Using verbal model, oci.tl policy makers
may identify appropriate problems. With formal models,
system anal ysti may determine the possible consequences of
alternative responses to the problem. Finally, the subjective
judgment of those involved in the outcome can be used in
picking from the possible outcomes those that most satisfy
social goals. This cooperative process between verbal and
formal models involves nurny stages that are still poorly
understood. Thus, an important focus of research on im-
proved models would be the process of model development
.and use.
The above comments have been general in nature. To con-
elude this statement, I would like to present a specific agenda
for research, one I compiled while working with several sys-
tern analysts from the United States, Europe, and the Soviet
Union, to identify the unsolved problems in developing and
implementing improved social system forecasting techniques.
The questions pose a challenge to all who are interested in
increasing man's understanding of his own complicated social
systems.
QUESTIONS ABOUT MODEL
DEVELOPMENT AND USE
Managing model construction
(1) How could one categorize social goals to obtain a list
of questions that could be addressed through simulation
model studies?
(2) Is there any set of personal characteristics that one
;could use to identify persons who are more likely to make
useful models?
(3) Is there a typology one could use to decide which kind
of models a, specific decision maker might find more useful?
(4) What rules can be used to manage a large team of
scientists in the efficient construction of a model that requires
*np' is from several different disciplines?
:Designing the model
(5) A model on the computer interacts with mental models
of the analyst and the client. What procedures and hardware
would best facilitate this interaction?
(6) What formal rules can be used to decide whether a
given model should be more or less aggregated?
(7) how can hierarchical techniques be used to develop
a set of models that deal with related aspects of the same
system?
(8) What is the most efficient way to identify that part of
the model which is most in need of improvement?
(9) \Vleat formal procedures can be used to use sensitivity
analyses acrd information on time statistical properties of tlce
coeflieients in the model to provide an objective measure of
confidence in the nrrnlel results:'
real world?
(11) When expert opinion is the best available source of
information on model relationships and coefficients, how does
one evaluate the relative utility of alternative experts. and
how does one develop the "best" coefficients from the opinion:
of several experts?
(12) What precautionary measures must be used when
linear statistical inference techniques are used to estimate
the coefficients of a nonlinear model?
(13) What places does a computer model potentially have
in the total process of individual or societal decision ntakiag?
(14) We must recognize that the analyst and his model are
both part of the system the analyst is studying. What ethical
and procedural rules should govern the use of models to ad-
vocate some change in social policy?
(15) What are the cost/beuefit implications of advocating
change in an existing social system on the basis of current
models, rather than waiting until a better set of models is
available?
(16) How does one include in the model the indices of per-
formance which will permit the decision maker to pick the
preferred of several alternative system behaviors?
(17) blow can the decision maker identify the best of several
alternative models?
Until recently it has been possible for most individuals,
particularly natural scientists, to regard social systems as
outside the realm of predictive science. However, the avail-
ability of coriiputers that can handle complex models and the
urgent need to put current actions in the context of their
future consequences suggest we should change that attitude.
Relatively little effort is now invested in the development of
long-term forecasting methodologies, yet the effectiveness of
many current decisions will be impaired without a longer-terns,
view. The requirements and questions posed above are subject
to systematic investigation. Certainly the fruits of the re-
search could equal that from other areas of scientific endeavor.
It is time to begin in earnest the development of improved
social forecasting tools.
1. Council on Environmental Quality (ed.) (1972) Summary
of Long-Range Forecasting Activities Performed by the Federal
Agencies, August 11, 1972, Interagency memorandum.
2. Meadows, D. II. ct at. (1972) The LinciI to Growth (Universe
Books, New York); Meadows, I). L. & Meadows, D. H.
(eds.) (1972) Toward Global Equilibrium-Collected Papers
(Wright-Allen Press, Boston, Mass.), in press; Meadows,
D. L. et at. (1972) The Dynamics of Growth is a Finite World,
forthcoming.
3. The U.S. Bureau of 'Mines projects that the world's primary
demand for minerals may increase annually by
This forecast is equivalent to a doubling time of from 20 to
13 years. U.S. Bureau of Mines (1970) _llinrrctl Facts and
Problems (U.S. Government Printing Office), p. 3; [Time
series on pollution emissions are poor or nonesistalk t ill most
cases. liowever, energy production and, therefore, thermal
emissions are crude but useful indices of overall pollution.
Thermal wastes were projected by the SCE I' study to in-
crease gloliMly by 5.7% per year. (1970) .hum's Impact Olt
the Global Enc?irontnrnt (M.I.T. Press), p. 61.1
4. l;:utders, J. (1972) "System Simrtlation to 'l'est. Environ-
nccrttal Policy: A Sample Study of 1)1)T 1mfovucncret in the
l nvia,iuinent,'' International Journal of I:nriroairnntal
St tidies, Lund am, l'.11?1;cnd, November 1972.
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A Summary of Limits to Growth -
its Critics and its Challenge
Donella H. and Dennis L. Meadows
This discussion was originally presented at Yale University, September, 1972,
in the School of Forestry's symposium on limits to growth. An extended
version of the text appeared in Futures, February 1973.
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Introduction
Over the past two years we have worked with a group of scientists and
students to understand the long-term causes and consequences of growth in the
globe's population and material output. From our research we have been led to
conclude that current growth rates cannot be sustained even for the lifetimes
of the children being born today. If society maintains its current reliance on
growth to solve short-term problems, we believe that population and material
production will grow past sustainable limits, that the carrying capacity of
the earth will be eroded, and that there will then be an uncontrolled. decline
in population and economic activity. However, this outcome does not appear
inevitable. Mankind could instead begin to assess realistically the limits to
material growth. Society's goals and instituions could be altered to
reduce growth now and to move ultimately towards an orderly accommodation with
the finite constraints of the globe. If these changes were made, it would
probably be possible to sustain the world's population more or less indefinitely
and to provide for all its basic needs.
Our view of growth and its consequences were developed through the constructs
of Wcrld3, a mathematical model of the physical, biological, psychological,
geological and other causes underlying growth. Many objections have been raised
to our approach and results. in this presentation we would like to describe the
history of our work, to summarize the basic foundations of our thesis, and to
respond to the most common criticisms of our conclusions.
Historical Summary
With the publication of World Dynamics l, Professor Jay W. Forrester
challenged the world's scientists and decision makers to extend their time
horizons and to examine in holistic fashion the long-term causes and consequences
of growth in the world's population and material output. To contribute to analysi.
and understanding of global problems Forrester proposed a formal model of the
interactions among population, capital, and several factors that influence their
growth: food, resources, and pollution. Recognizing that his model was not
perfect or complete, Forrester emphasized that no perfect or complete model
exists, and that the models on which decisions are now based are not even
explicit enough to be discussed and improved:
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In spite of the tentative nature of the world model described here;'
various conclusions are draw from it. Man acts at all times on
the models he has available. Mental images are models. We are now
using those mental models as a basis for action.
It is hoped that those who believe they already have some different
model that is more valid will present it in the same explicit detail,
so that its assumptions and consequences can be examined and compared.
To reject this model because of its shortcomings without offering
concrete and tangible alternatives would be equivalent to asking that
time be stopped.
(World Dynamics, p. ix)
In order to facilitate the development of improved long-term global models,
our group has since prepared three additional documents on the dynamic implications
of physical growth in the global system. In World Dynamics, Professor-Forrester
described the basic objectives of the world modeling effort initiated by the
Club of Rome and presented the structure of a preliminary model called World2.
This model was subsequently expanded by our team'and related more thoroughly to
empirical data. The revised model was called World3. (Henceforth, when we are
discussing a point that applies to both World2 and World3, we will speak simply
of the World models.);
In Limits to Growth, we described several attributes of growth in population
and material output; attributes that give the world system a tendency toward
unstable behavior.2 We proposed material equilibrium as a sustainable alterna-
tive to the goal of perpetual growth that is the implicit basis of most
contemporary policies.
Thirteen short papers that discuss the history and the implications of our
project and that describe the detailed simulation submodels underlying the
World models were published in the technical.'.iterature. They have now been
collected into a third book, Toward Global Equilibrium: Collected Papers.3
Our technical report, The Dynamics of Growth in a Finite World, is the
fourth and final report on our work for the Club of Rome.4 This technical
report presents the assumptions, equations, and data underlying World3 and
analyzes the model's behavior under alternative assumptions.
Foundations of The Limits to Growth
The Limits to Growth (henceforth referred to as Limits) deals with fundamental
properties of the world system such as exponential growth, finite limits, and
feedback delays. These properties are the real basis of our concern about
physical grow t
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precise'numerical assumptions of any model. In fact it was to call attentio
these dynamic properties, rather than the model equations, that we presented
to a nontechnical audience in a publication separate from the technical mode:
description. We shall summarize here the five main points from Limits and
discuss critical responses to them.
1. Exponential ctroath is an inherent property of population and industx
capital but not of technology. Population and material capital grow exponent
by the very nature of the reproductive and investment processes. This is not
an arbitrary assumption, it is a fact derived from empirical evidence and
knowledge of underlying causes. New people can only be produced by other peo;
and machines and factories are needed to generate other machines and factories
Whenever the change in a quantity depends on the quantity itself, the change
tends to be exponential in form. The numerical exponent, or the rate of growt
varies, both in the real world and in the World models. The growth process is
nevertheless, inherently exponential.
It may be true that human knowledge is also inherently exponential;
knowledge can aid in the accumulation of more knowledge. However, it does
not follow that any given technological application of that knowledge is
inherently exponential. To bring a new technical discovery into widespread use
requires social recognition of the existence of a problem. It may also require
that new institutions be established, often at the expense of the old, and that
investment be diverted from some other possible use into physical capital that
embodies the new techniques. Social perception and consensus, institutional
change, and the diversion of capital to new needs are not inherently exponential
Discovery of oil is not in the long run made easier by the fact that certai
fields of oil have already been discovered. The next increment of pollution
abatement is not directly facilitated by the increment that went before. One
doubling of land yield does not enhance the possibilities for the next doubling.
Any suggestion that these "exponential" technologies are inevitable is based on
a profound misunderstanding of the inherent cause of exponential growth. The
suggestion also implies a rather sweeping disregard for: the social basis of
technological change, the second law of thermodynamics and the law of diminishing
returns.
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2. There. are piysicai izmz s to popular-ion an capita grow he
World models are built upon the Malthusian assumption that the earth is finite,
and that some change in current exponential growth processes will thus be
necessary to aceomodate man's physical presence and activities to the earth's
limits. The purpose of the models is to investigate what kinds of changes
might and should occur. We chose to investigate a Malthusian view of a limited
world because our own impressions and much empirical data suggest that the world
is finite in several important ways. It seems to us not only more realistic,
but more socially responsible and more useful to investigate the ways in which
society might adjust itself to earthly limitations, rather than to assume away
all such limitations.
The World models express the idea of the earth's limits through four
explicit assumptions: there is a finite stock of exploitable nonrenewable
resources, there is a finite capacity for the environment to absorb pollutants,
there is a finite amount of arable land, and there is a finite yield of food
obtainable from each hectare of arable land. No one has exact information about
where these limits are. In fact it is probably impossible to express any one
of. these limits by a single number since they all vary with time. We know that
to a certain extent they are expandable by technology. We also know that they can
be reduced by misuse.
By attempting to represent the world's limits and the growth of the physical
system toward them we did not expect to gain any more precise information about
the location or values of the limits themselves. We did try to achieve two
other purposes. First, we sought a framework in which many growth processes
and limits could be considered together, to illustrate that solutions proposed
for any one problem related to growth are meaningless without considering the
system as a whole. The traditional approach 'of specialists in any one area, for
example, resource economics, food production, or environmental deterioration,
amply illustrates how easily any single resource, food, pollution, or population
problem can be mentally "solved" by assuming that sufficent capital, energy,
labor, land, material and time can be allocated to that one problem. Because
they are holistic, the World models force one to explore the possibility that
several of these problems-may have to be solved simultaneously. We are interested
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 in that Poovec~-Vo" 'le~99 /63'R30P RbR8Ql~i6O~r fl&~4{%JL2
pp QAR(Mh indicates
to us that these problems will not come slowly, one at a time.
Our second concern was to represent not only the forces that can increase
the earth's carrying capacity for human activity but also the forces that can
reduce it. From our Malthusian point of view, Western man is entirely too prop
to rejoice in his newly-irrigated land, underwater oil-drilling rigs, Green
Revolutions, and catalytic converters and to ignore the eroded, salinized,
or strip-mined land, the dumps of wasted resources, the depleted ore bodies,
the simplified ecosystems, and the deprivation of other humans in other
cultures that he leaves in the wake of his "progress". The World models
contain assumptions of possibilities for considerable future progress, but
they also take into account mankind's fallibility. They assume that the limits
can be pushed downward, as well as upward, by man's activities.
There are, of course, other limits we have not included in the World models
The most obvious omissions are the limits to the sustainable rate of use of
renewable resources - fresh water, timber, fish, and game for example. We also
recognized the importance of social limits, but omitted them from specific
analysis. We stated in Limits (pp. 45-46) that social limitations (unjust
distribution, waste, wars) would only decrease the possibilities for growth
allowed by physical limits. -
3. There are long delays in the feedback processes that control the rate
of physical growth in the world system. Delays are the main source of instabilit
in the global system. When rapid growth is coupled with a long delay between
cause and effect, the growth may proceed far beyond sustainable limits before
the effects that can stop it come into play. We have not assumed that mankind is
unresponsive to the changing situation around him. We have simply assumed that
social institutions respond only to situations about which they have information,
that the information they act on is often incomplete and late, and that the
social response is not immediate but is itself delayed. The response delay can
be caused by political, physical, or biological processes. It is increased by
the time required to invent/construct/test/perfect new technologies. Many
response delays are beyond control, such as the delays inherent in the population
age structure or in the propagation of persistent materials through the environmer
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The combination of three major assumptions causes the "overshoot mode"
of the models: the assumption of feedback delays, the assumption of limits
to the earth's carrying capacity, and the assumption that the human value
system will promote population and material growth until counteracted by very
strong forces. When, in the "equilibrium" mode, we assume a change in man's
value system in favor of stability and against sustained population and capital
growth, the overshoot no longer occurs. The overshoot could also be eliminated,
or minimized, by assuming that the society can avoid the implications of
delays by conducting accurate long-term planning. Of course our purpose in
publishing Limits was to encourage both the value-change and the long-term
planning processes.
4. There are two possible social responses to the limits to growth;
weaken growth forces or remove the symptoms of impending limits. The common
response of modern social systems to the pressure caused by limitation of any
resource is to remove the pressure so that growth can continue. Highways are
jammed; build more highways. Copper reserves are depleted; import copper.
Electric power is insufficient; develop nuclear power plants- People are
hungry; buy fertilizer.
It is only very'recently and very weakly that an alternative set of
solutions has been seriously proposed; reduce the use of automobiles, use less
electric power, extend the useful lifetime of material goods, have fewer
children. This second set of responses recognizes that the problem to be solved
is not scarcity of a specific resource; highways, copper, power or food. These
scarcities are symptoms, or signals, of the underlying problem; population and
material growth against a finite resource base. The first set of responses serve
to remove temporarily the adverse symptoms of growth. If they are not accompanied
by responses of the second-type, that weaken the social values causing growth,
further growth will eventually cause different resource scarcities. These
scarcities will call for additional technological solutions to remove the signals
of impending resource limits. The real danger of responses of the first type,,
responses that ease the symptoms of the problem is that they are often used to
discourage responses of the second type, those that control. growth itself. The
more successfully the signals of resource scarcity are masked and denied, the
more likely it is that the necessary social value change will come too late-
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technology. Combined with the necessary value changes that will control physi
growth, carefully selected new technologies can create magnificieent possibilit
for human society. We are, however, concerned that technological Successes
have almost invariably been used to enhance, rather than reduce, the strengths
of the positive population and capital feedback loops that drive the global
system. We do not oppose technology. We do oppose the present trend of
technological "progress" that is not only poorly guided by social wisdom or
restraint, but is used as an excuse not to develop that wisdom or restraint.
5. The equilibrium state may be a desirable option, wherever the limits
to growth may be. It is riot necessary to agree with the' World models or to
believe in the imminence of any physical. limits to growth to become intrigued
by the nature and potential of an equilibrium state. An equilibrium state is
a society that has stabilized its population at a desired level and that
supplies its material needs with a minimum throughput of nonrenewable, pollutic
creating resources. Limits ends with a rather Utopian description of such a
state. We sincerely believe that some form of deliberate material and
population equilibrium is attainable, not immediately,but within a generation
or two. We also believe that the exercise of understanding and planning how su
a state might work is both exciting and useful in that it might provide the
realistic, sustainable, long-term goal that is now lacking in nearly every part
of world society. it seems impossible to us that material growth can be
successfully controlled unless there is some well-defined goal towards which it
may be directed. There is no way of deliberately changing the composition of
growth or its distribution unless there is a clear vision of what growth is for
The specifics of the goal will change and develop as more is learned about the
world. We feel that it is only important to have such a goal and to keep it
consistent with present knowledge.
The idea of a physically non-growing society is so foreign to some people
that they have invested the idea with some strange mental models of their own.
They have suggested that an economy at material equilibrium must be stagnant
intellectually or technologically; that it must he rigid and dictatorial; that
it must preserve the present maldistribution of resources or income. We have
already suggested in Limits that we would expect just the reverse. We would
hope that more imaginative respondents will accept the challenge of thinking
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 through the A i'86@d4o le;id%ii ff3F D CFi ~-1 # ~ I~IOS ~'1~2~~A4 185- We
suspect that the exercise would be more than theoretical; that it would
illuminate some of the current economic and sociological problems- of a grGwiny
state as well.
We have not suggested in Limits or elsewhere that the equilibrium ste-te
should be attained immediately, or that physical growth should be brought to a
sudden halt. On the contrary we have pointed out long delays in the social
system and the necessarily gradual nature of demographic change, and we have
suggested that an orderly shift to equilibrium from present rates of growth
may take as long as 100 years. Thus although the first steps toward equilibrium
should be small ones, they should be taken soon. A good beginning might be a
-common recognition that physical growth cannot be forever substituted for'the
social resolution of difficult choices.
In summary, we believe the basic points of our modeling effort, as
described in Limits, merit consideration even though none of them can be supported
by rigorous proof. No social model can be rigorously proved true. Together
these points constitute a holistic hypothesis about the world system that is
generally consistent with real-world observations. We do not believe that the
same can be said for the mental models on which important decisions with long-
term implications are currently based.
Price, Technology, and Values
Let us turn now to the three mechanisms that many critics of Limits believe
will allow mankind to sustain and control material growth without any changes
in the current system - price, technology, and social value change. All three
are actually included in the World models, but in implicit and oversimplified
form. Of course all three are important, complex, dynamic subsystems in them-
selves. We will describe here, very briefly, how more complete representations
of these subsystems might be constructed. However, none of the added details
would alter the basic conclusions of our work.
Economic price is a function of two socially determined variables---the
current value society places on a certain good or service and the
apparent cost of supplying that good or service. Economists postulate
that the long-term stabilizing role of price in a growing system is to signal
resource scarcity. They point out that price changes guide social values and
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the economic system so that the declining supply of a scarce resource is
utilized more efficiently.
When increasing scarcity causes the price of some material to rise,
nurrerous social responses may be triggered. There may be a more intensive
search for natural deposits of that material, or increased recycling of discardec
products containing it. Food shortages leading to rising food prices may
stimulate farmers to adopt more efficient methods of production, governments
to irrigate more land or people to eat less food. These dynamic effects of
the price mechanism will indeed influence the way in which a growing system
approaches its physical limits.
World3 contains several causal relationships between the real supply of
some economic quantity (such as food, nonrenewable resources, industrial
capital, service capital) and the response of the economic system to scarcity
of that supply (develop more agricultural land, allocate more capital to
resource production, increase investment rates). These relationships are most
realistically represented with price as an intermediate variable:
decrease in supply - rise in price----social response
In World3 we have simplified the real dynamics of the price mechanism by
eliminating explicit reference to price, the intermediate variable: The
representation of the causal chain has been shortened to:
decrease in supply
--~ social response
The ultimate regulating effect of the price system is thus included, but price
does not explicitly appear in the model.
The only purpose.of eclipsing the price mechanism in this way is to
increase the model's simplicity and understandability. Omission of price is
equivalent to assuming that the signals provided by the price system are availabl(
to social decision points with a delay that is insignificant on a 200-year time
scale. To check the validity of this omission, several of our submodels ex-
plicitly included price and its effects on technological advance and resource
availability. The general long-term behavior of these submodels was similar
to that of the World model's resource sectors.
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To the extent that prices do not immediately reflect actual resource costs
in the real world, the price system will be a source of additional instability
in the world system. Instability will also be increased if cost information
is transmitted im*.nadiately but to institutions that can adjust their production
or consumption patterns only after a long delay. In either case, the delay
between decreased availability and social. response will zeduce the stability
of the economic system as it adjusts itself to any limit. Thus by assuming
in World3 that the price system works instantaneously we have omitted a scarce
of system instability. To the extent that prices are actually delayed signals
of scarcity, our model will underestimate the tendency of real economic
systems to overshoot physical limits.
We view technology, like price, as a social phenomenon - it is the
application of man's general knowledge about the world to the solution of a
specific, perceived human problem. If we were to make a complete dynamic model
of the development of a given technology, we would include the following:
-a level of accumulating general knowledge, with the rate of
accumulatioi3 dependent on the resources devoted to basic research.
-a widespread perception of some human problem.
-an allocation of physical resources, human eifort, and time to search
for a technical solution to the problem, with a realization that the
solution may not be found if the level of knowledge is not yet great
enough.
-a delay to allow social acceptance and implementation of the new
technology, the length of the delay dependent on the magnitude of the
required departure from the present way of doing things.
- a representation of the total impact of the technology on the system,
including social, energy, and environmental costs.
.This model of technological advance might be contrasted with the one
advanced in separate papers by Boyd, Cerlemans, and the Sussex group.6'7'8
Each assumed that technology is inherently exponential and that the appropriate
technical capabilities are instantaneously available whenever needed. They
have supposed that technological advance costs nothing, requires no capital
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investment, has no harmful side effects, and encounters no resistance from
institutions already present. Not surprisingly, when their representations
of technology were inserted in World2, the model grew far beyond the original
point. of collapse. We would suggest that their theories of technological advan
are so completely foreign to anything available in the real world, that their
revisions of World2 provide no useful information whatsoever about the real
implications of physical growth in a finite world.
Nearly every causal relationship in the World models could conceivably be.
changed by some sort of new technology. In the past various technologies have,
directly or indirectly, improved birth control effectiveness, increased land
productivity, and increased the average generation of persistent pollution per
unit of industrial output. The advance of technology has created more costly
and destructive weapons, increased life expectancy through medical advance,
and hastened the rate of land erosion. it is by no means certain that
technologies will continue to do any of these things in the future, since the
human values and social institutions that govern technological development are
always subject to change.
In other Words, we view technology as socially-determined, discontinuous,
infinitely varied, and delayed. It is nevertheless an important determinant
of the functioning of the world system. How can such a concept be included
in a world model? Since so many causal relationships might be altered by
some conceivable technological change, we had to consider building technological
change into each relationship as we formulated-it. We did this by assigning
possible technologies to three categories; those that are already feasible and
institutionalized, those that are feasible but not institutionalized, and those
that are not yet feasible.
Some causal relationships have historically been altered by technology
and continue to be altered regularly today. These are in areas where there is
social agreement about the desirability of change, and where resources and
institutions to bring about that change are already integral parts of the system
Examples are medical technology to improve health, industrial technology to
raise production efficiency, agricultural technology to increase land yields,
birth control technology to plan family size, and mining technology to discover
and exploit lower-grade nonrenewable resources. 11 significant fraction of the
world's people have adopted the value system that will continue to l.roLnotc the-se
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technologies as long as their costs can be afforded. They are effectively built
into the world socio-economic system. Therefore, they are also built into the
relationships of the World models, with the assumption that they will continue
to develop and spread through the world, without delay, as long as there is
economic support for them.
There are other technologies that have not been so widely accepted that
they can be considered a functioning part of the world system. It is not yet
clear that all the nations of the world are willing to institutionalize and
pay for technologies such as pollution control, resource recycling, capture
of solar energy, preservation of soil fertility, alternatives to the internal
combustion engine, or increased durability of manufactured goods. All of
these technologies are feasible, and there are signs of the social value changes
necessary to incorporate them into the world system. It is not possible to knew
when or even whether they will be adopted on a worldwide scale. Therefore we
have not assumed them in the model relationships, but we have included many of
them-as optional functions, which a model operator can "turn on" at any specified
time in the future.-- The model can be used to test the possible impact of any or
all of these technologies and the relative advantages of adopting them sooner
rather than later.
There is a third set of technologies that is not included in the model at
all. That is the set of discoveries we cannot possibly envision from our perspec-
tive in time. Of course no model, mental or formal, can incorporate these
unimaginable technologies as they will actually occur. That is one reason why
no model can accurately predict the future. Any long-term model that is being
used to aid the policy making process must therefore be updated constantly to
incorporate surprising discoveries as they occur, and to assess how they may
change the options of human society.
It is possible, of course, to include in the model the assumption that some
unimaginable discovery will come along in time to solve every human problem,
including the limited resource base of the earth. Many mental models seem to
be based on that assumption. However, our bias as both modelers and managers is
to search for understanding and for better policies based on the constraints of
the system as it appears now, not to rely on developments that may or may not
come in the future.
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 Lr'aA a~civ Ee~i el ~DQ5 3 t~h'~i~.` j i ~2 dynamic
elements directly dependent upon the values, needs,and choices characteristic
of the human society. Of course values underlie many of the other dynamic
elements of interest in a model of physical growth. In fact the whole socic-
economic system might be thought of as a constant interplay of human desires
and goals within physical and biological constraints. Therefore, although the
World models are not intended to be models of social value change, they must
contain some assumptions about the dynamics of Truman values insofar as they
influence and are influenced by the processes of physical growth.
In the difficult task of modeling human values we have tried to include
only those most basic values that can be considered globally common. These
basic values begin with requirements for survival, such as food,.and.go on
to include a hierarchy of other desires; for longevity, children, material
goods, and social services such as education. Some of these values are
represented explicitly in the model as variables that have an important influence
on economic decisions. Examples from World3 are desired completed family size,
.and preferences among food, material goods, and services at different income
levels. Others are included implicitly, for example in the allocation of
service output to health services or in the quantity of nonrenewable resources
used per capita.
All of the values included in World3 are assumed to be responsive to the
actual physical and economic condition of the system; they are all involved in
feedback loops. The patterns of dynamic value change included in the model,
however, are limited to the patterns of change historically observed in
individual countries over the last hundred years or so. During that time the
major force behind value change in the world sytem has been the process of
industrialization, a process that is still underway in most of the nations of
the world. Therefore the values that both shape and respond to the development
of the model system follow the historic pattern of industrialization. As
industrialization increases in our model (measured, say, by the level of
industrial capital per capita) the aggregate social demand in our model shifts
i? emphasis from food to material goods and finally to services. Other changes
occur in.the model in the preferences for children, education, and health care,
and in the distribution of various goods and services throughout the industrializi
population.
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We have not built into World3 any global shifts in values other than
those that might be expected to take place as the world becomes more industrialized.
Again, the model cannot predict value changes, but it can serve as a test device
to show the results of any given assumption about the future evolution of values.
f!uman values, like human technologies, may evolve in the future in directions we
cannot possibly foresee at this mordent in history- Therefore we have also
included, in several model relationships, test switches that can be used to
activate postulated value changes at any date specified by the operator.
(Examples of such changeable values are desirr.d family size, fraction of output
consumed, and the relative desires for food and services. All of these are
changed to produce the model's "equilibrium" runs) We have used these
switches extensively. As we demonstrated in Limits, an appropriate set of
value changes can bring the model system into a stable and desirable equilibrium
state. That set of value changes is not one that has occurred historically as
a result of industrialization in any country. We believe that such value
changes-are possible to achieve in the future, but only by a concerted and
conscious effort. The shift in values that normally accompanies industrialization,
the one we might ex c.t to take place if the world continues, "bus- ness as
usual", is the very value shift that leads to the overshoot and decline behavior
mode.
The Modeler and his Environment
It has been suggested that the World models arose only because of the
sudden widespread concern about the environment in modern western societies.
Of course computer models, like any product of man's intellect, must be evaluated
as part of the cultural context within which they are constructed. This statement
s also true for the mental models of the critics of Limits and for the models
it guide current public policy.
Every model of a social system must omit some details of the real world.
~.fication is the essence of model building. A model is constructed to
understanding of the nature and implications of complex relationships
-al. world. If the model were identical to the real. world in all.
it would be as difficult as the real world to understand.
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It is a very fundamental principle indeed that knowledge is always
gained by the orderly loss of information, that is by condensing
and abstracting and indexing the great buzzing confusion of in-
formation that comes from the world around us into a form which
we can appreciate and comprehend.9
Thus even if we had comprehensive and accurate information on all important
aspects of the real world, our models would be simplifications of reality.
Human judgment is inextricably involved in the choice of the issues
addressed by a model and in the identification of those "unimportant" details
that may be eliminated without detracting significantly from the explanatory
power of the model. Every model is thus inevitably influenced by prevailing
social values and goals. In short, there is no model useful for understanding
all issues and no "scientific" or "objective" way to construct a perfect model.
The greatest advantage of formal, or written, models over mental models
is that their constituent assumptions are precise and explicit and thus subject
to the scrutiny of critics. This is no guarantee against error or against the
effects of unwarranted social biases, but it makes the discovery of errors
and biases more likely. Most critics of Limits have not defined the bias that
underlies their own approach, nor have they presented assumptions explicit
enough to be judged by their audience.
The accusation that the World models have been unduly influenced by the
prevailing environmental concern seems to imply that the models are
addressing random, unimportant, or spurious issues. The latest wave of
environmentalism may indeed turn out to be a fad, - merely the product of rising
expectation, or boredom, or alarmist journalists, or all of these. However,
there is an alternate possibility. The current concern with the environment may
be a response to a correct perception of a changed external reality. It may
be a result of the first glimmerings of human understanding about total systems
and the first perception of a real worldwide negative impact of man's activities
on the ecosystem. If so, the World models may represent a small manifestation
of a healthy social reaction to an environmental change; a reaction that will
lead to new values, technologies, and economic prices that attempt to adapt
socioeconomic systems to the newly-perceived constraints. In that case the
critics, the technological optimists, the foot-draggers who claim that there
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are no constraints and no reasons to change values from the present pro-growth
set, represent exactly the social and institutional delays that tend to de-
stabilize the system and send it shooting past its ultimately sustainable limits.
Growth and Income Distribution
Some critics have rejected the no-physical-growth argument as irrelevant to
the "really important" problems of the composition and distribution of growth.
As we have already indicated, we find it impossible to view the rate of physical
growth, its composition and its distribution as independent or mutually
exclusive problems. Human societies will not achieve a more equitable
distribution of wealth until they better understand the processes of growth.
Historically at least, growth of population and of capital has been correlated
with the concentration of wealth and with rising gaps between the absolute incomes
of the rich and the poor. We believe that there are at least two basic reasons
for these trends. First, physical growth inevitably worsens the resource/
population balance. When there are fewer available resources per person, there
are also fewer real social options to resolve conflicts of interest. Second,
by relying on the false promise of growth, social institutions are able to
delay facing the very'important and difficult tasks of making social tradeoffs
.and defining social goals. Until these tasks are squarely. faced there will be
no real redistribution of income.
The no-growth argument is an appeal for readjusting the composition and
distribution of economic output. The pro-growth argument is an attempt to
postpone this readjustment; to confer it on future generations. Simultaneously
this approach ensures that those generations will have fewer resources and thus
fewer real choices to make. Our sociopolitical concerns are actually quite
similar to those who argue that redistribution must come first. We differ only
in our perception of how to deal with those concerns. Our own choice was to begin
by questioning what we view as the basic cause of the growing gap between the
rich and the poor - unexamined, uncontrolled physical growth.
V. The Concept of Man
This brings us to the final point that we regard as basic to all discussions
among ecologists, "environmentalists", Malthusians, economists, industrialists,
pessimists, and optimists. The pro- and anti-growth factions are organized
around two very different concepts of man.
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One concept of man, the one held by advocates of indefinite growth, is
that Homo sapiens is a very special creature whose unique brain gives him
not only the capability but the right to exploit for his own short-term
purposes all other creatures and all resources the world has to offer. This
is an age-old concept of man, one firmly rooted in Judeo-Christian tradition
and newly strengthened by stunning technical achievements in the last few
centuries.
Not only ingenuity but, increasingly, understanding; not luck but
systematic investigation; are turning the tables on nature, making
her subservient to man.10
According to this belief man is essentially omnipotent, he can develop at no
cost a.technology or a social change to overcome any obstacle, and such develop:mi
will occur instantly upon the perception of the obstacle. Underlying this view
is also the belief that mankind's social, economic, political, and technical
institutions operate flexibly and without error, and the best response to any
apparent problem is to encourage these institutions to do more of whatever they
have done in the past.
The opposite concept of man is also an ancient one, but it is more closely
related to the 'Eastern religions than to the Western ones. It assumes that man
is one species with all other species embedded in the intricate web of natural
processes that. sustains and constrains all forms of life. It acknowledges that
man is one of the more successful species, in terms of competitiveness, but
that his very success is leading him to destroy. and simplify the natural sus-
taining web, about which he understands very little. Subscribers to this view
feel that human institutions are ponderous and short-sighted, adaptive only
after very long delays, and likely to 4ttack complex issues with simplistic and
self-centered solutions. They would also point out that much of human technology
and "progress" has been attained only at the expense of natural beauty, human
dignity, and social integrity, and that those who have suffered the greatest loss
of these amenities have also had the least benefit from the economic "progress".
People who share this concept of man, as we do, would also question strongly
whether technology and material growth, which seem to have caused many problems,
should he looked to as the sources of solution of these same problems in the futu:
Technological optimists invariably label this view of the fallibility of man as
"pessimistic"; Malthusians would simply call it "humble".
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Wle see no objective way of resolving these very different views of man
and his role in the world. It seems to be possible for either side to look
at the same world and find support for its view. Technological optimists see
only rising life expectancies, more comfortable lives, the advance of human
knowledge, and improved wheat strains. Malthusians see only rising populations,
destruction of the land, extinct species, urban deterioration, and increasing
gaps between the rich and the poor. They would say that Malthus was correct
both in his own time and today in his observation that:
...the pressure arising from the difficulty of procuring subsistence
is not to be considered as a remote one which will be felt only when
the earth refuses to produce any more, but as one which actually exists
at present over the greatest part of the globe.11
The Challenge
One glaring problem confronts mankind, if it should choose to conceive
of man as a humble part of the biosphere. There is essentially no body of
knowledge from which to design the new institutions, and values consistent
with that concept of man. Two hundred years of growth has left biases and
blind spots throughout the physical and social sciences. There is today no
economic theory of a technological-based society in which there are essentially
zero interest rates, no net accumulation to society's productive capital, and
in which the principal concern is equality rather than growth. There is no
equilibrium sociology which is concerned with the social aspects of a stable
population, whose age composition is skewed toward the elderly. There is no
equilibrium political science in which we might look for clues to the ways
democratic choice could be exercised when short-term material gain is ruled out
as the basis for political success. There is no equilibrium technology that
places high emphasis on the recycling of all matter, on the use of the sun's
pollution-free energy, and on the minimization of both matter and energy flows.
There is no psychology for the steady state which might provide man with a new
self-image and with feasible aspirations in a system where material output is
constant and in balance with the globe's finite limits.
Each of our traditional disciplines could respond to the challenge of
working out the details of a viable and attractive equilibrium society. The
effort would pose many difficult technical and conceptual problems, whose
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solutions would be intellectually satisfying and of enormous social value.
After all, we are not merely talking of a distant and unattainable Utopian
state. Physical growth of population and capital will stop on this finite
planet. The only uncertainties lie in when it will stop and how - by deliberate
social choice and under careful human management, or by the harsh backlash of a
disturbed and depleted natural environment.
We may all find that the study of a steady-state society may be the
best possible preparation for the real future - a future that we are shaping
already, with every social and individual decision we make. We will almost
certainly discover as we become better acquainted with the possibilities for an
equilibrium society that we would prefer the end of physical growth to occur
under our own management and sooner, rather than later. Those of us'who have
already spent several years adjusting to the idea of a no-material-growth
society find without exception that we agree with John Stuart Mill, who contem-
plated the limits to growth more than one-hundred years ago:
I cannot, therefore, regard the stationary state of capital and
wealth with the unaffected aversion so generally manifested towards
it by political economists of the old school. I am inclined to
believe that it would be, on the whole, a very considerable im-
"provement on our present condition. I confess I an, not charmed
with the idea of life held out by those who think that the normal
state of human beings is that of struggling to get on; that the
trampling, crushing, elbowing, and treading on each other's
heels, which form the existing type of social life, are the most
desirable lot of humankind.... It is scarcely necessary to remark
that a stationary condition of capital and population implies no
stationary state of human imprcvement. There would be as much
scope as ever for all kinds of mental culture, and moral and social
progress; as much room for improving the Art of Living and much more
likelihood of its being improved.12
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References
1. Forrezter, J.W., World Dynamics, Wright-Allen Press, Cambridge, Mass.,
1971.
2. Meadows, D.H., et. al., The Limits to Growth, Universe Books, New York,
New York, 1972.
3. Meadows, D.L. and D. H. Meadows (Eds.), Toward Global Equilibrium:
Collected Papers, Wright-Allen Press, Cambridge, Mass., 1973.
4. Meadows, D.L., et. al., The Dynamics of Growth in a Finite World, Wright-
Allen Press, Cambridge, Mass., forthcoming Spring 1973.
5. Several have already started, such as Kenneth Boulding, Ezra Mishan,
Herman E. Daly, Nicholas Georgescu-Roegen.
6. Boyd, R., "World Dynamics: A Note", Science, Vol. 177, Aug. 11, 1972.
7. Oerlemans, T. W., et. al., "World Dynamics: Social Feedback may give
Hope for the Future", Nature, Vol. 238, August 4, 1972.
8. "Freeman, C., et. al., "Looking Toward the Future, A Critique of Limits
to Growth", Futures, February 1973.
9. Boulding, K. E., Economics as a Science, McGraw-Hill, New York, 1971.
10. Barnett, H.J. and C. Morse, Scarcity and Growth, Johns Hopkins Press.
11. Malthus, T.R., A Summmary View of the Principle of Population, 1830.
12. Mill, J.S., Principles of Political Economy, 1848.
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