Abstract established by Eduard Pestel
A Report to The Club of Rome (1972),
by Donella H. Meadows, Dennis l.
Meadows, Jorgen Randers, William W. Behrens III
'The Limits to Growth'
Our world model was built specifically
to investigate five major trends of global concern – accelerating
industrialization, rapid population growth, widespread malnutrition,
depletion of nonrenewable resources, and a deteriorating
The model we have constructed is, like every model, imperfect,
oversimplified, and unfinished.
In spite of the preliminary state of our work, we believe it is
important to publish the
model and our findings now. (...) We feel
that the model described here is already sufficiently developed to
be of some use to decision-makers.
Furthermore, the basic behavior
modes we have already observed in this model appear to be so
fundamental and general that we do not expect our broad conclusions
to be substantially altered by further revisions.
Our conclusions are :
1. If the present
growth trends in world population, industrialization, pollution,
food production, and resource depletion continue unchanged, the
limits to growth on this planet will be reached sometime within
the next one hundred years. The most probable result will be a
rather sudden and uncontrollable decline in both population and
2. It is possible to alter these growth trends and
to establish a condition of ecological and economic stability
that is sustainable far into the future. The state of global
equilibrium could be designed so that the basic material needs
of each person on earth are satisfied and each person has an
equal opportunity to realize his individual human potential.
If the world’s people decide to strive
for this second outcome rather than the first, the sooner they begin
working to attain it, the greater will be their chances of success.
All five elements basic to the study reported here —population, food
production, and consumption of nonrenewable natural resources— are
increasing. The amount of their increase each year follows a pattern
that mathematicians call exponential growth.
A quantity exhibits exponential growth when it increases by a
constant percentage of the whole in a constant time period.
Such exponential growth is a common process in biological,
financial, and many other systems of the
Exponential growth is a dynamic phenomenon, which means that it
involves elements that change over time.
(...) When many different quantities are growing simultaneously in a
system, however, and when all the quantities are interrelated in a
complicated way, analysis of the causes of growth and of the future
behavior of the system becomes very difficult indeed.
Over the course of the last 30 years there has evolved at the
Massachusetts Institute of Technology a new method for understanding
the dynamic behavior of complex systems. The method is called
Dynamics. The basis of the method is the recognition that the
structure of any system —the many circular, interlocking, sometimes
time-delayed relationships among its components— is often just as
important in determining its behavior as the individual components
The world model described in this book is a System
Dynamics model Extrapolation of present trends is a time-honored way
of looking into the future, especially the very near future, and
especially if the quantity being considered is not much influenced
by other trends that are occurring elsewhere in the system. Of
course, none of the five factors we are examining here is
Each interacts constantly with all the others. We have already
mentioned some of these interactions.
population cannot grow without
food production is increased by growth of capital
capital requires more resources
discarded resources become
pollution interferes with the growth of both population
Furthermore, over long time periods each of these factors also feeds
back to influence itself. In this first simple world model, we
are interested only in the broad behavior modes of the
population-capital system. By behavior modes we mean the tendencies
of the variables in the system (population or pollution, for
example) to change as time progresses.
A major purpose in constructing the world model has been to
determine which, if any, of these behavior modes will be most
characteristic of the world system as it reaches the limits to
growth. This process of determining behavior modes is “prediction”
only in the most limited sense of the word.
Because we are interested at this point only in broad behavior
modes, this first world model needs not be extremely detailed. We
thus consider only one general population, a population that
statistically reflects the average characteristics of the global
We include only one class of pollutants —the long-lived,
globally distributed family of pollutants, such as lead,
asbestos, and stable pesticides and
radioisotopes— whose dynamic
behavior in the ecosystem we are beginning to understand. We plot
one generalized resource that represents the combined reserves of
all nonrenewable resources, although we know that each separate
resource will follow the general dynamic pattern at its own specific
level and rate.
This high level of aggregation is necessary at this point to keep
the model understandable. At the same time it limits the information
we can expect to gain from the model.
Can anything be learned from such a highly aggregated model? Can its
output be considered meaningful? In terms of exact predictions, the
output is not meaningful. On the other hand it is vitally
important to gain some understanding of the causes of growth in
human society, the limits to growth, and the behavior of our
socio-economic systems when the limits are reached.
All levels in the model (population, capital, pollution, etc.) begin
with 1900 values. From 1900 to 1970 the variables agree generally
with their historical value to the extent that we know them.
Population rises from 1.6 billion in 1900 to 3.5 billion in 1970.
Although the birth rate declines gradually, the death rate falls
more quickly, especially after 1940, and the rate of population
growth increases. Industrial output, food and services per capita
The resource base in 1970 is still about 95
percent of its 1900 value, but it declines dramatically thereafter,
as population and industrial output continue to grow.
The behavior mode of the system is that of overshoot and collapse.
In this run the collapse occurs because of nonrenewable resource
The industrial capital stock grows to a level that
requires an enormous input of resources.
In the very process of that
growth it depletes a large fraction of the resource reserves
As resource prices rise and mines are depleted, more and
more capital must be used for obtaining resources, leaving less to
be invested for future growth.
Finally investment cannot keep up
with depreciation, and the industrial base collapses, taking with it
the service and agricultural systems, which have become dependent on
industrial inputs (such as fertilizers, pesticides, hospital
laboratories, computers, and especially energy for mechanization).
For a short time the situation is especially serious because
population, with the delays inherent in the age structure and the
process of social adjustment, keeps rising.
Population finally decreases when the
death rate is driven upward by
lack of food and health services. The exact timing of these events
is not meaningful, given the great aggregation and many
uncertainties in the model. It is significant, however, that growth
is stopped well before the year 2100. We have tried in every
doubtful case to make the most optimistic estimate of unknown
quantities, and we have also ignored discontinuous events such as
wars or epidemics, which might act to bring an end to growth even
sooner than our model would indicate.
In other words, the model is
biased to allow growth to continue longer than it probably can
continue in the real world. We can thus say with some confidence
that, under the assumption of no major change in the present system,
population and industrial growth will certainly stop within the next
century, at the latest.
To test the model assumption about available resources, we doubled
the resource reserves in 1900, keeping all other assumptions
identical to those in the standard run. Now industrialization can
reach a higher level since resources are not so quickly depleted.
The larger industrial plant releases pollution at such a rate,
however, that the environmental pollution absorption mechanisms
become saturated. Pollution rises very rapidly, causing an immediate
increase in the death rate and a decline in food production. At the
end of the run resources are severely depleted in spite of the
doubled amount initially available.
Is the future of the world system bound to be growth and then
collapse into a dismal, depleted existence? Only if we make the
initial assumption that our present way of doing things will not
change. We have ample evidence of mankind’s ingenuity and social
flexibility. There are, of course, many likely changes in the
system, some of which are already taking place. The Green Revolution
is raising agricultural yields in non industrialized countries.
Knowledge about modern methods of birth control is spreading
Although the history of human effort contains numerous incidents of
mankind’s failure to live within physical limits, it is success in
overcoming limits that forms the cultural tradition of many dominant
people in today’s world. Over the past three hundred years, mankind
has compiled an impressive record of pushing back the apparent
limits to population and economic growth by a series of spectacular
Since the recent history of a large part of
human society has been so continuously successful, it is quite
natural that many people expect technological breakthrough to go on
raising physical ceilings indefinitely.
Will new technologies alter the tendency of the world system to grow
Let us assume, however, that the technological optimists are correct
and that nuclear energy will solve the resource problems of the
Let us also assume a reduction in pollution generation all sources
by a factor of four, starting in 1975.
Let us also assume that the
normal yield per hectare of all the world’s land can be further
increased by a factor of two.
Besides we assume perfect birth
control, practiced voluntarily, starting in 1975.
means we are utilizing a technological policy in every sector of the
world model to circumvent in some way the various limits to growth.
The model system is producing nuclear power, recycling resources,
and mining the most remote reserves; withholding as many pollutants
as possible; pushing yields from the land to undreamed-of heights;
and producing only children who are actively wanted by their
parents. The result is still an end to growth before the year 2100.
Because of three simultaneous crises.
Overuse of land leads to
erosion, and food production drops.
Resources are severely depleted
by a prosperous world population (but not as prosperous as the
present US population).
Pollution rises, drops, and then rises again
dramatically, causing a further decrease in food production and a
sudden rise in the death rate.
The application of technological
solutions alone has prolonged the period of population and
industrial growth, but it has not removed the ultimate limits to
Given the many approximations and limitations of the world model,
there is no point in dwelling glumly on the series of catastrophes
it tends to generate. We shall emphasize just one more time that
none of these computer outputs is a prediction. We would not expect
the real world to behave like the world model in any of the graphs
we have shown, especially in the collapse modes.
The model contains
dynamic statements about only the physical aspects of man’s
activities. It assumes that social variables — income distribution,
attitudes about family size, choices among goods, services, and
food — will continue to follow the same patterns they have followed
throughout the world in recent history.
These patterns, and the human value they
represent, were all established in the growth phase of our
civilization. They would certainly be greatly revised as population
and income began to decrease. Since we find it difficult to imagine
what new forms of human societal behavior might emerge and how
quickly they would emerge under collapse conditions, we
have not attempted to model such social changes. What validity our
model has holds up only to the point in each output graph at which
growth comes to an end and collapse begins.
The unspoken assumption behind all of the model runs we have
presented in this chapter is that population and capital growth
should be allowed to continue until they reach some “natural” limit.
This assumption also appears to be a basic part of the human value
system currently operational in the real world.
Given that first
assumption, that population and capital growth should not be
deliberately limited but should be left to “seek their own levels”,
we have not been able to find a set of policies that avoids the
collapse mode of behavior.
The hopes of the technological optimists center on the ability of
technology to remove or extend the limits to growth of population
and capital. We have shown that in the world model the application
of technology to apparent problems of resource depletion or
pollution or food shortage has no impact on the essential problem,
which is exponential growth in a finite and complex system.
attempts to use even the most optimistic estimates of the benefits
of technology in the model did not prevent the ultimate decline of
population and industry, and in fact did not in any case postpone
the collapse beyond the year 2100.
Unfortunately the model does not indicate, at this stage, the social
side-effects of new technologies. These effects are often the most
important in terms of the influence of a technology on people’s
lives. Social side-effects must be anticipated and forestalled
before the large-scale introduction of a new technology.
While technology can change rapidly, political and
social institutions generally change very slowly. Furthermore, they almost
never change in anticipation of social need, but only in response to
one. We must also keep in mind the presence of social
delays — the delays necessary to allow society to absorb or to prepare
for a change. Most delays, physical or social reduce the stability
of the world system and increase the likelihood of the overshoot
The social delays, like the physical ones, are becoming
increasingly more critical because the processes of exponential
growth are creating additional pressures at a faster and faster
rate. Although the rate of technological change has so far managed
to keep up with this accelerated pace, mankind has made virtually no
new discoveries to increase the rate of social, political, ethical,
and cultural change.
Even if society’s technological progress fulfills all expectations,
it may very well be a problem with no technical solution, or the
interaction of several such problems, that finally brings an end to
population and capital growth. Applying technology to the natural
pressures that the environment exerts against any growth process has
been so successful in the past that a whole culture has evolved
around the principle of fighting against limits rather than
to live with them.
Is it better to try to live within that limit by accepting a
self-imposed restriction on growth? Or is it preferable to go on
growing until some other natural limit arises, in the hope that at
that time another technological leap will allow growth to continue
still longer? For the last several hundred years human society has
followed the second course so consistently and successfully that the
first choice has been all but forgotten.
There may be much disagreement with the statement that population
and capital growth must stop soon. But virtually no one will argue
that material growth on this planet can go on forever. At this point
in man’s history, the choice posed above is still available in
almost every sphere of human activity. Man can still choose his
limits and stops when he pleases by weakening some of the strong
pressures that cause capital and population growth, or by
instituting counter-pressures, or both. Such counter-pressures will
probably not be entirely pleasant.
They will certainly involve
profound changes in the social and economic structures that have
been deeply impressed into human culture by centuries of growth. The
alternative is to wait until the price of technology becomes more
than society can pay, or until the side-effects of technology
suppress growth themselves, or until problems arise that have no
technical solutions. At any of those points the choice of limits
will be gone.
Faith in technology as the ultimate solution to all problems can
thus divert our attention from the most fundamental problem —the
problem of growth in a finite system— and prevent us from taking
effective action to solve it.
On the other hand, our intent is certainly not to brand technology
as evil or futile or unnecessary. We strongly believe that many of
the technological developments mentioned here —recycling,
pollution-control devices, contraceptives— will be absolutely vital
to the future of human society if they are combined with deliberate
checks on growth. We would deplore an unreasoned rejection of the
benefit of technology as strongly as we argue here against an
unreasoned acceptance of them.
Perhaps the best summary of our
position is the motto of the Sierra Club :
“Not blind opposition to
progress, but opposition to blind progress”.
We would hope that society will receive each technological advance
by establishing the answers to three questions before the technology
is widely adopted. The questions are:
• What will be the
side-effects, both physical and social, if this development is
introduced on a large scale?
• What social changes will be necessary before this
development can be implemented properly, and how long will it
take to achieve them?
• If the development is fully successful and removes some
natural limits to growth, what limit will the growing system
meet next? Will society prefer its pressures to the ones this
development is designed to remove?
We are searching for a model that
represents a world system that is:
1. sustainable without
sudden and uncontrollable collapse
2. capable of satisfying the basic material
requirements of all of its people
The overwhelming growth in world
population caused by the positive birth-rate loop is a recent
phenomenon, a result of mankind’s very successful reduction of
worldwide mortality. The controlling negative feedback loop has been
weakened, allowing the positive loop to operate virtually without
There are only two ways to restore the resulting imbalance. Either
the birth rate must be brought down to equal the new, lower death
rate, or the death rate must rise again. All of the “natural”
constraints to population growth operate in the second way — they
raise the death. Any society wishing to avoid that result must take
deliberate action to control the positive feedback loop — to reduce
the birth rate.
But stabilizing population alone is not sufficient to prevent
overshoot and collapse; a similar run with constant capital and
rising population shows that stabilizing capital alone is also not
sufficient. What happens if we bring both positive feedback loops
under control simultaneously? We can stabilize the capital stock in
the model by requiring that the investment rate equal the
depreciation rate, with an additional model link exactly analogous
to the population-stabilizing one.
The result of stopping population growth in 1975 and industrial
capital growth in 1985 with no other changes is that population and
capital reach constant values at a relatively high level of food,
industrial output and services per person. Eventually, however,
resource shortages reduce industrial output and the temporally
stable state degenerates. However, we can improve the model behavior
greatly by combining technological changes with value changes that
reduce the growth tendencies of the system.
Then the stable world population is only slightly larger than the
population today. There is more than twice as much food per person
as the average value in 1970, and world average lifetime is nearly
70 years. The average industrial output per capita is well above
today’s level, and services per capita have tripled.
income per capita (industrial output, food, and services combined)
is about half the present average US income, equal to the present
average European income, and three times the present average world
income. Resources are still being gradually depleted, as they must
be under any realistic assumption, but the rate of depletion is so
slow that there is time for technology and industry to adjust to
changes in resource availability.
If we relax our most unrealistic assumption — that we can suddenly and
absolutely stabilize population and capital, replacing them with the
1. The population has access
to 100 percent effective birth control.
2. The average desired family size is two children.
3. The economic system endeavors to maintain average
industrial output per capita at about the 1975 level.
Excess industrial capability is employed
for producing consumption goods rather than increasing the
industrial capital investment rate above the depreciation rate.
We do not suppose that any single one of the policies necessary to
attain system stability in the model can or should be suddenly
introduced in the world by 1975. A society choosing stability as a
goal certainly must approach that goal gradually. It is important to
realize, however, that the longer exponential growth is allowed to
continue, the fewer possibilities remain for the final stable rate.
Many people will think that the changes we have introduced into the
model to avoid the growth and collapse behavior mode are not only
impossible, but unpleasant, dangerous, even disastrous in
themselves. Such policies as reducing the birth rate and diverting
capital from production of material goods, by whatever means they
might be implemented, seem unnatural and unimaginable, because they
have not, in most people’s experience, been tried, or even seriously
Indeed there would be little point even in discussing
such fundamental changes in the functioning of modern society if we
felt that the present pattern of unrestricted growth were
sustainable into the future. All the evidence available to us,
however, suggests that of the three alternatives —unrestricted
growth, a self-imposed limitation to growth, or a nature-imposed
limitation to growth— only the last two are actually
Achieving a self-imposed limitation to growth would require much
effort. It would involve learning to do many things in new ways. It
would tax the ingenuity, the flexibility, and the self-discipline of
the human race. Bringing a deliberate, controlled end to growth is a
tremendous challenge, not easily met. Would the final result be
worth the effort? What would humanity gain by such a transition, and
what would it, lose?
Let us consider in more detail what a
world of non-growth might be like.
We have after much discussion, decided to call the state of constant
population and capital, by the term “equilibrium”. Equilibrium means
a state of balance or equality between opposing forces. In the
dynamic terms of the world model, the opposing forces are those
causing population and capital stock to increase (high desired
family size, low birth control effectiveness, high rate of capital
investment) and those causing population and capital stock to
decrease (lack of food, pollution, high rate of depreciation or
The word “capital” should be understood to mean service, industrial,
and agricultural capital combined. Thus the most basic definition of
the state of global equilibrium is that population and capital are
essentially stable, with the forces tending to increase or decrease
them in a carefully controlled balance.
There is much room for variation within that definition. We have
only specified that the stocks of capital and population remain
constant, but they might theoretically be constant at a high level
or a low level — or one might be high and the other low. The longer a
society prefers to maintain the state of equilibrium, the lower the
rates and levels must be.
By choosing a fairly long time horizon for its existence, and a long
average lifetime as a desirable goal, we have now arrived at a
minimum set of requirements for the state of global equilibrium.
1. The capital plant
and the population are constant in size. The birth rate equals
the death rate and the capital investment rate equals the
2. All input and output rates —birth, death,
investment, and depreciation— are kept to a minimum.
3. The levels of capital and population and the
ratio of the two are set in accordance with the values of the
society. They may be deliberately revised and slowly adjusted as
the advance of technology creates new options.
An equilibrium defined in this way does
not mean stagnation. Within the first two guidelines above,
corporations could expand or fail, local populations could increase
or decrease income could become more or less evenly distributed.
Technological advance would permit the services provided by a
constant stock of capital to increase slowly. Within the third
guideline, any country could change its average standard of living
by altering the balance between its population and its capital.
Furthermore, a society could adjust to changing internal or external
factors by raising or lowering the population or capital stocks, or
both, slowly and in a controlled fashion, with a predetermined goal
in mind. The three points above define a dynamic equilibrium, which
need not and probably would not “freeze” the world into the
Capital configuration that happens to exist at present time. The
object in accepting the above three statements is to create freedom
for society, not to impose a straitjacket.
What would life be like in such an equilibrium state? Would
innovation be stifled? Would society be locked into the patterns of
inequality and injustice we see in the world today? Discussion of
these questions must proceed on the basis of mental models, for
there is no formal model of social conditions in the equilibrium
state. No one can predict what sort of institutions mankind might
develop under these new conditions.
There is, of course, no guarantee that the new society would be much
better or even much different from that which exists today. It seems
possible, however, that a society released from struggling with the
many problems caused by growth may have more energy and ingenuity
available for solving other problems. In fact, we believe, that the
evolution of a society that favors innovation and technological
development, a society based on equality and justice, is far more
likely to evolve in a state of global equilibrium than it is in the
state of growth we are experiencing today
Population and capital are the only
quantities that need be constant in the equilibrium state. Any human
activity that does not require a large flow of irreplaceable
resources or produce severe environmental degradation might continue
to grow indefinitely. In particular, those pursuits that many people
would list as the most desirable and satisfying activities of
man —education, art, music, religion, basic scientific research,
athletics, and social interactions— could flourish.
All of the activities listed above depend very strongly on two
factors. First, they depend upon the availability of some surplus
production after the basic human needs of food and shelter have been
met. Second, they require leisure time. In any equilibrium state the
relative levels of capital and population could be adjusted to
assure that human material needs are fulfilled at any desired level.
Since the amount of material production would be essentially fixed,
every improvement in production methods could result in increased
leisure for the population — leisure that could be devoted to any
activity that is relatively non-consuming and nonpolluting, such as
those listed above
Technological advance would be both
necessary and welcome in the equilibrium state. The picture of the
equilibrium state we have drawn here is idealized, to be sure. It
may be impossible to achieve in the form described here, and it may
not be the form most people on earth would choose. The only purpose
in describing it at all is to emphasize that global equilibrium need
not mean an end to progress or human development. The possibilities
within an equilibrium state are almost endless.
An equilibrium state would not be free of pressures, since no
society can be free of pressure. Equilibrium would require trading
certain human freedoms, such as producing unlimited numbers of
children or consuming uncontrolled amounts of resources, for other
freedoms, such as relief from pollution and crowding and the threat
of collapse of the world system. Is possible that new freedoms might
also arise — universal and unlimited education, leisure for creativity
and inventiveness, and, most important of all, the freedom from
hunger and poverty enjoyed by such a small fraction of the world’s
We can say very little at this point about the practical, day by-day
steps that might be taken to reach a desirable, sustainable state of
global equilibrium. Neither the world model nor our own thoughts
have been developed in sufficient detail to understand all the
implications of the transition from growth to equilibrium.
Before any part of the world’s society embarks deliberately on such
a transition, there must be much more discussion, more extensive
analysis, and many new ideas contributed by many different people.
The equilibrium society will have to weigh the trade-offs engendered
by a finite earth not only with consideration of present human
values but also with consideration of future generations. Long-term
goals must be specified and short term goals made consistent with
We end on a note of urgency. We have repeatedly emphasized the
importance of the natural delays in the population-capital system of
the world. These delays mean, for example, that if Mexico’s birth
rate gradually declined from its present value to an exact
replacement value by the year 2000, the country’s population would
continue to grow until the year 2060. During that time the
population would grow from 50 million to 130 million.
We cannot say
with certainty how much longer mankind can postpone initiating
deliberate control of its growth before it will have lost the chance
for control. We suspect on the basis of present knowledge of the
physical constraints of the planet that the growth phase cannot
continue for another one hundred years. Again, because of the delays
in the system, if the global society waits until those constraints
are unmistakably apparent, it will have waited too long.
If there is cause for deep concern, there is also cause for hope.
Deliberately limiting growth would be difficult, but not impossible.
The way to proceed is clear, and the necessary steps, although they
are new ones for human society, are well within human capabilities.
Man possesses, for a small moment in his history, the most powerful
combination of knowledge, tools, and resources the world has ever
known. He has all that is physically necessary to create a totally
new form of human society — one that would be built to last for
The two missing ingredients are a realistic, long-term
goal that can guide mankind to the equilibrium society and the human
will to achieve that goal. Without such a goal and a commitment to
it, short-term concerns will generate the exponential growth that
drives the world system toward the limits of the earth and ultimate
collapse. With that goal and that commitment, mankind would be ready
now to begin a controlled, orderly transition from growth to global