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The Limits to Growth
Abstract established by Eduard Pestel
by Donella H. Meadows, Dennis L. Meadows,
Jorgen Randers, William W. Behrens III
A Report to The Club of Rome (1972)
Short Version of 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 environment.
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 industrial
capacity.
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 world.
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 System Dynamics. The basis of the method is the
recongnition 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 themselves. 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 occuring elsewhere in the system. Of course, none
of the five factors we are examining here is independent. Each
interacts constantly with all the others. We have already
mentioned some of these interactions. Population cannot grow
without food, food production is increased by growth of capital,
more capital requires more resources, discarded resources become
pollution, pollution interferes with the growth of both population
and food.
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
population. We include only one class of pollutants -- the
long-lived, globally distributed family of pollutants, such as
lead, mercury, 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 increase exponentially. 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
depletion. 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
available. 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 th 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 rapidly.
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 technological advances. 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 and collapse?
Let us assume, however, that the technological optimists are
correct and that nuclear energy will solve the resource problems
of the world.
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.
All this 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 siumultaneous crises. Overuse of land leads to
erosion, and food production drops. Resources are severly 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 that growth.
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. Our
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,
insitutions 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
mode. 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 learning 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 counterpressures, or both. Such counterpresures will
probably not be entirely pleasant. They will certainly involve
profund 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; and
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 constraint. 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
temporily stable state degenerates. However, we can improve the
model behavior greatly by conbining 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. Total average
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 following:
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 suggested. 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 possible.
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 easiliy
met. Would the final result be worth the effort? What would
humanity gain by siuuch a transition, and what would it,lose? Let
us consider in more detail what a world of nongrowth 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 effectivness, high
rate of capital investment) and those causing population and
capital stock to decrease (lack of food, pollution, high rate of
depreciation or obsolescence). 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.
They are:
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 depreciation rate.
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 population
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 basixc human needs of fod 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 nonconSuming
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 desribed 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 people today.
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 them.
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 generations. 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
equilibrium.
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