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ON LIMITS TO GROWTH


	1. Many quantities grow exponentially in time for a while.  Examples
include a population of bacteria, the human population, the industrial
production of a country, and the use of electrical energy.

	2. There are two ways of arriving at the conclusion that a quantity
is growing exponentially.  First, it can be determined theoretically
that its rate of growth is proportional to the amount present.  This is
true of populations when resources are abundant and also of industrial
economies when resources are abundant and there is an abundant supply of
labor that can be taken from unemployment or agriculture.  It is also true
of the size of a firm as long as it is small compared to the economy.
The second way of arriving at a conclusion of exponential growth is by
fitting an exponential curve to observed data.  This applies to the
exponential curves for energy usage.  Fitting exponential curves represents
to some extent an arbitrary decision, because one could fit other kinds
of curves just as well.

	3. Both methods of getting exponential curves can lead to mistaken
results if done blindly.  A growth model that does not take into account
the limitation of a resource or a demand will fit the data perfectly until
this limitation comes into action.  When the bacteria use up all the agar or
encounter the walls of the Petri dish, the exponential growth curve will
be distorted.  Mark Twain's famous example of extrapolation should also be
cited.  He noted that the Mississipi river had shortened by 100 miles in 100
years by the cutting off of meanders and extrapolated to the time when the
river would be all gone.  One could concoct another such example by considering
fitting an exponential curve to American beef production between 1870 and 1890
and predicting that if something weren't done about it, each American would have
to eat a cow a day by 1930.

	4. In my opinion, the growth of the consumption of energy in the
United States has certain resemblances to the beef example.  Namely, we now
have certain uses for energy.  These uses lead to a demand that depends on
the distribution of income in the population.  However, the present uses
will saturate at a calculatable level of energy production.  Further increase
in demand beyond this point will depend on the development of new uses.
Given the present collection of uses, we can ask whether we can afford the
energy required to saturate the demand, from both a resource and an
environmental point of view.  In my opinion, the scientific knowledge and
the technological development has already proceeded to the point where this
question can be answered affirmatively, not only for the United States but
for the world.  If new major energy consuming applications develop, we shall
have to  examine whether we can afford them.  I don't really see any such
applications now but don't want to exclude them.  My guess would be that
use of energy will saturate at less than three times the present U.S.
per capita use.

	5. The Limits of Growth book by Meadows uses a model of the economy
in which a fixed proportion of GNP is reinvested into productive facilities.
Such a model is appropriate to a society that is far from saturating the
demand for goods and services.  They then predict that unless we take some
drastic measures, we will be overwhelmed by the consequences of increased
production.  In my opinion, as soon as further investment will not produce
goods that are a net benefit to the population, this investment will stop.
The Meadows view is like looking at a man eating dinner and noting that if
he doesn't eventually stop eating he will burst and proposing that we make
him stop.  He will stop when he has had enough.  Therefore, the question that
needs to be asked about American or world production is not what will happen
if it continues to grow indefinitely, but merely whether the next increment
is worthwhile.