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Law of the minimun

Now, let's hear from David Laing, a graduate student in the Department of Geological Sciences at Harvard University:

"Forgive-me if I try to shake your faith in the 'most hope-inspiring graph' in Jay Forrester's book ... In that graph, the world's human population is shown as indefinitely stabilized, ideally, at its present level of about 3.5 billion. I submit that this will be impossible.

"The real problem with 'model' situations such as the ones in Forrester's book is that they usually only consider broad categories of phenomena in the prediction of future trends. In actuality, any one phenomenon within a category may impose much narrower limits on the model than are anticipated. Such is certainly the case with the category of natural resources and the particular case of phosphate rock.
"I've just finished a study on United States phosphate rock reserves, from which vantage I can offer the following sober conclusions:

“1) The present world population is about two billion above what the Earth could support without the use of phosphate nitrate fertilizers.

"2) Given present US reserves of phosphate rock— including very low grade ore not minable under present economic and technical conditions— and given present trends, these reserves will be exhausted no later than 110 years hence. The US has the world's largest reserves.

"3) Phosphate is progressively lost during agricultural, industrial, and domestic use by dissemination in soil and water, and, unlike nitrate, cannot be reconcentrated except by tertiary sewage treatment— which, assuming a theoretically possible efficiency of 90 percent could reclaim about 12 percent of the phosphate consumed— and by geological processes that are not only very slow but also rather unusual.

"4) Phosphate-fertilizer use must increase 2.7 times faster than agricultural yield— an empirical discovery— due to inefficiency of organic uptake. The excess winds up in our natural water systems, intensifying problems of eutrophication along with nitrate, which, unlike phosphate, is toxic in concentrations that are being exceeded now.

"Thus, we have an immediate dilemma: the problem of growing eutrophication and toxification of our natural water supplies, and a more distant dilemma: the eventual exhaustion of our phosphate reserves. The former will probably somewhat delay the latter because there will come a point where the pollution problem will create a feedback resistance to increases in fertilizer application. With the brake on agriculture, this will be the point where we start 'farming the sea' (and the lakes!) for phytoplankton (especially blue-green algae) to feed our exploding masses. Then, when our phosphate reserves are finally exhausted, we must bring the population down to a level— between one and two billion— that the Earth can support without artificial fertilizers."

Mr. Laing stretches the truth a little in saying that the "most hope-inspiring" graph in World Dynamics shows population "indefinitely stabilized." Professor Forrester, in his book, and I, in my review, both called attention to a down-turn in the population curve in the latter part of the next century, indicating that despite corrective measures that had produced fairly long-term stability, depletion of natural resources had again become a limit on population. By coincidence, in fact, the graph shows a population downturn almost exactly 110 years hence, when Mr. Laing says phosphate reserves will be exhausted. I agree with Mr. Laing, and I'm sure Professor Forrester does, too, that the stability indicated in the "most hope-inspiring" graph cannot be permanently sustained short of total recycling with 100 percent efficiency. What this impermanent stability does that inspires hope is buy time for us to evolve more lasting solutions— one of which, I agree with Mr. Laing, must be population reduction.

There is no reason I know of why the facts about phosphates outlined by Mr. Laing could not be built into a world model, but there probably wouldn't be much point in it unless the model builders could be certain that phosphates would be the limiting factor. Do we know enough to be sure that some other essential— something essential, that is, to the maintenance of an inflated population of four billion or more— won't give out before phosphate rock does? What if we have only a 60-year supply of something else essential to sustain our overinflated population? In that case, incorporating the facts about phosphate rock into the world model wouldn't improve its predictive capacity.

The Law of the Minimum provides, as I understand it, that if you have less than the minimum amount needed of any essential, it does you no good whatever to have surpluses of every other essential. The obvious question arises, what essential will we run short of first? Mr. Laing suggests that it may be phosphates. And so it may. But until that is pretty well- established, phosphate figures probably don't belong in a world model, which, in the nature of things, must be general rather than specific and simple rather than complex.

Query: Do any readers of NMA have substantial reason to believe that the Law of the Minimum will become operative while we still have phosphate reserves because we've run out of some other essential? Do you have a candidate for the essential resource that, by running short, will soonest become a limitation on population? If so, let us hear from you.

Mr. Laing has a valid point, it seems to me, in saying that a single, particular natural resource, by hearing exhaustion, might impose a limit on growth while "natural resources" as a broad category were still in relatively plentiful supply. And he is right in saying that Forrester's world model does not take this into consideration. But this does not dampen my enthusiasm for the model one whit. Why? Because I do not conceive of the model as being predictive in a chronological sense. At least, that doesn't seem to me to be its special virtue. The Forrester model's special virtue, it seems to me, is in predicting ultimate outcomes: not so much when a pollution crisis will occur under certain circumstances, but that under those circumstances, a pollution crisis will ultimately occur; not so much when resource shortages will impose limits on growth, but that shortages will ultimately limit growth.

You might argue that if I'm right, Forrester's model merely demonstrates the obvious. Well, in a sense that's right. It has been obvious to a few people for a long time, and to a growing number of us for a short while, that growth cannot continue indefinitely in a finite world with finite resources. Nevertheless, it's still vitally important to demonstrate this "obvious truth" in convincing fashion. There's not a single nation so far as I know, nor any lesser political jurisdiction, that systematically bases public policy on the obvious truth that aspirations for perpetual growth can lead only to ultimate collapse.

Query: Can any readers furnish exceptions to the rule that political jurisdictions do not yet base public policy on the fact that perpetual growth is impossible? We would be interested to hear of any laudable examples.

Based on his knowledge of agricultural yields in the absence of artificial fertilizers, Mr. Laing calculates that a world without such fertilizers could support between one and two billion people— one half or less of our present world population. This doesn't mean, of course, that a world population of between one and two billion would be optimal, or even that a population of such size could necessarily be sustained permanently. Shortage of another natural resource, or shortages of a combination of them, might impose even lower limits on population. Which brings up a concept that fascinates me: that of "optimum population."

Optimum population is generally defined, I believe, as the number of people that can be permanently sustained on Earth at a tolerable standard of living. Mr. Laing's hypothetical population of one to two billion is "optimal," 1 take it, only in relation to agricultural productivity in the absence of artificial fertilizers. Does this presuppose efficiency in the distribution of food that may not be attainable when mechanized transportation is seriously affected by shortages of fuels and lubricants? If so, "optimum population" may be a good deal smaller than one or two billion, and the problems involved in voluntarily contracting population to a sustainable level may be correspondingly greater.

Query: Has any reader of NMA firm convictions, based on reasoning that he can share with us, about the optimum population of the Earth? Can any reader, whether he has worked on the problem yet or not, suggest what might be the best way to determine what the optimum population of Earth is?

The "most hope-inspiring" graph in World Dynamics doesn't presage Utopia. A continuation of its natural resources curve indicates the complete exhaustion of nonrenewable resources in about 700 or 800 years (even assuming a quite high level of recycling). The quality of life curve stabilizes for about one century at the peak 1950 level before veering down again, but let's not forget that the average quality of life in America in the fifties was unsatisfactory, and in the world as a whole, average quality of life at its historic peak was pretty pitiful. The capital investment curve remains at current levels through the year 2100— which accounts for the steady and ominous drain on non-renewable resources. The pollution curve also stays level through the next century, but many of us would insist that current levels of pollution are too high. Interpreted in this way, the "most hope-inspiring" graph justifies little long-term optimism. It does Indicate, however, as Professor Forrester puts it, that a no-growth condition of stability is at least "conceptually possible." And it indicates that in theory, at least, we can attain a tolerable condition of stability that may last long enough— about a century— to enable us to work toward conditions compatible with long-term stability and survival.

We thank Mssrs. Hirst and Laing for their contributions to this discussion, and hope that they, together with the rest of you, will feel moved to carry it further. For the editors agree with Professor Forrester— and with The Club of Rome, which sponsored his work— that the necessity of achieving a transition from growth to equilibrium is "The Predicament of Mankind." Not a predicament; the predicament.