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The Future Size Of World Population

By Peter Goodchild

09 June, 2012

There are three principal ways of determining future global population: on the basis of arable land, on the basis of fossil-fuel production, and on the separate basis of the question of sustainable agriculture. The three figures we arrive at by these methods are quite different from one another. The first indicates that 6 billion people could be supported for an indeterminate length of time, and the second gives a figure of 2 billion for the year 2050. The third gives us the much smaller figure of only 10 million, which is less than one percent of the present population -- in fact it is only one seventh of one percent.

The first method involves multiplying the number of hectares of arable land by the number of people that could be supported per hectare. For example, in a study of corn (maize) production in Mexico that used only manual labor, David Pimentel claims that the average yield per hectare was 1,944 kg. He also notes that in a typical farm-based culture an adult burns about 1 million kilocalories ("calories") a year. Simplifying his various calculations considerably, we might say that these 1,944 kg of corn will provide about 9 million calories a year, or enough for 9 people. (There are uncertainties based largely on the question of what factors to be listed as input or output of calories. The term "net energy" sometimes suffers from a lack of clearly defined parameters.) By contrast, although there are many figures available on modern industrialized corn production, they tend to hover at around 6,000 kg or more.

Combining figures on land use from the CIA and the FAO, we can say that in the entire world there are now about 1.5 billion hectares of arable land. This is about 10 percent of the world's total land area. If we multiply the figure of 1.5 billion hectares by the 9 people per hectare, we then apparently arrive at the "fact" that we can support 13.5 billion people without using fossil fuels.

For various reasons, unfortunately, things are not quite that simple. Arable land is not evenly distributed in relation to the world's population. Much of the arable land is not really used for that purpose. Arable land can also be relatively unproductive, either because of natural factors such as mineral imbalance or harsh climate, or because it has been overworked for centuries. A certain amount of land must be left aside for fallowing in order to prolong the retention of nutrients and moisture. We must consider the fact that corn has a much higher yield in calories than most other crops, so these latter crops require more land per person. We must also take into consideration any rise in population beyond the present 7 billion.

When we include all these peripheral factors, we might need to start reducing the figures toward about 4 people per hectare. If that is the case, it would seem we can still support 6 billion people with the world's arable land. However, about a third of the world's countries are already outside that 4:1 ratio; the worst areas are western Europe, the Middle East, most of southern and eastern Asia, and the islands of the Pacific. In view of all these qualifications and uncertainties, it might be best simply to discard the inquiry into future human population merely on the basis of arable land.

The second method of determining future population involves looking at the relationship between population and the supply of oil and other fossil fuels. Human population has risen dramatically since the development of an oil-based global economy. That is because oil provides most of the energy, for end uses of any sort, in that economy: an increase in oil production results in an increase in population. One might argue about the extent to which that relationship is one of strict causality -- i.e. about whether there is a clear distinction between "causing" and "allowing" -- but it can at least be said that abundant oil allows a large population, and that without abundant oil a large population would not be possible.

The world's population has gone from 1.7 billion in 1900 to over 7 billion now. Conversely, as oil declines so must population. Based partly on the mathematics of the Hubbert curve, most estimates indicate that in the year 2050 oil production will be about 2 billion barrels. The same amount of oil production occurred in the year 1930, when there were 2 billion people. The same population figure as in 1930 may therefore be case for the year 2050: 2 billion people.

These two methods of determining population produce quite different results: a population of 6 billion versus one of 2 billion. Yet they are both probably wide of the mark, because they both refer to a world that is based on agriculture. It is easy to regard agriculture as a "given" for human society. But that is not the case. Hominids have lived on Earth for about 2 million years. Agriculture, on the other hand, was invented only about 10 million years ago; largely by definition, that is the line that separates the Palaeolithic from the Neolithic. At this dividing line, the world's population was only about 10 million.

Several scholars have pointed out that agriculture cannot be maintained indefinitely, and certainly not with a large population. Agriculture causes the destruction of arable land: the more we farm, the more the farmland becomes eroded. "Organic" farming and similar practices can reduce the rate of loss, but only to a certain extent: essential elements such as phosphorus and calcium get washed away, as well as humus, and the soil is gradually ruined. In spite of the popular misconception, to plow the earth is to "go against Nature," since it means disturbing the soil, the intricate, complex surface of the planet; even the slightest and shallowest disturbance causes chemical and biological losses of various sorts. No matter how we try to rationalize our behavior as farmers, the "peaceable kingdom" of agriculture is to some extent a figment of our imagination. Eventually, the result of ever-increasing agriculture is ever-increasing famine.

We must regard a final global population of about 10 million, as existed 10,000 years ago, just before the development of agriculture, as more likely, because agriculture itself is just not "sustainable." That word, however, though beloved by politicians, is a terribly vague one and is perhaps best avoided. "Sustainable" for a week? For eternity? Let us say, in any case, that agriculture cannot be maintained as a steady state for thousands of years. The only way of life that can truly be preserved for a great length of time is foraging -- hunting and gathering -- or some other means of sustenance that does not involve disturbing the soil.


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Clugston, C. O. (2012). Scarcity: Humanity's final chapter. Booklocker.

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Pimentel, D. (1984). Energy flows in agricultural and natural ecosystems. CIHEAM (International Centre for Advanced Mediterranean Agronomic Studies). Retrieved from http://www.ressources.ciheam.org/om/pdf/s07/c10841.pdf

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------, & Pimentel, M. H. (2007). Food, energy, and society. 3rd ed. Boca Raton, Florida: CRC Press.

Salonius, P. (2008, October 20). Agriculture: Unsustainable resource depletion began 10,000 years ago. The Oil Drum. Retrieved from http://www.theoildrum.com/node/4628a

Peter Goodchild is the author of Survival Skills of the North American Indians , published by Chicago Review Press. His email address is prjgoodchild[at] gmail.com


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