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8. Global environment and population carrying capacity

Shunji Murai

Criteria for sustainable development
Scenario of sustainable development
Supportable human population


Uncontrolled population increase appears as the biggest crime of humankind, because it induces both environmental and ecological destruction through excessive deforestation, urbanization, agricultural development, overgrazing, etc.

The development in the twentieth century, particularly after the Second World War, has accelerated towards a crisis of famine and even extinction of the human civilization, as a result of extreme consumption of natural resources.

Although sustainable development has become a common target since the Earth Summit held in Rio de Janeiro in 1992, this goal cannot be achieved without very severe controls based on a mutual understanding supported by a new philosophy. It will be impossible to continue the current prosperous, but aggressive, development that has been experienced in the twentieth century.

Criteria for sustainable development

Dennis L. Meadows presented his paper entitled "It Is Too Late to Achieve Sustainable Development, Now Let Us Strive for Survivable Development" at the Eighth Toyota Conference held in Mikkabi, Japan, in November 1994 (Meadows 1995). According to his scenario, the current situation would lead to "overshoot and collapse," based on the present trends in population increase, industrial production, metal consumption, and grain production.

Table 1 Criteria for Sustainable Development

Human activity Sustainable Critical Destructive
Population increase <0.5% p.a. 1.0-1.5% p.a. >2% p.a.
Economic development 3% < GNP < 5% 8% < GNP <10% GNP > 10% (overdevelopment) GNP < 0% (underdevelopment)
Deforestation rate <0.1% p.a. 0.5-1.0% p.a. >1% p.a.
Forest coverage > 30% 15-20% < 10%
Agricultural development >0.3% ha per capita 0.15-0.2 ha per capita 0.1 ha per capita
Self-support ratio > 91)% 60-70% < 50%
  Population density <50 per ha 100-150 per ha >200 per ha
  Population of a city < 0.5 million > 1 million > 10 million

I fully agree with this prediction despite its "non-scientific" approach. The author makes an attempt to define the three criteria of "sustainable," "critical," and "destructive" development from his personal experience, even though the view is not yet scientifically verified. Table 1 summarizes the criteria for sustainable development.

Population Increase

If one reviews the rate of agricultural development or grain production, population increase of over two per cent per year would be destructive. The rate of less than 0.5 per cent may be sustainable or supportable with a healthy development. A rate of 1.0-1.5 per cent will be critical for sustainability.

Economic Development

Overdevelopment of a GNP increase of over 10 per cent per year, as well as underdevelopment with a negative growth rate, will have a destructive impact on the consumption of natural resources and pollution. A GNP increase of 3-5 per cent per annum would be ideal for stabilizing the economy.

Deforestation Rate

An annual deforestation rate of more than one per cent has already been shown to be destructive by the examples of the Philippines in the 1970s and Thailand in the 1980s. On the other hand, for example in the nineteenth-century Malaysia during the colonial period, the deforestation rate was highly controlled and amounted only to less than 0.1 per cent, which was very sustainable. A rate of 0.5-1.0 per cent may be a critical threshold for its sustainability. In my opinion, each country should aim to retain more than 30 per cent of forest cover for stabilizing the climate, groundwater, anti-disaster capability, soil conservation, agricultural production, etc.

In my view, a country with less than 10 per cent forest land is hopeless. A range of 15-20 per cent forest land is a warning signal.

Agricultural Development

The Japanese experience of complete self-reliance in the Edo period demonstrated the sustainability of more than 0.3 hectares per capita given for agriculture, even though the country was not very rich. With less than 0.1 hectare per capita it would be very difficult to maintain even the minimal nutrition level. Note that the world average has decreased from 0.25 hectares per capita in the 1950s to 0.15 hectares per capita in the 1990s, which may be critical for a sustainable level in the future.

Self-support Ratio

Japan has only a 33 per cent self-support ratio, which results in the import of 27 million tons of grain, or 77 per cent of its grain. South Korea imports 68 per cent of its grain, while the figure for Taiwan is 74 per cent. Now China is starting to import grain. Lester R. Brown and Hal Kane estimate in their book Full House that in the year 2030 there will be a large gap between grain production and consumption; 204 million tons only in the four largest countries, the USA, China, India, and the former Soviet Union (Brown and Kane 1994).

A self-support ratio of over 90 per cent will be sustainable, while less than 50 per cent will be hopeless at the time when grain production becomes insufficient on a global scale.


Immigration into big cities has been a critical transition in the twentieth century, because overdevelopment and rapid industrialization cause high consumption of energy and resultant pollution. The urban environment can be maintained very well with a population density of 50 persons per hectare, while over 200 persons per hectare will produce a concrete jungle. The population of a city should be less than 0.5 million for a comfortable environment, while over 10 million in a city is against humanity, with severe pollution and inconvenience.

Scenario of sustainable development

There will be two scenarios for carrying capacity presented below.

Figure 1 Uncontrolled Development, "Overshoot and Collapse"

Scenario 1: Uncontrolled Development

As shown in figure 1, consumption of natural resources, including deforestation, is very rapid. In the present in developing countries it pushes up the carrying capacity very quickly, but only in the short term. In the longer term, it will have drastic environmental and ecological consequences. The population will increase as the carrying goes up and will continue even after it starts to decrease. The result will be a deficit between population and the carrying capacity, which may result in famine or refugees. Desertification will progress for many long years leading to extinction of civilization. There is much evidence for this in human history: consider for example Egypt, Greece, Mesopotamia, etc.

Such a pattern is called "overshoot and collapse." The world is presently on this route.

Scenario 2: Sustainable Development

As proposed in table 1, it is very difficult to meet the criteria for sustainable development. In order to do so, consumption of natural resources and industrial production should be controlled.

The increase of carrying capacity will be much more moderate, which will allow a gentle curve of population increase, and finally an equilibrium, as shown in figure 2. The birth and the death rate may be almost the same at an equilibrium, with an increased number of aged persons. The goal of reaching such a curve is not attractive to ambitious politicians, but we should establish a consensus among nations for sustainable development.

Figure 2 Sustainable Development

Supportable human population

The limit for human population is set with the constraints of crop production. A question arises as to how much population can be potentially supported with respect to crop production. In order to answer the question, the potential crop land must be estimated. According to the author's philosophy, new crop land should be developed only in areas of existing grassland, but not in forested areas, because further deforestation will cause a drastic decrease of carbon stock, further accelerating the greenhouse effect.

Table 2 shows an estimate of potential crop land that has been computed by the author and his colleagues (Mural et al. 1990) for five continents, as well as the existing agricultural land and forest area.

The Food and Agriculture Organization of the United Nations (FAO) gives out annually statistics of agricultural production, in particular related to the main crops that are important for the survival of mankind. Based on FAO statistics, the existing and potential agricultural productivity in calories were calculated (table 3).

As seen in table 3, there is potential still to increase agricultural production by a factor of 1.56. The potential habitability of the earth can be estimated with the information on the amount of food energy in kcal that is necessary to support one person. In this study, three different cases of energy consumption, as shown in table 4, were considered in order to estimate the potential for supporting a human population on earth.

The current world population, as of 1994, is about 5.4 billion. This implies that we have already passed the earth's carrying capacity if everybody should maintain North American food-consumption levels. If the entire world population would assume the current consumption levels, the limit to the world population would be only 7.34 billion people. Even at this level, the world population level will be saturated in the coming about 20 years.

Table 2 Potential Arable Land, Existing Agricultural Land, and Forest Area (Source: Murai 1995) (1,000 kmē)

  Africa North America South America Asia Europe Oceania World
Potential arable land 4,681 4,604 1,446 8,832 1,812 21,375
Existing farm land 1,688 2,671 1,163 7,752 478 13,732
Forest area 8,383 8,038 12,221 15,221 1,586 45,774

Table 3 Existing and Potential Agricultural Productivity (1012 kcal)

  Africa North America South America Asia Europe Oceania World
Existing prod. (A) 293 1,369 361 3,643 68 5,734
Potential prod. (B) 857 2,533 702 4,407 424 8,923
B/A 2.93 1.85 1.95 1.21 6.23 1.56

Table 4 Potential Carrying Capacity Based on Three Levels of Consumption (109 people)

Case Food consumption Population potential
1 At present levels for each country 7.34
2 World average 8.97
3 North American standard 4.01


A guideline for achieving sustainable development has been proposed by the author, with criteria and a scenario for sustainability.

The global habitability was estimated with the use of the global vegetation index data in terms of agricultural productivity. If only present grassland can be converted to agricultural land, without deforestation, the world can support a total population of 7.34 billion people under the condition that each country retains the present food-consumption levels. Supposing that the current rate of population increase, 1.7 per cent per annum, continues, the world's population carrying capacity will become critical in only about 20 years.


Brown, L.R. and H. Kane. 1994. Full House: Reassessing the Earth's Population Carrying Capacity. W.W. Norton, New York.

FAO. 1987. Production Yearbook. Food and Agriculture Organization of the United Nations, Rome.

Meadows, D.L. 1995. It is too late to achieve sustainable development, now let us strive for survivable development. In: S. Murai (ed.), Toward Global Planning of Sustainable Use of the Earth: Development of Global Eco-engineering, 359-374. Elsevier, Amsterdam.

Murai, S. 1995. Development of Global Eco-engineering using Remote Sensing and Geoinformation Systems. In: S. Murai (ed.), Toward Global Planning of Sustainable Use of the Earth: Development of Global Eco-engineering, 1-11. Elsevier, Amsterdam.

Murai, S., Y. Honda, K. Asakura and S. Goto. 1990. An Analysis of Global Environment by Satellite Remote Sensing: What Population Can the Earth Feed? Institute of Industrial Science, University of Tokyo.

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