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Une autre analyse par Gretchen, Anne H. Ehrlich et Paul R. Ehrlich (en Anglais)

Population and Environment: A Journal of Interdisciplinary Studies Volume 15, Number 6, July 1994 01994 Human Sciences Press, Inc.


Optimum Human Population Size
Gretchen C. Daily University of California (Berkeley) Anne H. Ehrlich and Paul R. Ehrlich Stanford University (July 1994)

Although the tremendous size and rate of growth of the human population now influence virtually every aspect of society, rarely does the public debate, or even consider, the question of what would be an optimum number of human beings to live on Earth at any given time? While there are many possible optima depending on both the criteria defining "optimum" and on prevailing biophysical and social conditions, there is a solid scientific basis for determining the bounds of possibilities. All optima must lie between the minimum viable population size, MVP (Gilpin & Soule, 1986; Soule, 1987) and the biophysical carrying capacity of the planet (Daily & Ehrlich, 1992). At the lower end, 50-100 people in each of several groups, for a total of about 500, might constitute an MVP.

At the upper end, the present population of 5.5 billion, with its resource consumption patterns and technologies, has clearly exceeded the capacity of Earth to sustain it. This is evident in the continuous depletion and dispersion of a one-time inheritance of essential, non-substitutable resources that now maintains the human enterprise (e.g., Ehrlich & Ehrlich, 1991; Daily & Ehrlich 1992). Numerous claims have been made that Earth's carrying capacity is much higher than today's population size. A few years ago, for example, a group of Catholic bishops, misinterpreting a thought exercise by Roger Revelle (1976), asserted that Earth could feed 40 billion people (Anonymous, 1988); various social scientists have made estimates running as high as 150 billion (Livi-Bacci, 1989). These assertions are based on preposterous assumptions, and we do not deal further with them here.

Nonetheless, we are left with the problem of determining an optimum within wide bounds. Above the minimum viable level and within biophysical constraints, the problem becomes a matter of social preference. Community-level, national, and international discussions of such social preferences are critical because achieving any target size requires establishing social policies to influence fertility rates. Human population sizes have never, and will never, automatically equilibrate at some level. There is no feedback mechanism that will lead to perfectly maintained, identical crude birth and death rates. Since prehistoric times, societies have controlled fertility and mortality rates to a substantial degree, through various cultural practices (Harris & Ross, 1987). In the future, societies will need to continue manipulating vital rates to reach desired demographic targets. Most important, societies must reach a rough consensus on what those targets should be as soon as possible because the momentum behind the growth of the present population ensures at least a doubling before any decline is possible (UNFPA, 1992).

This commentary, given at the First World Optimum Population Congress (convened in London, U.K., 1993) is a contribution to that necessary dialogue. What follows is a brief statement of our joint personal views of the criteria by which an optimum should be determined (in no particular order).

1. An optimum population size is not the same as the maximum number of people that could be packed onto Earth at one time. The maximum would have to be housed and nurtured by methods analogous to those used to raise bakery chickens, and the process would inevitably reduce the planet's longterm carrying capacity. Many more human beings could exist if a sustainable population were maintained for thousands to millions of years than if the present population overshoot were further amplified and much of Earth's capacity to support future generations were quickly consumed. Thus, an optimum size is a function of the desired quality of life and the resultant per-capita impacts of attaining that lifestyle on the planet's life support systems.

2. An optimum population size should be small enough to guarantee the minimal physical ingredients of a decent life to everyone (e.g., Ehrlich et al., 1993), even in the face of an inequitable distribution of wealth and resources and the uncertainty regarding rates of longterm, sustainable resource extraction and environmental impacts. We agree with Nathan Keyfitz (1991): "If we have one point of empirically backed knowledge, it is that bad policies are widespread and persistent. Social science has to take account of them." The grossly inequitable distribution of wealth and basic resources prevailing today is highly destabilizing and disruptive. While it is in nearly everyone's selfish best interest to narrow the rich-poor gap, we are skeptical that the incentives driving social and economic inequalities can ever be fully overcome. We therefore think a global optimum should be determined with humanity's characteristic selfishness and myopia in mind. A further downward adjustment in the optimum should be made to insure both against natural and human-induced declines in the sustainable flow of resources from the environment into the economy and against increases in anthropogenic flows of wastes, broadly defined, in the opposite direction.

3. Basic human rights in the social sphere (such as freedom from racism, sexism, religious persecution, and gross economic inequity) should be secure from problems generated by the existence of too many people. Everyone should have access to education, health care, sanitary living conditions, and economic opportunities; but these fundamental rights are difficult to assure in large populations, especially rapidly growing ones. Political rights are also related to population size, although this is seldom recognized (Parsons, 1977). Democracy seems to work best when populations are small relative to resource bases; personal freedom tends to be restricted in situations of high population density and/or scarce resources.

4. We think an optimum population size should be large enough to sustain viable populations in geographically dispersed parts of the world to preserve and foster cultural diversity. It is by no means obvious that the dominant and spreading "western" culture has all the secrets of longterm survival (Ehrlich, 1980)—to say nothing of cornering the market on other values. We believe that cultural diversity is an important feature of our species in and of itself. Unfortunately, many cultures borne by small groups of people are in danger of being swamped by the dominant culture with its advanced technologies and seductive media, or worse, of being destroyed deliberately because of social intolerance or conflicts over resources.

5. An optimum population size would be sufficiently large to provide a "critical mass" in each of a variety of densely populated areas where intellectual, artistic, and technological creativity would be stimulated. While creativity can also be sparked in sparsely populated areas, many cultural endeavors require a level of specialization, communication, and financial support that is facilitated by the social infrastructure characteristic of cities.

6. An optimum population size would also be small enough to ensure the preservation of biodiversity. This criterion is motivated by both selfish and ethical considerations. Humanity derives many important direct benefits from other species, including aesthetic and recreational pleasure, many pharmaceuticals, and the very basis and security of agricultural production. Furthermore, the human enterprise is supported in myriad ways by the free services provided by healthy natural ecosystems, each of which has elements of biodiversity as key working parts (Ehrlich & Ehrlich, 1992). Morally, as the dominant species on the planet, we feel Homo sapiens should foster the continued existence of its only known living companions in the universe.

In general, we would choose a population size that maximizes very broad environmental and social options for individuals. For example, the population of the United States should be small enough to permit the availability of large tracts of wilderness for hikers and hermits, yet large enough to create vibrant cities that can support complex artistic, educational, and other cultural endeavors that lift the human spirit.

Innumerable complexities are buried in this short list of personal preferences, of course. But with the world's population size now above any conceivable optimum and (barring catastrophe) destined to get much larger still (UNFPA, 1992), it appears that many decades are available in which to debate alternative optima before even stopping growth of the population, much less approaching an optimum. During that time, human technologies and goals will both change, and those changes could shift the optimum considerably.

It is nonetheless instructive to make a tentative, back-of-the-envelope calculation of an optimum on the basis of present and foreseeable consumption patterns and technologies. Since the human population is in no imminent danger of extinction due to underpopulation, we focus here on the upper bound of an optimum. We begin by using humanity's energy consumption as a rough, indirect measure of the total impact civilization inflicts on Earth's life-support systems (Holdren & Ehrlich 1974). Energy, especially that provided by fossil fuel and biomass combustion, directly causes or underpins many of the global environmentally damaging activities that are recognized today: air and water pollution, acid precipitation, land degradation, emissions of carbon dioxide and other greenhouse gases, and production of toxic and hazardous materials and wastes.

At present, world energy use amounts to about 13 terawatts (TW = 1012 watts), about 70% of which is being used to support somewhat over a billion people in rich countries and 30% to support more than four billion people in developing countries. This pattern is both ethically undesirable and biophysically unsustainable, because of the gross disparity between rich and poor societies, and because of the environmental damage that results. The consumption of 13 TW of energy with current technologies is leading to the serious ecological impacts indicated above, all of which contribute to several forms of deleterious global change, including a continuous deterioration of ecosystems and the essential services they render to civilization (Ehrlich & Ehrlich, 1991; Ehrlich et al., 1993).

An examination of probable future trends leads to dismal conclusions. The world population is projected to increase from 5.5 billion in 1993 to somewhere between 10 and 14 billion within the next century. Suppose population growth halted at 14 billion and everyone were satisfied with a per-capita energy use of 7.5 kilowatts (kW), the average in rich nations and about two thirds of that in the United States in the early 1990s. A human enterprise that large would create a total impact of 105 TW, eight times that of today and a clear recipe for ecological collapse.

A scheme that might possibly avoid such a collapse was proposed by John Holdren of the Energy and Resources Group at the University of California, Berkeley. The Holdren scenario (Holdren, 1991) postulates expansion of the human population to only 10 billion and a reduction of average per-capita energy use by people in industrialized nations from 7.5 to to 3 kilowatts (kW), while increasing that of the developing nations from 1 to 3 kW. The scenario would require, among other things, that citizens of the United States" cut their average use of energy from almost 12 kW to 3 kW. That reduction could be achieved with energy efficient technologies now in hand and with an improvement (by most people's standards) in the standard of living.

While convergence on an average per-capita consumption of 3 kW of energy by 10 billion people would close the rich-poor gap, it would still result in a total energy consumption of 30 TW, more than twice that of today. Whether the human enterprise can be sustained even temporarily on such a scale without devastating ecological consequences is unclear, as Holdren recognizes. This will depend critically on the technologies involved in the future as reserves of fossil fuels, especially petroleum, are depleted. Perhaps through funkier development and widespread application of more benign technologies (such as various forms of solar power and biomass-derived energy), environmental deterioration at the peak of human activities could be held to that of today.

Against that background, what might be said about the upper limits on an optimum population size, considering present attitudes and technologies?

In view of the environmental impacts of a civilization using 13 TW today, to say nothing of the threats to the future prospects of humanity, it is difficult to visualize a sustainable population that used more than 9 TW with present and foreseeable technologies.

One might postulate that, with careful choices of energy sources and technologies, 9 TW might be used without degrading environmental systems and dispersing nonrenewable resources any more rapidly than they could be repaired or substituted for. Under similar assumptions, a 6 TW world would provide a 50% margin for error, something we deem essential considering the unexpected consequences that often attend even very benign-appearing technological developments (the invention and use of chlorofluorocarbons being the most instructive case to date). A more conservative optimum would be based on a 4.5 TW world, giving a 100% margin for error. Which upper limit one wished to choose would depend in pan on some sort of average social risk aversion combined with a scientific assessment of the soundness of the 9 TW maximum impact.

In the real world, the maximum sustainable population might well be determined in the course of reducing population size and overall impact -- by discovering the scale of the human enterprise at which ecosystems and resources seemed to be holding their own. For our thought experiment, let us consider a 6 TW world. If we assume a convergence of all societies on 3 kW percapita consumption, that would imply an optimum population size of 2 billion people, roughly the number of human beings alive in 1930. Such a number seems at first glance to be reasonable and well above the minimum number required to take advantage of both social and technical economies of scale. In the first half of the twentieth century, there were many great cities, giant industrial operations, and thriving ens and lepers. A great diversity of cultures existed, and members of many of them were not in contact with industrializing cultures. Large bans of wilderness remained in many pans of the world. A world with 1.5 billion people using 4.5 TW of energy seems equally plausible and would carry a larger margin of safety. This is about the same number of people as existed at the turn of the century.

To summarize this brief essay, determination of an "optimum" world population size involves social decisions about the life styles to be lived and the distribution of those life styles among individuals in the population. To us it seems reasonable to assume that, until cultures and technology change radically, the optimum number of people to exist simultaneously km in the vicinity of 1.5 to 2 billion people. That number, if achieved reasonably soon, would also likely permit the maximum number of Homo sapiens to live a good life over the long run. But suppose we have underestimated the optimum and it actually is 4 billion? Since the present population is over 5.5 billion and growing rapidly, the policy implications of our conclusions are still clear.


This work was supported by grants from the W. Alton Jones, Winslow, and Heinz Foundations, and the generosity of Peter and Helen Bing.


Anonymous. (Nov. 19, 1988). Agriculture could feed 40 billion. Washington Post, p. C-15.

Daily, G.C., & Ehrlich, P.R. (1992). Population, sustainability, and Earth's carrying capacity. BioScience 42:761-771.

Ehrlich, P.R. (1980). Variety is the key to life. Technology Review, 82(5):58-68. Massachusetts Institute of Technology, Cambridge, Mass.

Ehrlich, P.R., Daily, G.C., & Goulder, L.H. (1992). Population growth, economic growth, and market economies. Contention 2:17-35.

Ehrlich, P.R., & Ehrlich, A.H. (1990). The population explosion. New York: Simon and Schuster.

Ehrlich, P.R., & Ehrlich, A.H. (1991). Healing the planet. New York: Addison Wesley.

Ehrlich, P.R., & Ehrlich, A.H. (1992). The value of biodiversity. Ambio 21:219-226.

Ehrlich, P.R., Ehrlich, A.H., & Daily, G.C. (1993). Food security, population, and environment. Population and Development Review 19(1):1-31. >

Gilpin, M.E., & Soul, M.E. (1986). Minimum viable populations: The processes of species extinctions. In M. Soul (Ed.). Conservation biology: The science of scarcity and diversity, pp. 13-34. Sunderland Mass: Sinauer Associates .

Harris, M. & Ross, E.B. (1987). Death, sex, and fertility: Population regulation in preindustrial and developing societies. New York: Columbia University Press

Holdren, J.P. (1991). Population and the energy problem. Population and Environment 12:231 -255.

Holdren, J.P. & Ehrlich, P.R. (1974). Human population and the global environment. American Scientist 62:282-292.

Keyfitz N. (1991). Population and development within the ecosphere: One view of the literature. Population Index 57:5-22

Livi-Bacci, M. (1987). A concise history of world population. Cambridge, MA: Blackwell.

Parsons, J. (1977). Population fallacies. London: Elek/Pemberton.

Revelle, R. (1976). The resources available for agriculture. Scientific American 235 (3):164

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Peut être aussi lu avec intérêt ce qui suit : "Une autre analyse par Gretchen et ali.".
D’autres débats permettant de mieux appréhender les différentes facettes du concept Optimum de population sont présentés ci-dessous (en Anglais).

Optimum and Malthusian theory of population

by Vivek Malhotra

What is the Optimum theory of population? Comparison between Optimum and Malthusian theory.

Modern economists rejected the Malthusian theory of population. We are concerned with the size of population in relation to the total wealth of a country and not merely with the food supply alone. Once should not be frightened by the mere size of population in a country. If the productive system is efficient, a country can certainly support a large population. A country should develop its resources nature and economic and procedure wealth. Moreover, the wealth should be evenly distributed among the people. So the problem of population is neither of numbers not of food supply. As Seligman, observed the problem of population is not one of mere size but of efficient production and equitable distribution.

Meaning of Optimum :

The problem of population should be studied in relation to the total health of country. In this connection, ‘Cannan’ and others have introduced the idea of optimum population. Optimum population means the total population that a country should have considering its resources. Given the natural and capital resources and the state of technical knowledge, a country should have certain size of population to utilize the resources. Optimum population is that population which secures the maximum real income per head.

Over and Under Population:

If the actual population of a country is less than the optimum size, the country is said to be under populated. The population is less than the number required to work out the natural and economic resources properly. Then the real income per head is less than what is could be as the resources could not be worked properly. With every increase in population there will be increasing returns if the output will increase more than proportionately. When increasing returns are fully exploited the average product is at its maximum. The population which provides this optimum number of labourers is optimum population.

If population increases beyond this level there would be diminishing returns. The productivity per head diminishes. The population is more than what is required to work out the resources properly. The country is then said to be over populated.

Optimum size if not fixed size:

So the optimum size of the population is not a fixed size. It depends upon the natural and economic resources and the sate of technical knowledge. If new resources are developed, a county can support larger population. On the other hand, if some of the resources are exhausted, the existing population may become overpopulation. The change in the state of technical knowledge will also alter the optimum size.


Dalton framed the following formula for judging the character of a country’s population. If ‘A’ stands for the actual number of people. ‘O’ for the optimum number of people and ‘M’ for the degree of maladjustment,

M = (A-O)/ 0

When M is positive, we have population, if it is negative we have under population and if it is equal to zero, the population is of optimum size, Since, changes in ‘O’ cannot be measured, the formula is of doubtful utility to us.

Comparison between Malthusian & Optimum Theories

Let us make a comparison between optimum theory and Malthusian theory of population. We may try to find out in the first instance how optimum theory is an improvement on the Malthusian theory.

1. Optimum theory is optimistic and Malthus was pessimist:

He made the glory prophecy that all are bound to die whenever population increases.

Beyond the means of subsistence

The optimum theory is highly optimistic. Growth of population is not always a curse. An increase in population is desirable if the actual number is less than the optimum size. As long as increasing returns operate growth of population is desirable.

Further, Malthus is always concerned with securing food is to an individual. The goals of optimum theory are concerned with securing maximum income per head.

2. It hold correct ratio:

Malthus established are ratio between population and food supply. The ratio ought to have been held between population and total wealth. A country which produces enough quantity of manufactured goods and export them and important food stuffs. It is thus enable them to maintain large population even though it does not produce enough population is relation to total health. The theory places the problem of population in an altogether new and right perspective.

3. Test of overpopulation:

According to Malthus, a country is said to be over populated when positive checks like famine, disease, war etc. are positive checks that operate. But according to the new theory, the criteria are altogether different. If the real income per head can be increased by increase in population, country is said to be overpopulated. Even a country of millionaires may be regarded as overpopulated if per capita income increases by a reduction in population.

Defects of Optimum Theory:

1. Not a population theory:

The optimum theory is not a population theory. It is merely discusses the relationship between population and productive resources. It does not state anything as to how population grows.

2. Difficult to know Optimum:

It is very difficult to know the population that gives maximum per capita income and technical knowledge and resources do not remain the same. The search for optimum is therefore, a search often the mirage. Unless optimum size is known one cannot say whether a country is overpopulated or under-populated. The economists have introduced merely the familiar concept of optimum in population problem.

Essay on the Theory of Optimum Population

The relationship between population and resources forms the basis of the optimum population, theory. Edwin Cannan (1861- 1935), an English Economist, has been given the credit for defining what later came to be known as the concept of "Optimum Population."

The first beginnings of this concept may be traced to the writings of a German professor, Karl Winkelblech (1810-1865), who while describing population theory and policy, classified nations into three categories according to the size of their population: (1) Under-populated nations; (2) Over-populated nations; and (3) Nations with normal populations, meaning a size favourable to the greatest possible productivity.

Cannan used the term "optimum population" as synonymous with the best possible population, and clarified this in the following words, "At any given time, the population which can exist on a given extent of land, consistent with the greatest productiveness of industry at that time, is definite."

The concept of optimum population has been interpreted in several ways, "to mean the size of the population which results in the highest per capita income, the highest productivity as measured in different manners, or the highest level of other less well-defined economic indicators, such as economic welfare, level of living, real income and, in some cases, employment."

Some writers, considering the concept of the economic optimum as being too restrictive, have included in it the total well-being, health, and longevity of a nation, the ideal family size, and the conservation of natural resources, power, defense and other spiritual, cultural and aesthetic factors.

According to most writers, however, the economic optimum was the main consideration in the optimum population theory, and gradually the idea of a population of optimum size for maximum production was accepted. Later developments, however, provoked a critical re-examination of this theory.

One noteworthy aspect of the concept of optimum population was that it was a reconciliation of the optimistic and the pessimistic theories of population, for it implied that the growth of population was beneficial up to a certain point, after which any further growth was harmful.

This theory has been criticised on several grounds. Several writers have challenged its practical applicability by expressing doubts whether optimum population in the sense of an optimum point can ever be determined.

Actually, very few attempts have been made to determine the optimum population of any country. (An American demographer put the optimum population size for the United States of America at 120 million.

Alfred Survey worked out a figure of between 50 and 75 million for France. Coale and Hoover arrived at the conclusion that one-fourth of the rural population of India was useless).

Some, critics of this theory have challenged the very concept of optimum population, which is essentially a static concept. According to these critics, the theory is based on the assumption of a ceteris paribus condition for all other factors such as technology, resources, social structure, external trade, etc. Such an assumption is, of course, highly unrealistic.

The idea of an optimum population attracted much attention in the 1920's and the 1930's. In recent times, Survey has once again discussed this theory at great length and has defined optimum Population as that population which best assures the realisation of Pre-determined objective, not so much as an absolute theoretical concept but as a convenient tool.


Global Challenges Facing Humanity

Please enter your comments in the space provided at the end of each challenge.

3. How can population growth and resources be brought into balance?

World population is expected to grow another 1 billion in just 12 years, creating unprecedented demand for food, water, energy, and employment. Population growth is expected to be most rapid in the 49 least developed countries, which will double the size from around 900 million today to 1.8 billion in 2050. There were only1 billion humans in 1804; 2 billion in 1927; 6 billion in 1999; and 7.2 billion by 2013. UN forecasts a range from 8.3 billion to 10.9 billion people by 2050, with 9.6 billion as the mid-projection.

Population dynamics are changing from high mortality and high fertility to low mortality and low fertility, with an increasingly elderly population worldwide. The world’s fertility rate has fallen from 6 children in 1900 and 5 in 1950 to 2.5 today. If fertility rates continue to fall, world population could actually shrink to 6.2 billion by 2100, creating an elderly world difficult to support. Today life expectancy at birth is 68 years, which is projected to grow to 81 by 2100; with advances in longevity research, this projection will increase. About 20% of the world will be over 60 by 2050, and 20% of the older population will be aged 80 or more. Some 20% of Europeans are 60 or older, compared with 10% in Asia and Latin America and 5% in Africa.

More than 20 countries have falling populations, which could increase to 44 by 2050, with the vast majority of them in Europe. By 2050 there could be as many people over 65 as under 15, requiring new concepts of retirement. Countering this “retirement problem” is the potential for future scientific and medical breakthroughs that could give people longer and more productive lives than most would believe possible today. People will work longer and create many forms of tele-work, part-time work, and job rotation to reduce the economic burden on younger generations and to maintain living standards.

To keep up with population and economic growth, food production should increase by 70% by 2050. Meat consumption is predicted to increase from 37 kg/ person/year in 2000 to over 52 kg/person/year by 2050; if so, then 50% of cereal production would go to animal feed. Farm processing insects for animal feed may offer a more sustainable option as "Insects are everywhere and they reproduce quickly, and they have high growth and feed conversion rates and a low environmental footprint," according to FAO. Some 2 billion people worldwide already supplement their diet with insects today. FAO’s Food Price Index as of April 2013 is about 9% lower than its peak in February 2011. However, food prices may rise again due to increasing affluence (especially in India and China), soil erosion and the loss of cropland, increasing fertilizer costs (high oil prices ), market speculation, aquifer depletion, falling water tables and water pollution, diversion of crops to biofuels, increasing meat consumption, falling food reserves, diversion of water from rural to urban, and a variety of climate change impacts.

The number of hungry people declined by 132 million between 1990-92 and 2010-12. Yet, about 870 million people, or one in eight in the world, are chronically undernourished today. FAO lists 35 countries that are in need of external food assistance and WFP provides food assistance to more than 90 million people in 73 countries. Yet in some of these countries, agricultural lands (mostly in sub-Saharan Africa) are being sold or leased to foreign investors to feed people in their own countries. Since 2006, more than 400 large-scale land-grabs covering nearly 35 million hectares of land in 66 countries have been reported. European- and Asian-based investors account for about two-thirds of the deals listed by GRAIN. Grain imports to the Arab countries in the Middle East and North Africa increased to 70 million tons in 2011, more than doubling since 1990. OECD estimates that the private sector’s investment in farmland and agricultural infrastructure is as much as $25 billion and could double or triple over the next three to five years. Responsible Agricultural Investment, backed by the World Bank and UN agencies, aims to promote investment that respects local rights and livelihoods, but it is heavily criticized by NGOs as a move to legitimize land grabbing.

Massive wheat damage by the Ug99 fungus in 2009 was less in 2010; its genome is now sequenced and Ug99-resistant wheat is now available; nevertheless, creating alternatives would be wise to avoid future pandemics like the Ug99 fungus. Conventional farming relying on expensive inputs is not resilient to climatic change. Agricultural productivity could decline 9–21% in developing countries by 2050 as a result of global warming. Small-scale farmers can double food production within 10 years by using ecological methods. Agroecological farming projects have shown an average crop yield increase of 80% in 57 countries, with an average increase of 116% for all African projects. GM cotton crops in China have cut pesticide use in half since the introduction of insect-resistant BT cotton in 2007, but monocultures undermine biodiversity, which is critical for agricultural viability.

New agricultural approaches are needed, such as producing pure meat without growing animals, better rain-fed agriculture and irrigation management, genetic engineering for higher-yielding and drought-tolerant crops, reducing losses from farm to mouth, precision agriculture and aquaculture, planting sea grass to bring back wild fish populations, and saltwater agriculture (halophytes) on coastlines to produce food for human and animals, biofuels, and pulp for the paper industry as well as to absorb CO2, reduce the drain on freshwater agriculture and land, and increase employment. The global market for organic food and beverages increased threefold in the past decade, with organic agriculture found on 37 million hectares in 160 countries.

Examples of other ways to help balance future populations and resources include: encourage vegetarianism, anticipate potential impacts of synthetic biology and other longevity technologies that could make aging healthier and more productive, accelerate safe nanotech R&D (to help reduce material use per unit of output while increasing quality), encourage telemedicine (including online self-diagnosis expert software) and mobile phone tele-education (although the vast majority of the world is literate, there are still 1.4 billion who are not, and illiterates are the majority in 21 countries), integrate urban sensors to create smarter cities, and teach urban systems ecology. Some 52% of the world’s population currently lives in urban areas; by 2025 it will increase to 58%. In 2025, 4.3 billion urban residents will generate 2.2 billion tons of solid waste per year, an increase from 1.3 billion tons per year today.

Without more intelligent human-nature symbioses, increased migrations, conflicts, and disease seem inevitable. ICT continues to improve the match between needs and resources worldwide in real time, and nanotech will help reduce material use per unit of output while increasing quality.
Challenge 3 will be addressed seriously when the annual growth in world population drops to fewer than 30 million, the number of hungry people decreases by half, the infant mortality rate decreases by two-thirds between 2000 and 2015, and new approaches to aging become economically viable.

Regional Considerations

Africa: More than half of global population growth between now and 2050 is expected to occur in Africa. Africa’s population doubled in the past 27 years to reach 1 billion. It is projected to reach 2.7 billion in 2060, and possibly growing to 3.6 billion by 2100. Half of Africa’s population is age 17 or less, and the active population age 15–64 will triple between 2005 and 2060. By 2050, one in every three births will be African, and almost one in three children under the age of 18 will also be African. UNICEF estimated 60% of urban dwellers live in slum conditions today; children in these conditions are less likely to go to school and have poor nutrition, increasing future unemployment and probabilities of prolonged social conflicts. Very rapid growth of the young population and low prospects for employment in most nations in sub-Saharan Africa and some nations in the North Africa could lead to prolonged instability until at least the 2030s. Historically, however, growing populations have often led to the economic growth. Yet increasing population density, coupled with degrading soil fertility and climate change, will put immense pressure on natural resources. Hence, increasing investments into rural nutritionally rich agriculture and women, who lead African agriculture, will reduce malnutrition—Africa’s greatest public health problem. Much of the urban management class is being seriously reduced by AIDS, which is also lowering life expectancy. Only 28% of married women of childbearing age are using contraceptives, compared with the global average of 62%. Conflicts continue to prevent development investments, ruin fertile farmland, create refugees, compound food emergencies, and prevent better management of natural resources.

Asia and Oceania: China plans to spend some 40 trillion yuan ($6.5 trillion) on urbanization, bringing 400 million people to cities over the next decade. China has more than 170 cities with populations over 1 million, and the number could increase to 221 by 2025. China has to feed 22% of the world’s population with less than 7% of the world’s arable land. There were six Chinese children for every one elder in 1975; by 2035 there will be two elders for every one child. China is growing old before it has grown rich. The median age of Japan is almost 45 years; by 2040 it will be 55 and its population decreases from 127 million to 106 million. Suicide and depression cost Japan $32 billion. Suicides have exceeded 30,000 annually since 1998. Approximately a third of the population in the Middle East is below 15; another third is 15–29; youth unemployment there is over 25%. New concepts of employment may be needed to prevent political instability. Farmers in Asia are getting older; the average age of Thai farmers was 42 in 2010, a jump from 31 in 1985. About 5 million people are estimated to be severely food-insecure. Mandatory labeling of GM food will be introduced in India from January 2013. Indonesia has banned exports of 14 un-processed raw minerals. China is reducing its export of scarce strategic rare earth metals. By 2030, Australia will be the second largest LNG producer after Qatar if planned projects go ahead.

Europe: By 2030 Europe’s population is expected to peak and then decline, losing as much as 100 million people in the next 50 years. Women’s life expectancy at birth in EU by 2060 could reach 89.1 years, up from 82.5 in 2010; men’s could be 84.6 years, up from 76.7 in 2010. About 30% of the population will be 60 or older in 2060, and the number of workers supporting pensioners will decrease from four to two. The Center for Strategic and International Studies forecasts that people of Muslim origin will grow to 25% of France and 33% of Germany by 2050. Europe’s low fertility rate and its aging and shrinking population will force changes in pension and social security systems, incentives for more children, and increases in immigrant labor, affecting international relations, culture, and the social fabric. East to West European migrations are expected to continue and rural populations are expected to shrink, freeing additional land for agriculture. Russia’s population peaked at 149 million in 1991 and then began a decade-long decline, falling at a rate of about 0.5% per year due to declining birth rates, rising death rates, and emigration; the last few years, however, have seen some population growth, increases in life expectancy, and immigration. About 2.5% of Russia’s economically active population in 2011 was legal migrants. Nearly two-thirds of the youth in Greece are jobless.

Latin America: About 85% of the region will be urban by 2030, requiring massive urban and agricultural infrastructural investments. Over 53 million people are malnourished. Brazil, Ecuador, Venezuela, Guatemala, Honduras, and Nicaragua have approved food security laws to ensure local agricultural products are primarily used to feed their own populations and not for export; nine more countries are planning the same. Latin America’s elderly population is likely to reach 188 million in 2050 or 18.5% of the total population. By 2050, half of Mexico’s population will be older than 43, with an 18-year increase in median age. As fertility rates fall in Brazil and longevity increases by 50% over the next 20 years, the ability to meet financial needs for the elderly will diminish; hence, the concept of retirement will have to change, and social inclusion will have to improve to avoid future intergenerational conflicts. Peru imposed a 10-year moratorium on imports of GMO products; Peru is one of the world’s leading exporters of organic food, with $3 billion in annual revenue.

North America: Minorities in the United States are now the majority of those under one year old. The number of elderly prisoners jumped 1,300% since the 1980s. The number of those 65 or older in the U.S. is expected to grow from about 40 million in 2009 to 72 million in 2030. Less than 2% of the U.S. population provides the largest share of world food exports, while more than 10% of households are food-insecure and two-thirds of people in the U.S. are overweight or obese. The prevalence of type 1 diabetes among American youth increased 23% from 2002 to 2009. Reducing “throw-away” consumption could change the population-resource balance. Biotech and nanotech are just beginning to have an impact on medicine; hence dramatic breakthroughs in longevity seem inevitable in 25–50 years. Vancouver, Toronto, and Calgary are among the five most livable cities of the world. North American farmers are increasingly asking: “How can we ensure that our farming systems are resilient enough to withstand weather extremes?” Global warming should increase Canadian grain exports.

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