Sunday, June 4, 2017

Demography, carrying capacity and entrapment

Preamble: This is an adaptation of the second chapter of my doctoral thesis (Inequality and Sustainability), which was supervised by Professor JC (Jack) Caldwell, a co-recipient of the 2004 UN Population Prize. It was awarded the Borrie Prize by the Australian Population Association (APA) in 2002.
This essay traces the rise and fall of Malthusian thinking within demography. Despite winning the Borrie Prize, versions of this paper were rejected by many demographic journals, include the Journal of Population Research (the APA’s journal), the Population and Development Review and at least five more. Today, despite having successfully published at least 50 articles, chapters and reports of relevance to global population dynamics, I have not yet been published in a primarily demographic journal. I share Maurice King’s opinion that mainstream demography has been corrupted by neoliberal forces who deny limits to growth, not only physical but social.
I have added a comment today (2017) about the figure, shown in PURPLE CAPITAL LETTERS

The concept of non-human carrying capacity -- the population of a species supportable by a given set of resources -- is a commonplace, generally accepted and understood not only by ecologists but also by the general public. Yet the related topic of human carrying capacity, though once also widely accepted, has in recent decades received little attention among demographers and economists. The recent reluctance by demographers to contribute to this debate, though heir to an intellectual tradition containing much that is relevant to it, is regrettable, and undermines the credibility of global population scenarios forecast by demographers.

The suggestion proposed by some “cornucopian” economists that humans, unlike other animal species, can indefinitely evade carrying capacity limits has no basis. The agnosticism of most demographers regarding this debate does a disservice to demography and increases the risk of highly undesirable future global population scenarios.


The concept of a limited carrying capacity for non-human species was once widely accepted by ecologists (Klein, 1968)[1] and the general public. While aspects of it became controversial from the 1950s its most important element – that of limits to growth – remains unchallenged. Although it has fallen into some Indeed, this appreciation is not a uniquely human characteristic, but intuitively appreciated, though of course not verbalised, by all territorial species (Boehm, 1999).[2] Likewise, this concept must also have been long understood by our own species, since the time that bands of humans first explored new territories and were rewarded by the discovery of less-exploited resources further along the coast or across the sea (Flannery, 1994).

The concept of human carrying capacity – the maximum human population supportable over a prolonged period by a given set of resources, including human ingenuity and knowledge – appears, until recently, to have also been well understood and accepted by many in both the general public and the academy. In the last few decades, the influence of this school of thought has become increasingly marginal, especially among social scientists. 

The best-known author in this field in recent years is the ecologist Paul Ehrlich (Ehrlich, 1968; Ehrlich and Ehrlich, 1990; Ehrlich et al., 1995). Many mainstream social scientists, particularly economists, have at times ridiculed Ehrlich’s position, characterising him and his supporters as “doomsayers” (Kasun, 1988; Economist, 1994). The discipline of ecological economics is an important exception (Arrow et al., 1995), but though intellectually robust (Daly and Cobb, 1989; Daly, 1996) it remains politically uninfluential (Butler et al., 2001). Few demographers now treat or study the issue of global human carrying capacity seriously, despite the privileged position accorded to this profession in its preparation of future global population scenarios (United Nations Population Division Department of Economic and Social Affairs, 2001).

Global human carrying capacity

No credible writer on the subject of human carrying capacity denies that it is elastic. An irrefutable example of this elasticity is the massive increase in human population in the last ten millennia made possible by agriculture. More recently, the industrial and Green revolutions have enabled substantially larger increases in both human population and global carrying capacity. However, while further increases are likely, driven by ongoing improvements in resource utilisation, ingenuity, social organisation and technology (Boserup, 1965), it is far from certain that the marginal increase in global carrying capacity will continue to exceed the marginal demand placed upon it by additional people. Like a balloon, human carrying capacity is elastic, but this does not mean its indefinite inflation is possible.

The recent success at increasing global human carrying capacity has led to a number of extreme claims. For example, the African Academy of Science, at the New Delhi “Science Summit” on population in 1993 stated:

“Whether or not the Earth is finite will depend on the extent to which science and technology is able to transform the resources available for humanity. There is only one earth - yes, but the potential for transforming it is not necessarily finite" (African Academy of Sciences, 1994) (emphasis added).

Lawrence Summers, Under-Secretary in the US treasury in the Clinton administration, exhibited a similar exuberance:

“There are no...limits to the carrying capacity of the earth that are likely to bind any time in the foreseeable future. There isn't a risk of an apocalypse due to global warming or anything else. The idea that we should put limits on growth, because of some natural limit, is a profound error and one that, were it ever to prove influential, would have staggering social costs” (George and Sabelli, 1994: 109) (emphasis added).

In fact, no matter how ingenious humans become, effective limits to the maximum size of the human population will remain. As human population continues to increase, within an earth system that is closed, evidence is increasingly accruing to suggest that these limits are approaching. The limits that now seem closest are not the exhaustion of easily recoverable trace elements, nor of compressed, portable forms energy; concerns that were highlighted by the Limits to Growth debate of the 1970s (Meadows et al., 1972; 1992). Instead, it is increasingly clear that the capacity for the Earth system to absorb waste products of human civilisation has been exceeded (Vitousek et al., 1997a). For example, the atmospheric concentration of many greenhouse gases has increased substantially. Carbon dioxide concentration has increased by a third in the last two centuries, while that of methane has almost trebled. Chlorofluorocarbons, a synthetic gas, have reduced the stratospheric ozone layer by over 10% (Butler, 2000a). Though the fixing of atmospheric nitrogen, first accomplished in 1913, greatly increased soil fertility and consequently the human population (Meyer, 1996) many adverse ecological consequences of nitrogen overload have also resulted (Vitousek et al., 1997b).[3]

Clearly, the Earth system is able to tolerate a substantial degree of waste accumulation. Less certain is the degree to which this can continue without commensurate damage to the human civilisation supported by the biosphere. Waste products continue to accumulate, as do adverse ecological effects on a global scale. For example, the Intergovernmental Panel on Climate Change has predicted that global warming, consequent to the accumulation of waste greenhouse gases, is likely to increase the average global temperature over the next century by 1.4 to 5.8 degrees Celsius (Intergovernmental Panel on Climate Change, 2001). Computer models (Knutson et al., 1998) and tentative empirical evidence (Easterling et al., 2001) suggest this will be accompanied by increasingly severe weather events, including more powerful storms and stronger winds, an intensification of the El Niño Southern Oscillation cycle (Timmermann et al., 1999) and changing patterns of drought and rainfall (Fischer et al., 2001). As well, global sea level is predicted to increase by between 9 and 88 cms (Intergovernmental Panel on Climate Change, 2001) over the next century.

These changes, resulting simply from climate change, are likely to have profound adverse effects to the economy, especially to poor populations. Although some optimists (Lomborg, 2001) contend that economic growth in the next century will allow societies that are currently poor to successfully cope with these additional stresses, there is a non-trivial possibility that the reverse could occur. The ecological and environmental stresses predicted consequent to “planetary overload” (McMichael, 1993) could trap many millions of people into lives characterised by decreasing choices and increasing poverty.

Such “ecological entrapment” (Butler, 1997) seems particularly plausible if recent global economic policies, characterised by increasing national and global inequality (Butler, 2000a; Milanovic, 2002) continue. These policies have been exacerbated by the abandonment of once widely-accepted aid targets (Jha et al., 2002) and increased awareness, by the poor, of their relative poverty. These factors may well lead to resentment, despair, and, ultimately, mutually destructive attacks launched by excluded populations and their supporters against populations perceived as wealthy, dominant, and exploitative (Sachs, 2001; Butler, 2001a).

The rise and fall of Malthusianism

The disregard of the carrying capacity debate in recent decades by most demographers is particularly surprising given that until recently it was a central issue for population scientists. Many past scholars recognised and discussed regional human carrying capacity, including in ancient Babylon, Rome, Greece and China (Cohen, 1995; Demeny, 1988; Sallares, 1991). Ecclesiastes (5:11) records that “when goods increase they are increased that eat them”. In China, Hung Liang-Chi (1744-1809) wrote, independently of Thomas Malthus (1766-1834), of population outstripping food supply, survival of the fittest, and the reliance on the natural “checks” of flood, drought, plague, pestilence and warfare to limit population growth (Silberman, 1960; Borrie, 1974).

In the western tradition, many of the concepts embedded in this debate are known eponymously, as Malthusianism. Malthus’s main work An essay on the principle of population (1798) predicted that population would grow “geometrically” (in multiples) while food production would only grow “arithmetically” (in additions). Thus, food production would never keep pace with population growth. This pessimistic forecast was lightened by later editions that allowed the possibility of “moral restraint”, including delayed marriage, to slow population growth, rather than the checks of famine and war (AtKisson, 1999; Boserup, 1978; Keyfitz 1993; Johnson, 1999a).

Malthus’s arguments had considerable influence, including to the theory of evolution (Desmond and Moore, 1991: 264-265) and to British economic policy, including its response to the Irish famine of the hungry 1840’s. Malthusian thought dominated the population debate in Europe at least until the “optimistic 1860s” (Boserup, 1978;  Desmond and Moore, 1991: 266), but persisted far longer in less industrialised, low-income and famine-prone countries such as India (Caldwell, 1998).

Though never entirely absent, public concern over Malthusian arguments diminished further in the 20th century. In that period, global population increased almost fourfold, as innumerable technological advances not only curtailed death rates, but also allowed food production to pull ahead of population, at least temporarily. However, in the 1960s, fears of a global food shortage resurged (Paddock and Paddock, 1967; Ehrlich, 1968). This period experienced the maximum rate of global population increase (slightly over 2% per annum) (United Nations Population Division Department of Economic and Social Affairs, 1995: 99), a severe grain shortage in India (Brown, 2001; Kasun, 1988) and a massive, though largely secret and man-made famine in China (Smil, 1999). However, concerns rapidly abated in the following decade, as the Green Revolution dramatically improved crop yields throughout much of the world.

Perhaps as a sign of the widespread relief felt at the abatement of these concerns, the agricultural scientist Norman Borlaug was awarded the 1970 Nobel Peace Prize for his work in promoting this revolution. But, in his acceptance speech, Borlaug warned:

“The Green Revolution has won a temporary success in man's war against hunger and deprivation; it has given man a breathing space. If fully implemented, the revolution can provide sufficient food for sustenance during the next three decades. But the frightening power of human reproduction must also be curbed; otherwise the successes of The Green Revolution will be ephemeral only” (Tribe, 1994: 16) (emphases added).

In the following decade, per capita global grain production continued to rise and memory of Borlaug’s warning faded. China’s introduction of its one child policy in 1979 imposed an accelerated demographic transition upon one quarter of humanity.

In the US, the election of Ronald Reagan (1981) broke a chain of presidents from J.F. Kennedy to Jimmy Carter (Kasun, 1988; Nixon, 1992; Finkle and MacIntosh, 1994) each of whom[4] had expressed grave concern about the rate and sustainability of Third World population growth. In contrast, the Reagan administration was marked by a progressive reduction in funding for Third World family planning programmes (Kasun, 1988; Cincotta and Crane, 2001) and by increasingly influential economic arguments that claimed to justify this position.

In the 1950s, the classic Malthusian scenario of rapid population growth leading to food scarcity had been broadened to examine the relationship between rapid population growth and economic growth. Influential publications by Nelson (1956) and Leibenstein (1954; 1957) theorised that capital-poor governments and populations struggling to provide the infrastructure needed to escape poverty could instead be trapped in a negative feedback spiral, fuelled by excessively rapid population growth. Nelson (1956) called this a “low level equilibrium trap”.

The harmful effects of rapid population growth, especially in capital-poor Third World countries, were widely accepted in the following decades, and were an important cause of the one child policy introduced by China in 1979 (Kane and Choi, 1999). However, in 1980, the conservative economist Julian Simon attacked this theory in an article entitled There is no low-level fertility and development trap (Simon, 1980). In 1986, a report from the US National Academy of Sciences report substantially revised warnings issued by a previous report from 15 year earlier. Importantly, this latter report claimed to discredit the economic reasons that until then had underpinned concerns about rapid population growth (Eberstadt, 1992).

Davidson has not only argued that economics is not a value free science, but also likened the role of economists to priests, whose most valued role is to assuage the guilt of those who are most powerful and wealthy:

“It is good to be rich. It is even better to feel good about it. Much of the theoretical baggage associated with economic rationalism provided the ethical justification for the credo of the 1980s... the real task of the economic rationalist is the not the creation of wealth-it is to convince the rich that their greed is the engine whose generation creates wealth for the whole community”.

Similarly, it can be argued that the radically altered conclusions of the 1986 National Academy Report were based on a substantially different set of values to the previous report. In particular, the 1980s were characterised by a significant change to the political right, with an ascendancy of neo-liberal economic policies, particularly in the English speaking economies. A theory advanced by Julian Simon and his supporters, though intellectually porous, nevertheless served the purpose of assuaging the concerns of the public about overpopulation in the Third World.

Essentially, this theory proposed that because every additional person had two hands and a mind, laissez faire population growth and free trade economic policies could help solve rather than hinder global development (Simon, 1980; 1981; Simon and Kahn, 1984).[5] Though vigorously attacked, including in several reviews in the Population and Development Review (Serageldin and Kantner, 1982; Timmer, 1982) Simon’s arguments were remarkably influential (Crane and Finkle, 1989; Beder, 1998).

Simon’s core argument dismissed or ignored many factors needed to realise human potential. These include education, transport facilities, and freedom from chronic diseases and certain kinds of pollution, especially in childhood (Jha et al., 2002). For example, lead pollution, micronutrient deficiency, especially of iodine and iron, and chronic caloric deficiency are all associated with substantial falls in intelligence (Darnton-Hill, 1999; Grantham-McGregor, 2002, Tong et al., 2000; Walgate, 2002). In well-organised, functioning societies, nutrition can be improved, roads built, and teachers trained. Societies can escape their poverty. But if infrastructure deteriorates, if educated workers flee in large numbers to richer countries seeking greater economic opportunity or to escape repression (Lwanda, 1998; Pang et al., 2002) or if as many or more teachers die of HIV/AIDS than graduate, then societies can spiral into a worsening cycle of entrapment (Piot, 2000).

Among the demographic community, the concept of entrapment lost favour, becoming at best a footnote to a new generation of students and teachers. A faint echo of this earlier view was recorded in 1992 by Panayotou:

“Where markets are not functioning, mobility is restricted, land and wealth are skewedly distributed, and government policies counter or block the avenues of individual and social response, a low-level trap is artificially created where diminishing returns to land lead to resource depletion and degradation, rather than to investment and innovation” (Cassen et al., 1992).

Outside the demographic literature, the concept of entrapment was revived, in a new form. In 1987 Lester Brown published a chapter called Analyzing the demographic trap (Brown, 1987) and the same term (“demographic entrapment”) was used by the eminent (King, 1967) public health worker Maurice King, whose article Health is a sustainable state (King, 1990) was published in the leading medical journal, The Lancet.[6] This and many subsequent articles, published mainly in the European and Indian medical and public health literature (King, 1990; 1991; 1999; Bonneaux 1994; Butler, 1994; 1997; 2000b; King and Elliott, 1996; 1997; McMichael and Powles, 1999; McMichael et al., 1999) [7] were highly controversial, fuelling a vigorous and still extant debate in the public health literature (Abbasi, 1999). This included proposals that significant conflict, including civil war, could sometimes arise as a consequence of severe entrapment, and that the Rwandan genocide represented such an example (Bonneaux 1994, Butler, 2000b).

These articles restated and expanded the economic entrapment theories of the 1950s, but did not explicitly acknowledge this earlier literature.[8] Many of King’s readers were probably unfamiliar with that literature; but, as an important corollary, they were also ignorant of the 1986 National Academy Report that had, ostensibly, discredited it (Eberstadt, 1992). Of crucial importance to the theme of this essay is the fact that, outside the public health literature, this debate has received scarcely any attention, not only from mainstream economists and demographers, but even from most analysts of the Rwandan genocide (Butler, 2000a). This has led King to postulate the existence of a profound intellectual barrier, which he calls the “Hardinian taboo” (King and Elliot, 1997).

The population scientist, Joel Cohen’s book, How Many People can the Earth Support provides a very rare exception, yet Cohen dismisses demographic entrapment theory by using a cursory opinion by the economist Robert Cassen (Cohen, 1995: 150). On the other hand, Cohen’s book amply demonstrates the seriousness with which he treats the subject of human carrying capacity, providing an extensive appendix on this topic.

Malthus and recent demographic agnosticism

Writing outside both the public health and demographic literatures, a number of other scientists have also continued to worry about global human carrying capacity. More than two decades after his original warning, Borlaug stated that: “I am deeply concerned that humankind is being taken to the brink of disaster in hopes that a scientific miracle at the last moment will save the day” (Borlaug, 1995). The World Scientist’s Warning to Humanity, originally issued in 1992, was signed by more than 1600 eminent scientists, including over a hundred Nobel laureates (Kendall et al., 1995). Both it and a similar document, called Population Growth, Resource Consumption and a Sustainable World, jointly released by the US National Academy of Sciences and The Royal Society (Atiyah and Press, 1992) warned of grave dangers if population growth and patterns of human activity remain unchanged.

Paul Demeny, editor of the Population and Development Review, has chastised his demographic colleagues for their recent abstinence from this debate. For example, in 1988, Demeny wrote:
“Despite the pertinence of the concept to their discipline, most demographers have tended to address the question of population carrying capacity gingerly, if at all ... they have always been conscious that such success (a rapid increase in human population size) cannot last long. To hammer home this simple truth, a truth that should be evident, as Malthus noted ... has been the time-honoured task of demographers. The demographic literature is thus replete with reminders that population growth is a necessarily transitory experience of the human species, but is rather short on specifics as to how exactly long that passing moment in history may last” Demeny (1988: 216) (note in brackets added).
In the following year, Demeny (1989) reviewed The Cassandra Conference (Ehrlich and Holdren, 1988), a book based on a conference that entirely presented neo-Malthusian arguments. In this, Demeny again appealed for greater engagement by demographers with the wider debate concerning human carrying capacity:

“A chapter in the book that should be obligatory reading for demographers is Garret Harden's contribution ... Hardin present an honor list of authors ‘whose works have contributed most to our understanding of population.’ Demographers are conspicuous by their absence in the list. Save for some exceptions, says Hardin, demographers either say nothing about the human significance of the figures they play with, or they tell us ‘not to worry’. They suffer from ‘pathological numeracy’. Apparently, no one rose to dispute the charge. Had there been a card carrying demographer present, his rebuttal to the ungallant diagnosis would have been probably less than vehement” Demeny (1989) (emphases added).

Hardin, a human ecologist, supports the main argument of this paper, that demographers have largely withdrawn from the neo-Malthusian debate. Hardin goes further, by suggesting that many have adopted a patronising tone concerning it. Demeny not only expresses sympathy with Hardin’s interpretation, but also hints that he may be trying to use his position to advocate greater engagement with these issues among demographers.

Joel Cohen, though dismissive of demographic entrapment, has also argued that demographers need to widen their horizons to more explicitly consider environmental issues. Cohen also has also referred to the demographer Kingsley Davis in support, quoting him as complaining “no one specialises in the study of population and resources as an integrated discipline” (Cohen, 1995:389).

Demeny has attempted to lead by example. Unfortunately, his most rigorous attempt to consider the issue of global human carrying capacity, an essay called Demography and the limits to growth (Demeny, 1988) suggests a significant unfamiliarity with the relevant environmental literature. Discussing the children’s riddle[9] used to illustrate the concept of exponential growth and the Limits to Growth, perceived by Meadows et al., (1972) Demeny asks:

“How is to be ascertained that we are on the 29th day and face the last chance ‘to save the pond’? Diagnosis is a simple matter if what is required is to look at a backyard lily pond, but is clearly less obvious in sizing up the state of the global population. On what basis can we discard the conjecture that the present corresponds, say, to the 24th day, when the global pond would be 1/64th full?” (Demeny, 1988).

This question reveals an apparent ignorance of a then recently published paper that  had argued that the human appropriation of the products of terrestrial photosynthesis already approximated 40% (Vitousek et al., 1986). Demeny’s paper mainly focussed upon responses to major limits to growth perceived a decade earlier, particularly of raw minerals and energy. In the subsequent years the debate had broadened, both to the capacity of the Earth system to absorb the waste products of civilisation, such as greenhouse gases and ozone depleting substances and, as Vitousek et al’s 1986 paper exemplifies, to estimates of the global “footprint” upon the biosphere (Wackernagel and Rees, 1995).
Though Vitousek et al’s paper can be criticised as an heroic, pioneering attempt, it remained, until the publication by Rojstaczer et al (2001), the most authoritative publication on this subject.[10] In contrast to Demeny’s ignorance of this paper, Vitousek et al (1986) not only explicitly referred to the proximity of a limit to global growth implied by their findings, but also demonstrated familiarity with both the cornucopian and demographic literature, citing Simon, Herman Kahn, and Demeny himself.
Demeny’s failure to discuss this paper fuels speculation that, possessed with a little more information, he may have more clearly expressed a neo-Malthusian viewpoint than he did. Instead, both in this paper and a number of book reviews (Demeny, 1982a; 1982b), Demeny settles on a position that, though not cornucopian, is far more optimistic than that of the ecologists.

With few exceptions (Day and Day, 1965; Day and Rowland, 1988; Day, 1998), most mainstream demographers and economists have continued to write as though the issue of global human carrying capacity is irrelevant in the foreseeable future – as though the world might safely accommodate at least another doubling of its population. A very recent exception to this is provided by the demographer Jon Bongaarts, who provides a rephrasing of entrapment theory:

“Rapid population growth leads to a young population, one in which as much as half is below the age of entry into the labor force. These young people have to be fed, housed, clothed and educated, but they are not productive, thus constraining the economy. Second, rapid population growth creates a huge demand for new jobs. A large number of applicants for a limited number of jobs exert downward pressure on wages, contributing to poverty and inequality. Unemployment is widespread, and often workers in poor countries earn wages near the subsistence level. … This points to another burden of rapid population growth: the inability of governments to cope with large additions of new people. In many developing countries, investments in education, health services and infrastructure are not keeping up with population growth” (Bongaarts, 2002) (emphasis added). 

Approaching the limits?

Several factors, acting synergistically, may soon force additional demographers and economists to reconsider the relevance of global carrying capacity. One is that, despite widespread denial of both its reality and significance, the trend of the per capita global grain harvest appears to have entered a period of sustained decline (see figure).

A second factor is that the increasing number of global refugees is arguably related to the overloading of regional carrying capacity in many impoverished parts of the world. Refugees, asylum seekers, and organised people smugglers, driven by strong “push” and “pull” factors, are proving an increasing problem for most wealthy countries. In addition, despite birth rates that are well below population replacement in most developed countries, the barriers to unskilled immigrants from poor population-surplus nations continue to steepen. Few commentators have explicitly connected both the push and the “block” factors to carrying capacity (Butler, 2001b).

Thirdly, as a consequence of climate and other global environmental changes, themselves mostly brought about by “planetary overload” (McMichael, 1993), it is plausible that total global carrying capacity may actually decline in the coming century, even if technology and agricultural yields continue to improve. The most likely path for this is if, as some global climate simulators predict, the agricultural capacity of the world changes markedly. Though most writers on this subject have concluded that the total global food growing potential capacity will remain roughly equivalent to today (Parry and Rosenzweig, 1993; Dyson, 1999a; 1999b; Parry et al., 1999), I am unaware of any that have discussed the implications of the marked shifts in regional agricultural capacity predicted by most models.

For example, modellers at the International Institute of Applied Systems Analysis, have warned that, by 2080, climate change may decrease agricultural capacity in large parts of South Asia, Indonesia and Sub-Saharan Africa (Fischer et al., 2001). The models suggest compensatory increased agricultural potential in parts of North Asia and Canada. This scenario of winners and losers presents many problems.

Falling food production in densely populated tropical and sub-tropical regions is likely to lead to widespread unemployment and hardship, especially for subsistence farmers, and increased urbanisation. In addition, the areas predicted to develop a more favourable agricultural climate (provided they also have suitable soil characteristics) are largely situated in countries other than those most likely to be adversely affected. Thus, farming populations made redundant by climate change are unlikely to be able to easily migrate to the virgin lands that changing weather patterns may open up for development. As well, agricultural developments in these areas are likely to be more capital intensive than those that are displaced, and thus unable to employ more than a fraction of the displaced workforce, even if migration is possible.

Two issues are even more problematic. Populations disadvantaged by climate change will not only need to generate sufficient funds to import food, but the developers of the new land are likely to need a strong economic incentive to do so. Finally, the climatic transition is unlikely to be temporally smooth; that is to say, there may be periods when the climate limits the harvest in both the new and old areas. This could lead to a significant shortfall in global food supplies, with resultant political and economic crisis.

While such a decline would not necessarily be catastrophic, it is likely to require a greater willingness by powerful populations to share their wealth than has been evident in recent decades (Butler, 2000a). At the worst case, excessive selfishness by a privileged minority could provoke a form of a “global guerrilla war” in which comparatively poor populations use increasingly desperate and violent means to express their frustration. Indeed, the recent terrorist attacks on the US, especially on September 11, 2001, can be interpreted in this way (Butler, 2001b). 

The global grain harvest

Data from the Food and Agricultural Organisation shows that the per capita global grain harvest peaked in 1985. The significance of the decline in the following decade has been extensively debated, but little attention has yet been paid to the decline that has occurred in more recent years. Advocates in this dispute have either expressed concern and called for more debate (McMichael, 1995; King and Elliott, 1996) or taken the view that decline is unimportant.

Supporters of the latter school have advanced two main arguments. Some have claimed that the decline is an artefact caused by aberrant economic factors in the mid-1980s and early 1990s (Dyson, 1999a; 1999b; Alexandratos, 1995; 1999; Ruttan, 1996). Others have suggested that even if the decline is real, it is unimportant because of “Simpson’s paradox” (Alexandratos, 1999; Johnson, 1999a; 1999b). This is that, using certain assumptions, it is possible to demonstrate mathematically that grain consumption can increase for both wealthy and poor populations, even if the average per capita global grain consumption declines, provided an increasing percentage of the global population is relatively poor.

Given the most sustained decline in the per capita grain harvest in each of the last five years, the first argument looks increasingly vulnerable. There are also plausible reasons for a decline in this indicator, other than the withdrawal of subsidies that may have irrationally stimulated excessive European grain production in the 1980s. Although grain yields are continuing to improve, their rate of increase is slowing. This is in part because many of the gains obtainable from easy fertilisation and irrigation of crops have already been made. As well, theoretical limits to the efficiency of photosynthesis may be approaching (Sheehy, 2001a). Finally, heat stress consequent to global warming (Sheehy, 2001b) and soil degradation are also reducing yield increases (Wood et al., 2000).

The second theory used to make the case that the fall in the per capita harvest is benign is also problematic. Without more data, Simpson’s paradox remains a speculative explanation. As well, it fails to explain why the paradox did not apply in the years prior to 1985, when the increase in the global grain harvest stayed comfortably ahead of population increase.

While it is true that the real international price of grain prices does not yet suggest an impending grain shortage, the price is artificially depressed by subsidies (Bongaarts, 2002). Furthermore, many poor populations lack adequate food entitlement (Sen, 1981). That is, these populations are unable to acquire sufficient money to generate effective demand. The size of this population is very large. Already, about 33% of children aged under five years in developing countries suffer moderate or severe growth retardation, and the prevalence rises to over 50% in some least-developed countries (Grantham-McGregor, 2002). This reflects chronic under-nutrition, and demonstrates that the price of grain, even if low compared to the purchasing power of wealthy populations, is too high for hundreds of millions of people.

Figure 1. World per capita grain production 1966-2001.
The per capita global grain harvest has declined since its maximum in 1985. Preliminary data for 2001 suggests a further decline. Data Food and Agricultural Organisation (2001), United Nations Population Division Department of Economic and Social Affairs (2001)



An encouraging exception to the general silence expressed by most demographers concerning global carrying capacity was recently provided by John Bongaarts:

“Considerable uncertainty in projections stems from unexpected events. Wars, natural disasters, economic crises, and similar events can generate streams of migrants, suppress fertility temporarily, and produce many premature deaths. On the positive side, unexpected biomedical breakthroughs may lead to large increases in life expectancy or provide new fertility options. Environmental crises that may loom in the future are an additional concern. Events of such types are not within the competence of demographers to predict. Their involvement in interdisciplinary work is essential to obtain a better appreciation of the likelihood and demographic implications of such events (Bongaarts et al., 2000) (emphasis added).

Though Bongaarts acknowledges that demographers are not trained to competently predict environmental crises, his sentiment that demographers need to seriously consider their possibility is refreshing, and would probably be applauded by both Cohen and Demeny.[11]

However, the vast majority of demographers and non-ecological economists have, in recent decades, ignored or greatly discounted human carrying capacity issues. Instead, most of the social science community has assuming, either explicitly or implicitly, that science, technology and free market economic policies will provide ready answers to cope with resource scarcities and the resulting tensions and conflicts likely to arise. This complacency is at odds with the repeated warnings of numerous elite scientists and scientific bodies (Atiyah and Press, 1992; Union of Concerned Scientists, 1992; 1997) who have instead argued that the only safe way to ensure adequate global carrying capacity is to reduce consumption levels and accelerate the global demographic transition.
Bongaarts’ appeal for greater engagement with this debate by demographers and economists warrants support. Bongaarts implies that demographers and economists lack sufficient training and skills to fully to fully appreciate the environmental literature relevant to global carrying capacity. A corollary of this is that they also lack any credible license to claim that this literature is invalid.

In recent decades, as public concern for overpopulation has diminished, so too has funding for family planning and foreign aid programmes. Collectively, the social science community bears substantial responsibility for this. Closer co-operation and greater humility, by parties on both sides of this debate are urgently needed if humanity is to safely traverse the shoals that clearly face it.


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[1] Klein describes a classic case-study of ecological imbalance with overpopulation. Two dozen reindeer were introduced in 1944 onto St. Matthew Island. Lichens were plentiful and there were no predators. The population increased rapidly, reaching a peak of about 6,000 in 1963. During the heavy snows of 1963-64 almost all of the animals died, leaving a herd of 41 females and 1 male. The deficiency in food, because of overgrazing, is thought to have contributed to the high death rate. The carrying capacity for this species on this island was clearly less than 10,000.

[2] Territorial species live and feed in given areas, marking and patrolling their borders and exhibiting hostility to invaders and competitors, even if of the same species. At the same time, species will generally not try to “invade” the territories of their neighbours. This behaviour has apparently evolved in response to carrying capacity limits.

[3] The amount of nitrogen fixed by humans now exceeds that from natural processes.

[4] With the possible exception of President Ford (1974-7).

[5] These propositions are sometimes, characterised as ‘cornucopianism” or “exemptionalism” (Cairns, 1999) 

[6] This journal has a long tradition of championing controversial causes (Kandela, 1998); it also has a wide international readership, including many health workers in poor countries.

[7] But not the American literature.

[8] A recent article, published on the internet, cites Leibenstein (1954). 

[9] If the lilies on the surface of a pond double in area every day, and the pond is covered by day 30, when is the pond half covered?

[10] Rojstaczer et al (2001) came to similar conclusions.

[11] The Encyclopaedia of Global Population and Demographics (Ness and Ciments, 1999) has also given substantial credence to neo-Malthusian arguments.