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Population and Environment: Assumptions, Interpretation, and Other Reasons for Confusion
Virginia Deane Abernethy
Vanderbilt University School of Medicine
Introduction
Women and couples in virtually every country in the world are decreasing their desired and actual family size, but the Oct. 16, 1998 issue of Science (p.420) describes an increase in the U.S. fertility rate, "from 1.77 to 2.08 births per woman between 1975 and 1990." In the 1970s, American women reduced their fertility rate to below replacement level, so their childbearing at young ages was low by historic standards. Extrapolation of that fertility behavior to the remainder of their reproductive careers gave the appearance, states John Bongaarts of the Population Council, of very low completed fertility. Bongaarts concludes that the low rate in 1970 was more apparent than real because he assumes that these deferred births were made up at later ages and account for the 2.08 births per woman reported in 1990 (Bongaarts 1998).
This is a nice try, very politically correct, at obscuring the reality that the United States was the recipient of heavy immigration during the 1970-1990 period, and that this flow of newcomers raised the fertility rate. In fact, the foreign-born are approximately 10 percent of the current U.S. population (and rising) and account for a disproportionate share of births. In 1994, for example, 18.3 percent of births, that is, 731,262 out of a total 3,995,767 births, were to the foreign-born (Ventura, et al. 1996).
The Hispanic sector in the United States averages approximately 3.5 births per woman and the tempo of births is rapid: women bear their first child at an earlier age than the U.S. average. Further, the teenage illegitimacy rate is higher in the second and third generations than in first-generation Hispanic immigrants, and is higher than among either white or black native-born Americans. Mexico is the single largest source of the total immigration flow and the principal reason that the U.S. fertility rate - a blend of the high fertility rate of the foreign-born sector and the significantly lower rate of the native-born (still well below the replacement rate) - is rising.
The Hispanic sector in the United States averages approximately 3.5 births per woman and the tempo of births is rapid: women bear their first child at an earlier age than the U.S. average. Further, the teenage illegitimacy rate is higher in the second and third generations than in first-generation Hispanic immigrants, and is higher than among either white or black native-born Americans. Mexico is the single largest source of the total immigration flow and the principal reason that the U.S. fertility rate - a blend of the high fertility rate of the foreign-born sector and the significantly lower rate of the native-born (still well below the replacement rate) - is rising.
The Bongaart example suggests the power of interpretation or, as christened in political circles, "spin." Numerous questions about spin arise, in fact, as one examines past population data and projections for future world population.
A standard demographic practice is to change the reported number of the total population in year x long after the year in question has passed. The revised number is then used as the base for recalculating the rate of growth through some further year. If the revised total is upward, it absorbs part of actual growth, so the rate of growth appears lower than it actually has been. For example, the UN estimated in 1973 that the 1970 world population was 3.610 billion; the 1982, 1884, and 1988 UN estimates raised the total to 3.683 then 3.693 then 3.698 billion, respectively (Umpleby 1990).
Which of the 4 totals for the 1970 population should be the base for calculating the growth rate between 1970 and, say, 1990? Demographers usually, but not always, use the most recently reported number, a practice that is defended on grounds that it uses the most up-to-date numbers available. But this ex-post facto technique regularly astonishes mathematicians.
Various projections of world population, with all their warts, are explored in this paper. Components of world population change are fertility and mortality.
Projections of World Population
The 1.77 and 3.5 in the lead example and similar numbers are a useful measure of fertility that is called, technically, the total fertility rate (TFR). This is an estimate of the "average number of births a woman would have if she were to live through her reproductive years (ages 15-49) and bear children at each age at the rates observed in a particular year or period" (Bongaarts and Feeney, 1998).
The concept of fertility rate came into broad use during the 1960s to replace birth rate. The birth rate measures the number of births per 1000 in the population at mid-year and is sensitive to the composition of the population. For example, a very large proportion of young women tends to result in a high birth rate for the population even if the average number of births per woman is small. Therefore, birth rate misses the component of individual behavior that, over the long run, is most determinative of the population growth rate.
Some analysts prefer to measure the reproduction rate, which is a refinement on fertility rate. It refers to number of daughters born, since females – because of the limited pregnancies any woman can successfully bring to term – place an upper bound on a generation’s population growth. The fertility rate statistic, however, is most commonly used.
Mortality rates have been less studied and are more straightforward. The mortality rate captures both infant and child survival and survival probabilities among the elderly and is usually expressed as the number of deaths per 1000 in the population at mid-year. It is, of course, sensitive to the composition of the population because, all else equal, a young population has a lower mortality rate.
The size, composition (age and sex), and fertility and mortality rates of national and world population are central to demographic forecasts of rates of growth and future population size. The population estimates impinge, in turn, on social, political, and economic scenarios. Population size and growth rates are relevant to almost all domains of personal and public life because they affect resource use, generation of waste products, public health, need for public expenditures on education and infrastructure, size of government, taxes, economic opportunity, crime rates and numerous other quality of life indicators.
The variety of effects linking population and environment is reflected in the term, carrying capacity. Carrying capacity refers to the number of individuals who can be supported without degrading the natural, cultural and social environment, that is, without reducing the ability of the environment to sustain the desired quality of life over the long term.
Principal sources of world population forecasts are the United Nations population projections and the Statistical Abstract of the United States published by the U.S. Census Bureau. Projections are not predictions but are, rather, an array of possibilities, each with its specific probability of actually coming to pass. The demographic method of forecasting the future entails assumptions about the key parameters of fertility and mortality.
The 1980s were a transition period characterized by considerable uncertainty, but since about 1990, the United Nations has reported progressively lower growth rates and lower totals in its array of projections of future world population size. The same, generally, is true of the U.S. Statistical Abstract, although the 1998 Abstract avoids projecting a further reduction in the most probable size of world population in 2050.
The apparent stability of the1998 Census Bureau forecast results from offsetting the current, higher-than-expected decline in the growth rate with a higher baseline, that is, calculations begin from a higher estimate of total population in earlier years. The interested layman has difficulty making independent calculations of past growth rates because UN and United States publications and editions of the U.S. Statistical Abstract use different benchmark years for reporting total population size.
It is conventionally agreed, nevertheless, that world population passed 6 billion around mid-year, 1999. This means that it took approximately12 years – since 1987 – to add the latest billion. It also means that the latest doubling of the population took approximately 39 years, because the population in 1960 was about 3 billion.
Some years ago it was thought that the ultimate world population size could be as high as 12 or even 14 billion persons, to be attained in the twenty-first century. Indeed, at the growth rates of over 2 percent annually observed during the 1970s this number could have been quickly upon us. Doubling time is calculated by dividing the number 70 by the percentage increase. Thus, 70/2 = 35 years to double.
By the late 1970s it began to seem that the rate of growth might be declining. This was confirmed with the following ten years’ data. The UN’s "medium variant" assumption published in their 1994 revision of World Population Prospects projected a total of 9.8 billion people by year 2050. Two years later the projection was revised downward to 9.4 billion. The late autumn 1998 projection was 8.9 billion. From over 2 percent annual growth, the rate as estimated in an early 1998 publication had slowed to less than 1.38 percent annually. At that rate of growth, the time for population to double increases from 35 to over 50 years (70/1.38 = 50.7).
The UN middle range estimate assumes that a fertility rate of 2.1 (approximately the replacement rate for the existing population) will be achieved within the next decade or so. This would result in population reaching 10.8 billion by 2150. But with a fertility rate just one-half child less, that is 1.6 births per woman, the population in 2150 would be 3.6 billion, i.e., smaller than today. And with one-half child more (i.e., 2.6 birth per woman), the 2150 population would be 27.0 billion (UN, February1998). Small differences in assumptions about fertility and mortality rates make enormous differences as one goes forward in time.
Both fertility and population growth rates are declining in virtually every country in the world, with the exception of the United States. Many populations in Europe may soon cease growing. Population growth in Japan will also soon cease. Fertility rates below the replacement level mean that many additional national populations in East Asia also will stabilize.
In Russia, rising mortality among middle age men, combined with very low fertility, caused negative growth (actual numbers, as opposed to decline in the rate of growth) during the political tumult of 1995. A Pyongyang survey concludes that the North Korean population shrank by 3 million between 1994 and 1998, pointing probably to a combination of foregone births and premature deaths in response to floods, crop failure, and famine (World Wide 1999). The UN and the U.S. Centers for Disease Control suggested in 1998 that political conflict and disease might throw sub-Saharan Africa into a negative growth mode within 20 years, in sharp contrast to its experience of extremely rapid population growth over at least 40 years.
In contrast, the United States is continuing a rate of growth slightly over 1 percent, and it is far from clear that this rate is declining. Indeed, post-1989 Census Bureau forecasts of U.S. population size have had repeatedly to be raised. The 1989 middle projection estimated a population stabilizing in 2020 at less than 300 million. Subsequent to their 1989 projection, the Census Bureau has several times raised all forecasts in their arrays of projections. Between its 1989 and 1992 projections, for example, the Census Bureau raised the middle projection for 2050 by 28 percent, to 383.2 million (Ahlburg, 1993). A February, 1996, Census Bureau revision raised that middle scenario to 393.9 million in 2050, with no end to growth in sight.
The estimate for the year 2050 would be higher had the Census Bureau not changed a key assumption: the estimate of the number emigrating annually was raised, so net immigration does not fully reflect the increasingly large number of arrivals. Analysis of the raw data by a private think-tank, the Center for Immigration Studies, suggests that immigration and U.S. births to immigrants accounted for 70 percent of U.S. population growth during the 1990s (Camarota 1999). The numbers and the rate of population growth seem unlikely to decrease without federal legislation to halt mass immigration.
Demographers Dennis Alhburg and J.W. Vaupel suggested soon after publication of the 1989 Census Bureau projections that the Census Bureau estimates were too low. Their calculations projected a most likely mid-century population of approximately one-half billion. "We conclude that their [the Census Bureau’s] high projection might be treated as a reasonable middle forecast" (Alhburg and Vaupel, 1990). Peter Pflaumer (1992) also projects a larger population - 488.8 million in his year 2050 middle scenario - than foreseen by the Census Bureau.
Looking farther forward, Ahlburg and Vaupel state that, "By 2080 our high projection is more than 300 million people bigger than their [the 1989 Census Bureau report] high projection. A U.S. population of 800 million may seem incredible, but the annual average growth rate that produces it runs at only 1.3 % per year" (Alhburg and Vaupel, 1990).
With remarkable disregard for net legal and illegal immigration numbers that are already substantially higher than their estimate, Table 4 of the Statistical Abstract, 1997, assumes that net immigration will be 820,000 from now through the year 2050. Projections based on this number inevitably under-estimate the size of the future U.S. population, if current trends persist.
U.S. demography does not, nevertheless, dominate world statistics. Most population growth is in the third world. Country by country population surveys and censuses – however flawed – are establishing beyond doubt that the rate of world population growth is declining. After three centuries of increase at an increasing rate – becoming especially rapid after World War II – the rate of growth is declining.
Thus, although the exact rate may be in doubt, it appears that, if present trends continue, the population in 2050 will not exceed 9 billion. Moreover, the ultimate population size, to be reached no later than one century later, would be no greater than 11 billion. This long-range projection is nearly 7 percent lower that the 11.6 billion projected by the United Nations in 1992. The 1998 UN low fertility rate scenario suggests, indeed, a world population of no more than 8 billion, to be reached in less than two score of years.
Error is likely to be on the side of faster decline than demographers report because of understandable reluctance to acknowledge the various Malthusian checks that appear to be operating. Nor are the UN projections without critics among model-builders. Mathematical curve-fitting is an alternate method for forecasting future population size, and the results are substantially different.
Although both mathematical and demographic methods begin with historic population data, this is their only feature in common. The demographic method, as described, depends upon combining the age and gender distributions of current populations with assumptions about future fertility and mortality rates (plus migration flows for country estimates). Assorted values of these parameters are combined to produce an array of projections.
The mathematical method derives the equation – through trial and error - that best fits the historic data. No use is made of assumptions about future fertility and mortality because the equation, alone, is used for forward projection. The trajectory of future population growth is simply an extension of the historic curve.
The mathematical method is an adaptation of that developed by the American geologist M. King Hubbert, who used past oil production figures to estimate all ultimately recoverable oil (and, by subtraction, remaining recoverable oil). Contrary to all accepted wisdom of the era, Hubbert predicted in 1956 that U.S. oil production in the lower 48 states would peak in 1969, plus or minus some months. The production peak came in 1970, well within Hubbert’s interval (Campbell and Laherre 1998; Younquist 1997; 1998; Duncan 1997; Ivanhoe 1995).
Application of mathematical curve-fitting to forecasting future population size is an innovation developed by ecologist Kenneth F.Watt (2000). Using U.S. Census Bureau figures for global population in years 1950-1996, Watt finds that the equation that best describes the historic curve of modern population growth is:
Equation (1) P =1849 + exp(-1121 + .8387Y - 6.853E - 8Y3),
where P denotes world population size in millions, and Y represents the actual year corresponding to this population number.
Watt’s curve for actual and projected human population size from approximately 1925 through 2070 is shown in Figure 1. A solid line that represents actual population numbers extends through 1996. The points after 1996 are an extrapolation of the historic curve, based on the equation that was derived from fitting to historic data. The model suggests that total world population will peak at less than 7 billion around the year 2019, that is, in less than two decades. The 2019 A.D. population is projected to halve by 2070.
[Figures 1 and 2 about here]
Figure 2 plots the historic data from the beginning of the Industrial Revolution to 1996, and uses the equation to project forward to the period beyond the estimated end of the Oil Interval. The fundamental idea of the Oil Interval is that the world economy depends upon an inheritance of petrochemicals that was stored up approximately half a billion years ago. This dependence on oil as a principal energy source gradually increased from its beginning with Col. E.L. Drake’s first oil well in Titusville, Pennsylvania, which began production in 1859. U.S. oil production peaked in1970, and world oil production is expected to peak sometime around 2012, plus or minus ten years. The exact year of the peak will depend upon production, which is to say, world demand for energy, in the next decade. Economic recession reduces demand.
The largest remaining fields are thought to be in the mid-East and the Caucasus. The transition from cheap and plentiful energy to more expensive and specialized sources is likely to be extremely difficult and may affect both fertility and mortality rates. (For further discussion, see Colin Campbell and J.H.Laherrere 1998, based in Great Britain and France, respectively; and in the United States, L.F. Ivanhoe 1995; Richard Duncan, 1997; Walter Youngquist 1997; 1998; and Watt 2000).
The twentieth century availability of cheap and plentiful oil, as well as technology that turns oil into an exponentially growing list of useful applications, may explain much of the recent population growth. Note, however, that projections from the mathematically fitted equation do not depend upon any assumptions about the adequacy of future energy resources to support the current population. The equation derives solely from historic population data.
In summary, the demographic and curve-fitting models both show that the rate of growth of world population is declining. Their projections of the timing and ultimate population maximum are vastly different, however, as shown in Figure 3, the work of Kenneth Watt (2000).
[Figure 3 about here {Sources: Watt 2000; Figure 1 and Table 1331, Statistical Abstract of the United States, 1997, U.S. Bureau of the Census}.]
The thin line in Figure 3 denotes actual world population, by year, up to and including 1996, and projections by the U.S. Census Bureau Statistical Abstract - 1997 thereafter. The thick line is a projection of the curve based on the mathematical equation shown above, as in Figures 1 and 2.
Note that the U.S. Census Bureau projection (the thin line after 1996), which is similar to the UN middle projection, indicates a rate of descent that is slower than the computed (thick) trend line. The diverging forecasts mean either that the population trend line revealed by the curve-fitting procedure is wrong or, if it is correct, demographers are underestimating future mortality or overestimating future fertility, or both.
Perhaps official projections are about to repeat the pattern of the 1960s and 70s, lagging the rate of change, except that now they will underestimate decline, instead of acceleration, in the growth rate. Such systematic error could reflect a desire to avoid forecasting rapid change, which might be expected to alarm the public.
On the other hand, official sources may be correct; their assumptions about future fertility and mortality rates may justify deviation from a mathematically established trajectory. But demographers have often been wrong in forecasts of fertility, most notably during the 1930s when they confidently predicted continuing low fertility in industrialized countries (they missed the "baby booms") and then in suggesting that "development" would automatically reduce fertility in the third world. In my view, the burden of proof is on those who use no theory, or demonstrably wrong theory, to make assumptions about future patterns of behavior.
Evaluating Scenarios
The corollaries of rapid decline in the rate of population growth are that growth will stop sooner than expected and proceed into decline in actual population numbers, that is, negative growth. The two processes that could lead to rapid decline in the growth rate and then to negative growth are 1)fertility that is far below the replacement rate and 2)an increase in mortality.
Fertility
In fact, periods of rapid fertility declines are already well documented. For a six-month period after the collapse of Communism, the East German fertility rate declined to below one child per woman. Similarly, the Russian fertility rate fell to approximately one child per woman in the aftermath of Communism’s demise. Very rapid declines, but from a high level, have been observed in Moslem countries in North Africa, Peru, other South American countries, and East Asian countries among others.
A sense of scarcity and insecurity, such as is sweeping many nations and regions, appears to promote caution in entering upon marriage or increasing one’s number of dependents through childbearing. Historically and cross-culturally, indeed, delayed marriage, long spacing between births within marriage, and early termination of child-bearing are very frequently observed patterns of behavior.
The sense of scarcity is a subjective phenomenon. Perceived scarcity does not depend on either absolute poverty or threats to subsistence, so extremity is not a necessary condition of fertility decline. Afflictions no greater than frustrated aspirations or marginal deterioration in economic conditions stir a sense of scarcity in most people. The native-born sector in most industrialized countries has low fertility – not because they live in absolute want, but because aspirations for themselves and their children exceed their grasp.
Stable societies in all times and places have probably had an understanding of scarcity, that is, more attractive uses for resources than could be satisfied. Development economist Georg Borgstrum was cited in 1971, to the effect that,
A number of civilizations, including India and Indonesia, "had clear idea of the limitations of their villages and communities" before foreign intervention disrupted the traditional patterns. "Technical aid programs… "made them believe that the adoption of certain technical advances was going to free them of this bondage and of dependence on such restrictions" (Population Reference Bureau, 1971, p.19).
Data from many societies show that understandings of scarcity were the principal source of the motivation to limit family size (Ohlin 1961; Davis 1963; Demeny 1968; 1986; Abernethy 1979; 1993; 1994; 1997). Conversely, the perception that resources and opportunity are expanding usually leads to accelerating marriage plans, raising family size targets and, almost inevitably, the number of children born, per woman. So great can become the tone of optimism that many people believe that economic security and even windfalls of opportunity will continue indefinitely, and traditional values and practices that once limited family size are cast off.
These responses are summed up by the "fertility opportunity" hypothesis, an explanation which suggests that most humans have a biological urge toward reproduction and are only deterred by the perception that early or frequent childbearing is detrimental to the family or individual. In sociobiological terms, selection for sensitivity and responsiveness to environmental cues would be expected to enhance individual "inclusive fitness" (Abernethy 1979, 1993, 1994; 1997; 1998; 1999).
Anecdotal data, suggestive rather than conclusive, offer an intuitive introduction to the fertility opportunity hypothesis. Note the regret, even wistfulness, with which people describe their decisions to avoid having children: a Russian mother of two who relied on abortion to limit family size muses, "‘I would have had more children if life were better’" (Walt, 1995, p. 48). In Thailand, a laborer and father of two "would like to have one more child, but he understands that is beyond his means" (Moffett, 1994, p. 137). Near Mexico City, a mother of two defends her use of contraception with, "‘Things are difficult here... Jobs are hard to come by’" (Moffett, 1994, p. 229). Pondering what she would do differently if she were rich, an Ethiopian mother of five says, "`If I were wealthy, say if I had horses and a better house, I'd have more children’" (Walt, 1995, p. 38).
A few examples of the associations of growing optimism with high (even rising) fertility - and of the sense of contracting opportunity and scarcity with declining fertility - are summarized below. I also have predicted fertility declines (from already low levels) in the former "tigers" of East Asia that experienced shattering economic collapses after summer, 1997 (Abernethy 1998), and I confidently await these data.
In fact, fertility declined in many developing countries after collapses in world commodity prices, a reduction in international aid, disillusionment with experiments in democracy as well as with populist revolutions, or increasing competitive stresses within a the lower and middle working class. For example, phosphates were Morocco’s key export when a price collapse in 1974-75 forced withdrawal of government subsidies on food, education, and health care. This reduction in families’ real income coupled with higher taxes added insult to injury, and was immediately followed by a decline in the fertility rate - 20 percent over 4 years (Courbage, 1995).
Similarly, after two decades when Peru’s fish exports and fertility rate had risen in tandem, the anchoveta industry plateaued in the 1960s. This decline in economic expectations was followed by a fertility decline that accelerated as the economy collapsed in near free-fall and political institutions became chaotic (Abernethy 1997).
Further, the growing wealth disparity between the upper-income 20 percent and almost all others in certain industrialized countries appears to be depressing the fertility rate of the native-born population (Abernethy, 1999). The consumption ethos that overtakes the middle class in many societies also promotes caution before undertaking to establish a family. In a consumer society, whatever one has it could be more – and caring for children is usually in competition with the acquisition of goods.
Worldwide, in fact, people with enlarged aspirations are being forced to become more self-reliant, and most no longer have unquestioning faith that their government or international aid will make the future brighter. This shift in expectations is associated with declining fertility. Even in sub-Saharan Africa and countries such as Pakistan and most oil-rich – but temporarily cash-poor - Arabian countries, fertility rates that were persistently high for decades are now falling rapidly (Abernethy 1997; 1998).
The experience in Nigeria combines many of the elements cited above. During the 1970s to mid-1980s, oil wealth and international assistance rolled into Nigeria, the infant mortality rate declined, healthcare and education programs became widely available, and many more women had access to education. Consistent with prevailing theory associated with the demographic transition-development literature, these elements of modernization were expected to reduce fertility rates from the very high level where they had remained for over two decades.
As the 1980s rolled on, however, early marriage, closely spaced births, and disinterest in contraception showed no sign of abating. While disappointing, the lag was dismissed as inconsequential when, finally in 1990-91, the Nigerian fertility rate began to fall. The operative factors, later marriage and a new level of receptivity to modern contraception, were readily attributed to development and modernization (Caldwell et al. 1992).
A different interpretation is possible. The fertility opportunity hypothesis finds support in both the initial persistence of high fertility, and then the timing of the eventual fertility decline. The unprecedented advantages enjoyed by the average person and the pervasive optimism of the earlier period predicts no fertility decline. In contrast, the economic downturn, diminishing international aid, reduced subsidies for education and healthcare, more difficulty in finding remunerative employment, and widespread disappointment in the late 1980s and early 1990s is consistent with individual adaptive efforts that include delayed marriage and avoidance of childbearing. Indeed, Yoruba-speakers interviewed in two Nigerian villages said that an important factor in their decision to use contraception was the "hard economic times" (Caldwell et al. 1992, pp. 236-237). Specifically, "Most of the respondents believed that child mortality had risen over the previous five years of economic difficulty" (p.226), and "Two thirds of all respondents claimed that the major force behind marriage postponement and the use of contraception to achieve it was the present hard economic conditions" (p.229).
A search of the literature turns up many more parallel instances, of which a small fraction is mentioned here. The conclusion I draw is that fertility is falling at an accelerating rate, nearly worldwide, because individuals and families are aspiring to consumption opportunities they cannot afford. Alternately, they are trying to adapt to, and avoid, the worst effects and insecurities of the deteriorating environmental, social, and economic conditions around them.
The cause of such deterioration is, in some cases, population growth itself. In this light, population overshoot – that is, growth in excess of the long-term carrying capacity - is self-correcting. What is less easy to contemplate is that destruction of the carrying capacity also leads to loss of species diversity, the impoverishment of human populations, and indeed, much suffering.
Mortality
Mortality is the further dimension that may be changing very fast. In fact, the UN acknowledged in 1998 that AIDS-related deaths are changing population projections for sub-Saharan Africa and parts of southeastern Asia. In addition to the rising burden of disease, various political disruptions may be associated with loss of life and a greater toll than reported internationally, or reported in time, at least, to be integrated into the most recently available demographic projections.
Disease as the source of rising mortality is likely to involve pathogens as yet unknown as well as tuberculosis, HIV/AIDS, and malaria (Nabarro and Tayler 1998). The likelihood that new diseases will arise relates to the increasing probability that infectious pathogens will jump the species barrier - from animal to human – as the human population grows and people increasingly impinge on the natural habitat of other species. In fact, it is now thought that the HIV virus jumped from chimpanzees, where it is harmless, to humans about thirty years ago.
Mostly but not wholly in the third world, the prevalence of tuberculosis, HIV/AIDS, forms of hepatitis, and malaria has been rising as more people crowd together. Travel between continents speeds transmission. Cholera, leprosy, tuberculosis, malaria, and hepatitis B and C have all been detected in the United States within the last dozen years as the result of contagion from overseas. Tuberculosis, for example, was nearly eliminated in the United States by the 1980s but has made a strong comeback, particularly in cities with large foreign populations and among vulnerable patient groups such as those infected with HIV.
New treatments and preventive measures have led to decline in the annual number of new HIV infections in the United States and certain other countries including Thailand, but HIV/AIDS is nonetheless reaching unforeseen proportions in some parts of the third world. Whereas in Thailand the prevalence of HIV infection in the general population peaked at 3.7 percent in mid-1993 but had leveled off at 1.9 percent by 1997 (Phoolcharoen, 1998), prevalence probably remains high in Myanmar (Burma) and southern China, other points of the Golden Triangle. Most Asian and African governments did not follow Thailand’s lead in taking an extremely proactive public health approach toward the epidemic.
HIV/AIDS is rising in India, particularly within the lower classes. Truck drivers spread AIDS between communities; prostitution transfers it into the resident heterosexual population (HIV Incidence, 1998, p.1864). This transmission vector also describes the early spread of the HIV virus in sub-Saharan Africa during the 1970s. In 1993, the U.S. Centers for Disease Control modeled HIV/AIDS transmission in East Africa, by which time its prevalence was highest among the upper class. At that time, the AIDS epidemic, alone, was expected to reduce annual population growth in sub-Saharan African by about one percentage point by the year 2015. That is, from nearly 3 percent, the annual population increase was expected to be less than 2 percent (Way and Stanecki, 1993).
Subsequent reports suggest that the epidemic in Africa is more widespread and more serious than previously thought. The prevalence of HIV infection among adults, estimated through 1997, includes a stunning 12.8 percent in South Africa with rates of "at least 25%" in Botswana and Zimbabwe and 4.1 percent in Nigeria. Outside of Africa, countries where prevalence is high include Cambodia (2.4%) and Honduras (1.46%). Worldwide, nearly twice as many people as previously thought are being infected annually, and the incidence of new cases has doubled (HIV Incidence, 1998, p.1864). "AIDS is now one of the leading infectious causes of death in the world and has brought down life expectancy at birth in the worst-affected African countries to levels of the 1960s" (The Science of AIDS, 1998, p.1844; Specter, 1998)
High young-adult mortality from AIDS results in many children being orphaned. Moreover, between 17 and 25 percent of babies born to HIV-infected mothers are also infected with HIV if the mother and infant are not treated perinatally, and the virus is further transmitted through breast-feeding. The result is a 50 percent increase in infant and child mortality (Altman 1998).
A further contributor to rising mortality is famine. Death is seldom attributed to starvation, however, because malnutrition creates vulnerability to opportunistic disease, and death often intervenes at an early stage of the process. Such vulnerability particularly affects the young. Mortality and morbidity among pre-adolescents due to contagious disease and infection - rather than by chronic diseases of the elderly - is reminiscent of the mortality regimen through the nineteenth century in many parts of the world including Europe.
Mortality rates have fallen steadily through twentieth century. In consequence, perhaps, the magnitude of premature mortality sometimes goes unrecognized. An early-1960s famine in China in the aftermath of the failed "Great Leap Forward" contributed to a probable thirty million deaths. During the 1970s in Nigeria, the Hausa were instrumental in isolating and starving several million Ibo in reprisal over Ibo claims to control the rights and profit from oil found in their homelands. The international community intervened to avert famine in Ethiopia, the Sahel, and Somalia during the 1970s and 80s. But famine, reportedly, had caused 2 million deaths in North Korea by spring, 1998, in part because North Korea refused to give guarantees of nuclear nonproliferation in exchange for aid. This said, it is unclear that the international community will be able, even if willing, to forestall devastation from most future famines and outbreaks of disease.
A factor that often drives famine and outright killing is ethnic, religious, or clan conflict. In Somalia, fighting continues among ethnically-almost-identical opposing clans despite major "peace-keeping and nation-building" efforts by the United States and UN, which resulted in loss of life among military units detailed to help. In Rwanda, Burundi, and the Democratic Republic of Congo (Zaire), ethnically distinct Hutu and Tutsi tribes remain locked in long-standing contention that no international peace-keeping force seems able to neutralize. Antagonists in Indonesia are the indigenous peoples and overseas Chinese. Sudan is divided by the antagonisms of Arab Muslims and Sub-Saharan African Christians. The former Yugoslavia pits Muslims, Greek Orthodox Christians, Russian Orthodox Christians, and Albanians each against the other, although all but Albanians are Slavs by ancestry. Ethnic diversity in the Caucuses region including Eastern Turkey seems likely to be a non-ending source of dispute, feuding, or guerrilla action. This short list of conflicts accounts for violent deaths climbing into the millions (Hutu Rebels, 1998; Landler, 1998; McKinley, May 28, 1998; Mydans, June 2, 1998; French, 1998).
Such conflicts result in population loss at the same time that population pressure may be a factor that drives conflict (Homer-Dixon 1992). Pursuit of goals by armed force often requires one to define the enemy as "the other." Ethnic cleansing is the whole point when one group believes that its living space and opportunity – call it carrying capacity – have been usurped (Esman, 1994).
Thus, localized instances of conflict, separate from and yet contributing to malnutrition and outbreaks of disease, suggest that an increase in the mortality rate is occurring must soon be reported. On the other hand, most developing countries have a very young population, which lowers the general mortality rate. Higher mortality than assumed in current projections would be the second factor, along with rapidly declining fertility, which would preclude future world population from attaining the high levels now foreseen by the UN and U.S. Census Bureau.
What to Wish For
"Be careful what you wish for, because you may get it," is ancient wisdom. Wishing for declining rates of population growth, population stabilization, and eventual reduction in human numbers has come to be a habit. Retrenchment to lower levels of population in all continents could lay the basis for environmental sustainability. I have no doubt that reduction in human numbers is devoutly to be desired, but getting decently from here to there is the challenge.
The UN middle scenario for stabilizing population size is probably too gradual to avert continuing catastrophic losses in species diversity and environmental quality in all parts of the world. This scenario leads in the long run to enormous human suffering – and perhaps to non-recoverable losses of human genetic pools and civilization. On the other hand, population stabilization and decline within the next two or three decades, as projected by the equation-fitting method, can occur only if there is a substantial short-term rise in mortality. One assumes that such population loss would not be allowed to occur unless major industrial nations were unable – because of their own travails or the scope of disasters – to intervene. How could this happen?
The Population-Environment Connection
The controversy surrounding the upper limit to the carrying capacity of Earth often reverts to Malthus – was he right or wrong? Will human numbers inevitably outpace food production or devastate the quality of most people’s lives?
This battle is often waged on the economic rather than the environmental front. Although most experts in international development have concluded that rapid population growth is an obstacle to economic growth and human dignity, some analysts of industrialized countries assert that population growth is an essential ingredient of prosperity. A common fear is that population stabilization or negative growth leads to economic stagnation. The recession in Japan, where population size is nearly stable and 15 percent of the population in 1997 was over age 65, is alleged to support this hypothesis. The prescribed correctives include higher birth rates and immigration.
Those who dwell on the positive aspect of a growing population tend to confound growth in GDP with economic health. However, the economic wellbeing of the average person is reflected in per capita GDP, rather than the aggregate figure. Moreover, a distinction should be made between mean per capita income, which is influenced by extreme values, and the median, which is a better indicator of the distribution of wealth. Median income describes the economic condition of the middle class.
Bearing on the prosperity of the middle class is the relationship between labor supply and the availability of capital and technology. In fact, growth in the supply of labor must be matched by an appropriate increase in capital investment, or else labor productivity declines and the real compensation for work (inflation-adjusted salary and wages) declines as well.
The capital requirement for creating a U.S.-type job varies from approximately $150,000 to $200,000 per net new job, and capital is in perennially short supply or the interest rate would be zero. When the number of workers increases in the absence of commensurate investment per job, wages and salaries are competed down. This process is occurring worldwide, as globalization (free trade and immigration) prevents a nation from protecting its own people.
Economic discussion, however valid, should never obscure the relationship between human wellbeing and natural resources. Nations not endowed with natural resources labor to import them, and some financial and trading powers - such as Great Britain, the Netherlands, Singapore, and Japan - have been notably successful. As a matter of logic, however, not all nations can be net importers of natural resources. Economics does not make the Malthusian question disappear.
The clear fact that more people are supported today than ever before, and at a higher level of material wellbeing, obscures four important observations about resources. First, world population growth has been enabled by technology that uses increasingly concentrated forms of energy, progressing from wood to coal to petrochemicals. Second, fossil fuels are limited in quantity. Third, many essential renewable resources – such as groundwater, timber, and topsoil – are being depleted at rates that exceed their ability to be replenished or reconstituted. Fourth, the confident assertion that technology will somehow save us, is more often heard from politicians than from scientists and engineers.
Energy sources, particularly oil, are particularly important in modern human history. For example, nitrogen fertilizer is manufactured in a fossil-fuel-intensive process perfected in the 1920s. Showing that exponential growth in population density followed, in one country after another, the introduction and more widespread use of nitrogen fertilizer, Vaclav Smil (1997) convincingly argues that new applications of energy to agriculture have, in fact, played the key role in enabling population growth. In the United States, indeed, about 17 percent of petrochemical use is dedicated to the agricultural sector (Gever et al.1986). The present level of food exports could not be maintained if agriculture were deprived of oil.
Per capita energy use is an accepted proxy for standard of living (Koshland 1991). Each new energy source increases the material wellbeing of the population – until population growth diminishes the per capita availability of the resource. In the United States, energy consumption per capita barely increased between 1970 and 1990, although total consumption increased approximately 25 percent. Population growth accounted for 93 percent of the increase (Holdren 1990).
Between 1991 and 1996, a period of substantial economic growth, total energy use in the United States grew at an annual rate of 2.14 percent. Population growth in this period was just over 1 percent annually, so it accounted for not quite half of the increase in total consumption (Bartlett, 1998). If continued, a 2.14 percent annual rate of growth doubles energy consumption in just under 33 years. Not only the dwindling supply of domestic oil, but also the "greenhouse gases" produced as it is burned - which may be altering climate - suggest that this rate of increase is unsustainable.
No known source of energy, including solar, fully substitutes for oil. All of the nation’s plant biomass together captures less than half of the solar energy equivalent of the fossil fuel energy burned annually (Pimentel and Pimentel, 1997).
Oil production is projected to peak within 20 years, and then the world will turn for its petrochemicals to natural gas, with a life-expectancy at this higher rate of use of about 40 years. Coal, if it must shoulder the burden of being the world’s major energy source, is projected to be adequate for about 60 years after this. By then nuclear fission may (or may not) replace fusion in the production of electricity, and assorted localized technologies such as solar and wind power have the potential to supplement electricity supply. No known or likely technology seems likely, however, to be as cheap, plentiful, and versatile as was oil in the twentieth century (Younquist 1997; Bartlett 1998).
Thus, the U.S. and world agricultural sectors seem at risk from the expense of energy inputs, even if topsoil and aquifer depletion were not a concern. However, topsoil in arable regions of the United States is being depleted about 13 times faster than it is rebuilt under ordinary conditions of agricultural use, and underground water is being consumed at a rate about 25 percent greater than it is replenished. After having been farmed for about a century, Iowa – with some of the richest agricultural lands in the nation - has lost about half of its topsoil. Three million acres of U.S. farmland or forest are degraded or paved over annually (Pimentel and Pimentel, 1996; 1997; Pimentel et al. 1995; 1998). Modern agriculture is sometimes described as process for using land to turn oil into food. With less land and oil, the world will await the revolutionary technology of post-modern agriculture.
Conclusion
Environmental and conservation battles are perennially re-fought because the needs of people, reasons for intruding into the habitats of wild species, and the imperative to use now rather than save, grow approximately in proportion to the number of people. People's wants trump protection of natural resources. Consumption habits compound the effects of large populations. Consumption and population in excess of the carrying capacity degrade the environment. Environmental degradation shrinks the carrying capacity, so fewer people can be supported on a sustainable basis in the future.
It is small wonder that numerous students of carrying capacity, working independently, conclude that the sustainable world population, one that uses much less energy per capita than is common in today’s industrialized countries, is in the neighborhood of 2 to 3 billion persons. Note the congruence with Watt’s projection of rapidly declining population size near the end of the Oil Interval. The absence of cheap, versatile, and easily used sources of energy, and other resources, seems likely to change the quality of human life and may even change, for many, the odds of survival.
Do such scenarios suggest that certain economic and demographic policies should change? Does one deny that demographic facts and their interpretation have potentially major social and economic ramifications? Demographers Dennis Ahlburg and James Vaupel are not in doubt. They write that, "Population projection is not a bloodless technical task, but a politically charged craft of great interest to policymakers and the public" (1990, p. 646).
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Figure 1. Total Human Population, Actual Data through 1996 and Thereafter Projected
from Mathematical Forecasting Mod |
