Trends in Global Population Growth

Abstract

As of 2015, the world's population was approximately 7.3 billion and increasing rapidly despite a decline in overall rates of population growth during the early twenty-first century. Population growth is distinctly uneven worldwide, and these differences are reflected in the allocation and use of resources. This article gives a brief overview of population growth processes and surveys recent trends in population statistics, including fertility, contraception, sex ratios, nutrition, HIV/AIDS, urbanization, aging, migration, income distribution, consumption, and biocapacity. Current population trends are indicators of the near future, providing a basis for ongoing attention and research on population issues.

Overview

Population-Growth Processes

Demographers track several population processes to estimate and project population change. For most of history, and likely pre-history, the world's population change has been marked by high fertility rates, high crude birth rates, high infant mortality rates, high crude death rates, high mortality rates, and low life expectancy. When added together, this means that the world's population turned over rapidly, but absolute numbers grew only slightly or not at all. In demography, a relatively stable condition of no net decrease or increase in numbers is called a population replacement rate.

By 1830, the global population had reached one billion. The second billion in population increase took only 100 years, the third billion about 30 years, the fourth billion 15 years, and the fifth billion only 12 years (Population Reference Bureau, 2007). Figure 1 illustrates this exponential growth of world population since 1950, providing projections through the year 2050 (US Census Bureau, 2011).

By 2015, the world's population had reached approximately 7.3 billion, according to estimates by the United Nations. Around 1990, we see the beginning of a downward trend in the overall population growth rate. As shown in Figure 2 (US Census Bureau, 2012), if this decreasing trend continues, the rate of population growth will have slowed significantly by 2050.

Factors Affecting Population Growth

Obviously, genetic, biological, geographical, and ecological factors affect population processes. One of the most well-known theories of population growth was put forth in 1798 by Robert Malthus, who held that world population would grow at a rate just slightly higher than food production. Though "natural" population-limiting processes exist, such as disease, drought, and natural disasters, which tend to increase mortality rates, Malthus predicted a future in which widespread starvation would occur.

Cultural and social factors also have had a tremendous impact on population processes. It is no coincidence that the statistical techniques of demography became more sophisticated around the same time as the term "sociology" was first coined by Auguste Comte. The two fields are complementary to one another, just as social change and population change go hand in hand. For example, the potential of war to dramatically affect population numbers cannot be overstated. If natural conditions produce widespread starvation, social conditions that spur conflict and war can arise.

Demographic Transition Theory

A more recent and even better-known theory of population growth is known as demographic transition theory, which holds that populations move through four distinct stages of growth and decline processes, linked to the technological or developmental state of a given society.

In Table 1, the first stage is representative of most of human history up until the last few centuries. According to demographic transition theory, stages 2 and 3 are periods of expected increases in overall population as societies undergo processes of industrialization and the accompanying changes in food supply, sanitation, medicine, and working conditions. In stage 3, decreasing birth rates and increasing life expectancy begin a period of population decline. In stage 4, the birth rate can either stabilize or decrease. If birth rates are stable, the population again reaches replacement rate.

Applications

Recent Trends in Population Processes Fertility & Contraception

Fertility rates in industrialized nations have been declining since the early twentieth century. In many less industrialized countries, the idea of planning and timing children was quite revolutionary. Traditionally, with high rates of infant mortality, larger families held better chances of survival, gaining more status and wealth over time.

During the latter part of the twentieth century, attitudes toward childbearing began to change. The global fertility rates began to decline after 1960, as women in less industrialized countries began to limit the number of their children. Many factors contributed to the changes in fertility patterns in the less industrialized world. Some studies credit organized family planning programs with at least half of that decline (Kent & Haub, 2005).

Growing acceptance of the idea of family planning opened the door to multiple changes in childbearing behavior. In the 1960s and 1970s, surveys to measure knowledge and use of family planning were first conducted in a small number of countries around the world. These surveys found that less than 10 percent of women were using any family planning method. Family planning programs worldwide began to introduce women to more effective pregnancy prevention methods, including female sterilization, intrauterine devices (IUDs), and oral contraceptives. Condom usage, which protects from sexually transmitted diseases (STDs) as well as pregnancy, ranks in popularity below these others in every country; only around 8 percent of women worldwide relied on condoms as of 2011. Vasectomy, or male sterilization, was used by only about 2.4 percent of the worldwide population (United Nations Department of Economic and Social Affairs, 2013).

By the 1980s, most women were using at least one effective method of contraception, and by 2011, more than 60 of the world's women of reproductive age who were in a relationship were using some method of birth control (Kent & Haub, 2005; United Nations Department of Economic and Social Affairs, 2013). In less industrialized nations, the total fertility rate fell from about 6.2 in the 1950s to around 3.0 in 2005. At that time, contraceptive use was higher in some less industrialized countries than in many European countries (Kent & Haub, 2005).

A large body of research in the early 2000s links higher education for women and girls with reduction in fertility levels. Indeed, data from many countries show that women with at least a secondary-level education eventually give birth to one-third to one-half fewer children than do women with no formal education whatsoever. Educated women tend to delay marriage and opt for more control over their reproductive lives (Haub, 2007).

Sex Ratios

Across countries and time periods, both the sex ratio at birth and the population sex ratio generally varies little between human populations. In 2013, just over half of the human population was male, with males accounting for 50.3% of the global total. In some areas of the world the ratio of males to females is higher, while in other countries, including the United States, females outnumber males. Small variations do occur naturally, but reports began to appear in the 1990s of 100 million or so "missing women" across the developing world (Hesketh & Wei Xing, 2006; Sahni, et al., 2008).

Cultural traditions of preference for sons are seen in almost all patrilineal societies, which link inheritance of property to the males in a family. However, there seems to be some evidence that son preference has distorted expected sex ratios in large parts of Asia and North Africa in particular. The contention is that son preference is now practiced actively in these countries through the increasing availability and use of sex-selective abortion and through discrimination in caregiving practices for girls, which leads to higher female mortality (Hesketh & Wei Xing, 2006; Sahni et al., 2008).

Differential gender mortality in some areas has now been a documented problem for some time. Since the early 1990s, improved health care and conditions for women have resulted in reductions in female mortality, but these advances have now been offset by large numbers of "surplus" males now reaching adulthood. These males are predominantly of low socioeconomic class, and concerns have been expressed that their lack of marriageability and consequent marginalization in society may lead to antisocial behavior and violence, threatening societal stability and the further safety of women in these areas (Hesketh & Wei Xing, 2006).

Nutrition

Malnutrition continues to be a serious problem around the globe, with around 805 million people, or one in nine of the world’s population, continually undernourished as of 2014. In the developing world, around 13.5 percent of the total population was undernourished (Food and Agriculture Organization of the United Nations, 2014).

Inadequate dietary intake and disease are the direct causes of malnutrition. Underlying causes include inadequacies in access to food, health care, and sanitary services. Malnutrition contributes to nearly half of deaths among children under 5, according to the World Health Organization. In addition, malnourished mothers experience higher rates of morbidity and mortality and are more likely to have poor pregnancy outcomes. Insufficient pregnancy weight gain and micronutrient deficiencies affect child outcomes. While low- and middle-income countries (LMICs) have the highest rates, malnutrition affects both rich and poor countries, particularly the poorest in each nation (Levinson & Bassett, 2007).

By 2007, nearly 3 in 5 children under age 5 lived in countries where anemia was a severe problem. The prevalence was most severe in Africa and Asia, where, in some countries, more than 40 percent of preschool-age children had moderate or severe anemia. High rates of iron-deficiency anemia increase the probability of disability and death among women of childbearing age and points to higher rates of mortality among their children (Haub, 2007).

HIV/AIDS

UNAIDS estimates that in 2014, about 37 million adults and children worldwide were infected with HIV/AIDS, with the largest number of infections, 1.4 million, in sub-Saharan Africa (UNAIDS, 2015). The highest prevalence was found in Swaziland, where 7.2 percent of men aged fifteen to twenty-four and 15.5 percent of women of that age were estimated to be infected. Adult HIV/ AIDS prevalence among the least developed nations was put at 0.5 percent of the male population ages 15 to 24 and 0.8 percent of the female population in that age group, with southern Africa being the region most seriously affected, at 1.1 percent of the male population and 1.9 percent of the female population (Population Reference Bureau, 2015).r

Urbanization

Since the mid-twentieth century, the urban population has increased such that more than half of the world's population is estimated to live in cities. In contrast, in 1975, only 1 in 3 persons worldwide lived in an urban area, with most of the 1.5 billion urbanites living in areas of fewer than 1 million. In fact, in the first decade of the 2000s, many urban households were actually located in suburban communities of fewer than 50,000 residents (Haub, 2007). Some estimate there will be nearly 2 billion new urban residents by 2030 (McDonald, Kareiva, & Forman, 2008).

In an extreme of urban growth, many cities turn into mega-cities, urban areas of at least 10 million people. Between 1975 and 2015, the number of such large cities grew exponentially, from three to thirty-five (Haub, 2007; Population Reference Bureau, 2013). Not all mega-cities are located in highly industrialized countries. One of the largest such cities is Mexico City, Mexico, where much of the population lives in shacks or tents surrounding the main city, with no access to municipal services such as electricity, water, or waste disposal. In fact, growing numbers of such large cities are located in less industrialized nations.

Aging Populations

In areas of the globe where birth rates are stable and death rates are declining, the average age of the population is rising rapidly. Between 1950 and 2013, the number of individuals age 65 and older rose from 5 to 8 percent worldwide. The aging of populations in industrialized countries first became obvious in Europe and Japan. The same trend soon spread to North America, Australia, and New Zealand. By 2050, the aging of the populations of Latin America and Asia is expected to be more apparent (Haub, 2007; Population Reference Bureau, 2013). Some estimates put average life expectancy gains over the next hundred years or so at record setting levels, which will result in even older populations (Kinsella, 2005).

This aging of populations is particularly apparent in calculations of dependency ratios worldwide. Dependency ratios, which compare the number of elderly, disabled, and very young with the number of persons in productive work capacities, are used to look at policy issues affecting the elderly (Bartram & Roe, 2005). Dependency ratios tend to be higher in less industrialized countries, in part due to their younger populations; however, aging populations in the industrialized world, with Europe leading, mean that dependency ratios are rapidly on the rise in the more industrialized aging populations (Vaupel & Loichinger, 2006).

As various nations experience increases in the relative size of their working-age populations, the share of working-age population will continue to increase as long as growth in working-age population exceeds growth in number of people not in the workforce (Hayutin, 2010). However, as the number of people over age 65 increases and the working-age population levels off or falls, dependency ratios will climb. Many nations are now rethinking the concepts of "old age" and "retirement" (Reznik, Shoffner, & Weaver 2005; Vaupel & Loichinger, 2006).

Migration

In the modern world, migration is perhaps the most variable population process from country to country. The world's population has become increasingly mobile, with the numbers, origins, and destinations of migrant flows fluctuating rapidly in response to differing world events and economic and environmental conditions.

Migrant pathways are increasingly international. In 2013, about 243.7 million people, or over 3 percent of the world's population, were international migrants living outside their country of birth (United Nations Department of Economic and Social Affairs, 2015). While some of this activity reflects the increasingly international nature of world trade, it also reflects large refugee populations recently uprooted by war and natural disaster.

The flow from one industrialized country to another is relatively small, with a few exceptions. One such exception occurred between 1995 and 2000, when around 2.6 million migrants per year moved from less industrialized to more industrialized regions. More than half of these settled in the United States and Canada. About 40 percent of international migrants move from one less industrialized country to another (Haub, 2007).

Income Distribution

Persistent poverty and rapid population growth tend to go hand in hand. There is a clear inverse link between high-fertility, high-birth-rate population growth and per capita income, though the relationship is too complex to correctly state that one causes the other. On average, per capita income in high-fertility countries is less than one-twelfth the level in low-fertility countries (Kent & Haub, 2005). Much of the world's population still lives in conditions of extreme poverty, including significant numbers in industrialized nations. However, the bulk of global poverty still exists among the more youthful populations with relatively high fertility rates. This means that children still are the majority of those living in poverty.

There are definite global patterns of uneven distribution of income and assets such as land, capital, technology, and education between industrialized and less industrialized countries (United Nations, 2005). A report by Milanovic and Yitzhaki (2002) classified only 11 percent of the global population as middle class, with another 11 percent considered rich and 78 percent considered poor. While there was some shrinking of income disparities between countries in the 1990s, the gain may be smaller and more short-term than originally thought (Mann & Riley, 2007).

Although the percentage of people in poverty declined in almost all regions in the late twentieth and early twenty-first centuries, it remained quite high in many countries, and the few gains made in specific regions increased the relative importance of poverty as a global issue. There was little improvement in income and wealth in sub-Saharan Africa, North Africa, the Middle East, or Latin America. Furthermore, the number of people living in poverty increased substantially in Eastern Europe and Central Asia, growing from 2.5 billion to 2.7 billion between 1981 and 2001 (Kent & Haub, 2005).

Consumption & Biocapacity

Biocapacity can be defined as the capacity of a given ecosystem to provide the basic building blocks for life and sustain rates of consumption and waste. The same basic concept underlies the idea of an ecological footprint as a method to help people understand the impact of consumption and waste on the environment (Rees, 1992). The ability of any given ecosystem to support human populations, therefore, is linked directly to rates of consumption. In addition to the amino acids found in foodstuffs, large-scale consumables also include energy and water.

Average energy use per person is at least nine times greater in industrialized nations than in those less industrialized. Westerners, representing around 10 percent of the world population, consume more than one-third of the world's energy production: in 2011, 537.3 quadrillion British thermal units (BTUs) of energy were produced worldwide, of which North Americans consumed 118.7 quadrillion BTUs and Europeans consumed 82.1 quadrillion BTUs, according to the US Energy Information Administration (EIA). North Americans, particularly in the United States, tend to consume the most energy per capita. In 2011, per-capita energy use among Americans was 313 million BTUs—more than twice that of Europeans (134 BTUs), about six times that of Asians (52 BTUs), and 19.5 times that of Africans (16 BTUs), according to the EIA. In addition, non-OECD countries have begun consuming energy at increasing rates (US Energy Information Administration, 2014).

Industrialized countries tend to consume more water per capita than other nations as well. Clean water supplies in many parts of the world are insufficient to meet basic needs, much less demand. Some estimates place more than 2.7 billion people in areas of severe water shortages by 2025 if world consumption of water continues at current rates, with another 2.5 billion living in areas where it will be difficult to find sufficient fresh water to meet their needs. Other forecasts predict that, rather than remaining steady, consumption rates will actually increase up to 12 percent per decade until 2025 (Redding, 2007). If either scenario is close to the mark, water may soon become the most precious human resource on the planet.

Conclusion

Malthus's ideas were widely discounted as being out of date by subscribers to demographic transition theory for a number of years. Yet there have also been growing numbers of neo-Malthusian theorists who have been closely monitoring the capacity of our planet to sustain extremely large population numbers. Upon close examination, we must admit that there are accuracies in both theories. Trends are just that: current patterns in population processes. Although there are rigorous demographic and statistical techniques to project population numbers given current trends, these methods do have limitations. The confidence interval, or statistical probability of error, of projections tends to widen significantly after around two generations.

Predictions tend to break down whenever there is significant latitude for individual choice within cultures and societies. Current population trends are indicators of the near future and, in themselves, provide a basis for ongoing attention and research on population issues.

Terms & Concepts

Biocapacity: The capacity of a given ecosystem to provide the basic building blocks for life and sustain rates of consumption and waste.

Demography: The study of human population change.

Demographic Transition: Theoretical relation of human population change to the development of technologies for sustaining population growth.

Dependency Ratio: Ratio of the proportion of population active in the productive workforce to those not in the workforce.

Ecological Footprint: Roughly the area of land needed to support the consumption and waste of a specific person or population.

Food Insecurity: Widespread unavailability of food over long periods of time in a specific population or global region. Industrialization: Processes associated with the rise and growth of factory systems of economic productivity.

Life Expectancy: Statistical calculation of the longevity of the typical lifespan in a specific population.

Mega-cities: Urban areas of at least 10 million people.

Population Growth Rate: The net growth in a given year of a specific population.

Population Processes: The basic life processes used by demographers in the statistical calculation of population change, such as crude birth rate and crude birth rate.

Replacement Rate: A relative steady state of population processes wherein the number of annual births is approximately equal to the number of annual deaths.

Sex Ratio: The ratio of males to females in a specific population.

Urbanization: The process of concentration of populations into geographical areas that serve as hubs of social activity.

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Suggested Reading

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Firebaugh, Glenn. (2003). The new geography of global income inequality . Cambridge, MA: Harvard University Press.

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