Geographers study where and why people live in particular locations. Neither people nor resources are distributed uniformly across Earth. In regards to population growth, geographers emphasize three elements: the population size, the rate of increase of world population, the unequal distribution of population growth. Geographers seek to explain why these patterns exist.

The subject of overpopulation can be highly divisive, given the deep personal views that many people hold. Human geography emphasizes a geographic perspective on population growth as a relative concept. Human-environment interaction and overpopulation can be discussed in the contexts of carrying capacity, the availability of Earth’s resources, and the relationship between people and resources.

The study of the human population has never been more critical than it is today. There are over 7 billion people on the planet, but most of this growth has occurred in the last 100 years, mostly in developing nations. Humans do not live uniformly around the world but rather in clusters because of the earth’s physical geography. Environments that are too dry, wet, cold, or mountainous create various limiting factors to humans. Two-thirds of the world’s population is located within three significant clusters: East Asia (China), South Asia (India and Indonesia, and Europe, with the majority in East and South Asia.

Demographers, scientists that study population issues, and other scientists say there is more to the story than pure population growth. Ecologists believe that humans have outgrown the Earth’s carrying capacity. There is not enough of the world’s resources to give every human a standard of living expected by most Americans. If all the people on the planet lived the average American lifestyle, it would require over three Earths. At this level of consumption, the earth cannot sustain a population of 7 billion, though we are expected to reach 9 billion by 2100.

Distribution of the World’s Population

Economist Jeffrey Sachs, director of the Earth Institute at Columbia University, believes that there are two reasons why the global population and extreme poverty occur where they do:

• Capitalism distributes wealth to nations better than socialism or communism
• Geography is a significant factor in population distribution in relationship to wealth

For example, the population tends to be lower in extreme environments such as arid climates, rainforests, polar or mountainous regions. Another example is a nation with a large body of water within its boundaries or has extensive mineral deposits or resources likely to have more wealth and a larger population.

Humans only occupy five percent of the Earth’s surface because oceans, deserts, rainforests, and glaciers cover much of the planet (Figure 2.1.). The term for areas where humans permanently settle is ecumene. Population growth and technology dramatically increase the ecumene of humans, which affects the world’s ecosystems.

It is argued that the world cannot support all the humans on the planet. On some level, that is true, and on another, it is not. For example, we could pack all 7 billion humans in California, but that is not desirable, sanitary, or sustainable. The reality is that humans cannot live in many parts of the world due to moisture, temperature, or growing season issues. For example, 20 percent of the world is too dry to support humans. This mostly has to do with high-pressure systems around 30 degrees north and south of the equator, where constant sunny conditions have created some of the world’s largest deserts. Some of these include the Sahara, Arabian Peninsula, Thar, Takla Makan, and Gobi deserts. Most deserts do not provide enough moisture to support agriculture for large populations.

Regions that receive too much moisture also cause problems for human settlement. These are tropical rainforest regions located between the Tropic of Cancer (23.5 degrees North) and the Tropic of Capricorn (23.5 degrees South). The problem with these regions of the world has to do with the soil erosion due to high precipitation. High levels of precipitation greatly hinder agricultural production because nutrients in the soil are quickly washed away. This is partly why slash-and-burn agriculture occurs in these regions. Locals will burn part of the forest to put nutrients back into the ground. This only works for a short period because the precipitation washes away nutrients within a few years, so farmers move on to other parts of the forest with their slash-and-burn practices.

Additionally, regions that are too cold pose problems for large population clusters and food production. The cold Polar Regions have a short growing season, and many of the Polar Regions have limited amounts of moisture because they are covered by high- pressure systems (much like the desert regions). Thus, cold polar regions are defined by temperature and lack of moisture, despite access to snow, ice, and glaciers. Mountainous and highland regions lack population clusters due to steep slopes, snow and ice cover, and short growing seasons.

Population Profiles

Demographers use various ways to measure and analyze population density. The arithmetic density, also called population density, is the total number of people in proportion to land. This may not be the best indicator of actual population density because there are many environments humans cannot live comfortably in, including deserts, arctic, tropical forests, and mountainous regions. It also does not consider if the ground is used for producing food. The population’s physiological density is the total population in proportion to arable land suited for agriculture. Even more specifically, agricultural density refers to the number of farmers available compared to arable land. A high agricultural density suggests that the available agricultural land used for farming and the farmers capable of producing and harvesting food reaches its limit for that region. If the demand for food continues or rises, the risk is that there will not be enough arable land to feed their people. In contrast, an area with a low agricultural density has a higher potential for agricultural production. Economically, a low agricultural density would be favorable for future growth.

To understand these methods, let us look at an example. Let us say we have City X, which is home to 10,000 people, 6,000 are farmers and has a square area of 10,000 kilometers and a farmable square area of 4,000 kilometers. If we look at the arithmetic density, we develop a population density of 1 person per kilometer (10,000 people/10,000 kilometers). If we look at the agricultural density, we come up with 1.5 people per kilometer (6,000 farmers/4,000 kilometers of farmable land).

Finally, if we look at the physiological density, we come up with 2.5 people per kilometer (10,000 people/4,000 kilometers of farmable land). Each of these numbers tells us something different.

Of these three methods, physiological density is considered the best way to measure population density because it reflects population pressure on arable land. Arable land is any land that is suitable for growing crops. The higher the population density we find from this method, the faster the arable land will be used to reach its output limit. That means there will not be enough land for the people that are coming into the area. In our example, if 100,000 more people moved to the same area, we would end up with a physiological density of 27.5 people per square kilometer (110,000 people/4,000 kilometers of farmable land)

Scientists’ useful tool that focuses on demographics is a population profile, also called a population pyramid. A population profile visually demonstrates a particular region’s demographic structure concerning males and females and is often expressed in numbers or percentages.

The following are some characteristics of population profiles:

• A bell-shaped graph will indicate that a country has experienced high population growth in the past but is experiencing a slight decrease.
• Narrow triangles show countries with high population growth.
• As a country’s population boom begins to age, a strange profile shape can develop with a broader top and a narrower base.
• Populations that have stabilized have profiles where the bulge of past high birth rates migrates to older populations moderately and not quickly, while the base has a reasonably smaller but not dramatic base.
• When a country has a large immigrant population, specifically “guest workers” that usually tend to be men, the graph’s male side will be dramatically wider than the women’s side of the graph.
• If a country has experienced war, a catastrophic disaster, or a genocide that eliminates an entire generation, that generation will have a smaller number or percent than the generations before or after. For example, a significant war may reduce populations in their mid-20s and 30s, which would appear on the profile graph.

Global Population Trends

A region’s population will grow as long as their crude birth rates are higher than their crude death rates. A crude birth rate (CBR) is the total number of live births for every 1,000 people in a given year. A crude birth rate of 10 would mean ten babies are born every year for every 1,000 people in that region. Crude death rates (CDR) are the total number of deaths per 1,000 people in a given year.

When comparing CBRs to CDRs, a region’s natural increase rate can be determined. A natural increase rate (NIR) is when a population will grow per year, excluding annual migration. Usually, a NIR of 2.1 is required to maintain or stabilize a region’s population. Any more than that and the population will grow; any less than a NIR of 2.1 causes population contraction. The NIR percent is 2.1 and not 2.0 for stability because not every human will pair up and have a child because of genetics, choice, or death before childbearing years. Once we know the NIR, we can determine the doubling time. Doubling time is how many years it would take for a defined population to double in size, assuming that NIR stays the same over time. Currently, about 82 million people are added to the world’s global population every year.

Key Factors Influencing Population Change

When trying to predict or analyze population change, three key factors to understand are the total fertility rate, infant mortality rate, and life expectancy at birth. Total fertility rate (TFR) is the average number of children a woman would be expected to have during childbearing years (between 15-49 years old). The global average for TFRs is about 2.5, but in less developed countries, it is as high as 5.0 or higher, and in more developed countries, it is as low as 2.0 or less. Fertility patterns can vary widely within countries. Racial and ethnic minorities may have higher fertility rates than the majority, and families with low incomes or low education levels typically have more children than those who are affluent or well-educated. Women who work outside the home typically have fewer children than those who stay home, and rural families tend to have more children than city dwellers. In 2016, the number of births per 1,000 people worldwide was 20, with extremes ranging from a low of 8 or 9 (mainly in Northern and Western Europe and Hong Kong), to 60 or more in a few West African nations (Population Reference Bureau, 2016 World Population Data Sheet, pp. 10-19).

Mortality is the second significant variable that shapes population trends. A population’s age structure is an essential factor influencing its death rate. Death rates are highest among infants, young children, and the elderly, so societies with many older adults are likely to have more deaths per 1,000 people than those where most citizens are young adults. Developed countries with excellent medical services have more people in older age brackets than developing countries, so the developed societies can have higher death rates even though they are healthier places to live overall. Infant mortality rate (IMR) is determined by calculating how many children die before the age of 1 per 1,000 live births annually. The highest IMRs are in less developed countries where rates can be as high as 80 or more. Conversely, in a place like Europe, it is as low as 5 percent.

Life expectancy at birth is straightforward—it is an average of how many years a newborn is expected to live, assuming that mortality rates stay consistent. In more developed countries, the average life expectancy is over 80 years old, and in less developed countries, it is only around 40 years (Figure 2.6). When we compare CBRs, CDRs, and TFRs, we find that the world has a large population of youth, with the most substantial percent in less developed countries. This causes high stress on the education systems and, to some extent, the health care systems in poorer countries. However, more developed countries tend to have older demographics, causing stress on those countries’ health care and social safety nets. The dependency ratio discussed later in this chapter is used to understand these stresses and the number of people who are too young or too old to work compared to the number of people in their “productive years.” The larger the ratio, the greater the economic stress on those nations.

2.2 Demographic Transition Model

Human geographers have determined that all nations go through a four-stage process called the demographic transition model (DTM). Developed in 1929 by American demographer Warren Thompson, the DTM’s function is to demonstrate the natural sequence of population change over time, depending on development and modernization. This can help geographers and other scientists examine the causes and consequences of fertility, mortality, and natural increase rates. Though controversial, the DTM is used as the benchmark for forecasting human population growth regionally and globally.

STAGE 1: LOW GROWTH RATE

We have lived in the first stage of the Demographic Transition Model for most of human existence. In this first stage, CBRs and CDRs fluctuated significantly over time because of living conditions, food output, environmental conditions, war, and disease. However, the world’s natural increase was pretty stable because the CBRs and CDRs were about equal. However, around 8,000 BC, the world’s population grew dramatically due to the first agricultural revolution. Humans learn to domesticate plants and animals for personal use during this time and became less reliant on hunting and gathering for sustenance. While this transition allowed for more stable food production and village populations to grow, War and disease prevented population growth from occurring globally.

STAGE 2: HIGH GROWTH RATE

Around the mid-1700s, global populations began to grow ten times faster than in the past for two reasons: The industrial revolution and increased wealth. The Industrial Revolution brought with it a variety of technological improvements in agricultural production and food supply. Increased wealth in Europe and later North America because of the Industrial Revolution meant that more money and resources could be devoted to medicine, medical technology, water sanitation, and personal hygiene. Sewer systems installed in cities led to public health improvements. All of this dramatically caused CDRs to drop around the world. At first, CBRs stayed high as CDRs decreased; this caused populations to increase in Europe and North America. Over time, this would change.

Africa, Asia, and Latin America moved into Stage 2 of the demographic transition model 200 years later for different reasons than their European and North American counterparts. The medicine created in Europe and North America was brought into these emerging nations, creating what is now called the medical revolution. This diffusion of medicine in this region caused death rates to drop quickly. While the medical revolution reduced death rates, it did not bring wealth and improved living conditions and development that the Industrial Revolution created. Global population growth is highest in the regions that are still in Stage 2.

STAGE 3: MODERATE GROWTH RATE

Today, Europe and North America have moved to Stage 3 of the demographic transition model. A nation moves from Stage 2 to Stage 3 when CBRs begin to drop while CDRs simultaneously remain low or even continue to fall. It should be noted that the natural rate of increase in nations within Stage 3 is moderate because CBRs are somewhat higher than CDRs. The United States, Canada, and countries in Europe entered this stage in the early 20th Century. Latin American nations entered this stage later in the century.

Advances in technology and medicine cause a decrease in IMR and overall CDR during Stage 2. Social and economic changes bring about a reduction in CBR during Stage 3. Nations that begin to acquire wealth tend to have fewer children as they move away from rural-based development structures toward urban-based structures because more children survive, and the need for large families for agricultural work decreases. Additionally, women gain more legal rights and chose to enter the workforce, own property, and have fewer children as nations move into Stage 3.

STAGE 4: LOW GROWTH RATE

A nation enters Stage 4 of the demographic transition model when CBRs equal to or become less than CDRs. When CBRs are equal to CDRs, a nation will experience zero population growth (ZPG). It should be noted that sometimes a nation could have a slightly higher CBR but still experience ZPG. This occurs in many countries where girls do not live as long before they reach their childbearing years due to gender inequality.

When a country enters Stage 4, the population ages, meanwhile fewer children are born. This creates an enormous strain on the social safety net programs as it tries to support older citizens who are no longer working and contributing to the economy. Most of Europe has entered Stage 4. The United States would be approaching this stage if it were not for migration into the country.

A nation in the first two stages of the transition model will have a broad base of young people and a smaller proportion of older people. A country in Stage 4 will have a much smaller base of young people (fewer children) but a much larger elderly (decreased CDR). A nation with a large youth population is more likely to be rural with high birthrates and possibly high death rates. This can tell geographers a lot about the health care system of that nation. Moreover, a country in Stage 4 with a large elderly population will have fewer young people supporting the economy. These two examples represent the dependency ratio mentioned earlier in this chapter. This ratio is the number of people, young and old, dependent on the working force.

Human geographers like to focus on the following demographic groups: 0-14 years old, 15-64 years old, and 65 and older. Individuals who are 0-14 and over 65 are considered dependents (though this is changing in older generations). One-third of all young people live in emerging nations, which places considerable strain on those nations’ infrastructure, such as schools, hospitals, and day-care. Older individuals in more developed nations (MDL) benefit from health care services but require more help and resources from the government and economy. The author of this textbook uses the term “emerging nations” rather than “less developed” or “developing,” or “third-world” nations as a more inclusive and equitable term.

Another ratio geographers look at is the number of males compared to females. This is called the sex ratio. Globally, more males are born than females, but males also have a higher death rate than females. However, understanding a nation’s sex ratio and its dependency ratio helps human geographers analyze fertility rates and natural increase.

As noted earlier, population growth has increased dramatically in the last century. No country is still in Stage 1, and very few have moved into Stage 4. The majority of the world is either in Stage 2 or 3, both having higher crude birth rates than crude death rates; therefore, the world’s population is over 7 billion today.

In summary, the demographic transition model is a model that helps human geographers understand and predict the demographics of individual nations. In Stage 1, CBR and CDR are very high and thus produce a low natural increase. In Stage 2, a nation’s CBR stays relatively high, but the CDR drops dramatically, producing the population’s highest growth. In Stage 3, CDR stays low; however, changes in social customs and economic conditions result in a moderately low CBR. Finally, in Stage 4 have nearly equal CBR and CDR (sometimes higher CDR), creating a drop in natural increase.

2.3 Overpopulation

In 1798, Thomas Malthus published a short but revolutionary work called “An Essay on the Principle of Population.” In that essay, Malthus states that two facts and one opinion would determine future population growth. The facts were that food is necessary for survival and that men and women would continue to produce offspring. His view is that population growth will occur exponentially if the population is not restrained by war, famine, and disease. He also argues that agricultural production of food could only grow arithmetically. The overall assumption is that population growth will quickly grow beyond food production, leading to food shortages and famines.

Malthus’ theory has not come to fruition yet, due to technological advances in agriculture (fertilizers, insect and drought resistance, and better farming techniques). Some discredit Malthus because his hypothesis is based on a world supply of fixed resources rather than expanding. Humans can expand the quantity of food and other resources by using new technologies to offset the scarcity of minerals and arable land. Thus, we can use resources more efficiently and substitute scarce resources with new ones. Even with a global human population of 7 billion, food production has grown faster than the worldwide rate of increase (NIR). Better growing techniques, higher-yielding, genetically modified seeds, and more land cultivation have helped expand food supplies.

While new technologies have helped increase food production, there are not enough emerging technologies to handle supply and demand. Adding to the problem is the fact that many insects have developed a resistance to pesticides. These problems have caused a slowdown and a leveling-off of food production in many regions of the world. Without breakthroughs in safe and sustainable food production, the food supply will not keep up with population growth.

Others believe that population growth is not a bad thing. A large population could stimulate economic growth, and therefore, the production of food. Population growth could generate more customers and more ideas for improving technology. Additionally, some maintain that no cause-and-effect relationship exists between population growth and economic development. They argue that poverty, hunger, and other social welfare problems associated with a lack of economic development, famines, and war result from unjust social and economic institutions, not population growth.

Lately, there has been a rise in neo-Malthusian thought. One notable figure is Paul Ehrlich. In his book, The Population Bomb, Ehrlich argues that population growth cannot continue without controls because the planet will reach our species’ carrying capacity. In short, we must consider environmental factors as we discuss overpopulation concerns. For example, even though humans produce four times the amount of food that we consume, the environment pays an ecological price for our food production. The rapid population growth of the world has caused massive deforestation in the Boreal Forests and rainforests, increasing desertification that encroaches into arable land, over-fishing of the oceans, mass extinction of species, air and water pollution, and anthropogenic (human-induced) climate change. All of these things have economic and environmental costs that we must consider.

Population Policy

Governments and other entities can dramatically influence population change to increase or decrease population growth in their country by promoting anti-nationalist or pro-nationalist policies. Some countries take dramatic steps to reduce their population. For example, China’s One-Child Policy dictated that each family (husband and wife) could legally have only one child. The government or better housing often gave families that followed this policy more money. If a family illegally had another child, they would be fined heavily.

Children born illegally cannot attend school and have difficulty finding jobs, getting government licenses, or even getting married. Some have reported that the government would force abortions on families with more than one child. One of the significant consequences of this policy was a dramatic increase in abortions and infanticides, especially females. Female infanticide is linked directly to a global cultural trend that privileges males over females; baby boys are desired, especially if they are only allowed, one child. This specific focus on eliminating women is called gendercide. Half the Sky, written by Nicholas Kristof and Sheryl WuDunn, documents global gendercide and what is being done to combat this problem.

After the two great world wars, the United Nations Population Commission and the International Planned Parenthood Federation began to advocate for more global population control. Many groups who advocate for population control focus on:

• Changing cultural attitudes that keep population rates high (or low)
• Providing contraception to least developed countries (LDC)
• Helping countries study population trends by improving census counts
• Empowering women and emphasizing gender equality

It is believed that worldwide, over 60 percent of women between ages 15-49 use some form of contraception. This varies regionally. In the United States, contraception use is nearly 75 percent, whereas, in Africa, it is around 30 percent. Today’s consensus is that the focus on population planning should be on gender equality and improving women’s social status around the world. This is the focus of the International Conference on Population and Development.

Religious organizations are also concerned with population growth; however, they focus on contraception issues and not strictly population growth. Some religions and political entities find contraception use immoral, which has influenced some governments to illegally access and use them.

2.4 Migration

Migration is the physical movement of people from one place to another; it may be over long distances, such as moving from one country to another, and can occur as individuals, family units, or large groups. When referring to an international movement, migration is called immigration.

Some interesting patterns occur with migration. Most people that migrate travel only a short distance from their original destination and usually within their country, often due to economic factors. This is called internal migration. Internal migration can be divided further into interregional migration (the permanent movement from one region of a country to another region) and intraregional migration (the permanent movement within a single region).

The other type of migration is called international migration, which is the movement from one country to another. Some people can voluntarily migrate based on individual choice. At other times, an individual must leave against his or her will. This is forced migration. Ultimately, the distance people migrate depends on economic, gender, family status, and cultural factors. For example, long-distance migration tends to involve males looking for employment and traveling by themselves rather than risking to take their families.

Migration is very dynamic around the world, with peaks in different regions at different times. As noted earlier, there are several reasons why people migrate, but where are people relocating to or from? Migration transition is the change in migration patterns within a society caused by industrialization, population growth, and other social and economic changes that also produce the demographic transition. A critical factor in all forms of migration is mobility, the ability to move either permanently or temporarily.

There are several reasons why people migrate known as push and pull factors, and they occur on economic, cultural, or environmental lines. Push factors are events and conditions that compel an individual to move from a location. Pull factors are conditions that influence migrants to move to a particular location. The number one reason why people migrate is for economic purposes. This is because people either get “pushed” away from where they live due to a lack of employment opportunities or pulled because somewhere else either offer more jobs/higher-paying jobs.

Cultural push factors usually involve slavery, political instability, ethnic cleansing, famine, and war. People who choose to flee or are forced to flee due to these problems are often refugees. The United States Committee for Refugees classifies a refugee as someone who has been forced from their homes and cannot return because of their religion, race, nationality, or political opinion. In 2010, the United Nations High Commission for Refugees estimated that over 44 million people worldwide had been forcibly displaced. The number grows to another 27 million when considering internally displaced persons (IDPs). Cultural pull factors could include people who want to live in democratic societies, gender equality, or educational or religious opportunities.

There has been a dramatic increase in immigration into the United States from Latin America, Africa, and the Middle East. Some from these regions migrate to the U.S. out of economic necessity. We hear quite a lot about guest workers in the United States. These are individuals who migrate temporarily to take up jobs in other countries. This phenomenon is also known as transnational migration. Others migrate to escape conflicts such as the civil wars in Somalia, Sudan, and Ethiopia. Genocides in Rwanda (1994) and, more recently, Darfur, Sudan have forced internal and international migration. The wars in Afghanistan and Iraq have also forced migration from these regions. The U.N. High Commission for Refugees estimates that over 2 million Iraqis (nearly 8 percent of the pre-war population) have been forced to migrate to nearby Jordan, Syria, and Lebanon.

A variety of environmental push and pull factors also influence migration patterns. Environmental pull factors can include people wanting to live in particular environments. For example, many older adults like to live in Hawaii because they prefer recreational opportunities for retired individuals. Some people want to live where snow activities are available or near an ocean. Push factors often are related to the frequency of natural disasters such as earthquakes, tsunamis, hurricanes, or flash floods that a region could experience. Climatic push/pull factors, such as droughts, also influence migration patterns. A very recent example of this is the drought and famine in East Africa. As anthropogenic climate change becomes more pressing and hundreds of millions of people become displaced, the world will see more climate migrants forced from their homes.

The United States Agency for International Development (US AID) and the Famine Early Warning System Network track potential famines globally so that relief organizations can have a heads up and be more proactive when events occur. People who have been pushed for environmental reasons are called environmentally displaced persons, also called ecological refugees. The problem with these refugees is that they are not protected or given the same rights under the 1951 Refugee Convention. Under the convention, a refugee is a person with: “well-founded fear of being persecuted for reasons of race, religion nationality, and membership of a particular social group or political opinion, who is outside the country of his nationality and, owing to such fear, is unwilling to avail himself of the protection of that country.” However, more and more people are becoming environmental refugees because of climate change, droughts, flooding from large storm systems, water shortages, and more.

Questions for the Future

Global human populations are often controversial because there is no clear consensus on dealing with it. Demographers know that there are over 7.3 billion people on the planet, but they are not evenly distributed worldwide. One consistent global pattern is water; nearly 80 percent of the world’s population lives near a large body of water.

• Why do you think populations converge on large bodies of water?
• What happens to populations when there is a shortage of water?

There are various ways that geographers and demographers study population dynamics and profiles, often representing this data in diagrams, graphs, and, most importantly, maps. Social scientists have tried to describe historical, current, and future population trends with the Demographic Transition Model. The model attempts to explain how more developed countries progressed with their demographics than less developed countries today. Some argue that though the model predicts demographic trends in North America and Europe, the model does not accurately represent population trends in other regions of the world. Others say the model is too simplistic because of environmental and cultural factors.

Another debate area is the potential ramifications as the human population exceeds more than 8 and 9 billion by 2050. This debate started a while ago with the Malthus theory. Many ecologists believe humans have reached the earth’s carrying capacity and cannot sustain such large populations. Others argue that technology has consistently kept ahead of food scarcity concerns and that high populations could benefit less developed countries to improve development.

Geographers also understand that humans are migrating species, and with technology, today can move across great distances. The reason for migration varies, but it all comes down to push or pull factors related to economic, political, social, or environmental reasons. Many of these travelers are temporary living as guest workers until they need to move on. Today, many migrants are refugees, living in various living conditions from complex metropolitans to squatter towns or refugee camps. We know about human migration because most humans will die in the same town they were born in.