Chapter 4.
Population Growth and the
Environment
By G. Sherlin D. Moses
"Unlike plagues of the dark ages or contemporary diseases we do not
understand, the modern plague of overpopulation is soluble by
means we have discovered and with resources we possess. What is
lacking is not sufficient knowledge of the solution but universal
consciousness of the gravity of the problem and education of the
billions who are its victim." —Martin Luther King, Jr.
Learning Objectives
Understand population dynamics.
Understand how population can be regulated.
Learn the factors that influence population regulation.
Questions Students May Have
1. What is the carrying capacity of Earth?
2. What are the factors that influence the size of the human population?
3. Can and should human population growth be slowed?
Introduction
This chapter discusses the different perspectives on human population growth, the
dynamics associated with population change in response to environmental
conditions, and the factors that influence population growth and family size.
Population Growth and the Environment
Dynamics of Population Growth
On average, four or five children are born every second and two die every second,
which leads to a net gain of roughly 2.5 humans per second globally (Cunningham &
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Cunningham, 2015). With roughly 7 billion people living in the world as of 2011 and a
growth rate of 1.13% per year, the global population will double in a mere 62 years.
Humans impact the environment in more ways than all other species.
Overpopulation, which could lead to the depletion of natural and manmade
resources and cause environmental degradation, may be the planet’s greatest
challenge going forward. It is possible to manage the increased population growth by
judiciously using human ingenuity, technology, and enterprise (Cunningham &
Cunningham, 2015). Economists suggest that this is possible because of the increased
workforce, which can bring in better ideas and lead to improved technological and
economic growth. Ecologists also believe overpopulation could be a problem and that
both economic and population growth will have to be slowed.
A population is a group of individuals that live together in the same habitat and are
likely to interbreed. Each individual typically has a specific and unique physical
distribution in terms of size and space. A population will change over a period of time
according to the reproductive success of its members. Population dynamics indicate
that there is a fluctuation in the size of the population and that it is altered from one
place to another and from one period of time to another. Therefore, population
dynamics can be defined as the study of how the characteristics of a population such
as birthrate, death rate, and migration can change in response to variations in
environmental conditions (Miller & Spoolman, 2009). Reasons for fluctuation include
the prevalence of diseases such as the bubonic plague, which killed a third of
Europe’s population between 1348 and 1650. The Spanish flu pandemic killed 50
million people worldwide in 1918 as 20% to 40% of the world population became ill
(secondary infections such as pneumonia caused the deaths). In 2010, the World
Health Organization (WHO) declared an end to the H1N1, or Swine flu pandemic,
which killed more than 18,000 people and infected 89 million worldwide in 2009–
2010 (“Pandemic Flu History,” n.d.). Such outbreaks in a given area promote mass
migration. Other reasons for fluctuation include the mass extinction of organisms
due to fire or lack of food and resources (Miller & Spoolman, 2009).
In An Essay on the Principle of Population, written in 1798, Thomas Robert Malthus
theorizes that human population increases at an exponential or compounded rate,
whereas food production remains stable and increases slowly. This means the
population will outgrow the food supply. Famine and disease will constrain social
conditions, including economic constraints, which could lead to a reduced birthrate
and late marriages.
Human population growth follows an exponential model. In an exponential model,
the growth is slow initially and then increases rapidly. The population on Earth
reached one billion after two million years and grew to five billion within the next 12
years, indicating tripling of the human population. This rate exhibits a J-shaped curve.
The population growth is currently taking place at a rate of 1.55% and is projected to
reach 8.3 billion by 2025 (Miller, 1997). The growth rate is exceeding the food
production and distribution rate in areas such as Africa and Asia. The increase in
population is due to good quality nutrition, potable water, improved sanitation,
advances in science and technology, and advancements in medicine and public
health care. Exponential growth starts off slowly but increases rapidly to an
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exponential rate. It becomes stationary when the population reaches the carrying
capacity of the Earth.
Carrying capacity is the number of organisms of a given species that can be sustained
indefinitely in a given area. This results in an S-shaped curve, as the increase in
population will utilize all resources and will allow the population to exceed the
carrying capacity. One of the problems that results due to this type of exponential
growth is overconsumption of food reserves, which can lead to a temporary increase
in the population. This overshoot leads to a reproductive time lag, which is the time
period required for the birthrate to fall and death rate to rise. An excessive number
of individuals will have to migrate to areas with favorable conditions to avoid the
population fall. This phenomenon was observed in Ireland in 1845 when more than a
million people died after a fungus destroyed the potato crops (Immigration in
America, 2011). This famine caused many Irish to migrate to other countries,
including the United States. The Earth’s carrying capacity is variable and depends on
factors such as per capita use of resources, competition, immigration and emigration,
climatic changes, and natural catastrophes. Technological, social, and other cultural
changes have increased the carrying capacity, increased food production, and made
uninhabitable areas of the Earth habitable.
Population Growth Regulation
A population change occurs when the number of individuals increases or decreases
in response to environmental conditions. It is possible that a population will not
remain the same over a period of time, which is termed “unchanged.” The primary
factors that influence the population size are birth, death, and migration. An increase
in population is brought about by the number of births and the immigration or arrival
of new individuals into the population from different places. This immigration could
be due to drought, war, or lack of resources in the immigrants’ primary area of
residence, such as the Irish immigration to America mentioned previously. War and
job opportunities are the 21st century’s key determining factors. As of January 2012,
13.3 million legal immigrants live in the United States (Migration Policy Institute,
2012). In 2013, 69,909 people were given asylum or refugee status. This status is
given to individuals who are unable or refuse to return to their country of origin
because of persecution or fear of persecution due to race, religion, or political/social
group affiliation (Martin & Yankay, 2013). In a 2011 report released by the
Department of Homeland Security’s (DHS) Office of Immigration Statistics (OIS) (n.d.),
an estimated 11.5 million unauthorized immigrants resided in the United States
(Nwosu, Batalova, & Auclair, 2014). Two of the main reasons individuals are entering
the United States illegally are poor economic conditions and safety concerns due to
drug trafficking and gang violence.
A decrease in population is related to the number of deaths and the emigration of
individuals, or the movement of people out of an area. Factors that influence
emigration are associated with unfavorable conditions such as war, famine, and
poverty. Positive reasons include retirement, better job opportunities, and a better
quality of life.
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Birthrate or crude birthrate is the number of live births in a given year per 1,000
people in a given population. The crude death rate is the number of deaths per year
per 1,000 people.
According to Population Reference Bureau (2014), the global population in 2014 was
7.4 billion people. China is the planet’s most populous nation with 1.29 billion people,
India has 1.26 billion people, and the United States ranks third with 318 million
people (Population Reference Bureau, 2014). China and India collectively comprise
36.74% of the world’s population (Population Reference Bureau, 2014).
Figure 4.1
World Populations
Note. Source: “Half of the World’s Population Live in 6 Countries,” by Pew Research
Center, 2014. http://www.pewresearch.org/files/2014/07/FT_14.07.10_worldPop2.png
Population size is influenced by the birthrate, which is related to the fertility rate of
the population. There are two types of fertility rates: the replacement fertility rate
(RFR) and the total fertility rate (TFR). The replacement fertility rate indicates the
number of offspring a couple produces to replace themselves. Total fertility rate is an
estimate of the average number of children a woman produces during her
childbearing age.
When the birthrate and death rate factors are balanced, the population size remains
stable and is referred to as zero population growth (ZPG). It takes several generations
for ZPG to be reached. If the infant mortality rate is higher among children in a given
population, the birthrate is usually higher. Birthrates are lower in well-developed
countries since many individuals choose not to have children, have fewer children, or
lack the ability to have children due to fertility issues. A good example of a population
in decline is Brazil, where the fertility rate is at 1.8 children per woman. The
population of young Brazilians under 14 is very high. These children will grow and
have families, and there could be an increase in population over the next few
decades or generations, which is referred to as population momentum. A drastic
reduction in the population by declining fertility rates could affect the global
population by 2050.As stated earlier, the world's population in 2014 was about 7.4
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billion people with around half of the globe living in just a half dozen countries (Pew
Research Center, 2014). This distribution in population is driven by fertility rates, a
large number of people surviving to reproductive age, increased urbanization, and
migration—all critical factors that will influence world population dynamics for future
generations (“Population Dynamics,” 2011).
Figure 4.2
Global and Regional Total Fertility Rates
A country’s economy is impacted by population size and structure. Population size
influences country’s ability to provide social protections and access to health care,
education, housing, sanitation, water, food, and energy. Because population
dynamics vary widely, from countries trying to provide opportunities for enormous
youth populations to those coping with low fertility and aging policies dealing with
population issues must be tailored to their specific needs (“Population Dynamics,”
2011).
Global population increase is attributed to not only a rise in crude birthrate, but a
decline in the crude death rate due to overall improvement in the quality of peoples’
lives. This includes an increased food supply, the increased nutritional value of food,
the availability of medical access and medicines, and improved technology.
Pew Research Center data released in 2014 shows population growth was rapid from
1950 to 2010. The global population tripled and the U.S. population doubled in that
60-year span. The growth rate is projected to be significantly lower from 2010 to 2050
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and is expected to tilt strongly to the oldest age groups, both globally and in the
United States. Consider the following scenario.
Population in the United States: There is a steady decline in population growth rate,
which has remained at the replacement level since 1972. There is a significant decline
in population growth rate and the average number of children born has decreased
from more than three children in 1976 to two in 2012 (Monte & Ellis, 2014). Reasons
for the decline include the lower birthrate among adolescents, one in five women
were living in someone else’s home during childbirth, and a rise in the number of
women who had children while in a cohabiting relationship (most of them were
married when they had their first child) (Monte & Ellis, 2014).
Factors that affect the total fertility rate (TFR) and birthrate in a country
independently or interacting with one another include:
Urbanization: Number of children per family is lower in urban areas
when compared to rural areas and residents have better access to
family planning services.
Education and affluence: Birth and fertility rates are lower in most
developed countries (MDC) since education and affluence are higher
than in less developed countries (LDC).
According to the U.S. Census Bureau (2010), there has been a decline in the TFR since
1957 and it has remained at a low replacement level since 1972. However, between
2010 and 2050, the U.S. population is still projected to grow from 310 million to 439
million, an increase of 42%, and the nation will also become more racially and
ethnically diverse, with the aggregate minority population projected to become the
majority in 2042 (Vincent & Velkoff, 2010).
Reasons for the projected growth rate include:
Increased numbers of unmarried mothers.
Higher fertility rates of women in racial groups other than Caucasians.
Higher levels of legal and illegal immigration.
Religious beliefs that oppose birth control and abortions will favor
large families.
According to National Center for Health Statistics, NCHS, (2013), the following factors
influence the death rate:
Longer lifespans.
Lower infant death rates.
The availability of nutritious food.
Improvements in medical and health technology.
Better sanitation.
Awareness and availability of resources such as good health care.
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The overall health of a country and region is determined by its life expectancy, which
is the average number of years any person can be expected to live. Globally, life
expectancy has increased since 1965 to 74 in MDC and 64 in LDC. The infant mortality
rate is the number of babies out of every 1,000 born each year that die before their
first birthday. Infant mortality rates are a good indicator of a society’s quality of life
since they indicate nutritional levels and quality of health care. Higher infant mortality
rates indicate poor nutrition (or undernourishment) and higher infectious disease
rates.
Overall, the world’s mortality rate has a geographic element to it. Characteristics such
as age, distribution, and the total number of humans in a particular space influence
populations. Birthrate, death rate, and migration are factors that collectively
influence population growth.
Factors That Can Influence the Birthrate: Case Study
Brazil, one of the largest countries in South America, has shown an abrupt decline in its
birthrate compared to most other countries. A member of the so-called BRIC countries (Brazil,
Russia, India, and China), Brazil has the sixth largest economy, the sixth largest population, and
has a gross domestic product growth higher than 5%. This increase in economic growth has
enhanced the quality of life and the standard of living for Brazilians. The average wage has
improved fivefold when compared to 50 years ago and average number of years of education
has improved from 2 years to 8.6 years for girls. The fertility rate, however, is only 1.8, which is
a significant decrease from the previous rate of 6.2 children (Cunningham & Cunningham,
2015). Economic growth, the empowerment of women, urbanization, and media and television
exposure to lifestyles of people from other parts of the world are a few reasons that have led
to Brazil’s decline in birthrate. Industrialization influenced urban migration and 87% of Brazil's
population live in urban areas with smaller families (Cunningham & Cunningham, 2015). This
arrangement increases the economic advancements (as seen in families with both parents
working) and educational opportunities, which helps parents raise fewer children with a good
education, better job opportunities, and economic improvements.
Television in Brazil has played a big role in reducing the population. The media actively
showcases small families with higher incomes, successful careers, many material possessions,
and personal freedoms. These factors can contribute to the reduction in birthrate. One
interesting fact is that there have been no government interventions to reduce the population.
This is perhaps due to Brazil's identity as a predominantly Catholic nation. The empowerment
of women, the availability of birth control and the morning-after pills, and the option for
women to have tubal ligations done when they go in for caesarian delivery of babies also
prevents population expansion (Miller, 1997).
How to Slow and Reduce Population Growth
Family Planning
Family planning methods involve adopting measures to reduce births such as late
marriage, using contraceptives, adopting abstinence, and aborting unplanned
pregnancies. Controlling fertility rates dates back to the hunter-gatherer people of
the !Kung San of the Kalahari Desert in Southwest Africa. The women in this
community breastfed their offspring until the children were 3 to 5 years old, which
could prevent ovulation. They also maintained abstinence. Abortion, infanticide, and
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folk medicine were common practices. Although these practices may be viewed as
primitive, they helped the !Kung San maintain their population size.
There are many different family planning options available. Most of the current
options are hormonal and help prevent pregnancy. There are injections to prevent
sperm production in men and vaccines to prevent pregnancy are being researched
and developed. Devices that can permanently cause sterilization are also available.
Although fertility can be restored if there is an interest in conceiving a child,
sometimes it may take longer to conceive. There are many benefits to family
planning. It allows future parents to plan the number of children they want to have as
well as the timing of each child’s birth. This lowers abortion rates and allows women
to plan ahead and ensures they are in good health before pregnancy. This planning
can improve the quality of life for women and allows them to attain a better
education, better employment, and improve the well-being of their family.
Empowering Women
Education plays a significant role in empowering women to make decisions about
their lives and reproductive behavior. Poor women who cannot read tend to have
more children when compared to educated women who live in places where their
human rights are respected. Seventy percent of the world's poor and 64% of illiterate
adults are women (Miller & Spoolman, 2009). This has to change in order to stabilize
population growth and reduce environmental degradation.
Conclusion
Population growth is a complicated process. The human population has been
growing rapidly over the last two centuries. There is a constant debate as to whether
natural resources will be depleted due to the increased population, leading to
starvation, disease, crime, and misery. Overpopulation will lead to water shortage, a
decline in food production, and the sporadic spread of diseases such as malaria and
dengue fever. Population growth will force people to settle in flood-prone valleys and
on unstable hillsides where deforestation and climate change have increased their
vulnerability to disasters such as hurricanes.
Clean, renewable energy and investments in alternative energy sources are needed.
A stronger enforcement of treaties and cooperation amongst influential E9 countries
are critical factors in improving the environmental impact as nearly 75% of global
greenhouse gas emissions arise from these countries (World Population Awareness,
2014). Reducing per capita energy consumption, along with resource consumption,
should be beneficial in the long run. This, along with human ingenuity, resilience, and
effective governance will help maintain a sustainable global population. There are
varied opinions about the availability of resources and whether population growth is
the leading cause of environmental deterioration and poverty; these could also be
indicators of extant social and political factors within nations. Increasing population
necessitates increasing intelligence and ingenuity to uncover new resources, to
discover new materials, and to find better ways of doing things. The current global
trend is lowered birthrates and the world population may reach nine billion people by
2050. Drastic measures could even bring the rate down to seven billion by 2050. If the
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Earth has to sustain the population of seven or even nine billion who can lead happy
and comfortable lives, all individuals must find and adapt sustainable ways of living.
Review Learning Outcomes
Population dynamics is the study of how the characteristics of a
population such as birthrate, death rate, and migration can change in
response to changes in environmental conditions.
Population size can be affected by birthrates and death rates and the
balance between the rates.
Chapter 4 Practice Quiz
References
Cunningham, W. P., & Cunningham, M. A. (2015). Environmental science: A global
concern (13th ed.). McGraw Hill.
Department of Homeland Security. (n.d.). Yearbook of immigration statistics.
http://www.dhs.gov/files/statistics/publications/yearbook.shtmImmigration in
America. (2011). http://immigrationinamerica.org/528-great-irish-famine.html
Martin, D. C., & Yankay, J. E. (2013). Refugees and asylees: 2013.
http://www.dhs.gov/sites/default/files/publications/ois_rfa_fr_2013.pdf
Migration Policy Institute, (2012). Estimates of the legal permanent resident population
in 2012.
https://www.dhs.gov/sites/default/files/publications/ois_lpr_pe_2012.pdf
Miller, G. T. (1997). The Human Population. Environmental Science Working with the
Earth. 6th edition. Wadsworth Publishing Company.
Miller, G. T., & Spoolman, S. E. (2009). Living in the Environment (17th ed.). Belmont, CA:
Cengage Learning.
Monte, L. M., & Ellis, R. R. (2014). Fertility of women in the United States 2012:
Population characteri
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