Chapter 7 Envi sci
Terms in this set (71)
Human population growth
the global human population has grown more rapidly in the last 400 years than at any other time in history
Global human population growth trend: past and modern
past: deaths and births used to occur in roughly equal #'s
modern: every 5 days the global population increases by more than a million lives
The human population began to increase drastically 400 years ago when agricultural output increased and sanitation began to improve. Better living conditions caused death rates to fall, but birth rates remained relatively high.
Current human population
Over 7 billion
Under ideal conditions all populations grow exponentially. In most cases, exponential growth slows or stops when an environmental limit is reached
Limiting factors determine the carrying capacity of a habitat
One of the first to suggest that the human population could exceed Earth's carrying capacity. He observed that Earth's population was growing exponentially while the food supply was only growing linearly. Malthus concluded that the population size would eventually exceed the food supply
Once carrying capacity is reached, the rate of population will decline
Some scientists argue that the carrying capacity will not be reached.
They argue that the growing population of humans provides an increasing supply of intellect that leads to increasing amounts of innovation.
For example, in the past whenever the food supply seemed small enough to limit the human population, major technological advances increased food production. (1. Arrows made hunting more efficient, which allowed hunters to feed a larger number of people - 2. Early farmers increased crop yields with hand plows and later with oxen or horse-driven plows.
^Each of these inventions increased the planet's carrying capacity for humans
Influences on population growth
1. Population size
2. birth and death rates
4. life expectancy
the study of human populations and population growth
Demographers analyze the influences on population growth (Population size, birth and death rates, fertility, life expectancy, migration) and offer insights into how and why human populations change and what can be done to influence rates of change
Changes in population size
If there are more births than deaths, there are more inputs than outputs and the system expands. When demographers look at population trends in individual countries, they take into account inputs and outputs.
increases population size
Examples: immigration and births
decreases population size
Examples: emigration and deaths
the movement of people into a country or region from another country or region
the movement of people out of a country or region
How do demographers determine yearly birth and death rates?
Crude birth rate and crude death rate
Crude birth rate (CBR)
the number of births per 1,000 individuals per year
Crude death rate (CDR)
the number of deaths per 1,000 individuals per year
Worldwide, there were 20 births and 8 deaths per 1,000 people in 2014. We do not factor in migration for the global population because, even though people move from place to place, they do not leave Earth. Thus, in 2014, the global population increased by 12 people per 1,000 people. This rate can be expressed mathematically as a percentage.
Global population growth rate=
------------ = --------- = 1.2%
To calculate the population growth rate for a single nation, we take immigration and emigration into account:
National population growth rate =
[(CBR + immigration) - (CDR + emigration)]
If we know the growth rate of a population and assume that growth rate is constant, we can calculate the number of years it takes for a population to double known as doubling time.
the number of years it takes for a population to double
Doubling time can be approximated mathematically using a formula called the rule of 70
Doubling time (years) = 70/% growth rate
Therefore a population growing at 2 percent per year will double every 35 years
Earths population has doubled several times since 1600, however, it is almost certain that earths population will not double again
By 2050 demographers believe the population will be somewhere between...
8.1 and 9.6 billion
By 2100 demographers believe that the population will stabilize between...
6.8 and 10.5 billion
Total fertility rate (TFR)
An estimate of the average number of children that each woman in a population will bear throughout her childbearing years (between the onset of puberty and menopause)
Unlike crude birth rate and crude death rate, TFR is NOT calculated per 1,000 people. Instead it is a measure of births per woman
The TFR required to offset the average number of deaths in a population so that the current population size remains stable.
Typically, replacement-level fertility is just over 2 children. Two children replace the parents who conceive them when the parents die.
Replacement level fertility is higher than 2, however, because it also must account for children who die before they are able to have children or people who otherwise do not have children.
The rate of death among children depends on a country's economic status
Countries with relatively high levels of industrialization and income, typically, with a replacement level fertility of about 2.
A country with relatively low levels of industrialization and incomes of less than $3 per person per day.
A TFR of greater than 2.1 is needed to achieve replacement level fertility. Replacement level fertility is higher in developing countries because mortality among young people tends to be higher.
TFR is equal to replacement level fertility and immigration is equal to emigration --> stable population
A country with a TFR below 2.1 and no net increase from immigration is likely to experience a population decrease because that country's TFR is below replacement-level fertility
In contrast, a developed country with a TFR of more than 2.1 and no net decrease from emigration is likely to experience population growth because that country's TFR is above replacement-level fertility
The average number of years that an infant born in a particular year in a particular country can be expected to live, given the current average life span and death rate in that country.
Life expectancy is higher in countries with better health care
A high life expectancy is indicative of high resource consumption rates and environmental impacts
In general, males have higher death rates than females, and, therefore, have shorter life expectancies
In addition to biological factors, men have historically tended to face greater dangers in the workplace, made more hazardous lifestyle choices, and have been more likely to die in wars.
As more women enter the workforce and the armed forces, the life expectancy gap between men and women will probably decrease
Infant mortality rate
The number of deaths of children under 1 year of age per 1,000 live births
Child mortality rate
The number of deaths of children under age 5 per 1,000 live births
If a country's life expectancy is relatively high and its infant mortality is relatively low, it is likely that the country has a high level of available health care, an adequate food supply, potable drinking water, good sanitation, and a moderate level of pollution
Conversely, if its life expectancy is relatively low and its infant mortality rate is relatively high, it is likely gay the country's population does not have sufficient health care or sanitation and that potable drinking water and food are in limited supply. Pollution and exposure to other environmental hazards may also be high.
Availability of prenatal care is an important predictor of the infant mortality rate.
For example, the infant mortality rate is 63 in Liberia, where women commit have access to prenatal care, compared to Sweden's 2.6
Life expectancy and infant mortality in a given sector of a country can differ greatly from the life expectancy of the country as a whole. For example, whereas the infant mortality rate for the U.S. population as a whole is 6.0, it is 12.4 for African Americans, 8.5 for Native Americans, and 5.3 for Caucasians. This variation in infant mortality rates is probably related to socioeconomic status and varying degrees of access to adequate nutrition and health care
Even with a high life expectancy and a low infant mortality rate, a country may have a high crude death rate due to a large number of older individuals.
For example, U.S. has a CDR of 8 and Mexico has a CDR of 5. This higher CDR results from the much larger elderly population in the United States, with 13% of its population aged 65 years or older, compared to Mexico with 6% of its population aged 65 or older.
Disease is an important regulator of human populations
Infectious diseases, those caused by microbes that are transmissible from one person to another, are the second biggest killer worldwide after heart disease.
Tuberculosis and malaria used to be the two deadliest infectious diseases. Today, the most infectious diseases are HIV and AIDS.
Because HIV disproportionately infects people aged 15-49, the most productive years in a person's life span, HIV has had a more disruptive effect on society than other illnesses that affect the very young and the very old
Regardless of its birth and death rates, a country may experience population growth, stability, or decline as a result of migration
Net migration rate
The difference between immigration and emigration in a given year per 1,000 people in a country
A positive net migration rate means there is more immigration than emigration. A negative net migration rate means the opposite.
Net migration rate equation
Net migration= # of immigrants per year/# of people in the population
Example: about 1 million people immigrate to the U.S. per year and very few emigrate. With a. Population of 315 million, the net migration rate equals 3.2 immigrants per 1,000 people
A country with a relatively low CBR but a high immigration rate may still experience population growth. For example the U.S. has a TFR of 1.9, but it has a high net migration. As a result, the U.S. population will probably increase by 30% by 2050
In countries with a negative net migration rate and a low TFR, the population actually decreases over time. Example: Georgia, in western Asia, has a growth rate of .2 percent, a TFR of 1.7, and a net migration rate of -5 per 1,000 people. Georgia is projected to have a 20 percent population decrease by 2050
Age structure diagram
visual representations of the number of individuals within specific age groups for a country, typically expressed for males and females.
Each horizontal bar of the diagram represents a 5-year age group. The total area of all the bars in the diagram represents the size of the whole population.
Age structure diagram that is widest at the bottom and narrowest at the top (more younger people than older people)
Typical of developing countries, such as Venezuela and India
The wide base of the graph indicates that the population will grow because a large number of females aged 0-15 have yet to bear children
continued population growth after growth reduction measures have been implemented
It occurs because there are relatively large numbers of individuals at reproductive maturity in the population
Population momentum is the reason why a population keeps on growing after birth control policies or voluntary birth reductions have begun to lower the CBR of a country. Eventually, over several generations, those actions will bring the population to a more stable growth rate but the momentum of all the individuals who have recently reached child-bearing age will carry the population forward for a number of years.
Theory of Demographic Transition
As a country moves from a subsistence economy to industrialization and increased affluence, it undergoes a predictable shift in population growth.
The theory of demographic transition models the way that birth, death, and growth rates for a nation change with economic development.
PHASE 1: pre-industrial period characterized by high birth rates and high death rates
PHASE 2: as the society begins to industrialize death rates drop rapidly, but birth rates do not change. Population growth is greatest at this point.
PHASE 3: birth rates decline
PHASE 4: the population stops growing and sometimes begins to decline as birth rates drop below death rates
Phase 1 (slow growth)
The size of the population will not change very quickly because the high birth and death rates offset each other. In other words, CBR = CDR.
This pattern is typical of countries before they begin to modernize. In these countries, life expectancy for adults is short due to poor working conditions. The infant mortality rate is also high because of disease, lack of health care, and poor sanitation
(in a subsistence economy where most people are farmers, having children is an asset)
Today, crude birth rates exceed crude death rates in almost every country, so even the poorest nations have moved beyond phase 1.
Phase 2 (rapid growth)
death rates decline while birth rates stay high
modernization, better sanitation, clean drinking water, increased access to food and goods, access to health care, including childhood vaccinations, all reducing the infant mortality rate and CDR.
India is in phase 2
Phase 3 (stable growth)
a country enters phase 3 when its economy and education system improve.
As family income increases, people have fewer children. As a result, the CBR begins to fall.
^^ as societies transition from subsistence farming to more complex economic specializations, having large numbers of children may become a financial burden rather than an economic benefit
Population growth levels off during this phase, and population size does not change very quickly, because low birth rates and low death rates cancel each other out.
Phase 3 is typical of many developed countries such as the United States and Canada
Phase 4 (Declining growth)
Phase 4 is characterized by declining population size and often by a relatively high level of affluence and economic development. Japan, the United Kingdom, Germany, Russia, and Italy are phase 4 countries.
CBR is below CDR.
Less young people, more older people
The state of having plentiful wealth including the possession of money, goods, or property
regulation of the number or spacing of offspring through the use of birth control
As education improves fertility decreases
When women have the option to use family planning, crude birth rates tend to drop.
6.0 billion live in developing countries
1.2 billion live in developed countries
Developing countries are growing more rapidly than developed countries
Developed countries' population growth has ceased
United States has greatest ecological footprint
An equation used to estimate the impact of the human lifestyle on the environment
Developed by Barry Commoner, Paul Ehrlich, and John Holdren
Impact= Population x affluence x technology
Although it is written mathematically, the IPAT equation is a conceptual representation of the three major factors that influence environmental impact
Higher population=higher environmental impact
Higher affluence=higher environmental impact
Gross Domestic Product (GDP)
the value of all products and services produced in one year in one country.
GDP consists of four types of economic activity: consumer spending, government spending, investments, and exports minus imports
A country's GDP often correlates with its pollution levels
(high pollution=high GDP; low pollution=low GDP)
As a nation's GDP increases further, it may reach a turning point. It can afford to purchase equipment that burns fossil fuels more efficiently and cleanly, which helps to reduce pollution levels.
Most commonly used measure of a nation's wealth
Local and Global Resources
two commonly overused local resources are the land itself and woody biomass from trees and other plants
Global impacts are more common in affluent or urban societies because they tend to specialize production in the industrial and high technology sectors. For example, more than half the ecological footprint of the United States comes from its use of fossil fuels, of which approximately 50 percent are imported.
Families in suburban areas of developed countries consume far fewer local resources than rural families in developing countries.
When families are affluent they are more likely to use imported goods
contains more than 386 people per square kilometer (1,000 people per square mile)
75% of the population of developed countries lives in urban areas