1. Human populations:Population growth. Limits to growth
2. Basic Demographic processes.
3. Urban problems in developing & developed countries
4. Ways to achieve urban sustainability
1. Human populations:
World population now: 6.93 billion (Jan, 2011)
Demography is the study of the factors that affect rates of birth, death, and growth in populations. In making predictions about a population's growth, it is necessary to know its age structure.
Current Birth and Death Rates
Every second: about 4 children are born, while about 2 other people die
72 mln humans added to the world population every year.
Demographic transition theprocesswhereby a country moves from relatively high birth and death rates to relatively low birth and death rates due to improved living conditions, that usually accompanies economic development.
Stage 1 Preindustrial: high birth and death rates, so population grows very slowly.
Stage 2 Transitional high birth rate and lowered death rate, so population grows very rapidly.
Stage 3 Industrial a decline in birth rate and low death rate, so slow population growth occurs. In developed countries low fertility rate is due to high female literacy.
Stage 4 Postindustrial a population grows very slowly or not at all.
Population pyramids- is the age structure that is illustrated as a pyramid with the length of each tier showing the number of males (left side) and number of females (right side) in a particular age group of individuals: Prereproducti\e Reproductive and Postreprodictive. Because of age structure, a population that reduces its fertility rate to the replacement level (2.1 children)will continue to grow for another 30 to 50 >ears. This phenomenon, called population momentum, occurs because of the large number of prereproductive individuals that exist in the population.
Age group of individuals:
- Pre-reproductive (014 years)
- Reproductive (1544 years)
- Post-reproductive (45 years and older)
Age structure pyramid
These population pyramids, showing distribution of population bv age. indicate that Country B has a much greater growth potential than Country A has stable growing
Replacement level = 2.1 children
2. Population growth. Limits to Growth.
Overpopulation causes resource depletion and environmental degradation
Human ingenuity and technology will allow us to overcome any problems - more people may be beneficial
Resources are sufficient to meet everyone's needs - shortages are the result of greed, waste, and oppression:
There is a sufficiency in the world for man's need, but not for man's greed. ~Mohandas Gandhi~
For most populations, limiting factors recognized as components of environmental resistance can be placed into 4 main categories:
Raw material availability
Accumulation of waste products
Interactions among organisms
World is divided into 2 segments based on economic development:
More-developed countries - 1.4 bln: per capita income > $10,000.
Europe, Canada, US, Japan, Australia, New Zealand.
Expected to grow 3% by 2050.
Less-developed countries - 5.53 bln: per capita income < $5,000.
High population growth rates. Will grow 52% by 2050 (86% of world population).
Ecological footprint is a measure of land area required to provide human food, energy, water, housing, transportation & waste disposal for one person.
To be ecologically sustainable, each person should consume no more than 1.8 ha of land (ecological footprint).
Data in table is given as global hectares per capita. The world-average ecological footprint in 2007 was 2.7 global hectares per person (18.0 billion in total). With a world-average biocapacity of 1.8 global hectares per person (12 billion in total), this leads to an ecological deficit of 0.9 global hectares per person (6 billion in total). If a country does not have enough ecological resources within its own territory, then there is a local ecological deficit and it is called an ecological debtor country. Otherwise, it has an ecological remainder and it is called an ecological creditor country
Population in millions
Ecological Footprint in gha/pers
Biocapacity in gha/pers
Ecological remainder (if positive) in gha/pers
Factors That Influence Human Population Growth
- Humans (unlike other species) are influenced by biological, social, political, economic, and ethical factors.
Able to make conscious decisions and adjust lives accordingly.
Main factor of population growth rate: # of women with children & # of children each woman has.
Total fertility rate- # of children a woman has during her lifetime: rate of 2.1 = replacement fertility level;
Zero population growth: birth rate = death rate
Education level of women: If level of education increases, fertility rates fall. Why?
a) Financial independence leads to later marriage.
b) Educated women are more likely use birth control.
In some cultures women desire large families:
Where infant mortality is high, it is traditional to have large families since not all children may survive.
Parents feel secure when there are many children to look after them in old age.
In less developed countries, the economic benefits of children are extremely important.
Even young children can be given jobs that contribute to the family economy, such as protecting livestock, gathering firewood, or carrying water.
- In the developed world, large numbers of children are an economic drain.
- They are prevented from working.
- They must be sent to school at great expense.
- They consume large amounts of the family income.
Governments can reward or punish high fertility rates.
European countries are concerned about low birth rates à policies to encourage having more children:
Paid maternity leave & guaranteed job fo a mother.
Child tax deductions.
Most developing countries are concerned about fast population growth à programs to limit growth:
Education of population: family planning, maternal & child health.
Free or low-cost contraceptives.
One-child policy in China
Factors usually included in an analysis of standard of living:
Social status and mobility
Economic measure of standard of living is average purchasing power per person.
Gross national income (GNI) is an index of purchasing power measuring total goods and services generated by citizens of a country.
Human populations can increase in size only if other plant and animal populations decrease in size
3. Basic demographic processes:
v Births = Natality
v Deaths = Mortality Note: mortality ≠ morbidity!
Demographic balancing equation:
Population change = (Births Deaths) + (Immigrants Emigrants)
∆P = Pt P0 = (B D) + (I E) (1)
where P0 is the initial population and Pt is the population after time t.
Demographic balancing equation (1) can be split into 2 basic components:
Natural increase = Births (B) Deaths (D)
Net Migration = Immigration (I) Emigration (E)
Natural increase is the most important component of the overall population change.
Population Growth Rates
Each component of population change (births, deaths, migration) can be expressed as an absolute number (pop change) crude values or more commonly, as annual rates expressed in %.
Demographic rates are ordinarily calculated per 1000 persons per year.
Birth Rate = Humans born per 1000 individuals per year.
Death Rate = Humans died per 1,000 individuals per year.
Since population is changing throughout the year, we use for calculations mid-year population, which is the population in the middle of the particular year.
Crude Birth Rate (ÑBR) = total number of live births per year per thousand mid-year population.
Crude Death Rate (ÑDR) = total number of deaths per year per thousand mid-year population.
CBR = 1000, where # births is number of births during one year, is mid-year population. Mid-year population can be calculated as average number between two population values: at the beginning and at the end of the year.
CDR = 1000, where # deaths is number of deaths during one year, is mid-year population.
Crude (Natural) Growth Rate (CGR) = natural (population) growth per year per thousand mid-year population:
CGR = CBR CDR
This is a natural growth rate. The total growth rate is different, since it includes immigration, emigration.
Crude (Natural) Growth Rate, or just Crude Growth Rate may be also calculated this way:
CGR = 1000, where - population change during one year.
Note:CGR as well as other crude rates, may be expressed in %.
Example 1:suppose that CGR = 15. How many percent was population growth?
It means that natural increase in population is equal to 15 persons per 1000 population per year. To convert it to %, use the following proportion:
15 people à per 1000 population
X people à per 100 population
Solving proportion, find X:
You may have noticed that 1.5% can be obtained from 15 by just dividing by 10!
1.5% represents annual rate of population growth.
The average rate of population growth over some extended time period can be calculated if the population size at two points in time is known.
Exponential growth formulas:
Population growth is described by exponential function:
Pt = P0×(1+r)t (1)
where Po is the initial population, Pt is population at the end of t years, r is annual growth rate expressed as a decimal.
For t = 1 year, that is for annual population growth the formula (1) will look simple:
Pt = P0×(1+r) (2)
Example 2. Annual population growth rate is 6%. Assuming that the initial population of certain country at the beginning of the year was 10 mln, find its population by the end of the year.
P0 = 10 mln r = 0.06 (6%) Pt = ?
Using formula (2), we get:
Pt = 10 mln *(1+0.06) = 10.6 mln people
Applying fundamental limit rule to formula(1) at high t values (more accurately, at ), we get:
where Pt- population in t years from 0 time; P0 - population in time 0;
t represents number of yrs and r is annual rate of growth ( decimal).
Formula (3) is convenient for calculations and even at relatively small t gives good approximation.
Populationdoubling time = the number of years until the population will double if the annual rate of growth remains constant.
Rule of 70 for calculating doubling time: T2 = , where r is annual growth rate in %.
5. Urban problems in developing & developed countries
In developing contries:
· Dense traffic, smoky factories, use of wood or coal fires cause excessive air pollution.
· Lenient pollution laws, corrupt officials and ignorance cause even more pollution.
· Only 35% of urban residents in developing countries have satisfactory sanitation services.
In developed countries
The rapid growth of central cities in Europe and North America has now slowed or even reversed.
The good news is better air and water quality, safer working conditions, fewer communicable diseases.
The bad news is urban decay and sprawl and transportation issues have worsened
Urban Sprawl - is a Current Developed World Problem
In most American metropolitan areas, the bulk of new housing is in large, tract developments that leapfrog beyond city edges in search of inexpensive land.
Urban sprawl consumes about 200,000 ha of US agricultural land annually.
Planning authorities are often divided among many small local jurisdictions.
Most American cities devote ~1/3 of their land area to cars.
Freeways have reshaped our lives.
Public transportation is expensive and difficult to establish.