Transcript Scientists Disagree on Earth`s Carrying Capacity

Chapter 7
The Human Population
Scientists Disagree on Earth’s
Carrying Capacity
Figure
7.1
• Every 5 days the human population
increases by 1 million people
• Current human population – 7.7
billion people
Scientists Disagree on Earth’s Carrying
Capacity
•The following graphs show
theoretical models of food
supply and population size.
Scientists Disagree on Earth’s Carrying
Capacity
• 1798 – Thomas Malthus – human populations grew
exponentially while food supply grew linearly.
•Population will reach carrying capacity and then decline.
Scientists Disagree on Earth’s Carrying
Capacity
• Other scientists theorize that growing populations
provide a supply of intellect leading to innovation.
•Humans can alter the earth’s carrying capacity (ie. Horsedriven plows to harvesters.
Review…
• What determines the carrying capacity
of a habitat?
• How might humans differ from other
organisms when it comes to carrying
capacity?
• Will human exceed Earth’s carrying
capacity? What evidence can you use
to justify your argument?
Factors that Drive Human Population
Growth
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Demography- the study of human
populations and population trends.
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Changes in Population Size
Fertility
Life Expectancy
Age Structure
Migration
Changes in Population Size
• Immigration- the movement of people into a
country
• Emigration- the movement of people out of a
country.
• Net migration rate- the difference between
immigration and emigration in a given year
per 1,000 people in the country.
Changes in Population Size
• 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.
• Global population growth rate =
(CBR- CDR)/ 10 (used to create a %)
• National population growth rate =
(CBR+ immigration) - (CDR + emigration)/ 10
• Doubling time (in years)- 70/growth rate
The rule of 70
• Doubling time (in years)- 70/growth
rate
• How long will it take a population with a
yearly 2% growth rate to double?
• 70/2 = 35 years
• Will grow this fast regardless of size
The rule of 70
• Most demographers believe that the
human population will be between 8.1
billion and 9.6 billion by 2050 and will
stabilize between 6.8 and 10.5 billion
by 2100.
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Fertility
Total fertility rate- an estimate of the average
number of children that each woman in a population
will bear. (TFR – 2008 in the US was 2.1)
Replacement level fertility- the total fertility rate
required to offset the average number of deaths in a
population and for the current population size to
remain stable.
Usually just over 2
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Fertility
Developed countries- countries with relatively
high levels of industrialization and income.
(TFR = 2.1)
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Developing countries- countries with relatively
low levels of industrialization and income of less
that $3 per person per day.
(TFR = greater than 2.1)
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Life Expectancy
Life expectancy- 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 of
that country.
Life Expectancy
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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.
Life Expectancy
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2009 – (global) IMR = 46 (per 1,000 births)
• US = 6.6
• 13.6 –African Americans Socioeconomic
status
• 8.1 – Native Americans (environmental
justice)
• 5.8 - Caucasians
• Liberia = 99
Women do not have
access to prenatal
• Bolivia = 50
care
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Life Expectancy
Even with high life expectancy and low IMR - a
high CDR (crude death rate) is possible due to
older individuals.
US – 13% are 65 yrs or older
Mexico - 6% are 65 yrs or older
Disease
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Infections diseases 2nd biggest killer worldwide
Today – HIV resopnsible for more deaths
annually between TB and Malaria
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More disruptive effect on society than other
illnesses affeting young and old
Age Structure
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Age structure diagrams (population pyramids)visual representations of age structure within a
country for males and females.
Each horizontal bar represents a 5 year age
group.
The total area represents the size of the whole
population.
Population
pyramid –
developing
countries
Slow
population
growth
rate –
developed
country
TFR less than
2.1 –
populations
will eventually
shrink (C,D)
Migration
• Countries with low CBR but high
immigration may still experience
population growth (US)
• Net migration rate – difference between
the immmigration and emigration in a
year per 1,000 people.
Do the Math pg. 187
• New Zealand popn: 4.3 million
• TFR: 2.1
• NMR: 2 per 1,000
• How many people will New Zealand
gain next year as a result of
immigration?
Do the Math pg. 187
• Net migration rate:
# of immigrants/ # of people in population
2/1,000 = x/4,300,000
X=8,600 people/year (added each year)
Rate of increase? 8,600 people/year
4,300,00 people
0.2 %/ year
=
Do the Math pg. 187
• Rule of 70 = 70/% growth = doubling
time
• What is the doubling time of this
population?
• 70/0.2 per year = 350 years
Review…
• What are the main factors that influence
human population growth?
• How does age structure infuence the
population growth rate?
• How do a country’s total fertility rate and
net migration rate determine population
growth?
The Demographic Transition
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Theory that states: as a country moves from a subsistence
economy to industrialization and increased affluence, it
undergoes a predictable shift in population growth.
The Stages of the Demographic Transition
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Phase 1: Slow population growth because there are high
birth rates and high death rates which offset each other.
Phase 2: Rapid population growth because birth rates
remain high but death rates decline due to better sanitation,
clean drinking water, increased access to food and goods,
and access to health care.
Phase 3: Stable population growth as the economy and
educational system improves and people have fewer
children.
Phase 4: Declining population growth because the
relatively high level of affluence and economic develop
encourage women to delay having children.
Wealthier nations tend to have
lower TFRs
Family Planning
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Family planning- the regulation of the number or
spacing of offspring through the use of birth
control.
Review…
• What is the theory of demographic
transition?
• How do education and demographic
transition relate to each other?
• In what ways are phase 1 and phase 3
in a demographic transition similar?
The 12 Most Populous Countries in the
World
The relationship between economic development
and population growth rate for developing
nations.
• Developed contries consume more than
½ of the world’s energy and resources.
• One person can have 2-10x the impact
of those in a developing country.
• World’s avg. ecological footprint 2.7 ha
(6.7 acres)
• US – largest of any nation – 9 ha (22
acres) per capita.
Ecological Footprints
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Affluence - having a lot of wealth such as
money, goods, or property.
US Ecological
Footprint
• 2,810 million ha (6,944 acres)
The IPAT Equation
• To estimate the impact of human lifestyles on
Earth we can use the IPAT equation:
• Impact= Population X Affluence X Technology
(destructive)
• Global vs Local vs Urban Impacts…
The Impact of Affluence
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Gross domestic product (GDP)- the value of all
products and services produced in a year in that
country.
GDP is made up of consumer spending,
investments, government spending, and exports
minus imports.
A countries GDP often correlates with its
pollution levels.
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As GDP goes up pollution can increase
Discuss…
• Some scientists argue that increaseing
the GDP of developing nations is the
BEST way to save the environment…
• What do you think?
Review…
• What is the IPAT equation?
What does
it describe?
• How do local and global environmental
impacts differ? Where do we tend to
see one versus the other?
• How does a country’s degree of
development influence its environmental
impact?
How can sustainable development be
achieved?
• 2005 – Millennium Ecosystem
Assessment project
• Global analysis of effects of human
population on ecosystem services.
• Drew several conclusions…
How can sustainable development be
achieved?
• If human pop. Continues ecosystem
sustainability will be threatened
• Continued alterations to the ecosystem
will exacerbate poverty for some
populations
• If we establish sustainable practices, we
may be able to improve the standard of
living for many people.
How can sustainable development be
achieved?
“human actions are depleting Earth’s
natural capital, putting such strain on
the environment that the ability of the
planet’s ecosystems to sustain further
generations can no longer be taken for
granted.”
Review
• What is the difference between
economic development and sustainable
development?
• How is the Millenium Ecosystem
Assessment project a blueprint for
sustainable development?
• What factors have we discussed that
make sustainable development difficult
to achieve?
Pg.199 #1-10
Human Footprint…
• http://channel.nationalgeographic.com/c
hannel/human-footprint/consumptioninteractive.html