World Population: Growth & Trends

Carrying Capacity

Physical carrying capacity = “packing density”,
limited only by space and resources
Cultural carrying capacity is always less
Still there is a large difference of opinion
regarding how many people the earth can
support.
Accepted range for K is 10-20 billion people
Factors affecting Growth
Rate

Growth rate = Birth Rate - Death Rate
1.1% = 1.9% - 0.8% (as of 2012)
Of these the Birth Rate is the most important
contributor, specifically the Fertility Rate
(#children/woman)
Why? Because death rates have stabilized...
World Population Growth
World Population: 7.3
billion

As of Sept., 2014
World Population (1850-2007)
6
5
4
3
2
1
0
500
1000
1500
Year (AD)
(Super)exponential growth
0
2000
Population (in Billions)
7
Likely population by 2050: 9 billion

Population Pyramid

Age
Population in age class
World Population Problems

 Nature of the World Population Problem
 Stable population for 8,000 years
 Survival precarious for most people
 Since 1650 there has been rapid population growth
Population variables

 Population increases are a function of three
variables, i.e. fertility, mortality and migration
 Population formula:
 Population (now) = Population (then)
+ (births-deaths) +/- Migration
 World Population Growth






8,000 BC to 1650 AD = 500 million
1650 AD to 2000 AD = 5.6 billion
50,000 new mouths to feed every year in first period
50,000 new mouths to feed every 6 minutes today.
90 million people added every year today
Four stages of DT

1.
2.
3.
4.
The Preindustrial Stage when there is little population growth
because harse social conditions lead to both high death and
high birth rates.
The Transitional Stage, when industrialization begins and
health care improves, resulting in lowered death rates, but
birth rates remain high. Most of the developing world here.
The Industrial Stage, when the birth rate drops due to
modernization (and its accompanying social changes). Many
developed countries and a few developing countries here.
Finally, the Postindustrial Stage is recognized by further
reductions in birth rates, approaching or even below zero
population growth. Approximately 13% of the world
population (mostly European countries) is in this stage.
A complete DT exhibits both declining birth and death rates
Population Pyramids for the
four demographic transition phases

Why Population is so important
Thomas Malthus (1798)
Organism populations increase
exponentially, whereas the
“environment” is “fixed”
(actually decreases).
Factually correct, but a complex
problem...
Modern example: high populations
AND high quality of life
 Validity of Malthus’ Predictions

 Malthus proved to be poor prophet in 18
and 19th C
 Famine, disease, war did not result in decreased world
population
 Was Malthus premature?
 Paul Erlich’s Population Bomb
(neo-Malthusian position) vs.
Julian Simon’s Population as the Ultimate Resource.
(cornucopian position)
th
Neo-Malthusian
position

 Population growth straining the world’s resources
 Destruction of forests for development and/or food
production
 Energy and mineral consumption taxes resources
 Over-fishing
 Widening gap between rich and poor
 Inadequate development, refugee problems, donor
fatigue
 Belief in environmental responsibility leading to
sustainable growth
Cornucopian position

 Life expectancy doubled in 20th C (30yrs to 60 yrs)
 Global health and productivity expanding
 Overpopulation is scare talk of environmentalists
 The real issue of poverty not breeding
 Technology will solve all human problems
 Population growth creates jobs, opens markets,
expands opportunities
 Ecologists want sustainability; cornucopian economists
want economic growth, exploitation of markets and
resources

Thinking about this
issue
Take away concepts

Why is population growth so central to environmental
problems?
What is the current population? What will it be in
2050?
What factors affect population growth rates?
How do growth rate compare in developed vs.
developing countries?
What is a "demographic transition? What are its stages?
Interpreting Population Pyramids.
Understanding modern demographic trends.
Reducing population growth

Successful efforts to reduce population growth by
Japan, China, South Korea, Thailand, and Iran.
These countries were able to achieve replacement-level
fertility (enough children born to replace death of
parents) within 15-30 years - this is good news.
Key Factors were:
 Invest in Family Planning
 Reduce poverty
 Elevate the status of women
Views from Joel Cohen’s 1995 book
“How Many People Can the Earth Support?”

1.
Make a bigger pie: Increase human productive
capacities through technology and innovation.
2.
Put fewer forks on the table: Reduce numbers and
expectations of people through such means as
family planning and vegetarian diets.
3.
Teach better manners: Change the terms of
people’s interactions through improved planning
and government to enhance social justice.

Questions