Environmental Engineering Reference
In-Depth Information
The problems to be faced are vast and complex, but come
down to this: 6.5 billion people are breeding exponentially.
The process of fulfilling their wants and needs is stripping
earth of its biotic capacity to produce life; a climactic burst of
consumption by a single species is overwhelming the skies,
earth, waters, and fauna.
P
AUL
H
AWKEN
7-1 FACTORS AFFECTING HUMAN
POPULATION SIZE
Human Population History: An Overview
We have postponed reaching the limits of disease,
food, water, and energy supplies on human
population growth mostly by taking over much
of the earth and sharply reducing death rates.
For most of history, the human population grew slowly
(Figure 1-1, left part of curve, p. 5). But about 200 years
ago, our population growth took off (Figure 1-1, right
part of curve, and Figure 1-5, p. 9).
Three major reasons explain this development.
First
,thanks to our highly complex brain and tool-
using abilities, humans developed the ability to expand
into diverse new habitats and different climate zones.
Second
, the emergence of early and modern agri-
culture allowed more people to be fed per unit of land
area. This increase in the carrying capacity of land al-
lowed our population to grow.
Third
, we have managed to put off reaching the
limits of disease, food, water, and energy supplies on
overall population growth. We have used better sani-
tation and developed antibiotics and vaccines to help
control infectious disease agents, and we have tapped
into concentrated sources of energy (fossil fuels).
These changes allowed births to exceed deaths.
Can the world's life-support systems sustain the
8-11 billion people projected to be around when this
century ends? At what average level of resource con-
sumption will they live?
This chapter looks at the factors that affect the growth
of the human population and the distribution of peo-
ple between urban and rural areas. It addresses the
following questions:
How is population size affected by birth, death,
fertility, and migration rates?
■
How is population size affected by the percentage
of males and females at each age level?
■
How can we slow population growth?
■
What success have India and China had in slowing
population growth?
■
How is the world's population distributed be-
tween rural and urban areas, and what factors de-
termine how urban areas develop?
■
What are the major resource and environmental
problems faced by urban areas?
■
How do transportation systems shape urban
areas and growth, and what are the advantages
and disadvantages of various forms of
transportation?
■
How can cities be made more sustainable and
more desirable places to live?
■
Birth Rates and Death Rates: Entrances
and Exits
The human population in a particular area increases
because of births and immigration and decreases
through deaths and emigration.
Human populations grow or decline through the in-
terplay of three factors:
births, deaths,
and
migration.
Population change
is calculated by subtracting the
number of people leaving a population (through death
and emigration) from the number entering it (through
birth and immigration) during a specified period of
time (usually one year):
KEY IDEAS
■
The average number of children that a woman
bears has dropped sharply since 1950, but it is not
low enough to stabilize the world's population in the
near future.
■
The number of people in young, middle, and
older age groups determines how fast populations
grow or decline.
■
The best way to slow population growth is by in-
vesting in family planning, reducing poverty, and ele-
vating the status of women.
■
Cities are rarely self-sustaining. Supplying them
with resources and absorbing and diluting their
wastes can threaten biodiversity.
■
An ecocity allows people to walk, bike, or take
mass transit for most of their travel. It recycles and
reuses most of its wastes, grows much of its own
food, and protects biodiversity by preserving sur-
rounding land.
Population
change
(Births
Immigration)
(Deaths
Emigration)
When births plus immigration exceeds deaths plus
emigration, population increases; when the reverse is
true, population declines.
Instead of using the total numbers of births and
deaths per year, demographers use the
birth rate,
or
crude birth rate
(the number of live births per 1,000
people in a population in a given year), and the
death
rate,
or
crude death rate
(the number of deaths per 1,000
