Environmental Engineering Reference
In-Depth Information
Male
Female
Male
Female
Male
Female
Male
Female
Expanding Rapidly
Guatemala
Nigeria
Saudi Arabia
Expanding Slowly
United States
Australia
Canada
Stable
Spain
Portugal
Greece
Declining
Germany
Bulgaria
Italy
Prereproductive ages 0-14
Reproductive ages 15-44
Postreproductive ages 45-85+
Active Figure 7-8
Generalized population age-structure diagrams for countries with rapid population growth
(1.5-3%), slow population growth (0.3-1.4%), a stable population (0-0.2%), and a declining population. Popu-
lations with a large proportion of its people in the prereproductive ages of 0-14 (at left) have a large potential
for rapid population growth.
See an animation based on this figure and take a short quiz on the concept.
(Data
from Population Reference Bureau)
through the country's age structure, as shown in Fig-
ure 7-10 (p. 136).
Baby boomers now represent nearly half of all
adult Americans. As a result, they dominate the popu-
lation's demand for goods and services. They are also
playing increasingly important roles in deciding who
gets elected and what laws are passed. Baby boomers
who created the youth market in their teens and twen-
ties are now creating the 50-something market and
will soon move on to create a 60-something market. In
2011, the first baby boomers will turn 65, and the num-
ber of Americans older than age 65 will consequently
grow sharply through 2029.
According to some analysts, the retirement of
baby boomers is likely to create a shortage of workers
in the United States unless immigrant workers replace
some of them. Retired baby boomers are likely to use
their political clout to force the smaller number of peo-
ple in the baby-bust generation that followed them
(Figure 7-4) to pay higher income, health-care, and
Social Security taxes.
In other respects, the baby-bust generation should
have an easier time than the baby-boom generation.
Fewer people will be competing for educational op-
portunities, jobs, and services. Also, labor shortages
may drive up their wages, at least for jobs requiring
education or technical training beyond high school.
As these projections illustrate, any booms or busts
in the age structure of a population create social and
economic changes that ripple through a society for
decades.
Effects of Age Structure
on Population Growth
The number of people younger than age 15 is the
major factor determining a country's future
population growth.
Any country with many people younger than age 15
(represented by a wide base in Figure 7-8, far left) has a
powerful built-in momentum to increase its popula-
tion size unless death rates rise sharply. The number of
births rises even if women have only one or two chil-
dren because a large number of girls will soon be mov-
ing into their reproductive years.
What is perhaps the world's most important pop-
ulation statistic?
Twenty-nine percent of the people on the
planet were younger than 15 years old in 2005.
These 1.9
billion young people are poised to move into their
prime reproductive years. In developing countries, the
number is even higher: 32%, compared with 17% in
developed countries. We live in a
demographically di-
vided world,
as shown by population data for the
United States, Brazil, and Nigeria (Figure 7-9, p. 136).
Using Age-Structure Diagrams to Make
Population and Economic Projections
Changes in the distribution of a country's age groups
have long-lasting economic and social impacts.
Between 1946 and 1964, the United States had a
baby
boom
that added 79 million people to its population.
Over time, this group looks like a bulge moving up
