Environmental Engineering Reference
In-Depth Information
Average crude birth rate
Average crude death rate
Exponential population growth has not disap-
peared but rather has declined to a slower rate. The rate
of the world's annual population growth (natural in-
crease) dropped by almost half between 1963 and 2005,
from 2.2% to 1.2%. This is
good news.
Nevertheless,
during the same period the population base doubled
from 3.2 billion to almost 6.5 billion. The drop in the
rate of population increase is somewhat like learning
that a truck heading straight at you has slowed from
100 kilometers per hour (kph) to 45 kph while its
weight has more than doubled.
Although an exponential growth rate of 1.2% may
seem small, consider this: During 2005, it added about
78 million people to the world's population, compared
to 69 million in 1963 when the world's population
growth reached its peak. This increase is roughly equal
to adding another New York City every month, a
Germany every year, and a United States every 3.7
years.
There is a big difference between exponential pop-
ulation growth rates in developed and developing
countries. In 2005, the population of developed coun-
tries was growing at a rate of 0.1% per year. That of the
developing countries was 1.5% per year—15 times
faster.
As a result of these trends, the population of the
developed countries, currently 1.2 billion, is expected
to change little in the next 50 years. In contrast, the
population of the developing countries is projected to
rise steadily from 5.3 billion in 2005 to 8 billion in 2050
and then to level off by the end of this century (Fig-
ure 1-5, p. 9). The six nations expected to produce most
of this growth are, in order, India, China, Pakistan,
Nigeria, Bangladesh, and Indonesia.
China—1.3 billion in 2005, or one of every five
people in the world—and India—1.1 billion—are the
world's most populous countries. Together they have
37% of the world's population. The United States—296
million people in 2005—has the world's third largest
population but only 4.6% of its people.
World
21
9
All developed
countries
11
10
All developing
countries
23
8
Developing
countries
(w/o China)
27
9
Africa
38
15
Latin
America
22
6
Asia
20
7
Oceania
17
7
United
States
14
8
North
America
14
8
Europe
10
11
Figure 7-2
Average crude birth and death rates for various
groupings of countries in 2005. (Data from Population
Reference Bureau)
people in a population in a given year) in their analyses.
Figure 7-2 shows the estimated crude birth and death
rates for various parts of the world in 2005.
Population Growth Today: Slowing
but Still Growing
The rate at which the world's population is increasing
has slowed, but the population continues to grow
fairly rapidly.
Birth rates and death rates are coming down world-
wide, but death rates have fallen more sharply than
birth rates. As a result, more births are occurring than
deaths: Every time your heart beats, 2.4 more babies
are added to the world's population. At this rate, we
are sharing the earth and its resources with 214,000
more people per day—97% of them in developing
countries.
The rate of the world's annual population change
usually is expressed as a percentage:
Can you guess what regions of the world will likely have
the greatest population increases by 2025? Find out at
Environmental ScienceNow.
Doubling Time
Doubling time is how long it takes for a
population growing at a specified rate to double
its size.
One measure of population growth is
doubling time:
the time (usually in years) it takes for a population
growing at a specified rate to double its size. A quick
way to calculate doubling time is to use the
rule of 70:
70/percentage growth rate
Annual rate of
natural population
change (%)
Death rate
1,000 persons
Birth rate
100
Death rate
10
Birth rate
doubling time in years.
