Laboratory Manual for Introductory Geology 4e

FIGURE 18.13 Estimated human population
growth under three fertility scenarios.
Human population (billions)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
1800
1900
Moderate
fertility
Year
High
fertility
2000
Low
fertility
2100
18.2.5c Human Population Growth The human population
has grown steadily, reaching the 1 billion mark in 1804 after
tens of thousands of years. It then doubled in only 123 years,
doubled again 47 years later, and is predicted to double
yet again by 2024, about 50 years since the last doubling
(FIG. 18.13). Estimates of future population growth depend
on assumptions of fertility. The global population will remain
constant if the birth rate averages 2.01 births per woman, will
increase with higher birth rates, and will decrease with lower
birth rates. Barring a catastrophic epidemic, however, the
2024 doubling is certain to occur. The U.S. birth rate is just a
little higher than 2.01; the birth rates of Japan, Germany, and
Italy are somewhat lower; and those of developing nations are
typically much higher.
Human population growth may be the most serious problem
we will face in the near future because it affects all parts of
the Earth System. We will explore the impacts of an expanding
human population in Section 18.3.
EXERCISE 18.5
Elbow Room?
Name:
Course:
Section:
Date:
The land we live on provides room for dwelling, manufacturing, schools, and recreation; soil for growing crops and raising
livestock; streets and highways; mineral and rock resources; garbage disposal; and many other functions. It will take just
a few steps to calculate how much living space each human has now, how that will change in the future, and how human
population growth will affect the rest of the biosphere. Show your calculations for each of the following steps.
STEP 1: What is the Earth’s total surface area?
For this exercise, consider the Earth to be a sphere with a 4,000-mile radius. The formula for calculating the surface
area of a sphere is
Surface area 5 4pr 2
where p 5 3.14 and r is the Earth’s radius.
(a) The Earth’s total surface area is thus
square miles (mi 2 ). Show your calculations.
STEP 2: How much of the Earth is uninhabitable?
Much of the Earth is desert, ocean, or steep mountains. These areas must be subtracted from the total area available
for human habitation.
(b) Oceans cover 71% of the surface, including the north polar area covered by sea ice.
Ocean area 5 mi 2
The Earth’s land surface area 5 total area (Step 1) 2 ocean area 5 mi 2
(continued )
490 CHAPTER 18 LOOKING TO THE FUTURE