HUMAN BIOLOGY

484 Chapter 25

in the ground, known oil and gas reserves may be used

up in this cen tury. As the reserves run out in accessible

areas—with political and market forces increasing the

strain—pressure has mounted to drill in wilderness areas

in Alaska, offshore, and other fragile environments. Due

in part to the associated environmental costs, many people

oppose the idea.

Increased coal burning is not popular either. It has been

a major source of air pollution, because most reserves con­

tain low­quality, high­sulfur coal. In addition, extraction

and transportation of these fuels have harmful impacts.

Oil harms many species when it leaks from pipelines or

from ships. Strip mining for coal degrades the immediate

area and often lowers the water quality of nearby streams.

And as we have seen, burning fossil fuels also contributes

to acid rain and adds to the greenhouse effect.

Can “green” energy sources meet the need?

Fossil fuels are the main source of power for all forms of

transportation. The search for environmentally acceptable

alternatives has gone in several directions.

moving toward renewable energy sources

Figure 25.19 Currently, most of our energy comes from nonrenewable sources. This diagram links the sources of energy

used in the United States in 2006 to different sectors of users. For example, petroleum supplies 96 percent of the transportation

sector’s energy needs, and this amounts to 69 percent of all the petroleum consumed in the United States. (© Cengage Learning)

Petroleum

(supplies 39.8%

of total energy)

Natural gas

(supplies 22.4%

of total energy)

Coal

(supplies 22.6%

of total energy)

Renewable energy

(supplies 6.8%

of total energy)

Nuclear energy

(supplies 8.2%

of total energy)

Electric power

generation

(consumes 39.7%

of total energy)

Residential and

commercial uses

(consumes 10.3%

of total energy)

Transportation

(consumes 28.3%

of total energy)

Percent of source Percent of sector

Industry

(consumes 21.6%

of total energy)

1

96

2

2

45

37

9

9

21

72

6

2

16

52

10

21

69

24

5 2 3 9 7 9

35

33

29

<1

91

28

56

100

n Paralleling the growth of the human population

is a steep rise in energy consumption.

In theory, our planet has ample energy supplies to meet
human needs for transportation and other uses. For exam­
ple, world reserves of coal can meet our energy needs for
at least several centuries. There are pros and cons associ­
ated with all energy sources. But as society wrestles with
the rising costs and environmental risks associated with
nonrenewable forms of energy such as coal and petroleum,
pressure is building for a large­scale shift to renewable
energy sources such as solar and wind energy.
Figure 25.19 shows the percentages of different energy
sources used in the United States in 2006. Overall, devel­
oped countries use far more energy per person. This is a
major reason why consumers in developed countries have
a much larger ecological footprint.

There are growing issues with fossil fuels

Oil, coal, and natural gas are fossil fuels, the fossilized
remains of ancient forests. Although there is plenty of coal

25.8

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