Energy - Environmental Science - page 296

electricity. However, U.S. production of natural gas
has been declining for a long time, and this trend is
unlikely to be reversed. More natural gas could be im-
ported from Canada, but it will require building a ma-
jor pipeline between the two countries. Also, natural
gas production in Canada is expected to peak be-
tween 2020 and 2030. Then the United States and the
rest of the world would have to rely increasingly on
Russia and Middle Eastern countries for supplies of
natural gas.

T rade-Offs

Conventional Natural Gas

Advantages Disadvantages

Ample supplies
(125 years)

Nonrenewable
resource

High net energy
yield

Releases CO 2
when burned

Low cost (with
huge subsidies)

Science: Coal
Coal is an abundant energy resource that is burned
mostly to produce electricity and steel.
Coal is a solid fossil fuel that was formed in several
stages as the buried remains of land plants that lived
300-400 million years ago were subjected to intense
heat and pressure over many millions of years (Fig-
ure 13-14). Coal is mostly carbon but contains small
amounts of sulfur, which are released into the atmos-
phere as sulfur dioxide when the coal burns. Burning
coal also releases trace amounts of toxic mercury and
radioactive materials. Coal is burned to generate 62%
of the world's electricity (52% in the United States) and
to make three-fourths of its steel.
Coal is the world's most abundant fossil fuel. Ac-
cording to the U.S. Geological Survey, identified and
unidentified supplies of coal could last for 214-1,125
years, depending on our rate of usage. The United
States has one-fourth of the world's proven coal re-
serves, Russia has 16%, and China has 12%. In 2004,
slightly more than half of global coal consumption
was split almost evenly between China and the United
States.

Methane
(a greenhouse
gas) can leak
from pipelines

Less air pollution
than other
fossil fuels

Lower CO 2
emissions than
other fossil fuels

Difficult to transfer
from one country
to another

Moderate environ-
mental impact

Shipped across
ocean as highly
explosive LNG

Easily transported
by pipeline

Sometimes
burned off and
wasted at wells
because of low
price

Low land use

Good fuel for
fuel cells and
gas turbines Requires pipelines

Figure 13-13 Trade-offs: advantages and disadvantages of
using conventional natural gas as an energy resource. Critical
thinking: pick the single advantage and disadvantage that you
think are the most important.

Increasing heat and carbon content

Increasing moisture content

Peat
(not a coal)

Lignite
(brown coal)

Bituminous
(soft coal)

Anthracite
(hard coal)

Heat Heat

Heat

Figure 13-14 Natural capital:
stages in coal formation over mil-
lions of years. Peat is a soil material
made of moist, partially decom-
posed organic matter. Lignite and
bituminous coal are sedimentary
rocks, whereas anthracite is a meta-
morphic rock (Figure 12-6, p. 275).

Pressure Pressure Pressure

Highly desirable fuel
because of its high
heat content and
low sulfur content;
supplies are limited
in most areas

Low heat content;
low sulfur content;
limited supplies in
most areas

Extensively used
as a fuel because
of its high heat content
and large supplies;
normally has a
high sulfur content

Partially decayed
plant matter in swamps
and bogs; low heat
content