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054-58-Chapter3
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Climate
Main Ideas
• Climate reflects the seasonal
patterns of weather for a
location over a long period
of time.
• Global climatic changes may
be natural or human-made.
Places & Terms
convection
A HUMAN PERSPECTIVE Nineteenth-century fishermen along the
El Niño
Peruvian coast called the event El Niño—the Spanish name for the
infant Jesus—because the event occurred near Christmastime. Every
two to seven years, the waters off the Peruvian coast became warmer
than usual, resulting in poor fishing. Eventually, 20th-century scientists
studying worldwide climate changes confirmed the truth of this folk
knowledge. They discovered that El Niño brought about changes in
global weather patterns that disrupted not only fishing, but also other
economic activities. Droughts and floods in Asia, Africa, and North
America seemed to be related to El Niño. Scientists recognized that
weather and climate conditions are not isolated but are connected parts
of the global climate system.
greenhouse effect
Factors Affecting Climate
Four major factors influence the climate of a
region: wind and ocean currents, latitude, elevation, and topography.
Global Wind Currents
North Pole
90°N
WIND CURRENTS Wind and ocean currents help
distribute the sun’s heat from one part of the
world to another through convection, the transfer
of heat in the atmosphere by upward motion of
the air. As sunlight heats the atmosphere, the air
expands, creating a zone of low air pressure.
Cooler dense air in a nearby high-pressure zone
rushes into the low-pressure area, causing wind.
Global wind patterns are caused by the same
kind of circulation on a larger scale. The hot air
flows toward the poles, and the cold air moves
toward the equator. The winds would blow in
straight lines, but since the earth rotates they are
turned at an angle. In the Northern Hemisphere,
they turn to the right. In the Southern Hemisphere, they turn to the left. This bending of the
winds is called the Coriolis effect.
The map to the right shows that the wind patterns are mirror images of each other in the
Northern and Southern Hemispheres. Winds are
identified by the direction from which they blow;
a north wind blows from the north to the south.
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60°N
POLAR EASTERLIES
60°N
WESTERLIES
30°N
30°N
Tropic of Cancer
NORTHEASTERLY TRADE WINDS
Equator
0°
0°
SOUTHEASTERLY TRADE WINDS
Tropic of Capricorn
30°S
30°S
WESTERLIES
60°S
POLAR EASTERLIES
60°S
90°S
South Pole
SKILLBUILDER: Interpreting Maps
MOVEMENT From which direction do the wind currents blow
near the equator in the Southern Hemisphere?
LOCATION Between which latitudes do the westerlies blow?
Eq
h io
Ja
y
ATLANTIC
South Equatorial
n
INDIAN OCEAN
lia
ial
Be
ng
We s t W i n
Drift
Wes t W i n d
AUSTRALIA
ra
la
OCEAN
ue
Peru
Bra
zi
lian
l
30°S
West
ift
d Dr
l
Au
st
tra
tor
oria
us
ua
tA
l
uat
Equator
Ea s
Equatoria
SOUTH
AMERICA
Eq
Tropic of Capricorn
60°S
Eq
h
ea
t
h
OCEAN
rt
AFRICA
in
u
uth
n
pa
PACIFIC
Tropic of Cancer
o
OCEAN
u
S
r Current
So
ASIA
West Wind Drift
Antarctic Circle
ANTARCTICA
150°W
Warm current
Cool current
120°W
90°W
60°W
30°W
0°
30°E
60°E
90°E
120°E
150°E
Robinson Projection
SKILLBUILDER: Interpreting Maps
MOVEMENT What happens to the Peru Current as it reaches
the equator?
LOCATION Where does the West Wind Drift flow?
Making
Comparisons
How are wind
and ocean currents similar in
their effect on
climate?
A. Answer Both
move heat from
the earth’s surface
to other parts of
the globe.
OCEAN CURRENTS Ocean currents are like rivers flowing in the
ocean. Moving in large circular systems, warm waters flow away from
the equator toward the poles, and cold water flows back toward the
equator. Winds blowing over the ocean currents affect the climate of
the lands that the winds cross. For example, the warmth of the Gulf
Stream and the North Atlantic Drift help keep the temperature of
Europe moderate. Even though much of Europe is as far north as
Canada, it enjoys a much milder climate than Canada.
Ocean currents affect not only the temperature of an area, but also
the amount of precipitation received. Cold ocean currents flowing
along a coastal region chill the air and sometimes prevent warm air and
the moisture it holds from falling to earth. The Atacama Desert in South
America and the Namib Desert in Africa, for example, were formed
partly because of cold ocean currents nearby.
ZONES OF LATITUDE Geographers divide the earth into three general
zones of latitude: low or tropical, middle or temperate, and high or polar.
Tropical zones are found on either side of the equator. They extend to
the tropic of Cancer in the Northern Hemisphere and the tropic of
Capricorn in the Southern Hemisphere. Lands in tropical zones are hot
all year long. In some areas, a shift in wind patterns causes variations in
the seasons. For example, Tanzania experiences both a rainy season and
a dry season as Indian Ocean winds blow in or away from the land.
Climate 55
BASICS
rt h
0° Equatorial Counte
PACIFIC
Arctic Circle
No
No
ift
EUROPE
Gu
al
ori
Dr
l
Gulf
Stream
tl
nar
NORTH
AMERICA
hA
an
tic
ria
nia
lifor
Ca
t
r
rado
Lab
ka
rt
No
North Pacific
a
North Equ
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Alas
60°N
30°N
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Climate Controls
SKILLBUILDER: Interpreting Graphics
Latitude and elevation influence climate. Notice that as you
move along the latitude line, the climates at the lower
altitude change. However, the greater the altitude, the fewer
the climate zones no matter what latitude a location may be.
LOCATION At about what latitude and altitude would you find
a desert climate?
REGION How do the climate zones change as latitude gets
higher?
Elevation in feet
15000
ICECAP
TREE LINE
10000
Icecap
Humid subtropical
Tundra
Marine
Humid continental
5000
Subarctic
Tropical
wet
0
Tropical
wet and dry
Desert
30
Latitude in degrees
60
The high-latitude polar zones, which encircle the North Pole and
South Pole, are cold all year. Summer temperatures in the polar regions
may reach a high of only 50°F.
The earth’s two temperate zones lie at the middle latitudes, between
the tropics and the polar regions. Within the temperate zones, climates
can vary greatly, ranging from relatively hot to relatively cold. These
variations occur because solar heating is greater in the summer than in
the winter. So summers are much warmer.
ELEVATION Another factor in determining the climate of a region is ele-
vation, or distance above sea level. You would think that the closer you
get to the sun, the hotter it would become. But as altitude increases, the
air temperature drops about 3.5°F for every 1,000 feet. Therefore, the climate gets colder as you climb a mountain or other elevated location.
Climates above 12,000 feet become like those in Arctic areas—with
snow and ice. For example, Mt. Kilimanjaro in east Africa is capped by
snow all year long. The diagram above will help you see how latitude
and elevation are related.
TOPOGRAPHY Landforms also affect the climate. This is especially
true of mountain areas. Remember that moisture-laden winds cool as
they move up the side of a mountain, eventually releasing rain or snow.
By the time the winds reach the other side of the mountain, they are dry
and become warmer as they flow down the mountain.
Changes in Climate
Climates change over time. Scientists studying ice-core samples from
thousands of years ago have noted a variety of changes in temperature
and precipitation. Some of the changes in climate appear to be natural
while others are the result of human activities.
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90
Adapted from Physical Geography by Ralph Scott.
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BASICS
EL NIÑO The warming of the waters off the west coast of South
America—known as El Niño—is a natural change in the climate. About
every two to seven years, prevailing easterly winds that blow over the
central Pacific Ocean slow or reverse direction, changing the ocean temperature and affecting the weather worldwide. Normally, these easterlies bring seasonal rains and push warm ocean water toward Asia and
Australia. In El Niño years, however, the winds push warm water and
heavy rains toward the Americas. This can cause floods and mudslides
there, while Australia and Asia experience drought conditions.
When the reverse occurs—that is, when the winds blow the warmer
water to the lands on the western Pacific rim—the event is called La
Niña. La Niña causes increases in precipitation in places such as India
and increased dryness along the Pacific coasts of the Americas.
El Niño and La Niña
SKILLBUILDER: Interpreting Graphics
El Niño and La Niña act to transfer the
heat on the earth’s surface and in the
atmosphere to other parts of the globe.
MOVEMENT In which direction do winds and water move
in El Niño?
LOCATION Where does flooding occur during La Niña?
El Niño
Dry air descends,
and droughts occur.
Winds head east over
warm waters.
Warm air rises, producing rain and flooding
in parts of North and South America.
NORTH AMERICA
PACIFIC OCEAN
SOUTH
AMERICA
Warm water moves eastward.
Warm water pools
in eastern Pacific.
Cool water pools
in western Pacific.
Cold water rises from the deep
ocean to replace warmer water.
Strong winds push
warm water westward.
La Niña
PACIFIC OCEAN
Dry air descends,
and droughts occur.
NORTH AMERICA
SOUTH
AMERICA
Warm water pools
in western Pacific.
Warm water moves westward.
Cool water pools
in eastern Pacific.
Warm air rises, producing
rain and flooding in
Australia and Asia.
Climate 57
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Greenhouse Effect
S TO
P
GLOBAL WARMING Although controversy exists over the causes of global warming, scientists agree that air
temperatures are increasing. Since the
late 1800s, the temperature of the
earth has increased by one degree.
Some
However, estimates for the next cenheat
escapes
tury suggest that the increase will be
H E AT T R A P P I N G L AY E R
almost 3.5 degrees.
Some scientists believe that this
warming is part of the earth’s natural
warming and cooling cycles. For examHeat
ple, 18,000 to 20,000 years ago, the
CO2 and
trapped
other gases
earth was in the last of several ice ages,
when vast glaciers advanced over huge
portions of the land mass.
Other scientists argue that global
temperature increases are caused by
the greenhouse effect. The layer of
gases released by the burning of coal
and petroleum traps some solar energy, causing higher temperatures in
SKILLBUILDER: Interpreting Graphics
the same way that a greenhouse traps
HUMAN–ENVIRONMENT INTERACTION Which elements
in the illustration add heat to the environment?
solar energy.
MOVEMENT What might happen if more motor vehicles are
As more and more nations become
added to the picture?
industrialized, the amount of greenhouse gases will also increase.
Scientists predict that, if global warming continues, ice caps will melt, flooding some coastal areas, covering
islands, and changing the global climate. In the next section, you will
learn about world climate regions.
Places & Terms
Taking Notes
Explain the meaning of
each of the following
terms.
MOVEMENT Review the notes
• convection
• El Niño
• greenhouse effect
Climate
you took for this section.
• What are four factors that affect
climate?
• What are examples of forces that
Main Ideas
a. What role do wind and
ocean currents play in
climate?
b. How do latitude and
altitude affect climate?
c. How do El Niño and La
Niña affect climate?
Background
The air temperature in the period
between about
1500 and 1850
was so much
cooler than today
that it is known as
a “Little Ice Age.”
Geographic Thinking
Drawing Conclusions
Which of the factors affecting
climate has the greatest
impact on the climate in your
region? Think about:
• the four factors affecting
climate
• the climate where you live
produce climate changes?
RESEARCH LINKS
CL ASSZONE .COM
SEEING PATTERNS Review the information and diagram about El Niño and La Niña on page 57.
Use the Internet to find more information on these events. Create a multimedia presentation
explaining one of the events and how it affects the world-wide weather conditions.
58 CHAPTER 3