GeoJournalAs you read this chapter, note factors thataffect climate. Then write a description of theclimate in your community. List three factorsthat contribute to climate, and sketch a land-scape showing one kind of common weatherin this climate.

Chapter Overview Visit the Glencoe WorldGeography Web site at tx.geography.glencoe.comand click on Chapter Overviews—Chapter 3 topreview information about Earth’s climates.

Earth-SunRelationships

A Geographic ViewOur Home StarThrough a small occulting telescope[equipped to block the sun’s surfacefrom view] . . . I stared at the dark-ened face of the sun, ringed by its glowing, gauzy corona. Fromthat blazing disk high in theHawaiian sky comes the endlesspower that drives and rules alllife on earth: its plant growthand the food chains of all itscreatures; the winds, rains, and churning weather of theplanet; the ocean currents,forests, prairies, and deserts.

—Samuel W. Matthews, “Under the Sun: Is Our World Warming?” National Geographic, October 1990

From atop the Mauna Loa Observatory on theisland of Hawaii, scientists gather data about changes in the earth’satmosphere. Their research reveals information about the dynamic rela-tionships between the earth and the sun, which influence all life on Earth.In this section you will explore how earth-sun relationships affect climate.

Climate and WeatherClimate is often confused with weather, which is a short-term aspect

of climate. Weather is the condition of the atmosphere in one placeduring a limited period of time. When people look out the window orwatch the news to see whether they need umbrellas or sunscreen, theyare checking the weather. Climate is the term for the weather patternsthat an area typically experiences over a long period of time. Peoplewho live in Seattle, Washington, for example, frequently use umbrellas

Guide to ReadingConsider What You KnowNews reports sometimes featureunusual events such as solar eclipsesor solar flares, intense bursts ofenergy from the sun’s surface. Inwhat ways does the sun affecthuman activities?

Read to Find Out• How does Earth’s position in

relation to the sun affect temperatures on Earth?

• How does Earth’s rotation causeday and night?

• What is Earth’s position in relationto the sun during each season?

• How might global warming affectEarth’s air, land, and water?

Terms to Know• weather

• climate

• axis

• temperature

• revolution

• equinox

• solstice

• greenhouse effect

• global warming

Places to Locate• Tropic of Cancer

• Tropic of Capricorn

C h a p t e r 3 55

Flamingoes enjoy an oasis at thefoot of sand dunes in Namibia.

Sunset at the beach

because of the rainy, wet climate. Incontrast, people who live in the dry,desert climate of Arizona must protectthemselves from the sun.

Whether the climate in a particularregion is cool and wet or hot and dry isdetermined by many factors, the mostimportant of which is the earth’s posi-tion in relation to the sun.

The sun’s heat and light reach theearth as warmth and sunlight, but theydo not reach all parts of the earth at thesame time or with the same intensity.

Earth’s Tilt and Rotation

Earth’s tilt is one reason for varia-tions in sunlight. The earth’s axis—animaginary line running from the NorthPole to the South Pole through the planet’s cen-ter—is currently tilted at an angle of about 231/2º.Because of the tilt of this axis, not all places on theplanet receive the same amount of direct sunlightat the same time.

For this reason the angle of tilt affects thetemperature—the measure of how hot or cold aplace is. Areas that receive a large amount of directsunlight have warmer temperatures than placesthat receive little direct sunlight. Temperature isusually measured in degrees on a set scale. Themost common scales for measuring air tempera-ture are Fahrenheit (ºF) and Celsius (ºC).

Whether or not a particular place on Earthreceives light also depends on the side of theplanet that is facing the sun. Earth rotates on itsaxis, making one complete rotation every 24 hours.Rotating from west to east, the earth turns first onehemisphere and then the other toward the sun,alternating between the light of day and the dark-ness of night.

Earth’s RevolutionWhile planet Earth is rotating on its axis, it also

is traveling in an orbit around the sun, our neareststar. It takes the earth a few hours more than 365days—1 year—to complete one revolution, or triparound the sun.

Arizona LightningLightning and thunder are related weather events that result fromthe powerful air currents of thunderstorms during the warm-weather months.

Place What factor distinguishes weather from climate?

56 U n i t 1

The earth’s revolution and its tilt cause changesin the angle and amount of sunlight that reach dif-ferent locations on the planet. These changes fol-low a regular progression known as the seasons.During the course of a year, people on most partsof the earth experience distinct differences in thelength of days and the daily temperature as theseasons change.

The seasons are reversed north and south of the Equator. When it is spring in the Northern Hemi-sphere, it is fall in the Southern Hemisphere. When itis winter in the Southern Hemisphere, it is summerin the Northern Hemisphere. Around March 21, thesun’s rays fall directly on the Equator. This day iscalled an equinox (meaning “equal night”) becausedaylight and nighttime hours are equal. In theNorthern Hemisphere, the day on which thisequinox falls marks the beginning of spring.

The Tropics of Cancer and Capricorn

As the earth continues its revolution around thesun, it moves so that eventually the sun’s raysdirectly strike the latitude 231/2ºN. This latitude isknown as the Tropic of Cancer—the northernmostpoint on the earth to receive the direct rays of thesun. These direct rays reach the Tropic of Cancerabout June 21, bringing the Northern Hemisphere

C h a p t e r 3 57

its longest day of sunlight. This date, known as thesummer solstice, marks the beginning of summerin the Northern Hemisphere.

By about September 23, the earth has moved sothat the sun’s rays directly strike the Equatoragain. This equinox marks the beginning of fall inthe Northern Hemisphere. Gradually the sun’sdirect rays strike farther south, reaching theirsouthernmost latitude—231/2º S, or the Tropic ofCapricorn—about December 22. The winter sol-stice is the day of shortest daylight in the NorthernHemisphere, beginning the season of winter. Thiscycle repeats itself each year as the earth revolvesaround the sun.

The PolesThe amount of sunlight at the Poles varies most

dramatically as the earth’s revolution and tilt causethe changing seasons. For six months of the year,one Pole is tilted toward the sun and receives con-

tinuous sunlight, while the other Pole is tilted awayfrom the sun and receives little to no sunlight. AnArctic explorer describes the surreal quality of thewinter day:

“ The winter sun had completely disap-peared below the horizon, and the ‘days’were now only a few hours long. . . . I sawthe Arctic in a whole new way, with itstwilight days and auroral nights.”Keith Nyitray, “Alone Across

the Arctic Crown,” National Geographic, April 1993

At the North Pole, the sun never sets from aboutMarch 20 to September 23. At the South Pole, con-tinuous daylight lasts from about September 23 toMarch 20. The tilt of the earth’s axis as it revolvesaround the sun causes this natural phenomenon,known as the midnight sun. The occurrence of the

SunDirect rays

Direct rays

Tropic of Capricorn

Equator

Tropic of Cancer

North Pole

South Pole

North Pole

FALL(September 23)

WINTER(December 22)

SPRING(March 21)

SUMMER(June 21)

South Pole

Indirect rays Indirect rays

Indirect rays

Indirect rays

DIAGRAM STUDY

The Seasons in the Northern Hemisphere

1. Interpreting Diagrams Why are the seasons reversedin the Northern and Southern Hemispheres?

2. Applying Geography Skills Explain the differencebetween the equinoxes and the solstices.

Checking for Understanding1. Define weather, climate, axis,

temperature, revolution, equinox,solstice, greenhouse effect, globalwarming.

2. Main Ideas On a chart, list charac-teristics of the earth-sun relation-ship and describe their effects onclimate.

Critical Thinking3. Comparing and Contrasting

What differences in the weatherwould you expect in Alaska andin Florida? Explain.

4. Drawing Conclusions What effectsdoes the earth’s tilt on its axishave on your daily life?

5. Analyzing Information Whatwould you pack if you were visit-ing Argentina in December?

Analyzing Diagrams6. Location Study the diagram of

the seasons on page 57. In whatmonths do the sun’s rays strikethe Equator directly? The Tropicsof Cancer and Capricorn?

58 U n i t 1

7. Effects of Global WarmingReview the text in Section 1about global warming. Inwhat ways might agricul-ture be affected? Explain.

Applying Geography

midnight sun goes almost unnoticed in sparselypopulated Antarctica. Parts of northern NorthAmerica (including Alaska) and northern Europein the Arctic, however, have become populartourist destinations as “lands of the midnight sun.”

The Greenhouse EffectEven on the sunniest days in the warmest cli-

mates, only part of the sun’s radiation passesthrough the earth’s atmosphere. The atmospherereflects some radiation back into space. Enoughradiation, however, reaches the earth to warm theair, land, and water.

Because the atmosphere traps some heat andkeeps it from escaping back into space too quickly,Earth’s atmosphere is like the glass in a green-house—it traps the sun’s warmth for growingplants even in cold weather. Without this greenhouseeffect, the earth would be too cold for most livingthings. The diagram on page 70 shows the green-house effect.

In order to support plant growth, conditions in agreenhouse must be regulated. If too much heatescapes, the plants will freeze. If too much heat istrapped, the plants will wilt or dry out.

The greenhouse effect of Earth’s atmosphere fol-lows some of the same general rules. Normally, theatmosphere provides just the right amount of insu-lation to promote life on the planet. The 50 percentof the sun’s radiation that reaches the earth is con-verted into infrared radiation, or heat. Clouds andgreenhouse gases—atmospheric components such

as water vapor and carbon dioxide (CO2)—absorbthe heat reflected by the earth and radiate it backagain so that a balance is created.

Many scientists, however, claim that in recentdecades a rise in atmospheric CO2 levels has coin-cided with a general rise in global temperatures.This trend—known as global warming—isbelieved to be caused in part by human activities,such as the burning of coal, oil, and natural gas. Asmore fossil fuels are burned, greenhouse gasesenter the atmosphere and trap more heat.

Using computer models, some scientists predictthat global warming will make weather patternsmore extreme. Water, for example, will evaporatemore rapidly from oceans, increasing humidity andrainfall generally. Rapid water evaporation fromsoil, however, will cause land to dry out morequickly between rains. Some areas may evenbecome drier than before.

Scientists do not all agree on global warming andits effects. Some claim that a natural cycle, nothuman activity, is causing rising temperatures. Oth-ers claim that evidence for global warming is incon-clusive and that it is too early to forecast futureeffects.

Student Web Activity Visit the Glencoe World GeographyWeb site at tx.geography.glencoe.com and click on Student WebActivities—Chapter 3 for an activity about global warming.

Earth-Sun Relationships Effects on Climate

C h a p t e r 3 59

Guide to ReadingConsider What You KnowYou are familiar with the climate ofthe area where you live, such as theusual weather and temperaturerange for each season. What geo-graphic factors do you think affectyour climate?

Read to Find Out• How do latitude and elevation

affect climate?

• What role do wind patterns andocean currents play in Earth’s climates?

• How do landforms and climatepatterns influence each other?

Terms to Know• prevailing wind

• Coriolis effect

• doldrums

• current

• El Niño

• windward

• leeward

• rain shadow

Places to Locate• low latitudes

• high latitudes

• Arctic Circle

• Antarctic Circle

• mid-latitudes

Factors AffectingClimate

A Geographic ViewThe Stormy SeaAs I survey the wreckage [from my yacht]—broken steering wheel,patched sails, ruined winches, liferails ripped away by boundingseas . . . I can see it’s been a har-rowing 4,600 miles since the start[of this leg of the Whitbreadrace] in Cape Town, SouthAfrica. For eight of the twelvemen aboard, including PaulCayard, the skipper, the runeast has been their firstencounter with the ocean lati-tudes known as the roaring forties andfurious fifties, where gales blow year-round and seas buildto towering peaks, “the liquid Himalayas,” as one Kiwi [New Zealand] broadcaster calls them.

—Angus Phillips, “The Whitbread—Race Into Danger,” National Geographic, May 1998

Sailing in the Whitbread race can be frightening. Thepart of this journey from South Africa to Australia is dangerousbecause of high winds and strong ocean currents at these latitudes. Inthis section you will learn how latitude, wind and water patterns,and landforms combine with the earth-sun relationship to influenceEarth’s climates.

Latitude and ClimateThe influence of latitude on climate is part of the earth-sun relation-

ship. During the earth’s annual revolution around the sun, the sun’sdirect rays fall upon the planet in a regular pattern. This pattern can be

Sailing in the southern Indian Ocean

NPacificOcean

PacificOcean

AtlanticOcean

AtlanticOcean

IndianOcean

PacificOcean

Arctic Ocean

EQUATOR

TROPIC OF CAPRICORN

ANTARCTIC CIRCLE

TROPIC OF CANCER

ARCTIC CIRCLE

Horse latitudes (calm)

Doldrums (calm)Doldrums (calm)

Horse latitudes (calm)

Northeasterlytrade winds

Northeasterlytrade winds

Southeasterlytrade winds Southeasterly

trade winds

WesterliesWesterlies

WesterliesWesterlies

Polar Easterlies

Polar Easterlies

0°

60°E60°W 120°E120°W 0°

30°N

30°S

60°S

60°N

Winkel Tripel projection

3,000

3,0000 mi.

0 km

MAP STUDY

World Zones of Latitude and Wind Patterns

Find NGS online map resources @ www.nationalgeographic.com/maps

Warm wind

High latitudesMid-latitudesLow latitudes

Cold wind

Polar front

60 U n i t 1

correlated with bands, or zones, of latitude todescribe climate regions. Within each latitude zone,the climate follows general patterns.

Low LatitudesBetween the Tropic of Cancer and the Tropic of

Capricorn is a zone known as the low latitudes.This zone includes the Equator. Portions of the lowlatitudes receive the direct rays of the sun year-round. Places located in the low latitudes havewarm to hot climates. Because of the latitudes thatform its boundaries, this zone is called the Tropics.

High LatitudesThe earth’s polar areas are called the high

latitudes. When either the Northern or the South-ern Hemisphere is tilted toward the sun, its polar

area receives continuous, but indirect, sunlight.From about March 20 to about September 23, thepolar area north of the Arctic Circle (latitude 66ºN)experiences continuous daylight or twilight. Thepolar area south of the Antarctic Circle (latitude66ºS) experiences continuous daylight or twilightfor the other six months of the year.

Mid-LatitudesThe most variable weather on Earth is found in the

mid-latitudes between the Tropic of Cancer and theArctic Circle in the Northern Hemisphere andbetween the Tropic of Capricorn and the AntarcticCircle in the Southern Hemisphere. In summer themid-latitudes receive warm masses of air from theTropics. In winter, cold masses of air move into the mid-latitudes from the high latitudes. The

2. Applying Geography Skills If you were to sailwithin the low latitudes from India to Africa, inwhich direction would you sail to take advantageof the prevailing winds?

1. Interpreting Maps What air currents flow overthe mid-latitudes? The low latitudes?

C h a p t e r 3 61

mid-latitudes generally have a temperate climate—one that ranges from fairly hot to fairly cold—withdramatic seasonal weather changes.

Elevation and ClimateAt all latitudes elevation influences climate

because of the relationship between the elevation ofa place and its temperature. The earth’s atmospherethins as altitude increases. Thinner air retains lessheat. As elevation increases, temperatures decreaseby about 3.5ºF (1.9ºC) for each 1,000 feet (305 m).This effect occurs at all latitudes. For example, inEcuador, the city of Quito (KEE•toh) is nearly on theEquator. However, Quito lies in the Andes at an ele-vation of more than 9,000 feet (2,743 m), so averagetemperatures are about 32ºF (17ºC) cooler than in thenearby lowlands.

Sunlight is bright in Quito and other placeswith high elevation because the thinner atmos-phere filters fewer rays of the sun. Even in brightsunlight, the world’s highest mountains are cold,snowy places year-round.

Wind and Ocean CurrentsWind and water combine with the effects of the

sun to influence Earth’s weather and climate. Airmoving across the face of the earth is called wind.Winds occur because the sun heats up the earth’satmosphere and surface unevenly. Rising warm aircreates areas of low pressure, and falling cool aircauses areas of high pressure. The cool air thenflows in to replace the warm rising air. Thesemovements over the earth’s surface cause winds,which distribute the sun’s heat around the planet.

N

NORTHAMERICA

SOUTHAMERICA

A F R I C A

A N T A R C T I C A

AUSTRALIA

A S I AEUROPE

PacificOcean

PacificOcean

AtlanticOcean

AtlanticOcean

IndianOcean

PacificOcean

Arctic Ocean

EQUATOR

TROPIC OF CAPRICORN

ANTARCTIC CIRCLE

TROPIC OF CANCER

ARCTIC CIRCLE

0°

60°E60°W 120°E120°W 0°

30°N

30°S

60°S

60°NAlaskaCurrent

LabradorCurrent

North Equatorial Current

South EquatorialCurrent

Equatorial Countercurrent

NorthAtlantic Drift

CaliforniaCurrent

Guinea Current

Canary Current

EastAustralian

Current

KurilCurrent

Bra

zilCur

rent

Per

uC

urr

en

t

Current

Benguela

Japa

nCu

rrent

Gul

f Stream

West Wind Drift

West Wind Drift

West Australian Current

N. Pacific

Drift

Winkel Tripel projection

3,000

3,0000 mi.

0 km

MAP STUDY

World Ocean Currents

Find NGS online map resources @ www.nationalgeographic.com/maps

Warm currentCold current

1. Interpreting Maps Which current movesalong the northwestern coast of Africa?

2. Applying Geography Skills How do oceancurrents develop? How is this process similar to the development of wind currents?

62 U n i t 1

Wind PatternsGlobal winds blow in fairly constant patterns

called prevailing winds, shown on the map on page60. The direction of prevailing winds is determinedby latitude and is affected by the earth’s movement.Because Earth rotates to the east, the global winds aredisplaced clockwise in the Northern Hemisphereand counterclockwise in the Southern Hemisphere.This phenomenon, called the Coriolis effect, causesprevailing winds to blow diagonally rather thanalong strict north-south or east-west lines.

Winds are often named for the direction fromwhich they blow, but they sometimes were givennames from the early days of sailing. Named fortheir ability to move trading ships through theregion, the prevailing winds of the low latitudesare called trade winds. They blow from the north-east toward the Equator from about latitude30ºN and from the southeast toward the Equatorfrom about latitude 30ºS. Westerlies are the pre-vailing winds in the mid-latitudes, blowing diag-onally west to east between about 30ºN and 60ºNand between about 30ºS and 60ºS. In the high lat-itudes, the polar easterlies blow diagonally east towest, pushing cold air toward the mid-latitudes.

History

The Horse LatitudesAt the Equator, global winds are diverted north

and south, leaving a narrow, generally windlessband called the doldrums. Two other narrow bandsof calm air encircle the globe just north of theTropic of Cancer and just south of the Tropic ofCapricorn. In the days of wind-powered sailingships, crews feared being stranded in these wind-less areas. With no moving air to lift the sails,ships were stranded for weeks in the hot, stillweather. Meanwhile, food supplies dwindled,and perishable cargoes spoiled as the ships sat.The English poet Samuel Taylor Coleridgedescribed this frightening experience:

“ Day after day, day after dayWe struck, nor breath nor motion;As idle as a painted shipUpon a painted ocean.”Samuel Taylor Coleridge, The Rime

of the Ancient Mariner, 1798

To lighten the load so the ships could takeadvantage of the slightest breeze, sailors wouldtoss excess cargo and supplies overboard, includ-ing livestock being carried to colonial settlements.This practice gave rise to the name by which thecalm areas at the edges of the Tropics are known—the horse latitudes.

Ocean CurrentsJust as winds move in patterns, cold and warm

streams of water, known as currents, movethrough the oceans. Ocean currents are caused bymany of the same factors that cause winds, includ-ing the earth’s rotation, changes in air pressure,and differences in water temperature. The Corioliseffect is observed in ocean currents, too, causingthem to move in clockwise circles in the NorthernHemisphere and counterclockwise circles in theSouthern Hemisphere.

As ocean currents circulate, cold water from thepolar areas moves slowly toward the Equator, warm-ing as it moves through the Tropics. This water formsthe warm ocean currents. The warm water, in turn,moves away from the Equator, cooling to become acold ocean current.

Ocean currents affect climate in the coastal landsalong which they flow. Cold ocean currents coolthe lands they pass. Warm ocean currents bringwarmer temperatures. For example, the NorthAtlantic Drift, a warm-water extension of the GulfStream current, flows near western Europe. Thiscurrent gives western Europe a relatively mild cli-mate in spite of its northern latitude.

Weather and the Water CycleWind and water work together to affect weather

in another important way. Driven by temperature,condensation creates precipitation, moisture fallingto the earth in the form of rain, sleet, hail, or snow.The sudden cloudburst that cools a steamy sum-mer day is an example of how precipitation bothaffects and is affected by temperature. Watervapor forms in the atmosphere from evaporatedsurface water. As colder temperatures cool the ris-ing moist air, the vapor condenses into liquiddroplets, forming clouds. Further cooling causesrain to fall, which can help lower the temperatureon warm days.

C h a p t e r 3 63

El NiñoClimate is also affected by recurring phenomena,

or events, that alter weather patterns. The mostfamous of these recurring climatic events is the ElNiño (ehl NEE•nyoh) phenomenon. El Niño is aperiodic change in the pattern of ocean currentsand water temperatures in the mid-Pacific region.

El Niño does not occur every year, but its fre-quency appears to have increased in the latter halfof the 1900s. In an El Niño year, the normally lowatmospheric pressure over the western Pacificrises, and the normally high pressure over theeastern Pacific drops. This reversal causes thetrade winds to diminish or even to reverse direc-tion. The change in wind pattern reverses theequatorial ocean currents, drawing warm waterfrom near Indonesia east to Ecuador, where itspreads along the South American coast.

The changed air pressures resulting from ElNiño influence climates around the world in akind of domino effect. Precipitation increasesalong the coasts of North and South America,warming winters and increasing the risk of floods.Hawaii experiences reduced winds like those inthe doldrums, and also drier weather. In SoutheastAsia and Australia, drought and occasional mas-sive forest fires occur.

Scientists are not sure what causes El Niño orwhy it appears to be occurring more frequently.Preliminary studies have linked this climaticevent to global warming. The costs in humanand economic terms of the weather catastrophesassociated with El Niño make learning moreabout this climatic event vitally important.

Landforms and ClimateThe surface features of the earth, such as bodies

of water and mountains, also can affect and be af-fected by climate. The climates of places located atthe same latitude can be very different, dependingon the presence or absence of certain landforms.

Large bodies of water, for example, are slower toheat and to cool than land. As a result, water tem-peratures are more uniform and constant than landtemperatures. Coastal lands receive the benefit ofthis moderating influence and experience lesschangeable weather than do inland areas. Largelakes, such as the Great Lakes in the United Statesand Canada, also create this effect.

32

NORMAL CONDITIONS

NorthAmerica

SouthAmerica

Equator

Tahiti

60oN

40oN

60oS

40oS

20oN

20oS

0o

28

24

20

16

12

8

4

0

32

EL NIÑO CONDITIONS

NorthAmerica

SouthAmerica

Lower thannormal pressureover Tahiti

Tahiti

60oN

40oN

60oS

40oS

20oN

20oS

0o

28

24

20

16

12

8

4

Sea surface temperature data taken atone-degree intervals.

*

*Sea surface tem

perature (Celsius)

*Sea surface tem

perature (Celsius)

0

Equator

Subtropical Jet Stream

Subtropical Jet Stream

Cold Air

Warm Air

Cold Air

Warm Air

L

DIAGRAMSTUDY

El Niño

1. Interpreting Diagrams At what latitude does the subtropical jet stream flow under normalconditions?

2. Applying Geography Skills Describe theimpact of El Niño on the lives of people in different parts of the world.

Mountain ranges alsoinfluence precipitation andaffect climate. Winds thatblow over an ocean arepushed upward when theymeet a mountain range. Therising air cools and releasesmost of its moisture in theform of precipitation onthe windward side—theside of the mountainrange facing the wind.After the precipitation isreleased, winds becomewarmer and drier as theydescend on the opposite, orleeward, side of the moun-tains. The hot, dry air pro-duces little precipitation inan effect known as a rainshadow. The rain shadoweffect often causes dry areas—and even deserts—todevelop on the leeward sides of mountain ranges.

From the interaction of landforms, wind andwater currents, latitude, and elevation arise aremarkable variety of climates. In the next section,you will learn about the earth’s climate regions andthe kinds of natural vegetation that grows in each cli-mate region. You will also learn about the ways thatclimates have changed over millions of years and

64 U n i t 1

Checking for Understanding1. Define prevailing wind, Coriolis

effect, doldrums, current, El Niño,windward, leeward, rain shadow.

2. Main Ideas On a web diagram,fill in information about each ofthe factors affecting climate. Indi-cate whether these factors affectthe climate where you live.

Critical Thinking3. Comparing and Contrasting

Describe the general differencesin climate between the low lati-tudes and the mid-latitudes.

4. Predicting Consequences With-out the Coriolis effect, how mightthe earth’s climates be different?

5. Identifying Cause-and-EffectRelationships How does the pres-ence of mountain ranges influ-ence climate?

Analyzing Maps6. Location Study the map of wind

patterns on page 60. Where arethe high latitudes located?

7. Movement of Ocean CurrentsStudy the map on page 61. Ifyour ship were drifting fromwest to east in the EquatorialCountercurrent, what mighthappen as you drifted pastlongitude 120ºW?

Applying Geography

Climate

Warm moist air drops moisture

Cool moist air

Warm dry air in rain shadow

Mountain range

WINDWARD SIDE

LEEWARD SIDE

Ocean

North

South

DIAGRAM STUDY

The Rain Shadow Effect

explore the many natural causes of climate change.As you explore the ways that human activities maycause climate change, you will also learn about waysthat humans can protect their environment.

1. Interpreting Diagrams On which side of a mountain does precipitation fall?

2. Applying Geography Skills How dolandforms cause the formation of a rainshadow?

C h a p t e r 3 65

Guide to ReadingConsider What You KnowThink about the types of vegetationthat grow in the region where youlive. What does the vegetation revealabout the regional climate there?

Read to Find Out• How do geographers classify the

climate regions of the world?

• Which kinds of vegetation arecharacteristic of each climateregion?

• How do recurring phenomenainfluence climate patterns?

Terms to Know• natural vegetation

• oasis

• coniferous

• deciduous

• mixed forest

• chaparral

• prairie

• permafrost

• hypothesis

• smog

Places to Locate• Tropics

• Sahara

• Mediterranean Sea

World ClimatePatterns

A Geographic ViewDamage from El NiñoFrom South America, cradle of ElNiño, came reports of appallingflood damage. I headed south, past drought-stricken Mexico, and alighted on the soggy soil of Guayaquil, Ecuador. Threemonths before Christmas acolossal slab of warm water 450 feet thick had arrived offEcuador and Peru, smotheringthe cool ocean surface. Coastalfishing ceased, and the sim-mering sea brought rains thatthreatened to wash Ecuador into the sea. “Areasthat normally measure precipitation in inches have had ten feet,”said Jimmy Aycart, . . . director of emergency relief for the Guayaquil area.

––Thomas Y. Canby, “El Niño’s Ill Wind,” National Geographic, February 1984

The effects of El Niño are felt around the world. It hastriggered floods in southern California and droughts in Africa. How-ever, even ordinary climate patterns vary from region to region,depending on the climate factors present. In this section you willlearn how geographers classify the world’s climates and how climatechange occurs.

Climate RegionsGeographers often divide the earth into climate regions—tropical,

dry, mid-latitude, high latitude, and highlands. Because climatesvary within these broad regions, geographers further divide themajor regions into smaller ones. Each of these divisions has its own

Flooding in Ecuador caused by El Niño

66 U n i t 1

0˚

60˚E60˚W 120˚E120˚W 0˚

30˚N

30˚S

60˚S

60˚N

EQUATOR

TROPIC OF CANCER

TROPIC OF CAPRICORN

ANTARCTIC CIRCLE

ARCTIC CIRCLE

Johannesburg

Seattle

Mumbai(Bombay)

Los AngelesChicago

Rio de Janeiro

Washington

Ottawa

MexicoCity

Lima

Dakar

CapeTown

Santiago BuenosAires

Caracas

Cairo

Kinshasa

MoscowLondon

MadridTashkent

Jakarta

BeijingTokyo

Hong Kong

Bangkok

SydneyN

2,000

2,0000 mi.

0 kmWinkel Tripel projection

MAP STUDY

World Climate Regions

Find NGS online map resources @ www.nationalgeographic.com/maps

Tropical rain forestTropical savanna

SteppeDesert

Marine west coastMediterraneanHumid subtropicalHumid continental

SubarcticTundraIce capHighlands (climatevaries with elevation)

Tropical

Dry

Mid-Latitude

High Latitude

characteristic soils and natural vegetation—theplant life that grows in an area where the naturalenvironment is unchanged by human activity.

Tropical ClimatesTropical climates are found in or near the low

latitudes—the Tropics. The two most widespreadkinds of tropical climate regions are tropical rainforest and tropical savanna.

Hot and wet throughout the year, tropical rain forestclimates have an average temperature of 80ºF(27ºC). The warm, humid air is saturated with mois-ture, producing rain almost daily. Yearly rainfallaverages about 80 inches (203 cm). Lush vegetationis common in tropical climates, although the contin-ual rain tends to leach, or draw out, nutrients fromthe soil in these climates. Wildlife is also abundant.

2. Applying Geography Skills How do largebodies of water affect the climate in coastalareas?

“ Like an undiscovered continent encir-cling the globe, tropical rain forestsshelter an astonishing abundance oforganisms—probably more than halfthe Earth’s plant and animal species.”Edward O. Wilson, “Rain Forest

Canopy: The High Frontier,” National Geographic, December 1991

Tropical rain forest vegetation grows thickly inlayers. Tall teak or mahogany trees form a canopyover shorter trees and bushes. Vines and shade-loving plants grow on the forest floor. The world’slargest tropical rain forest is in South America’sAmazon River basin. Similar climate and vegeta-tion exist in other parts of South America, in theCaribbean area, and Asia and Africa.

1. Interpreting Maps Where are tropical climatesfound?

C h a p t e r 3 67

Tropical savanna climates have dry winters andwet summers, accompanied by high year-roundtemperatures. In the dry season, the ground iscovered with clumps of coarse grass. Fewer treesexist in savanna regions than in the rain forests.Tropical savannas are found in Africa, Centraland South America, Asia, and Australia.

Dry ClimatesGeographers have identified two types of dry

climates, based on the vegetation in each. Both desertand steppe climates occur in many parts of the world.

Dry areas with sparse plant life are called deserts.Yearly rainfall in deserts seldom exceeds 10 inches(about 25 cm), and temperatures vary widely fromthe heat of day to the cool of night and from seasonto season. Desert climates occur in just under

one-third of the earth’s total land area. The Saharaalone extends over almost the entire northern one-third of the African continent.

The natural vegetation of deserts consists of scat-tered scrub and cactus, plants that tolerate lowhumidity and wide temperature ranges. In somedesert areas, underground springs may support anoasis, an area of lush vegetation. Some desertshave dunes or rocky surfaces, and others have fer-tile soil that can yield crops through irrigation.

Often bordering deserts are dry, largely treelessgrasslands called steppes. Yearly rainfall in steppeareas averages 10 to 20 inches (25 to 51 cm). Theworld’s largest steppe stretches across easternEurope and western and central Asia. Steppes arealso found in North America, South America,Africa, and Australia.

0˚

60˚E60˚W 120˚E120˚W 0˚

30˚N

60˚N

60˚S

30˚S

EQUATOR

TROPIC OF CANCER

TROPIC OF CAPRICORN

ARCTIC CIRCLE

ANTARCTIC CIRCLE

Pacific

Ocean

Pacific

Ocean

Atlantic

Ocean

Atlantic

Ocean

Arctic

Ocean

Indian

Ocean

Washington, D.C.

Ottawa London

Caracas

Rio de Janeiro

Moscow

TashkentBeijing

Bangkok

Tokyo

Jakarta

Hong KongMumbai

(Bombay)

Johannesburg

Kinshasa

Dakar

Madrid

Cape Town Sydney

Cairo

Buenos AiresSantiago

Lima

Seattle

Chicago

Los Angeles

Mexico City

N

Winkel Tripel projection2,000

2,0000

0

mi.

km

C03-07NGS-664173

MAP STUDY

World Natural Vegetation Regions

Find NGS online map resources @ www.nationalgeographic.com/maps

2. Applying Geography Skills Explain why theamount of vegetation decreases as you movetoward higher latitudes.

Tropical forest

Chaparral

Deciduous and mixeddeciduous-coniferous forest

Coniferous forest

Tropical grassland

Temperate grassland

Desert scrub and desert waste

Tundra

Highlands (vegetation varieswith elevation)

Ice cap

1. Interpreting Maps What continents have largetropical forests?

68 U n i t 1

Mid-Latitude ClimatesThe world’s mid-latitudes include four temperate

climate regions. Mid-latitude climates experiencevariable weather patterns and seasonal changesthat give rise to a variety of natural vegetation.

Along western coastlines, between the latitudes of30º and 60º north and south, are regions with amarine west coast climate. The Pacific coast of NorthAmerica, much of Europe, and parts of South Amer-ica, Africa, Australia, and New Zealand have marinewest coast climates. In these areas ocean winds bringcool summers and damp winters. Abundant rainfallsupports the growth of both coniferous and decidu-ous trees. Coniferous trees such as evergreens havecones, needle-shaped leaves, and keep their foliagethroughout the winter. Deciduous trees, such as oak,elm, and maple, have broad leaves that change colorand drop in autumn. Typical of marine west coast cli-mates are mixed forests with both kinds of trees.

Lands surrounding the Mediterranean Sea havemild, rainy winters and hot, sunny summers. Thenatural vegetation includes chaparral (SHA•puh•RAL), thickets of woody bushes and short trees. Geo-graphers classify as Mediterranean any coastal mid-latitude areas with similar climate and vegetation.Such areas also include Southern California andparts of southern Australia.

In the southeastern United States and in southeast-ern parts of South America and Asia, a humid sub-tropical climate brings short, mild winters and nearlyyear-round rain. The wind patterns and high pres-sure related to nearby oceans keep humidity levelshigh in these areas. Vegetation consists of prairies, orinland grasslands, and forests of evergreen anddeciduous trees.

In some mid-latitude regions of the NorthernHemisphere, such as southern Canada, westernRussia, and northeastern China, landforms influenceclimate more than winds, precipitation, or ocean tem-peratures do. These humid continental climate regionsdo not experience the moderating effect of oceanwinds because of their northerly continental, orinland, locations. The farther north one travels inthese humid continental areas, the longer and moresevere are the snowy winters and the shorter andcooler are the summers. Vegetation in humid conti-nental regions is similar to that found in marine westcoast areas, with evergreens outnumbering decidu-ous trees in the northernmost areas of the region.

High Latitude ClimatesIn high latitude climates, freezing temperatures

are common throughout much of the year becauseof the lack of direct sunlight. As a result, theamount and variety of vegetation is limited.

Just south of the Arctic Circle lie the subarctic cli-mate regions. Winters here are bitterly cold, andsummers are short and cool. Subarctic regions havethe world’s widest temperature ranges, varyingfrom winter to summer by as much as 120ºF (49ºC).In parts of the subarctic, only a thin layer of surfacesoil thaws each summer. Below it is permanentlyfrozen subsoil, or permafrost. Brief summer grow-ing seasons may support needled evergreens.

Closer to the polar regions, tundra climateregions are very cold. Here the winter darknessand bitter cold last for half the year, and the sun’sindirect rays bring constant summer light but littleheat. In tundra regions, most of which lie in the farnorth of the Northern Hemisphere, the layer ofthawed soil is even thinner than in the subarctic.

Mid-latitude Vegetation Chaparral, whichincludes shrubs and olive trees, grows in Mediter-ranean climate zones.

Region What kind of vegetation grows in humidsubtropical climate zones? Humid continental?

Checking for Understanding1. Define natural vegetation, oasis,

coniferous, deciduous, mixed for-est, chaparral, prairie, permafrost,hypothesis, smog.

2. Main Ideas Create a table like theone below, adding informationand a brief description about eachof the world’s climate regions.

Critical Thinking3. Analyzing Information What

patterns of vegetation are typicalof tropical climates? Explain.

4. Comparing and Contrasting Whatfactors account for the similaritiesand differences between the sub-divisions in tropical climate zones?

5. Categorizing Information Howare the five major climate regionsrelated to the three zones of latitude?

6. Drawing Conclusions What arethe two main categories of fac-tors causing climate change?

Analyzing Maps7. Region Study the map of world

natural vegetation regions onpage 67. What vegetation typedominates Europe? Canada andthe United States?

Earth’s Climates

Climate Region Features

8. Climate and SettlementPatterns On the map ofworld climate regions onpage 66, locate the climateregions for Tashkent, CapeTown, Lima, Chicago, Lon-don, and Jakarta. What can you conclude about the relationship betweenclimate and settlement?

Applying Geography

Trees cannot establish roots on these frigid plains,so tundra vegetation is limited to low bushes, veryshort grasses, mosses, and lichens (LY•kuhns).

Snow and ice, often more than 2 miles (3 km)thick, constantly cover the surfaces of ice capregions. Lichens are the only form of vegetationthat can survive in these areas, where monthlytemperatures average below freezing. Earth’slargest polar ice cap covers almost all of Antarctica.Greenland’s interior also has an ice cap climate.

Highlands ClimatesElevation can determine a climate region, regard-

less of latitude. High mountain areas, even along theEquator, share some of the same characteristics ofhigh latitude climates because of the thinning of theatmosphere at high altitudes. The higher the eleva-tion, the cooler the temperatures. The natural vegeta-tion of highlands climates also varies with elevation.Mixed forests generally lie at the bases of mountainranges. Higher up, meadows with small trees,shrubs, and wildflowers line the mountainsides.

Climatic ChangesClimates change gradually over time, although

the causes of these changes are unclear. Scientistssearch for answers by studying the interrelationships

C h a p t e r 3 69

among ocean temperatures, greenhouse gases, windpatterns, and cloud cover.

During the last 1 to 2 million years, for example,the earth passed through four ice ages, eras whenglaciers covered large areas of the planet’s surface.One hypothesis, or scientific explanation, for theseice ages is that the earth absorbed less solar energybecause of variations in the sun’s output of energyor because of variations in the earth’s orbit.Another hypothesis suggests that dust cloudsfrom volcanic activity reflected sunlight back intospace, cooling the atmosphere and lowering sur-face temperatures.

Human interaction with the environment alsoaffects climate. Burning fossil fuels releases gasesthat mix with water in the air, forming acidsthat fall in rain and snow. Acid rain can destroyforests. Fewer forests may result in climaticchange. The exhaust released from burning fossilfuels in automobile engines and factories is heatedin the atmosphere by the sun’s ultraviolet rays,forming smog, a visible chemical haze in theatmosphere that endangers people’s health. Otherhuman-driven changes result from dams and riverdiversions. These projects, intended to supplywater to dry areas, may cause new areas to floodor to dry out and may affect climate over time.

The Glencoe Skillbuilder Interactive Workbook,

Level 2 provides instruction andpractice in key social studies skills.

Learning the SkillA diagram is a graphic design

that shows a process or event.Diagrams are extremely useful in communicating informationclearly and quickly. A diagram can show placement, relation-ships, cycles, and movement,using symbols and drawn ob-jects. Diagrams can be very use-ful for showing changes overtime or for comparing two ormore actions or relationships.Presenting information visuallycan make complex events orideas more understandable.

Newspapers, magazines, andthe Internet use diagrams tosupplement written information.Geographers use diagrams toexplain complex processes such asclimate and weather phenomena.A diagram can be a very effectiveway of communicating an idea.

Follow these steps to under-stand a diagram:

• Note its title, caption, andlabels. These features provideinformation that is importantfor understanding the diagram.

• Study carefully the objectsand symbols used. Some-times a diagram includes akey to the symbols.

• Look at the relationships oractions shown. If the dia-gram compares two or morethings, look for details thatshow how the relationship

or action changes under dif-ferent circumstances.

Practicing the SkillThe diagrams above explain

and compare two aspects of thegreenhouse effect. Use the dia-grams to answer the followingquestions.

1. Describe the two aspects ofthe greenhouse effect shownabove.

2. How is plant life different inthe two diagrams?

3. What objects are shown contributing more carbon to the atmosphere?

4. How is the amount of heatretained in the Earth’s atmo-sphere related to the amountof carbon in the atmosphere?

Reading a DiagramHave you ever assembled a model airplane or car? Kits and

how-to books give detailed instructions that often includediagrams. Because they present information visually, diagramscan help explain ideas and processes easily.

70 U n i t 1

Carbon in atmosphere Carbon in atmosphere

Out of balance—too muchcarbon in the atmosphere

Functioning—normal amountof carbon in the atmosphere

Heat from sunwarms the earth

Heat from sunwarms the earth

Heatrisinginto

atmosphere

Heatrisinginto

atmosphere

Greenhouse Effect

Design and draw a diagram thatexplains a natural process. Lookthrough newspapers or magazinesfor ideas relating to geography. Inthe diagram, include drawn objects,symbols, a title, and labels.

C h a p t e r 3 71

Key Points• The earth’s position in relation to the sun

affects temperatures on Earth.

• The rotation of the earth causes day and night.

• The earth’s revolution and its tilt in rela-tion to the sun produce the seasons.

• Global temperatures may be increasing as a result of human activity.

Organizing Your NotesUse a graphic organizer like theone below to help you organizeyour notes for this section.

Terms to Know• prevailing wind• Coriolis effect• doldrums• current• El Niño• windward• leeward• rain shadow

Key Points• Latitude and elevation affect climate.

• Wind patterns and ocean currents play a keyrole in the earth’s climates.

• Climate is affected by recurring phenomenasuch as El Niño.

• Landforms shape and are shaped by climatepatterns.

Organizing Your NotesUse a table like the one belowto help you organize informa-tion about climate.

Terms to Know• weather• climate• axis• temperature• revolution• equinox• solstice• greenhouse effect• global warming

Terms to Know• natural vegetation• oasis• coniferous• deciduous• mixed forest• chaparral• prairie• permafrost• hypothesis• smog

Key Points• Geographers divide the world into major

climate regions.

• Each climate region has its own characteristicnatural vegetation.

• Climate patterns change over time as a result of both natural processes and human activity.

Organizing Your NotesUse an outline like the onebelow to help you organize yournotes for this section.

SECTION 1 Earth-Sun Relationships (pp. 55–58)

SECTION 2 Factors Affecting Climate (pp. 59–64)

SECTION 3 World Climate Patterns (pp. 65–69)

SUMMARY & STUDY GUIDE

Earth’s Tilt and Rotation

Earth’sRevolution

GreenhouseEffect

Climate Factors

Location

Currents

SurfaceFeatures

I. Tropical climatesA. Tropical rain forest

1. High temperatures2. Rain all year

B.

Earth-Sun Relationship

Climate Patterns

Critical Thinking

1. Predicting Consequences How mightincreased global warming affect the earth’s climates? Give examples to support youranswer.

2. Making Generalizations Why do themid-latitudes have a temperate climate?

3. Categorizing Information Create a webdiagram like the one below. Connect theitems with a line to show that they arerelated. Describe the geographical events andphenomena associated with each category.

Reviewing Key TermsOn a sheet of paper, classify these key terms underthe correct heading: earth-sun relationship, cli-mate factors, or climate patterns.

greenhouse effect temperature El Niño

mixed forest prevailing wind oasis

equinox chaparral prairie

revolution doldrums current

deciduous permafrost solstice

Coriolis effect rain shadow axis

Reviewing FactsSECTION 1

1. What are the effects of the earth’s tilt, rota-tion, and revolution?

2. What are the differences in sunlight at the Tropic of Cancer,the Tropic of Capricorn, and the Poles?

3. How is CO2 related to the green-house effect?

SECTION 24. List three key factors that affect

climate.

5. Describe the changes in air pressurethat occur during an El Niño year.How do these changes affect windpatterns?

6. How do large bodies of waterand mountains affect climate?

SECTION 37. What are the major climate

regions into which geographersdivide the earth?

8. What main types of vegetationgrow in the earth’s major cli-mate regions?

9. In what ways might the burningof fossil fuels affect a region’svegetation?

Locating PlacesThe World: Physical Geography

Match the letters on the map with the appropriate places and physical features.Write your answers on a separate sheet of paper.

A

B

C

D

E

F

F G

G

0˚

60˚E60˚W 120˚E120˚W 0˚

30˚N

30˚S

60˚S

60˚N

Winkel Tripel projection2,000

2,0000

0

mi.

km

N

ASSESSMENT & ACTIVITIES

72 U n i t 1

Earth-SunRelationship

Types of Climate

Factors AffectingClimate

1. Equator2. Arctic Circle3. Tropic of Capricorn

4. Warm current,Atlantic

5. Tropic of Cancer

6. Antarctic Circle7. Cold current,

Pacific

C h a p t e r X 73

Read the title and labels on the graphcarefully to determine what is beingpresented. For example, the label on

the bottom of the graph tells you that only selectedregions are shown. The label on the left indicates the number of storms per year, but not the month in which they occur.

Self-Check Quiz Visit the Glencoe WorldGeography Web site at tx.geography.glencoe.comand click on Self-Check Quizzes—Chapter 3 toprepare for the Chapter Test.

Thinking Like a GeographerImagine that you have been asked to speak aboutglobal warming to a group in your community.Your goal is to persuade the audience to takesteps to reduce global warming. Write an outlineof the remarks you will make to the group, anduse visuals to support your arguments.

Problem-Solving ActivityProblem-Solution Proposal Research andanalyze the effects of a physical geographic pat-tern, such as El Niño, on world economies. Whatactions did countries take in response? Deter-mine what preparations might lessen the impactof this pattern in the future. Write a proposal inwhich you outline the problem, present severalpossible solutions, and recommend a course ofaction. Include diagrams, charts, maps, and othervisual elements.

GeoJournalCause and Effect Review your journal entriesabout factors affecting climate. Write a storythat takes place in the future. The climatein your community has changed. Include de-tails about how this change occurred and how ithas affected vegetation, economic activities, andhuman and animal populations. Use specific exam-ples as well as illustrations and concrete languageto make your story interesting and engaging.

Technology ActivityUsing the Internet for Research

Work with a team to search the Internet forinformation about the climate in your commu-nity. Include information such as climate region,local factors that influence climate, seasonalchanges, and any unusual climatic events. Thenchoose one aspect of your area’s climate andwrite a paragraph explaining its effect on peo-ple in your community. For example, if yourcommunity has experienced a weather-relateddisaster, such as a hurricane or tornado, whateffects did the event have on your community?

Use the graph below and your knowledge of geography to answer the question. If you have trouble answering the question, use theprocess of elimination to narrow your choices.

1. Which of the following statements canbe inferred from the graph?

F Severe tropical storms are rare in Oceania.G East and South Asia have about four

times as many severe tropical storms asSouthwest Africa.

H North and Central America never gothrough a month without a storm.

J South America does not have tropicalstorms.

C h a p t e r 3 73

0

5

10

15

20

25

30

Severe Tropical Storms

Nu

mb

er o

f St

orm

s p

er Y

ear

SouthwestAfrica

30

25

20

15

10

5

0Australia

and OceaniaEast and

South AsiaNorth and

Central America

79

1414

79

29

14

Selected RegionsSource: Encyclopedia Britannica