earth science, 12e world climates and global climate change chapter 20

Earth Science, Earth Science, 12e12e

World Climates and World Climates and Global Climate Global Climate

ChangeChangeChapter 20Chapter 20

The climate systemThe climate system

ClimateClimate is an aggregate of weather is an aggregate of weather Involves the exchanges of energy Involves the exchanges of energy

and moisture that occur among the and moisture that occur among the • AtmosphereAtmosphere• HydrosphereHydrosphere• LithosphereLithosphere• BiosphereBiosphere, and, and• CryosphereCryosphere (ice and snow) (ice and snow)

Figure 20.2Figure 20.2

World climates World climates

Every location has a distinctive Every location has a distinctive climateclimate

The most important elements in a The most important elements in a climatic description are climatic description are • Temperature, andTemperature, and• Precipitation Precipitation

Climate classification Climate classification

Brings order to large quantities of Brings order to large quantities of information information

Many climatic-classification Many climatic-classification systems have been devisedsystems have been devised

Köppen classificationKöppen classification of climates of climates • Best known and most used systemBest known and most used system• Uses mean monthly and annual Uses mean monthly and annual

values of temperature and values of temperature and precipitation precipitation

Climate classification Climate classification KöppenKöppen classification of climates classification of climates

• Five principal climate groupsFive principal climate groups• Humid tropical (A)Humid tropical (A)• Dry (B)Dry (B)• Humid middle-latitude with mild winters (C) Humid middle-latitude with mild winters (C) • Humid middle-latitude with severe winters Humid middle-latitude with severe winters

(D)(D)• Polar (E)Polar (E)

• A, C, D, and E climates are defined on A, C, D, and E climates are defined on the basis of temperature characteristicsthe basis of temperature characteristics

• Precipitation is the primary criterion for Precipitation is the primary criterion for the B groupthe B group

Climates of Climates of the world the world

based on the based on the Köppen Köppen

classificationclassification Figure 20.4

Climates of Climates of the world the world

based on the based on the Köppen Köppen

classification classification (continued)(continued)

Figure 20.4

Köppen climates Köppen climates Humid tropical (A) climatesHumid tropical (A) climates

• Winterless climates, with all months Winterless climates, with all months having a mean temperature above 18ºChaving a mean temperature above 18ºC

• Two main typesTwo main types• Wet tropicsWet tropics

• High temperatures and year-round rainfallHigh temperatures and year-round rainfall• Luxuriant vegetation (tropical rain forest)Luxuriant vegetation (tropical rain forest)• Discontinuous belt astride the equatorDiscontinuous belt astride the equator• Strongly influenced by the equatorial low Strongly influenced by the equatorial low

pressures pressures

Köppen climates Köppen climates

Humid tropical (A) climatesHumid tropical (A) climates • Two main typesTwo main types

• Tropical wet and dryTropical wet and dry• Poleward of wet tropics and Poleward of wet tropics and

equatorward of the tropical desertsequatorward of the tropical deserts• Tropical grassland (Tropical grassland (savannasavanna))• Seasonal rainfall Seasonal rainfall

Comparison of A-type Comparison of A-type climatesclimates

Figure 20.6


Dry (B) climatesDry (B) climates • Evaporation exceeds precipitation Evaporation exceeds precipitation

and there is a constant water and there is a constant water deficiencydeficiency

• Boundary determined by formulas Boundary determined by formulas involving the three variablesinvolving the three variables

• Average annual precipitationAverage annual precipitation• Average annual temperatureAverage annual temperature• Seasonal distribution of precipitation Seasonal distribution of precipitation

Köppen climates Köppen climates Dry (B) climates Dry (B) climates

• Two climatic types Two climatic types • Arid or desert (BW)Arid or desert (BW)• Semiarid or steppe (BS)Semiarid or steppe (BS)

• More humid than arid climateMore humid than arid climate• Surrounds desert Surrounds desert

• Causes of deserts and steppes Causes of deserts and steppes • In the low latitudes In the low latitudes

• e.g., North Africa to northwestern e.g., North Africa to northwestern India, northern Mexico, southwestern India, northern Mexico, southwestern U.S. U.S.

Arid and semiarid climates Arid and semiarid climates of the worldof the world

Figure 20.8

Köppen climates Köppen climates Dry (B) climatesDry (B) climates

• Causes of deserts and steppes Causes of deserts and steppes • In the low latitudes In the low latitudes

• Coincide with the dry, stable, subsiding Coincide with the dry, stable, subsiding air of the subtropical high-pressure belts air of the subtropical high-pressure belts

• Middle-latitude deserts and steppes Middle-latitude deserts and steppes • Due to their position in the deep Due to their position in the deep

interiors of large landmasses and/or the interiors of large landmasses and/or the presence of high mountains presence of high mountains

• Most are located in the Northern Most are located in the Northern Hemisphere Hemisphere

Comparison of B-type Comparison of B-type climatesclimates

Figure 20.9

Köppen climates Köppen climates Humid middle-latitude climates Humid middle-latitude climates

with mild winters (C climates)with mild winters (C climates)• Average temperature of the coldest Average temperature of the coldest

month is below 18˚C but above –3˚Cmonth is below 18˚C but above –3˚C• SubgroupsSubgroups

• Humid subtropicsHumid subtropics • Eastern sides of continentsEastern sides of continents• 25 to 40 degrees latitude range25 to 40 degrees latitude range• Hot, sultry summersHot, sultry summers• Mild wintersMild winters• Winter precipitation is generated Winter precipitation is generated

along fronts along fronts


Humid middle-latitude climates Humid middle-latitude climates with mild winters (C climates)with mild winters (C climates)• SubgroupsSubgroups

• Marine west coast Marine west coast • Western (windward) side of continentsWestern (windward) side of continents• 40 to 65 degrees north and south 40 to 65 degrees north and south

latitudelatitude• Onshore flow of ocean airOnshore flow of ocean air• Mild winters and cool summers Mild winters and cool summers


Humid middle-latitude climates Humid middle-latitude climates with mild winters (C climates)with mild winters (C climates)• SubgroupsSubgroups

• Dry-summer subtropicsDry-summer subtropics • West sides of continents between West sides of continents between

latitudes 30˚ and 45˚latitudes 30˚ and 45˚• Strong winter rainfall maximumStrong winter rainfall maximum• Often called a Often called a Mediterranean climateMediterranean climate

Comparison of C-type Comparison of C-type climatesclimates

Figure 20.10


Humid middle-latitude climates Humid middle-latitude climates with severe winters (D climates)with severe winters (D climates)• Average temperature of the coldest Average temperature of the coldest

month is below –3˚C and the warmest month is below –3˚C and the warmest monthly mean exceeds 10˚Cmonthly mean exceeds 10˚C

• Land-controlled climatesLand-controlled climates• Absent in the Southern Hemisphere Absent in the Southern Hemisphere

Köppen climates Köppen climates Humid middle-latitude climates with Humid middle-latitude climates with

severe winters (D climates)severe winters (D climates)• Subgroups Subgroups

• Humid continental Humid continental • Confined to the central and eastern Confined to the central and eastern

portions of North America and Eurasia portions of North America and Eurasia between 40 and 50 degrees north between 40 and 50 degrees north latitudelatitude

• Severe winter and summer Severe winter and summer temperaturestemperatures

• High annual temperature rangesHigh annual temperature ranges• Precipitation is generally greater in the Precipitation is generally greater in the

summer than in the wintersummer than in the winter• Snow remains on the ground for Snow remains on the ground for

extended periods extended periods

Köppen climates Köppen climates Humid middle-latitude climates with Humid middle-latitude climates with

severe winters (D climates)severe winters (D climates)• Subgroups Subgroups

• SubarcticSubarctic • North of the humid continental climateNorth of the humid continental climate• Often referred to as the Often referred to as the taiga climatetaiga climate• Largest stretch of continuous forests on Largest stretch of continuous forests on

EarthEarth• Source regions of cP air massesSource regions of cP air masses• Frigid winters, remarkably warm but Frigid winters, remarkably warm but

short summers short summers

Comparison of D-type Comparison of D-type climatesclimates

Figure 20.12

Köppen climates Köppen climates Polar (E) climatesPolar (E) climates

• Mean temperature of the warmest Mean temperature of the warmest month is below 10ºCmonth is below 10ºC

• Enduring coldEnduring cold• Meager precipitationMeager precipitation• Two types of polar climatesTwo types of polar climates

• Tundra climate (ET)Tundra climate (ET) • Treeless climateTreeless climate• Almost exclusively in the Northern Almost exclusively in the Northern

HemisphereHemisphere• Severe winters, cool summersSevere winters, cool summers• High annual temperature range High annual temperature range

Figure 20.14AFigure 20.14A

Köppen climates Köppen climates Polar (E) climatesPolar (E) climates

• Two types of polar climatesTwo types of polar climates• Ice cap climate (EF) Ice cap climate (EF)

• No monthly mean above 0ºCNo monthly mean above 0ºC• Permanent ice and snowPermanent ice and snow

Highland climatesHighland climates• Usually cooler and wetter than Usually cooler and wetter than

adjacent lowlandsadjacent lowlands• Great diversity of climatic conditionsGreat diversity of climatic conditions• Best described by the terms Best described by the terms varietyvariety

and and changeabilitychangeability

Comparison of E-type Comparison of E-type climatesclimates

Figure 20.15

Human impact on Human impact on global climate global climate

Humans have been modifying the Humans have been modifying the environment over extensive areas environment over extensive areas for thousands of yearsfor thousands of years• By using fireBy using fire• By overgrazing of marginal landsBy overgrazing of marginal lands

Most hypotheses of climatic Most hypotheses of climatic change are to some degree change are to some degree controversial controversial


Global warmingGlobal warming • Water vapor and carbon dioxide Water vapor and carbon dioxide

absorb heat and are largely absorb heat and are largely responsible for the greenhouse effect responsible for the greenhouse effect of the atmosphereof the atmosphere

• Burning fossil fuels has added great Burning fossil fuels has added great quantities of carbon dioxide to the quantities of carbon dioxide to the atmosphere atmosphere

Energy consumption in the Energy consumption in the United States, 2004United States, 2004

Figure 20.17


The atmosphere responseThe atmosphere response • Global temperatures have increased Global temperatures have increased

• Balance of evidence suggests a human Balance of evidence suggests a human influence on global climateinfluence on global climate

• Globally averaged surface temperature is Globally averaged surface temperature is projected to increase by 1.4 to 5.8ºC by projected to increase by 1.4 to 5.8ºC by the year 2100the year 2100

Average global temperature Average global temperature variations 1860–2006variations 1860–2006


The atmosphere’s responseThe atmosphere’s response • The role of trace gasesThe role of trace gases

• Atmospheric trace gases Atmospheric trace gases • MethaneMethane• Nitrous oxideNitrous oxide• Certain Certain chlorofluorocarbonschlorofluorocarbons

• The role of trace gasesThe role of trace gases• Absorb wavelengths of outgoing Earth Absorb wavelengths of outgoing Earth

radiationradiation• Taken together, their warming effects Taken together, their warming effects

may be nearly as great as carbon dioxidemay be nearly as great as carbon dioxide

Climate-feedback Climate-feedback mechanisms mechanisms

Possible outcomes of altering the Possible outcomes of altering the climate system climate system

Two types Two types • Positive-feedback mechanismsPositive-feedback mechanisms

reinforce the initial changereinforce the initial change• Negative-feedback mechanismsNegative-feedback mechanisms

produce results that are just the produce results that are just the opposite of the initial change and opposite of the initial change and tend to offset it tend to offset it

Table 20.2Table 20.2

Some possible consequences Some possible consequences of global warming of global warming

Altered distribution of the world’s water Altered distribution of the world’s water resources and the effect on the resources and the effect on the productivity of agricultural regionsproductivity of agricultural regions

Rise in global mean sea level Rise in global mean sea level Changing weather patterns Changing weather patterns

• Higher frequency and intensity of hurricanes Higher frequency and intensity of hurricanes • Shifts in the paths of large-scale cyclonic Shifts in the paths of large-scale cyclonic

stormsstorms• Changes in frequency and intensity of heat Changes in frequency and intensity of heat

waves and droughts waves and droughts

Figure 20.26AFigure 20.26A

Figure 20.26BFigure 20.26B

earth science, 12e world climates and global climate change chapter 20

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