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M10 CHRI5988 07 SE C10.QXD12/18/074:21 AMPage 276Palm–oak forest hammock (“shady place”), featuring a mixed hardwood forest. There are bromeliads(epiphytes) growing on the live oak trees and a few on the cabbage, or sabal, palms. This palm is Florida’sstate tree. A hammock is slightly higher ground, surrounded by wet prairies, mixed swamp, and cypressforest marshes. Such “islands” of vegetation result from having few fires, protected as they are by surroundingmarshes. These two photos are in Myakka River State Park, Sarasota County, about 15 miles inland from thecentral Gulf Coast. [Overhead and forest-floor photos by Bobbé Christopherson.]276

M10 CHRI5988 07 SE C10.QXD12/18/074:21 AMPage 277CHAPTER10Global ClimateSystems䊏Key Learning ConceptsAfter reading the chapter, you should be able to:䊏 Define climate and climatology, and explain the difference betweenclimate and weather.䊏 Review the role of temperature, precipitation, air pressure, and airmass patterns used to establish climatic regions.䊏 Review the development of climate classification systems, andcompare genetic and empirical systems as ways of classifyingclimate.䊏 Describe the principal climate classification categories other thandeserts, and locate these regions on a world map.䊏 Explain the precipitation and moisture efficiency criteria used todetermine the arid and semiarid climates, and locate them on aworld map.䊏 Outline future climate patterns from forecasts presented, andexplain the causes and potential consequences of climate change.Earth experiences an almost infinite variety of weather—conditionsof the atmosphere—at any given time and place. But if we considerthe weather over many years, including its variability and ex-tremes, a pattern emerges that constitutes climate. Think of climatic patterns as dynamic rather than static, owing to the fact that we are witnessingclimate change. Climate is more than a consideration of simple averages oftemperature and precipitation.277

M10 CHRI5988 07 SE C10.QXD278Part II12/15/071:14 AMPage 278The Water, Weather, and Climate SystemsToday, climatologists know that intriguing globalscale linkages exist in the Earth–atmosphere–ocean system. For instance, strong monsoonal rains in West Africaare correlated with the development of intense Atlantichurricanes; or, one year an El Niño in the Pacific is tied torains in the American West, floods in Louisiana andNorthern Europe, and a weak Atlantic hurricane season.Yet, the persistent La Niña in 2007 strengtheneddrought’s six-year hold on the West. The El Niño/LaNiña phenomenon is the subject of Focus Study 10.1.Climatologists, among other scientists, are analyzingglobal climate change—record-breaking global averagetemperatures, glacial ice melt, drying soil-moisture conditions, changing crop yields, spreading of infectiousdisease, changing distributions of plants and animals, declining coral reef health and fisheries, and the thawing ofhigh-latitude lands and seas. Climatologists are concernedabout observed changes occurring in the global climate,as these are at a pace not evidenced in the records ofthe past millennia. Climate and natural vegetation shiftsduring the next 50 years could exceed the total of allchanges since the peak of the last ice-age episode, some18,000 years ago. In Chapter 1, Geosystems began withthese words from scientist Jack Williams,By the end of the 21st century, large portions of theEarth’s surface may experience climates not found at present, and some 20th-century climates may disappear. . . .Novel climates are projected to develop primarily in thetropics and subtropics. . . . Disappearing climatesincrease the likelihood of species extinctions and community disruption for species endemic to particular climatic regimes, with the largest impacts projected forpoleward and tropical montane regions.*We need to realize that the climate map and climate designations we study in this chapter are not fixed but are on themove as temperature and precipitation relationships alter.In this chapter: Climates are so diverse that no twoplaces on Earth’s surface experience exactly the sameclimatic conditions; in fact, Earth is a vast collection ofmicroclimates. However, broad similarities among localclimates permit their grouping into climatic regions.Many of the physical elements of the environment,studied in the first nine chapters of this text, link togetherto explain climates. Here we survey the patterns of climateusing a series of sample cities and towns. Geosystems usesa simplified classification system based on physical factorsthat help uncover the “why” question—why climates arein certain locations. Though imperfect, this method iseasily understood and is based on a widely used classification system devised by climatologist Wladimir Köppen(pronounced KUR-pen). For reference, Appendix Bdetails the Köppen climate classification system and allits criteria.*Jack Williams et al., “Projected distributions of novel and disappearingclimates by A.D. 2100,” Proceedings of the National Academy of Sciences(April 3, 2007): 5739.Climatologists use powerful computer models tosimulate changing complex interactions in the atmosphere, hydrosphere, lithosphere, and biosphere. Thischapter concludes with a discussion of climate change andits vital implications for society. Climate patterns arechanging at an unprecedented rate. Especially significantare changes occurring in the polar regions of the Arcticand Antarctic.Earth’s Climate Systemand Its ClassificationClimatology, the study of climate and its variability, analyzes long-term weather patterns over time and space andthe controls that produce Earth’s diverse climatic conditions. One type of climatic analysis locates areas of similarweather statistics and groups them into climatic regions.Observed patterns grouped into regions are at the core ofclimate classification.The climate where you live may be humid with distinct seasons, or dry with consistent warmth, or moist andcool—almost any combination is possible. There areplaces where it rains more than 20 cm (8 in.) each month,with monthly average temperatures remaining above27 C (80 F) year-round. Other places may be rainless fora decade at a time. A climate may have temperatures thataverage above freezing every month yet still threatensevere frost problems for agriculture. Students readingGeosystems in Singapore experience precipitation everymonth, ranging from 13.1 to 30.6 cm (5.1 to 12.0 in.), or228.1 cm (89.8 in.) during an average year, whereas students at the university in Karachi, Pakistan, measure only20.4 cm (8 in.) of rain over an entire year.Climates greatly influence ecosystems, the natural, selfregulating communities formed by plants and animals intheir nonliving environment. On land, the basic climaticregions determine to a large extent the location of theworld’s major ecosystems. These regions, called biomes,include forest, grassland, savanna, tundra, and desert.Plant, soil, and animal communities are associated withthese biomes. Because climate cycles through periodicchange, it is never really stable; therefore, ecosystemsshould be thought of as being in a constant state of adaptation and response.The present global climatic warming trend is producing changes in plant and animal distributions. Figure 10.1presents a schematic view of Earth’s climate system, showing both internal and external processes and linkages thatinfluence climate and thus regulate such changes.Climate Components: Insolation,Temperature, Pressure, Air Masses,and PrecipitationThe principal elements of climate are insolation, temperature, pressure, air masses, and precipitation. The firstnine chapters discussed each of these elements. We reviewthem briefly here. Insolation is the energy input for the

M10 CHRI5988 07 SE C10.QXD12/15/071:15 AMPage 279Chapter 10Global Climate sATMOSPHERECompositionN2, O2, CO2, H2O, O3,aerosolsAtmosphereCRYOSPHEREIce SPHEREWind effectsSea iceHYDROSPHEREInternalprocessesIceLandOceanChanges in the land:elevation, vegetation,albedoChanges inatmosphericcompositionLITHOSPHEREOceanChanges in the oceanbasin shape, salinity,sea temperatureExternalprocessesFIGURE 10.1 A schematic of Earth’s climate system.Imagine you are hired to write a computer program that simulates Earth’s climates. Internal processes that influence climateinvolve the atmosphere, hydrosphere (streams and oceans), cryosphere (polar ice masses and glaciers), biosphere, andlithosphere (land)—all energized by insolation. External processes, principally from human activity, affect this climatic balanceand force climate change. [After J. Houghton, The Global Climate (Cambridge, UK: Cambridge University Press, 1984); and the GlobalAtmospheric Research Program.]climate system, but it varies widely over Earth’s surface bylatitude (see Chapter 2 and Figures 2.9, 2.10, and 2.11).Daylength and temperature patterns vary diurnally (daily)and seasonally. The principal controls of temperature arelatitude, altitude, land-water heating differences, andcloud cover. The pattern of world temperatures and theirannual ranges are in Chapter 5 (see Figures 5.14, 5.15,5.17, and 5.18).Temperature variations result from a coupling ofdynamic forces in the atmosphere to Earth’s pattern ofatmospheric pressure and resulting global wind systems(see Figures 6.10 and 6.12). Important, too, are the location and physical characteristics of air masses, those vastbodies of homogeneous air that form over oceanic andcontinental source regions.Moisture is the remaining input to climate. Thehydrologic cycle transfers moisture, with its tremendouslatent heat energy, through Earth’s climate system (seeFigure 9.1). The moisture input to climate is precipitationin all its forms. Figure 10.2 shows the worldwide distribution of precipitation, our moisture supply. Its patterns areimportant, for it is a key climate control factor. Averagetemperatures and daylength help us approximate POTET(potential evapotranspiration), a measure of naturalmoisture demand.Most of Earth’s desert regions, areas of permanentwater deficit, are in lands dominated by subtropical highpressure cells, with bordering lands grading to grasslandsand to forests as precipitation increases. The most consistently wet climates on Earth straddle the equator in theAmazon region of South America, the Congo region ofAfrica, and Indonesia and Southeast Asia, all of which areinfluenced by equatorial low pressure and the intertropical convergence zone (ITCZ, see Figure 6.11).Simply relating the two principal climatic components—temperature and precipitation—reveals general climatetypes (Figure 10.3). Temperature and precipitation patterns, plus other weather factors, provide the key to climateclassification.Classification of Climatic RegionsThe ancient Greeks simplified their view of world climatesinto three zones: The “torrid zone” referred to warmerareas south of the Mediterranean; the “frigid zone” was tothe north; and the area where they lived was labeled the“temperate zone,” which they considered the optimum climate. They believed that travel too close to the equator ortoo far north would surely end in death. But the world is adiverse place and Earth’s myriad climatic variations aremore complex than these simple views.