Featuring a Mixed Hardwood Forest. There Are Bromeliads (Epiphytes) Growing on the Live Oak Trees and a Few on the Cabbage, Or Sabal, Palms

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Palm–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’s state tree. A hammock is slightly higher ground, surrounded by wet prairies, mixed swamp, and cypress forest marshes. Such “islands” of vegetation result from having few fires, protected as they are by surrounding marshes. These two photos are in Myakka River State Park, Sarasota County, about 15 miles inland from the central Gulf Coast. [Overhead and forest-floor photos by Bobbé Christopherson.]

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CHAPTER 10 Global Climate Systems

᭿ Key Learning Concepts

After reading the chapter, you should be able to: ᭿ Define climate and climatology, and explain the difference between climate and weather. ᭿ Review the role of temperature, precipitation, air pressure, and air mass patterns used to establish climatic regions. ᭿ Review the development of climate classification systems, and compare genetic and empirical systems as ways of classifying climate. ᭿ Describe the principal climate classification categories other than deserts, and locate these regions on a world map. ᭿ Explain the precipitation and moisture efficiency criteria used to determine the arid and semiarid climates, and locate them on a world map. ᭿ Outline future climate patterns from forecasts presented, and explain the causes and potential consequences of climate change.

arth experiences an almost infinite variety of weather—conditions of the atmosphere—at any given time and place. But if we consider Ethe weather over many years, including its variability and extremes, a pattern emerges that constitutes climate. Think of climatic patterns as dynamic rather than static, owing to the fact that we are witnessing climate change. Climate is more than a consideration of simple averages of temperature and precipitation.

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278 Part II The Water, Weather, and Climate Systems

Today, climatologists know that intriguing global- Climatologists use powerful computer models to scale linkages exist in the Earth–atmosphere–ocean sys- simulate changing complex interactions in the atmo- tem. For instance, strong monsoonal rains in West Africa sphere, hydrosphere, lithosphere, and biosphere. This are correlated with the development of intense Atlantic chapter concludes with a discussion of climate change and hurricanes; or, one year an El Niño in the Pacific is tied to its vital implications for society. Climate patterns are rains in the American West, floods in Louisiana and changing at an unprecedented rate. Especially significant Northern Europe, and a weak Atlantic hurricane season. are changes occurring in the polar regions of the Arctic Yet, the persistent La Niña in 2007 strengthened and Antarctic. drought’s six-year hold on the West. The El Niño/La Niña phenomenon is the subject of Focus Study 10.1. Climatologists, among other scientists, are analyzing Earth’s Climate System global climate change—record-breaking global average and Its Classification temperatures, glacial ice melt, drying soil-moisture conditions, changing crop yields, spreading of infectious Climatology, the study of climate and its variability, ana- disease, changing distributions of plants and animals, de- lyzes long-term weather patterns over time and space and clining coral reef health and fisheries, and the thawing of the controls that produce Earth’s diverse climatic condi- high-latitude lands and seas. Climatologists are concerned tions. One type of climatic analysis locates areas of similar about observed changes occurring in the global climate, weather statistics and groups them into climatic regions. as these are at a pace not evidenced in the records of Observed patterns grouped into regions are at the core of the past millennia. Climate and natural vegetation shifts climate classification. during the next 50 years could exceed the total of all The climate where you live may be humid with dis- changes since the peak of the last ice-age episode, some tinct seasons, or dry with consistent warmth, or moist and 18,000 years ago. In Chapter 1, Geosystems began with cool—almost any combination is possible. There are these words from scientist Jack Williams, places where it rains more than 20 cm (8 in.) each month, with monthly average temperatures remaining above By the end of the 21st century, large portions of the 27°C (80°F) year-round. Other places may be rainless for Earth’s surface may experience climates not found at pre- a decade at a time. A climate may have temperatures that sent, and some 20th-century climates may disappear.... average above freezing every month yet still threaten Novel climates are projected to develop primarily in the severe frost problems for agriculture. Students reading tropics and subtropics. . . . Disappearing climates Geosystems in Singapore experience precipitation every increase the likelihood of species extinctions and com- month, ranging from 13.1 to 30.6 cm (5.1 to 12.0 in.), or munity disruption for species endemic to particular cli- 228.1 cm (89.8 in.) during an average year, whereas stu- matic regimes, with the largest impacts projected for dents at the university in Karachi, Pakistan, measure only poleward and tropical montane regions.* 20.4 cm (8 in.) of rain over an entire year. Climates greatly influence ecosystems, the natural, self- We need to realize that the climate map and climate desig- regulating communities formed by plants and animals in nations we study in this chapter are not fixed but are on the their nonliving environment. On land, the basic climatic move as temperature and precipitation relationships alter. regions determine to a large extent the location of the In this chapter: Climates are so diverse that no two world’s major ecosystems. These regions, called biomes, places on Earth’s surface experience exactly the same include forest, grassland, savanna, tundra, and desert. climatic conditions; in fact, Earth is a vast collection of Plant, soil, and animal communities are associated with microclimates. However, broad similarities among local these biomes. Because climate cycles through periodic climates permit their grouping into climatic regions. change, it is never really stable; therefore, ecosystems Many of the physical elements of the environment, should be thought of as being in a constant state of adap- studied in the first nine chapters of this text, link together tation and response. to explain climates. Here we survey the patterns of climate The present global climatic warming trend is produc- using a series of sample cities and towns. Geosystems uses ing changes in plant and animal distributions. Figure 10.1 a simplified classification system based on physical factors presents a schematic view of Earth’s climate system, show- that help uncover the “why” question—why climates are ing both internal and external processes and linkages that in certain locations. Though imperfect, this method is influence climate and thus regulate such changes. easily understood and is based on a widely used classification system devised by climatologist Wladimir Köppen Climate Components: Insolation, (pronounced KUR-pen). For reference, Appendix B Temperature, Pressure, Air Masses, details the Köppen climate classification system and all its criteria. and Precipitation The principal elements of climate are insolation, temper- *Jack Williams et al., “Projected distributions of novel and disappearing ature, pressure, air masses, and precipitation. The first climates by A.D. 2100,” Proceedings of the National Academy of Sciences nine chapters discussed each of these elements. We review (April 3, 2007): 5739. them briefly here. Insolation is the energy input for the M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 279

Chapter 10 Global Climate Systems 279

SPACE Insolation

Terrestrial radiation

Clouds ATMOSPHERE Composition N2, O2, CO2, H2O, O3, aerosols Atmosphere Precipitation Atmosphere CRYOSPHERE Atmosphere Land Evaporation Heat Ice BIOSPHERE Biomass Ocean Ice sheets, exchange HYDROSPHERE snow Wind effects Sea ice Ice Land Changes in HYDROSPHERE Ocean atmospheric Ocean composition Changes in the land: elevation, vegetation, Changes in the ocean Internal albedo basin shape, salinity, processes LITHOSPHERE sea temperature External processes

FIGURE 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 climate involve the atmosphere, hydrosphere (streams and oceans), cryosphere (polar ice masses and glaciers), biosphere, and lithosphere (land)—all energized by insolation. External processes, principally from human activity, affect this climatic balance and force climate change. [After J. Houghton, The Global Climate (Cambridge, UK: Cambridge University Press, 1984); and the Global Atmospheric Research Program.]

climate system, but it varies widely over Earth’s surface by Most of Earth’s desert regions, areas of permanent latitude (see Chapter 2 and Figures 2.9, 2.10, and 2.11). water deficit, are in lands dominated by subtropical high- Daylength and temperature patterns vary diurnally (daily) pressure cells, with bordering lands grading to grasslands and seasonally. The principal controls of temperature are and to forests as precipitation increases. The most consis- latitude, altitude, land-water heating differences, and tently wet climates on Earth straddle the equator in the cloud cover. The pattern of world temperatures and their Amazon region of South America, the Congo region of annual ranges are in Chapter 5 (see Figures 5.14, 5.15, Africa, and Indonesia and Southeast Asia, all of which are 5.17, and 5.18). influenced by equatorial low pressure and the intertropi- Temperature variations result from a coupling of cal convergence zone (ITCZ, see Figure 6.11). dynamic forces in the atmosphere to Earth’s pattern of Simply relating the two principal climatic components— atmospheric pressure and resulting global wind systems temperature and precipitation—reveals general climate (see Figures 6.10 and 6.12). Important, too, are the loca- types (Figure 10.3). Temperature and precipitation pat- tion and physical characteristics of air masses, those vast terns, plus other weather factors, provide the key to climate bodies of homogeneous air that form over oceanic and classification. continental source regions. Moisture is the remaining input to climate. The Classification of Climatic Regions hydrologic cycle transfers moisture, with its tremendous The ancient Greeks simplified their view of world climates latent heat energy, through Earth’s climate system (see into three zones: The “torrid zone” referred to warmer Figure 9.1). The moisture input to climate is precipitation areas south of the Mediterranean; the “frigid zone” was to in all its forms. Figure 10.2 shows the worldwide distribu- the north; and the area where they lived was labeled the tion of precipitation, our moisture supply. Its patterns are “temperate zone,” which they considered the optimum cli- important, for it is a key climate control factor. Average mate. They believed that travel too close to the equator or temperatures and daylength help us approximate POTET too far north would surely end in death. But the world is a (potential evapotranspiration), a measure of natural diverse place and Earth’s myriad climatic variations are moisture demand. more complex than these simple views. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 280

280 Part II The Water, Weather, and Climate Systems

80° ARCTIC OCEAN ARCTIC OCEAN ° 70 Arctic Circle

60° 60°

50° 50° 50° 50°

PACIFIC 40° 40° 40° 40° ATLANTIC OCEAN OCEAN 30° 30° 30° 30° Tropic of Cancer Tropic of Cancer ° ° ° 20 20 ARABIAN 20 160° SEA BAY OF PACIFIC BENGAL 10° 10° 10° OCEAN 140° 130° 120° 110° 100° 90° 0° 50° 60° 70° 80° 90° 140° 150° 0° Equator Equator INDIAN OCEAN 10° 10° 10° 10° 10° cm in. 120° 150° 160° 170° CORAL SEA 200 and 80 and° ° ° ° 20° 20° 20° over 20° over20 20 20 20 Tropic of Capricorn 150–199 60–79 ° 30° 30° 30° 30° 30° 30° 30° 30 100–149 40–59

40° 50–9940° 20–39 40° 40° 40° 40° 40° 25–49 10–19 110° 120° 130° 140° 150° 160° 180° ° 50° Under50 25° Under 1050° 50° 50° 50 0 1,000 2,000 3,000 MILES 0 1,0002,000 3,000 KILOMETERS MODIFIED GOODE'S HOMOLOSINE EQUAL-AREA PROJECTION

FIGURE 10.2 Worldwide average annual precipitation. The causes that produce these patterns should be recognizable to you: temperature and pressure patterns; air mass types; convergent, convectional, orographic, and frontal lifting mechanisms; and the general energy availability that decreases toward the poles. Global Patterns of Precipitation

Cold Polar ice sheet Cold Tundra Highland climates at elevation Taiga – cool summer

Cold steppe Humid continental, mild summer Cold desert Midlatitude Humid continental, warm-hot summer semiarid Midlatitude and steppe arid FIGURE 10.3 Climatic relationships. Mediterranean, Humid subtropics A temperature and precipitation hot Hot steppe desert dry summer subtropics schematic reveals climatic relationships. Based on general knowledge of your Tropical Tropical Seasonal wet-and-dry Monsoon Equatorial tropics – college location, can you identify its arid semiarid tropics – Savanna tropics Rain forest approximate location on the schematic Hot Hot Dry Wet diagram? Now locate the region of your Increasing precipitation birthplace.

Classification is the process of grouping data or phe- data of observed effects is an empirical classification. nomena in related categories. Such generalizations are Climate classifications based on temperature and precipi- important tools in science and are especially useful for the tation data are examples of empirical classifications. spatial analysis of climatic regions. Just as there is no Genetic classifications explain climates in terms of net agreed-upon climate classification system, neither is there radiation, thermal regimes, or air mass dominance over a a single set of empirical (statistical) or genetic (causal) cri- region. This chapter uses a system that draws on both a teria on which everyone agrees. Any classification system genetic and an empirical approach, which allows descrip- should be viewed as developmental, because it is always tion of the climatic regions and also provides information open to change and improvement. as to why such climates are found where they occur. A climate classification based on causative factors—for One empirical classification system, published example, the interaction of air masses—is a genetic clas- by C. W. Thornthwaite in 1948, identified moisture sification. A climate classification determined by statistical regions using the water-budget approach (Chapter 9) and

(text continued on page 283) M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 281

Chapter 10 Global Climate Systems 281

Focus Study 10.1

The El Niño Phenomenon—Global Linkages

Climate is the consistent behavior of cell dominating the eastern Pacific in and eastern Pacific during an ENSO, weather over time, but average weather the Southern Hemisphere. As a result, replacing the normally cold, up- conditions also include extremes that a location such as Guayaquil, Ecuador, welling, nutrient-rich water along depart from normal. The El Niño– normally receives 91.4 cm (36 in.) of Peru’s coastline. Such ocean-surface Southern Oscillation (ENSO) in the precipitation each year under dominant warming, the “warm pool,” may Pacific Ocean forces the greatest in- high pressure, whereas islands in the extend to the International Date Line. terannual variability of temperature Indonesian archipelago receive more This surface pool of warm water and precipitation on a global scale. than 254 cm (100 in.) under dominant is known as El Niño. Thus, the desig- The two strongest ENSO events in low pressure. This normal alignment of nation ENSO is derived—El Niño– 120 years hit in 1997–1998 and pressure is shown in Figure 10.1.2a. Southern Oscillation. This condition 1982–1983. The spring wildflower is shown in Figure 10.1.2b in illustra- bloom in Death Valley in 1998 pro- tion and satellite image. vides visible evidence of the resultant What Is ENSO? The thermocline (boundary of heavy rains (Figure 10.1.1). Peruvians Occasionally, for unexplained reasons, colder, deep-ocean water) lowers in coined the name El Niño (“the boy pressure patterns and surface ocean depth in the eastern Pacific Ocean. child”) because these episodes seem to temperatures shift from their usual The change in wind direction and occur around the traditional Decem- locations. Higher pressure than nor- warmer surface water slows the nor- ber celebration time of Christ’s birth. mal develops over the western Pacific mal upwelling currents that control Actually, El Niños can occur as early and lower pressure develops over the nutrient availability. This loss of nu- as spring and summer and persist eastern Pacific. Trade winds normally trients affects the phytoplankton and through the year. moving from east to west weaken and food chain, depriving many fish, ma- Revisit Figure 6.21 and see that can be reduced or even replaced by rine mammals, and predator birds of the northward-flowing Peru current an eastward (west-to-east) flow. The nourishment. dominates the region off South shifting of atmospheric pressure and Scientists at the National Oceano- America’s west coast. These cold wind patterns across the Pacific is graphic and Atmospheric Admin- waters move toward the equator and the Southern Oscillation. Chapter 6 dis- istration (NOAA) speculate that join the westward movement of the cussed the Pacific Decadal Oscillation ENSO events occurred more than a south equatorial current. (PDO) and its interrelation with dozen times since the fourteenth cen- The Peru current is part of the ENSO. tury. More recently, there was an normal counterclockwise circulation of Sea-surface temperatures in- ENSO in 1982–1983 (second-strongest winds and surface ocean currents crease, sometimes more than 8 C° event), 1986–1987, 1991–1993 (one around the subtropical high-pressure (14 F°) above normal in the central of the longest), and the most intense

(a) 1998 (b) 2002 FIGURE 10.1.1 El Niño’s impact on the desert. Death Valley, southeastern California, in (a) full spring bloom following record rains triggered by the 1997–1998 El Niño and (b) the same scene in spring 2002 in its stark desert grandeur. A dramatic effect caused by changes in the distant tropics of the Pacific Ocean. [Photos by Bobbé Christopherson.] (continued) M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 282

282 Part II The Water, Weather, and Climate Systems Focus Study 10.1 (continued)

SST* 28°C ° (82.4 F) 180° 150° W 30° N EI Nin~o/ EI Nin~a 15° N Indonesia Trade winds International Date Line Darwin, Northern Territory Equator Tahiti, Society Islands SST 25°C (77°F) 0° 40 cm 0 m 0 m Normal sea level Upwelling 50 m

Thermocline Australia South 200 m America

(a) *SST = Sea-surface temperature

SST 28°C 130° E 180° 150° W 30° N

15° N Indonesia International Trade winds Date Line Darwin 0° 30 cm Tahiti Equator 15 cm El Niño 0 m 0 m November 10, 1997 50 m New thermocline Upwelling blocked by Australia warm surface waters South 200 m America

(b)

(g) February 22, 2005 (h) August 26, 2007

FIGURE 10.1.2 Normal, El Niño, and La Niña changes in the Pacific. (a) Normal patterns in the Pacific; (b) El Niño wind and weather patterns across the Pacific Ocean and TOPEX/Poseidon satellite image for November 1997 (white and red colors indicate warmer surface water—a warm pool). (c) TOPEX/Poseidon image of La Niña conditions in transition in the Pacific in October 1998 (purple and blue colors for cooler surface water—a cool pool). (d) A persistent La Niña in a March 2000 satellite image. (e) Image from June 2001 showing no El Niño as equatorial waters slowly warm with sea-surface temperature near normal. (f) The warm pool of waters retreated westward, leaving neutral or a mild La Niña off South America, July 2004 image. (g) More neutral conditions February 22, 2005. (h) La Niña growing in size, August 26, 2007. [(a) and (b) adapted and author corrected from C. S. Ramage, “El Niño.” © 1986 by Scientific American, Inc.; (b)–(e) TOPEX/Poseidon and (f, g, and h) Jason–1 images courtesy of Jet Propulsion Laboratory, NASA.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 283

Chapter 10 Global Climate Systems 283

episode in 1997–1998 that disrupted Center for Atmospheric Research opening photo and discussed in global weather. The PDO shifted into (NCAR) scientist Kevin Trenberth, Chapter 15’s Focus Study 15.1 was in its negative phase in 1999, which El Niños occurred 31% and La Niñas part attributable to the 1982–1983 seems to dampen ENSO cycles and 23% of the time since 1950, with the El Niño. Yet, as conditions vary, other bring drier conditions to the Ameri- remaining 46% of the time the Pacific El Niños have produced drought in can West. being in a more neutral condition. the very regions that flooded during a The expected interval for recur- Don’t look for symmetry and opposite previous episode. rence is 3 to 5 years, but the interval effects between the two events, for Since the 1982–1983 event, and may range from 2 to 12 years. The there is great variability possible, ex- with the development of remote- frequency and intensity of ENSO cept perhaps in Indonesia where re- sensing satellites and computing events increased through the twenti- markable drought (El Niño) and heavy capability, scientists now are able to eth century, a topic of much research rain (La Niña) correlations seem identify the complex global intercon- by scientists to see if there is a relation strong. nections among surface temperatures, to global climate change. Recent pressure patterns in the Pacific, oc- studies suggest ENSO might be more Global Effects Related to ENSO currences of drought in some places, responsive to global change than pre- and La Niña excessive rainfall in others, and the viously thought. Surface temperatures Effects related to ENSO and La Niña disruption of fisheries and wildlife. in the central tropical Pacific returned occur worldwide: droughts in South Discovery of these truly Earth- to near normal (neutral) by mid-2001 Africa, southern India, Australia, and wide relations and spatial impacts is at (Figure 10.1.2e). the Philippines; strong hurricanes in the heart of physical geography. The the Pacific, including Tahiti and climate of one location is related to La Niña—El Niño’s Cousin French Polynesia; and flooding in climates elsewhere, although it should When surface waters in the central the southwestern United States and be no surprise that Earth operates as a and eastern Pacific cool to below mountain states, Bolivia, Cuba, vast integrated system. “It is fascinat- normal by 0.4 C° (0.7 F°) or more, the Ecuador, and Peru. In India, every ing that what happens in one area can condition is dubbed La Niña, Spanish drought for more than 400 years affect the whole world. As to why this for “the girl.” This is a weaker condi- seems linked to ENSO events. The happens, that’s the question of the tion and less consistent than El Niño. Atlantic hurricane season weakens century. Scientists are trying to make There is no correlation in the strength during El Niño years and strengthens order out of chaos,” says NOAA sci- or weakness of each. For instance, fol- during La Niñas. entist Alan Strong. (For ENSO moni- lowing the record 1997–1998 ENSO Precipitation in the southwestern toring and forecasts, see the Climate event, the subsequent La Niña was not United States is greater in El Niño Prediction Center at http://www. as strong as predicted and shared the than La Niña years. The Pacific ncep.noaa.gov/ or the Jet Propulsion Pacific with lingering warm water. Northwest is wetter with La Niña Laboratory at http://topex-www.jpl. Between 1900 and 1998 there than El Niño. El Niño–enhanced nasa.gov/mission/jason-1.html/ or were 13 La Niñas of note, the latest rains in 1998 produced the wildflower http://sealevel.jpl.nasa.gov/science/ in 1988, 1995, late 1998 to 2000 bloom in Death Valley pictured in jason1 or NOAA’s El Niño Theme (Figure 10.1.2c and d), and 2007 Figure 10.1.1. The Colorado River Page at http://www.pmel.noaa.gov/ (Fig. 10.1.2h). According to National flooding shown in the Chapter 9 toga-tao/el-nino/nino-home.html.)

vegetation types. Another empirical classification system is elements used include average monthly temperatures, the Köppen classification system. Wladimir Köppen average monthly precipitation, total annual precipitation, (1846–1940), a German climatologist and botanist, designed air mass characteristics, ocean currents and sea-surface the widely recognized system. His classification work began temperatures, moisture efficiency, insolation, and net ra- with an article on heat zones in 1884 and continued through- diation, among others. As we devise spatial categories and out his career. The first wall map showing world climates, boundaries, we must remember that boundaries really are coauthored with his student Rudolph Geiger, was intro- transition zones of gradual change. The trends and overall duced in 1928 and soon was widely adopted. Köppen contin- patterns of boundary lines are more important than their ued to refine it until his death. In Appendix B, you find a precise placement, especially with the small scales gener- description of his system and the detailed criteria he used to ally used for world maps. For more on boundaries, see distinguish climatic regions. The Köppen system provides us News Report 10.1. an outline and general base map. In this chapter, we focus on temperature and precipitation measurements and, for the desert areas, moisture Classification Categories The basis of any classifica- efficiency. Keep in mind these are measurable results tion system is the choice of criteria or causative factors produced by the climatic elements listed in the last para- used to draw lines between categories. Some climate graph. Figure 10.4 portrays six basic climate categories M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 284

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News Report 10.1

What’s in a Boundary?

The boundary between mesothermal New York City roughly along the for they are shifting. The Inter- and microthermal climates is some- Ohio River, trending westward until governmental Panel on Climate times placed along the isotherm it meets the dry climates in the Change (IPCC, discussed later in this where the coldest month is -3°C southeastern corner of Colorado. In chapter) predicts a 150- to 550-km (26.6°F) or lower. That might be an Figure 10.5 you see this boundary (90- to 350-mi) range of possible accurate criterion for Europe, but for used. A line marking -3°C as the poleward shift of climatic patterns in conditions in North America, the 0°C coldest month would run farther the midlatitudes during this century. (32°F) isotherm is considered more north along Lake Erie and the south- Such change in climate would place appropriate. The difference between ern tip of Lake Michigan. In addition, Ohio, Indiana, and Illinois within the 0 and -3°C isotherms covers an remember that from year to year, climate regimes now experienced in area about the width of the state of the position of the 0°C isotherm Arkansas and Oklahoma. As you ex- Ohio. Remember, these isotherm for January can shift several hundred amine North America in Figure 10.5, lines are really transition zones and do kilometers as weather conditions use the graphic scale to get an idea not mean abrupt change from one vary. of the magnitude of these potential temperature to another. Climate change adds another shifts. Boundaries are indeed A line denoting at least one dimension to this question of accurate dynamic. month below freezing runs from placement of statistical boundaries—

80° ARCTIC OCEAN ARCTIC OCEAN 70°

60° 60°

50° 50° 50° 50°

ATLANTIC PACIFIC 40° 40° 40° 40° OCEAN OCEAN 30° 30° 30° 30°

° ° ° 20 20 ARABIAN 20 160° SEA BAY OF PACIFIC BENGAL 10° 10° 10° OCEAN 140° 130° 120° 110° 100° 90° 0° 50° 60° 70° 80° 90° 140° 150° 0° INDIAN OCEAN 10° 10° 10° 10° 10° 120° 150° 160° 170° ° CORAL SEA ° 20° 20° 20° 20° 20° 20° 20 20

° 30° 30° 30° 30° 30° 30° 30° 30

40° 40° 40° 40° 40° 40° 40° 110° 120° 130° 140° 150° 160° 180° ° ° ° ° 50° 50° 50 50 50 50 0 1,000 2,000 3,000 MILES

0 1,0002,000 3,000 KILOMETERS MODIFIED GOODE'S HOMOLOSINE EQUAL-AREA PROJECTION

Rain forest Tropical Microthermal Highland Monsoon Humid continental (equatorial and tropical) (cold winter) (altitude effects) Savanna Subarctic

Tundra Mesothermal Humid subtropical Polar Ice caps and ice sheets (mild winter) Marine west coast Mediterranean Arid deserts Desert Semiarid steppes

FIGURE 10.4 Climate regions generalized. Global Climate Six general climate categories, keyed to the legend and coloration in the Figure 10.5 map. Maps, World Map Relative to the question asked about your campus and birthplace in the caption to References Figure 10.3, locate these two places on this climate map. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 285

Chapter 10 Global Climate Systems 285

and their regional types that provide us with a structure semiarid steppes (tropical, subtropical hot and for our discussion in this chapter. midlatitude cold) • Tropical (equatorial and tropical latitudes) rain forest (rainy all year) Global Climate Patterns Adding detail to Figure 10.4, monsoon (6 to 12 months rainy) we develop the world climate map presented in Figure 10.5. The following sections describe specific savanna (less than 6 months rainy) climates, organized around each of the main climate cate- • Mesothermal (midlatitudes, mild winter) gories listed previously. An opening box at the beginning humid subtropical (hot summers) of each climate section gives a simple description of the marine west coast (warm to cool summers) climate category and causal elements that are in opera- Mediterranean (dry summers) tion. A world map showing distribution and the featured • Microthermal (mid and high latitudes, cold winter) representative cities also is in the introductory box for humid continental (hot to warm summers) each climate. The names of the climates appear in italics subarctic (cool summers to very cold winters) in the chapter. • Polar (high latitudes and polar regions) Climographs exemplify particular climates for selected cities. A climograph is a graph that shows monthly tem- tundra (high latitude or high altitude) perature and precipitation, location coordinates, average ice caps and ice sheets (perpetually frozen) annual temperature, total annual precipitation, elevation, polar marine the local population, annual temperature range, annual • Highland (compared to lowlands at the same lati- hours of sunshine (if available, as an indication of cloudi- tude, highlands have lower temperatures—recall the ness), and a location map. Along the top of each climo- normal lapse rate) graph are the dominant weather features that are Only one climate category is based on moisture efficiency influential in that climate. as well as temperature: Discussions of soils, vegetation, and major terrestrial biomes that fully integrate these global climate patterns are • Desert (permanent moisture deficits) in Part IV. Table 20.1 synthesizes all this information and arid deserts (tropical, subtropical hot and midlati- enhances your understanding of this chapter, so please tude cold) place a tab on that page and refer to it as you read.

Tropical Climates (equatorial and tropical latitudes)

Tropical climates occupy about 36% of Earth’s surface, including both ocean and land areas—Earth’s most extensive climate category. The tropical climates straddle the equator from about 20° N to 20° S, roughly between the Tropics of Cancer and Capricorn, thus the designation tropical. Tropical Yangon, Myanmar climates stretch northward to the tip of Florida and south- Uaupés, central Mexico, central India, and Southeast Asia. These cli- Brazil Arusha, mates are truly winterless. Consistent daylength and almost Tanzania perpendicular Sun angle throughout the year generate this warmth. Important causal elements include: • Consistent daylength and insolation input, which produce consistently warm temperatures; Tropical rain forest Tropical savanna • Intertropical convergence zone (ITCZ), which brings rain Tropical monsoon as it shifts seasonally with the high Sun; • Warm ocean temperatures and unstable maritime air masses. Tropical climates have three distinct regimes: tropical rain for- 6 to 12 months), and tropical savanna (ITCZ present for less est (ITCZ present all year), tropical monsoon (ITCZ present for than 6 months).

mid-afternoon to late evening inland and earlier in the Tropical Rain Forest Climates day where marine influence is strong along coastlines. The tropical rain forest climate is constantly moist and Precipitation follows the migrating intertropical conver- warm. Convectional thunderstorms, triggered by local gence zone (ITCZ, Chapter 6). The ITCZ shifts north- heating and trade-wind convergence, peak each day from ward and southward with the summer Sun throughout the M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 286

286 Part II The Water, Weather, and Climate Systems

80° ARCTIC OCEAN cA Ice sheet Polar front 70° 70° (variable) Subarctic Tundra

60° 60° mP Highland Subarctic Icelandic mP cP ° Marine low ° 50 Aleutian west coast 50 low Humid Steppe continental

40° 40° Mediterranean Humid ATLANTIC subtropical 30° Desert mT 30° cT SH SH mT mT Atlantic OCEAN Pacific Tropic of Cancer 20° 20° Tropical PACIFIC Tropical Rain forest OCEAN

10° . July 10° C.Z I.T. Tropical mE Monsoon 140° 130° 120° 110° 100° 90° 40° 0° 0° I.T.C.Z. January Equator Tropical Rain forest

10° 10° 10° Tropical Desert Savanna

20° 20° 20° Highland 20° OCEAN CURRENTS (Fig. 6.21) SH Tropic of Capricorn Warm current Desert mT ° ° ° Humid 30° Cool current 30 mT 30 30 subtropical mT

Steppe INTERTROPICAL CONVERGENCE Mediterranean ZONE 40° 40° 40° 40° Figs. 6.10, 6.12 ITCZ July Marine 50° 50° 50° 50° ITCZ January west coast

AIR PRESSURE SYSTEMS (Fig. 6.10) mP SH Subtropical high L Low TROPICAL CLIMATES DESERT CLIMATES H High Tropical rain forest Arid deserts Rainy all year Tropical, subtropical (hot) AIR MASSES (Fig. 8.2) Tropical monsoon Midlatitude (cold) mP Maritime polar (cool, humid) 6 to 12 months rainy Semiarid steppes cP Continental polar (cool, cold, dry) Tropical savanna Tropical, subtropical (hot) Less than 6 months rainy Midlatitude (cold) mT Maritime tropical (warm, humid) cA Continental arctic (very cold, dry) cT Continental tropical (hot, dry summer only) mE Maritime equatorial (warm, wet)

FIGURE 10.5 World climate classification. Annotated on this map are selected air masses, near-shore ocean currents, pressure systems, and the January and July locations of the ITCZ. Use the colors in the legend to locate various climate types; some labels of the climate names appear in italics on the map to guide you. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 287

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ARCTIC OCEAN cA Tundra Polar front (variable) Arctic Circle Tundra Ice cap Subarctic Subarctic Tundra ° mP 60 Marine cP west coast

Humid Steppe 50° continental Highland Desert Steppe Humid mP continental

40° Mediterranean Desert 40° Steppe PACIFIC Highland 30° Steppe Humid 30° subtropical OCEAN SH Desert mT Tropical Tropic of Cancer Desert Monsoon 20° cT I ARABIAN BAY OF Tropical .T. C.Z SEA BENGAL Savanna Tropical . J mT mT uly Steppe Tropical Monsoon 10° Tropical Highland Monsoon Monsoon 140° 10° 0° Tropical 50° 60° mE 70° 80° 90° 0° Rain forest 0° mE Equator Tropical mE Rain forest INDIAN OCEAN

10° Tropical 10° ATLANTIC Savanna 120° Tropical 140° 150° 160° 170° T.C.Z. January Savanna I. CORAL SEA OCEAN I.T.C ary ° ° ° .Z. Janu Steppe ° 20 Desert 20 20 20 SH Steppe SH Desert Desert Tropic of Capricorn SH mT cT 30° mT Humid 30° 30° 30° subtropical Mediterranean Mediterranean Steppe Marine west coast 40° 40° 40° 40°

110° 120° 130° 140° 150° 160° 180° 50° 50° mP 0 1,000 2,000 3,000 MILES mP 0 1,000 2,000 3,000 KILOMETERS Polar front (variable) MODIFIED GOODE'S HOMOLOSINE EQUAL-AREA PROJECTION

MESOTHERMAL CLIMATES MICROTHERMAL CLIMATES POLAR CLIMATES HIGHLANDS Humid subtropical Humid continental Moist all year, hot summer Hot summers: moist all year Tundra Humid subtropical Asian winter-dry Ice cap and ice sheets Winter-dry, hot to warm summers Humid continental Highland temperature effects Marine west coast Mild summers: moist all year Moist all year, warm to cool summers Asian winter-dry Mediterranean Subarctic regions Summer dry, hot to warm summers Cool summers Subarctic regions Very cold winters M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 288

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High rainfall sustains lush evergreen broadleaf tree growth, producing Earth’s equatorial and tropical rain forests (Figure 10.6). The leaf canopy is so dense that little light diffuses to the forest floor, leaving the ground surface dim and sparse in plant cover. Dense surface vegetation occurs along riverbanks, where light is abundant. (Widespread deforestation of Earth’s rain forest is detailed in Chapter 20.) High temperature promotes energetic bacterial action in the soil so that organic material is quickly con- sumed. Heavy precipitation washes away certain minerals and nutrients. The resulting soils are somewhat sterile and can support intensive agriculture only if supplemented by fertilizer. Uaupés, Brazil (Figure 10.7), is characteristic of tropical rain forest. On the climograph you can see that the FIGURE 10.6 The tropical rain forest. lowest-precipitation month receives nearly 15 cm (6 in.), The lush equatorial rain forest and Sangha River, near and the annual temperature range is barely 2 C° (3.6 F°). Ouesso, Congo, Africa. [Photo by BIOS M. Gunther/Peter In all such climates, the diurnal (day-to-night) temperature Arnold, Inc.] range exceeds the annual average minimum–maximum (coolest to warmest) range: Day–night temperatures can range more than 11 C° (20 F°), more than 5 times the year, but it influences tropical rain forest regions all year annual monthly average range. long. Not surprisingly, water surpluses are enormous, The only interruption of tropical rain forest creating the world’s greatest stream discharges in the climates across the equatorial region is in the highlands Amazon and Congo rivers. of the South American Andes and in East Africa (see

ITCZ ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 Station: Uaupés, Brazil Elevation: 86 m (282.2 ft) (14) (100) Lat/long: 0°08' S 67°05' W Population: 10,000 32.5 32 Avg. Ann. Temp.: 25°C (77°F) Ann. Temp. Range: (13) (90) Total Ann. Precip.: 2 C° (3.6 F°) 30.0 27 291.7 cm (114.8 in.) Ann. Hr of Sunshine: 2018 (12) (80)

27.5 21 80° 60° 50° 40° (11) (70) 10° 25.0 16 (10) (60) 0° Uaupés 0° 22.5 10 (50) (9) BRAZIL ° 20.0 4 10 (8) (40) 0(32) 17.5 20° 20° (7) –1 (30) 15.0 –7 ° ° (6) (20) 30 0 1000 MILES 30

12.5 –12 0 1000 KILOMETERS (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30) –40 0 (–40) J FMAMJ J ASOND Month (a)

FIGURE 10.7 Tropical rain forest climate. (a) Climograph for Uaupés, Brazil (tropical rain forest). (b) The rain forest near Uaupés along a tributary of the Rio Negro. [Photo by Will and Deni McIntyre/Photo Researchers, Inc.] (b) M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 289

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Figure 10.5). There, higher elevations produce lower this climate type, as illustrated by the climograph and temperatures; Mount Kilimanjaro is less than 4° south of photograph in Figure 10.8. Mountains prevent cold air the equator, but at 5895 m (19,340 ft) it has permanent masses from central Asia getting into Yangon, resulting in glacial ice on its summit (although this ice is shrinking its high average annual temperatures. due to higher air temperatures). Such mountainous sites About 480 km (300 mi) north in another coastal city, fall within the highland climate category. Sittwe (Akyab), Myanmar, on the bay of Bengal, annual precipitation rises to 515 cm (203 in.) compared to Yangon’s 269 cm (106 in.). Therefore, Yangon is a drier Tropical Monsoon Climates tropical monsoon area than farther north along the coast The tropical monsoon climates feature a dry season that but still receives more than the 250-cm criteria. lasts 1 or more months. Rainfall brought by the ITCZ Tropical monsoon climates lie principally along falls in these areas from 6 to 12 months of the year. coastal areas within the tropical rain forest climatic (Remember, the ITCZ affects the tropical rain forest realm and experience seasonal variation of wind climate region throughout the year.) The dry season oc- and precipitation. Evergreen trees grade into thorn curs when the convergence zone is not overhead. Yangon, forests on the drier margins near the adjoining savanna Myanmar (formerly Rangoon, Burma), is an example of climates.

ITCZ ⎧ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎩

60.2 Station: Yangon, Myanmar* Elevation: 23 m (76 ft) Lat/long: 16°47' N 96°10' E Population: 6,000,000 Avg. Ann. Temp.: 27.3°C (81.1°F) Ann. Temp. Range: Total Ann. Precip.: 5.5 C° (9.9 F°) 55.9 268.8 cm (105.8 in.) 54.7 *(Formerly Rangoon, Burma) MYANMAR

Subtropical 36.8 Subtropical ° ° high high 20 20 ⎧ ⎪ ⎨ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ Sittwe 35.0 38 (14) (100) Yangon 32.5 32 (13) (90) 10° 10° 30.0 27 (12) (80) 27.5 21 INDIAN (11) (70) OCEAN

25.0 16 0 (10) (60) 500 MILES Equator 22.5 10 0 500 KILOMETERS (9) (50) 90° 100° 110° 20.0 4 (8) (40) 0(32) 17.5 (7) –1 (30) 15.0 –7 (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30) –40 0 (–40) J FMAMJ J ASOND Month (a) (b) FIGURE 10.8 Tropical monsoon climate. (a) Climograph for Yangon, Myanmar (formerly Rangoon, Burma) (tropical monsoon); city of Sittwe also noted on map. (b) The monsoonal forest near Malang, Java, at the Purwodadi Botanical Gardens. [Photo by Tom McHugh/Photo Researchers, Inc.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 290

290 Part II The Water, Weather, and Climate Systems

Tropical Savanna Climates Temperatures vary more in tropical savanna climates Tropical savanna climates exist poleward of the tropical rain than in tropical rain forest regions. The tropical savanna forest climates. The ITCZ reaches these climate regions regime can have two temperature maximums during the year for about six months or less of the year as it migrates with because the Sun’s direct rays are overhead twice—before the summer Sun. Summers are wetter than winters be- and after the summer solstice in each hemisphere as the cause convectional rains accompany the shifting ITCZ Sun moves between the equator and the tropic. Dominant when it is overhead. This produces a notable dry condi- grasslands with scattered trees, drought resistant to cope tion when the ITCZ is farthest away and high pressure with the highly variable precipitation, characterize the dominates. Thus, POTET (natural moisture demand) tropical savanna regions. exceeds PRECIP (natural moisture supply) in winter, Arusha, Tanzania, is a characteristic tropical savanna causing water-budget deficits. city (Figure 10.9). This metropolitan area of more

Subtropical Station: Arusha, Tanzania Elevation: 1387 m (4550 ft) ITCZ high Lat/long: 3°24' S 36°42' E Population: 1,368,000 ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎩ Avg. Ann. Temp.: 26.5°C (79.7°F) Ann. Temp. Range: 35.0 38 ° ° (14) (100) Total Ann. Precip.: 4.1 C (7.4 F ) 119 cm (46.9 in.) Ann. Hr of Sunshine: 2600 32.5 32 (13) (90)

30.0 27 0 50 MI (12) (80) 0 50 KM 27.5 21 Nairobi (11) (70) KENYA 25.0 16 (10) (60) 22.5 10 Mt. Kilimanjaro (9) (50) 20.0 4 Arusha (8) (40) Mombasa 17.5 0(32) TANZANIA (7) –1 (30) MASAI ° 15.0 –7 STEPPE Tanga 5 (6) (20) 40° 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30) –40 0 J FMAMJ J ASOND(–40) Month (a)

(b) (c)

FIGURE 10.9 Tropical savanna climate. (a) Climograph for Arusha, Tanzania (tropical savanna); note the intense dry period. (b) Characteristic landscape in Kenya, with plants adapted to seasonally dry water budgets. (c) Extreme northern Australia on the Cape York Peninsula; the tropical savanna features eucalyptus trees, grasses, and conical termite mounds, in an open savanna in Mungkan Kandju National Park. [Photos by (b) Stephen J. Krasemann/DRK Photo; (c) B. G. Thomson, courtesy of The Wilderness Society.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 291

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than 1,368,000 people is east of the famous Serengeti dryness from June to October, which defines changing Plains savanna and Olduvai Gorge, site of human dominant pressure systems rather than annual origins, and north of Tarangire National Park. Tempera- changes in temperature. This region is near the transi- tures are consistent with tropical climates, despite tion to the dryer desert hot-steppe climates to the the elevation (1387 m) of the station. Note the marked northeast.

Mesothermal Climates (midlatitudes, mild winters)

Mesothermal, meaning “middle temperature,” describes these warm and temperate climates where true seasonality begins San Francisco, and seasonal contrasts in vegetation, soil, and human lifestyle Chengdu, CA Bluefield, WV Sevilla, China adaptations are evident. Mesothermal climates occupy the Columbia, SC Nagasaki, Spain second-largest percentage of Earth’s land and sea surface— Japan more than half of Earth’s oceans and about one-third of its land area. Approximately 55% of the world’s population re- sides in these climates.

The mesothermal climates, and nearby portions of the mi- Dunedin, crothermal (cold winter) climates, are regions of great weather New Zealand variability, for these are the latitudes of greatest air mass interaction. Causal elements include: Marine west coast Humid subtropical • Shifting air masses of maritime and continental origin Mediterranean are guided by upper-air westerly winds and undulating Rossby waves and jet streams. • Migrating cyclonic (low-pressure) and anticyclonic (high- pressure) systems bring changeable weather conditions Mesothermal climates have four distinct regimes based on and air mass conflicts. precipitation variability: humid subtropical hot-summer • Sea-surface temperatures of offshore ocean currents (moist all year), humid subtropical winter-dry (hot to warm influence air mass strength: cooler water temperatures summers, in Asia), marine west coast (warm to cool summers, along west coasts (weaken) and warmer water along east moist all year), and Mediterranean (warm to hot summers, dry coasts (strengthen). summers). • Summers transition from hot to warm to cool as you move away from the tropics. Climates are humid, except where subtropical high pressure produces dry summer conditions.

Humid Subtropical Climates Orleans, and Columbia), Nagasaki’s winter precipitation The humid subtropical hot-summer climates are either moist is a bit less because of the effects of the Asian monsoon. all year or have a pronounced winter-dry period, as occurs However, the lower precipitation of winter is not quite in eastern and southern Asia. Maritime tropical air masses dry enough to change its category to a winter-dry. In generated over warm waters off eastern coasts influence comparison to higher rainfall amounts in Nagasaki humid subtropical hot-summer climates during summer. (196 cm, 77 in.), Columbia’s precipitation totals 126.5 cm This warm, moist, unstable air produces convectional (49.8 in.); compare to Atlanta’s 122 cm (48 in.) annually showers over land. In fall, winter, and spring, maritime (Figure 10.11b). tropical and continental polar air masses interact, generat- Humid subtropical winter-dry climates are related to ing frontal activity and frequent midlatitude cyclonic the winter-dry, seasonal pulse of the monsoons. They storms. These two mechanisms produce year-round extend poleward from tropical savanna climates and have precipitation. Overall, precipitation averages 100–200 cm a summer month that receives 10 times more precipita- (40–80 in.) a year. tion than their driest winter month. A representative Nagasaki, Japan (Figure 10.10), is characteristic of station is Chengdu, China. Figure 10.12 demonstrates an Asian humid subtropical hot-summer station, whereas the strong correlation between precipitation and the Columbia, South Carolina, is characteristic of the North high-summer Sun. American climate region (Figure 10.11). Unlike the The habitability of the humid subtropical hot-summer precipitation of humid subtropical hot-summer cities in and humid subtropical winter-dry climates and their ability the United States (Atlanta, Memphis, Norfolk, New to sustain populations are borne out by the concentration M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 292

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Asian monsoon effects ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 (14) (100) 32.5 32 (13) (90) 30.0 27 (12) (80) 27.5 21 (11) (70) 25.0 16 (10) (60) 22.5 10 (9) (50) 20.0 4 (8) (40) 0(32) 17.5 (7) –1 (30) 15.0 –7 (6) (20) (b) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 0 600 MILES (3) (–10) 0 600 KILOMETERS 5.0 –29 (2) (–20)

2.5 –34 50° (1) (–30) –40 CHINA 0 (–40) J FMAMJ J ASOND JAPAN Month Nagasaki FIGURE 10.10 Humid subtropical hot- Station: Nagasaki, Japan Elevation: 27 m (88.6 ft) 30° Lat/long: 32°44' N 129°52' E Population: 1,585,000 PACIFIC summer climate, rainy all year, Asian Avg. Ann. Temp.: 16°C (60.8°F) Ann. Temp. Range: OCEAN region. Total Ann. Precip.: 21 C° (37.8 F°) 20° (a) Climograph for Nagasaki, Japan (humid 195.7 cm (77 in.) Ann. Hr of Sunshine: 2131 110° 130° subtropical). (b) Landscape near Nagasaki. (a) [(b) Photo by Ken Straiton/First Light.]

of people in north-central India, the bulk of China’s Maritime polar air masses—cool, moist, unstable— 1.3 billion people, and the many who live in climatically dominate marine west coast climates. Weather systems form- similar portions of the United States. ing along the polar front and maritime polar air masses The intense summer rains of the Asian monsoon move into these regions throughout the year, making can cause problems, as they did each year between 2004 weather quite unpredictable. Coastal fog, annually totaling and 2007, producing floods in India and Bangladesh. Occa- 30 to 60 days, is a part of the moderating marine influence. sional dramatic thunderstorms and tornadoes are notable Frosts are possible and tend to shorten the growing season. in the southeastern United States, with tornado occur- Marine west coast climates are unusually mild for their rences seemingly breaking previous records each year. latitude. They extend along the coastal margins of the The monsoonal winter-dry climates hold several pre- Aleutian Islands in the North Pacific, cover the southern cipitation records. Cherrapunji, India, in the Assam Hills third of Iceland in the North Atlantic and coastal Scandi- south of the Himalayas, is the all-time precipitation record navia, and dominate the British Isles. It is hard to imagine holder for a single year and for every other time interval that such high-latitude locations can have average monthly from 15 days to 2 years. Because of the summer monsoons temperatures above freezing throughout the year. that pour in from the Indian Ocean and the Bay of Bengal, Unlike the extensive influence of marine west coast re- Cherrapunji has received 930 cm (30.5 ft) of rainfall in gions in Europe, mountains restrict this climate to coastal 1 month and 2647 cm (86.8 ft) in 1 year—both records. environs in Canada, Alaska, Chile, and Australia. The temperate rain forest of Vancouver Island is representative of Marine West Coast Climates these moist and cool conditions (Figure 10.13). (A temper- Marine west coast climates, featuring mild winters and ature graph for Vancouver, British Columbia, appears in cool summers, dominate Europe and other middle-to- Figure 5.12 with a photo of this marine west coast city.) high-latitude west coasts (see Figure 10.5). In the United The climograph for Dunedin, New Zealand, demon- States, these climates with their cooler summers are in strates the moderate temperature patterns and the annual contrast to the hot-summer humid climate of the south- temperature range for a marine west coast city in the eastern United States. Southern Hemisphere (Figure 10.14). M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 293

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Station: Columbia, South Carolina Elevation: 96 m (315 ft) Lat/long: 34° N 81° W Population: 116,000 Avg. Ann. Temp.: 17.3°C (63.1°F) Ann. Temp. Range: Charlotte ° ° Greenville 95 40 Total Ann. Precip.: 20.7 C (37.3 F ) N.C. 126.5 cm (49.8 in.) Ann. Hr of Sunshine: 2800 77 85 S.C. 26 Columbia Athens Myrtle Cyclonic Cyclonic 20 Augusta storm Subtropical storm 17 Beach ° tracks high tracks Macon 95 33 ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎨ ⎪ ⎩ Georgia Charleston 35.0 38 16 ATLANTIC (14) (100) 75 Savannah 32° OCEAN 32.5 32 0 50 MI 95 (13) (90) 80° 79° 0 50 KM ° 30.0 27 Brunswick 31 (12) (80) 27.5 21 (11) (70) 25.0 16 (10) (60) 22.5 10 (9) (50) 20.0 4 (8) (40) 17.5 0(32) (7) –1 (30) 15.0 –7 (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30) –40 0 J FMAMJ J ASOND(–40) (b) Month (a)

FIGURE 10.11 Humid subtropical hot-summer climate, rainy all year, American region. (a) Climograph for Columbia, South Carolina (humid subtropical). Note the more consistent precipitation pattern compared to Nagasaki, as Columbia receives seasonal cyclonic storm activity and summer convection showers within maritime tropical air. (b) The mixed deciduous and evergreen forest in southern Georgia, typical of the humid subtropical southeastern United States. (c) This scene is from the humid subtropical portion of Argentina along the Paraná River, northwest of Buenos Aires. [(b) and (c) Photos by Bobbé (c) Christopherson.]

An interesting anomaly occurs in the eastern United Appalachians and the Pacific Northwest have enticed States. In portions of the Appalachian highlands, in- many emigrants from the East to settle in these climati- creased elevation lowers summer temperatures in the sur- cally familiar environments in the Northwest. rounding humid subtropical hot-summer climate, producing a marine west coast cooler summer. The climograph for Mediterranean Dry-Summer Climates Bluefield, West Virginia (Figure 10.15), reveals marine Across the planet during summer months, shifting cells of west coast temperature and precipitation patterns, despite subtropical high pressure block moisture-bearing winds its location in the east. Vegetation similarities between the from adjacent regions. This shifting of stable, warm to M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 294

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Asian monsoon effects ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 Station: Chengdu, China Elevation: 498 m (1633.9 ft) (14) (100) Lat/long: 30°40' N 104°04' E Population: 2,500,000 32.5 32 Avg. Ann. Temp.: 17°C (62.6°F) Ann. Temp. Range: (13) (90) Total Ann. Precip.: 20 C° (36 F°) 30.0 27 114.6 cm (45.1 in.) Ann. Hr of Sunshine: 1058 (12) (80) 27.5 21 (11) (70) 0 600 MILES 25.0 16 (10) (60) 0 600 KILOMETERS 22.5 10 (9) (50) 20.0 4 50° (8) (40) 0(32) 17.5 (7) –1 (30) 15.0 –7 CHINA (6) (20) 12.5 –12 Chengdu 30° (5) (10) PACIFIC Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 OCEAN (4) (0) 20° 7.5 –23 90° 110° 130° (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30) –40 0 (–40) J FMAMJ J ASOND Month (a)

FIGURE 10.12 Humid subtropical winter-dry climate. (a) Climograph for Chengdu, China (humid subtropical). Note the summer-wet monsoonal precipitation. (b) Landscape of southern interior China characteristic of this winter-dry climate. This valley is near Mount Daliang in Sichuan Province. [Photo by Jin Zuqi/Sovfoto/Eastfoto.] (b)

hot, dry air over an area in summer and away from these regions in the winter creates a pronounced dry-summer and wet-winter pattern. For example, the continental tropical air mass over the Sahara in Africa shifts northward in summer over the Mediterranean region and blocks maritime air masses and cyclonic storm tracks. The Mediterranean climate designation specifies that at least 70% of annual precipitation occurs during the winter months. This is in contrast to the majority of the world that experiences summer-maximum precipitation. Worldwide, cool offshore ocean currents (the Cali- fornia current, Canary current, Peru current, Benguela current, and West Australian current) produce stability in overlying air masses along west coasts, poleward of subtropical high pressure. The world climate map (see Figure 10.5) shows Mediterranean dry-summer climates along the western margins of North America, central Chile, and the southwestern tip of Africa, as well as across southern Australia and the Mediterranean Basin—the cli- FIGURE 10.13 A marine west coast climate. mate’s namesake region. Examine the offshore currents Temperate rain forest in the Macmillan Provincial Park, central along each of these regions on the world climate map. Vancouver Island, British Columbia, Canada (marine west Figure 10.16 compares the climographs of the coast), features a Douglas fir forest, with western red cedar and hemlock. [Photo by Bobbé Christopherson.] Mediterranean dry-summer cities of San Francisco and M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 295

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Cyclonic storm Cyclonic storms tracks (summer convection) ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 35.0 38 (14) (100) (14) (100) 32.5 32 32.5 32 (13) (90) (13) (90) 30.0 27 30.0 27 (12) (80) (12) (80) 27.5 21 27.5 21 (11) (70) (11) (70) 25.0 16 25.0 16 (10) (60) (10) (60) 22.5 10 22.5 10 (9) (50) (9) (50) 20.0 4 20.0 4 (8) (40) (8) (40) 0(32) 17.5 0(32) (7) –1 17.5 (30) (7) –1 (30) 15.0 –7 15.0 –7 (6) (20) (6) (20) 12.5 –12 12.5 –12 (5) (10) Precipitation in centimeters (inches) (5) (10) Temperature ° C ( F)

Precipitation in centimeters (inches) 10.0 –18 Temperature ° C ( F) 10.0 –18 (4) (0) (4) (0) 7.5 –23 7.5 –23 (3) (–10) (3) (–10) 5.0 –29 5.0 –29 (2) (–20) (2) (–20) 2.5 –34 2.5 –34 (1) (–30) (1) (–30) –40 0 (–40) 0 –40 J FMAMJ J ASOND J FMAMJ J ASOND(–40) Month Month Station: Bluefield, West Virginia Elevation: 780 m (2559 ft) Station: Dunedin, New Zealand Elevation: 1.5 m (5 ft) Lat/long: 37°16' N 81°13' W Population: 11,000 Lat/long: 45°54' S 170°31' E Population: 120,000 Avg. Ann. Temp.: Ann. Temp. Range: Avg. Ann. Temp.: 10.2°C (50.3°F) Ann. Temp. Range: 12°C (53.6°F) 21 C° (37.8 F°) Total Ann. Precip.: 14.2 C° (25.5 F°) Total Ann. Precip.: 78.7 cm (31.0 in.) 101.9 cm (40.1 in.) Akron Penn. 80 77 Altoona (a) 71 (a) Pittsburgh 0 400 800 MILES Wheeling 70 68 0 400 800 KILOMETERS 30° Ohio Morgantown Md. R. io S h N O West I AUSTRALIA A Virginia T 66 77 79 N U Virginia 40° 64 Charleston O NEW M Charlottesville ZEALAND N 64 40° 64 I A Bluefield H C 81 A L 0 50 MI A P P Roanoke 0 50 KM Dunedin 81 A 50° (b) 160° 170° 180°

(b)

FIGURE 10.15 Marine west coast climate in the FIGURE 10.14 A Southern Hemisphere marine west coast Appalachians of the East. climate. (a) Climograph for Bluefield, West Virginia (marine west (a) Climograph for Dunedin, New Zealand (marine west coast). coast). (b) Characteristic mixed forest of Dolly Sods (b) Meadow, forest, and mountains on South Island, New Wilderness in the Appalachian highlands. [Photo by David Zealand. [Photo by Brian Enting/Photo Researchers, Inc.] Muench Photography, Inc.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 296

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Cyclonic Subtropical Cyclonic Cyclonic Subtropical Cyclonic storm tracks high storm tracks storm tracks high storm tracks ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩

35.0 38 35.0 38 (14) (100) (14) (100) 32.5 32 32.5 32 (13) (90) (13) (90) 30.0 27 30.0 27 (12) (80) (12) (80) 27.5 21 27.5 21 (11) (70) (11) (70) 25.0 16 25.0 16 (10) (60) (10) (60) 22.5 10 22.5 10 (9) (50) (9) (50) 20.0 4 20.0 4 (8) (40) (8) (40) 0(32) 0(32) 17.5 17.5 (7) –1 (7) –1 (30) (30) 15.0 –7 15.0 –7 (6) (20) (6) (20) 12.5 –12 12.5 –12 (5) (10) (5) (10) Precipitation in centimeters (inches) Precipitation in centimeters (inches) Temperature ° C ( F) Temperature ° C ( F) 10.0 –18 10.0 –18 (4) (0) (4) (0) 7.5 –23 7.5 –23 (3) (–10) (3) (–10) 5.0 –29 5.0 –29 (2) (–20) (2) (–20) 2.5 –34 2.5 –34 (1) (–30) (1) (–30) –40 –40 0 (–40) 0 (–40) J FMAMJ J ASOND JFMAMJJASOND Month Month

Station: San Francisco, California Elevation: 5 m (16.4 ft) Station: Sevilla, Spain Elevation: 13 m (42.6 ft) Lat/long: 37°37' N 122°23' W Population: 747,000 Lat/long: 37°22' N 6°00' W Population: 1,764,000 Avg. Ann. Temp.: Ann. Temp. Range: Avg. Ann. Temp.: Ann. Temp. Range: 14°C (57.2°F) 9 C° (16.2 F°) 18°C (64.4°F) 16 C° (28.8 F°) Total Ann. Precip.: Ann. Hr of Sunshine: Total Ann. Precip.: Ann. Hr of Sunshine: 47.5 cm (18.7 in.) 2975 55.9 cm (22 in.) 2862 (a) (b)

40° Sevilla 40° San Francisco 20°

0° 0° FIGURE 10.16 Mediterranean climates, California and Spain. ° 20° 20 Climographs for (a) San Francisco, California, with its cooler dry

40° 0 3,000 MILES summer and (b) Sevilla, Spain, with its hotter dry summer. 160° 120° 80° 40° 0° 80° 120° 160° (c) Central California Mediterranean landscape of oak savanna. 0 3,000 KILOMETERS (d) The countryside around Olvera, Andalusia, Spain. [Photos by (c) Bobbé Christopherson; (d) Kaz Chiba/Liaison Agency, Inc.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 297

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Sevilla (Seville), Spain. Coastal maritime effects moderate moisture, but water use usually exhausts soil moisture by San Francisco’s climate, producing a cooler summer. The late spring. Large-scale agriculture requires irrigation, transition to a hot summer occurs no more than 24–32 km although some subtropical fruits, nuts, and vegetables (15–20 mi) inland from San Francisco. The photos in are uniquely suited to these conditions. Natural vegeta- Figure 10.16 show oak-savanna landscapes near Olvera, tion features a hard-leafed, drought-resistant variety Spain, and in central California. known locally as chaparral in the western United States. The Mediterranean dry-summer climate brings summer (Chapter 20 discusses local names for this type of vegeta- water-balance deficits. Winter precipitation recharges soil tion in other parts of the world.)

Microthermal Climates (mid- and high-latitudes, cold winters)

Humid microthermal climates have longer winters than Churchill, Verkhoyansk, mesothermal climates, with summer warmth. Here the term Manitoba Russia Moscow, Russia microthermal means cool temperate to cold. Approximately New York, Dalian, China 21% of Earth’s land surface is influenced by these climates, NY equaling about 7% of Earth’s total surface. These climates occur poleward of the mesothermal climates and experience great temperature ranges related to continentality and air mass conflicts. Temperatures decrease with increasing latitude and toward the interior of continental landmasses and result in intensely cold winters. Precipitation varies between moist-all-year regions (the northern tier across the United States and Canada, Hot, humid continental Subarctic, cool summers eastern Europe through the Ural Mountains) and winter-dry Warm, humid continental Subarctic, very cold winters regions associated with the Asian monsoon. In Figure 10.5, note the absence of microthermal climates in the Southern Hemisphere. Because the Southern Hemi- • Hot summers cooling northward from the mesothermal sphere lacks substantial landmasses, microthermal climates climates, and short spring and fall seasons surrounding develop there only in highlands. Important causal elements winters that are cold to very cold. include: • Continental interiors serving as source regions for intense • Increasing seasonality (daylength and Sun altitude) and continental polar (cP) air masses that dominate winter, greater temperature ranges (daily and annually). blocking cyclonic storms. • Upper-air westerly winds and undulating Rossby waves, Microthermal climates have four distinct regimes based on which bring warmer air northward and colder air south- increasing cold with latitude and precipitation variability: ward for cyclonic activity, and convectional thunder- humid continental hot-summer (Chicago, New York); humid storms from mT air masses in summer. continental mild-summer (Duluth, Toronto, Moscow); and • Asian winter-dry pattern for the microthermal climates, subarctic climates featuring cool summers, such as Churchill, increasing east of the Ural Mountains to the Pacific Manitoba, and the formidable extremes of frigid, very cold Ocean and eastern Asia. winters in Verkhoyansk and northern Siberia.

Humid Continental Hot-Summer Climates Kansas) and the approximate location of the 51-cm Humid continental hot-summer climates are differentiated (20-in.) isohyet (line of equal precipitation). Further west, by their annual precipitation distribution. In the summer, the short-grass prairies reflected lower precipitation maritime tropical air masses influence both humid conti- receipts. nental moist-all-year and winter-dry climates. In North The dry winter associated with the vast Asian America, frequent weather activity is possible between landmass, specifically Siberia, results from a dry-winter conflicting air masses—maritime tropical and continental high-pressure anticyclone. The dry monsoons of south- polar—especially in winter. The climograph for New ern and eastern Asia are produced in the winter months York City and photo (Figure 10.17a, c) and Dalian, China by this system, as winds blow out of Siberia toward the (10.17b,d), illustrate these two hot-summer microthermal Pacific and Indian oceans. The Dalian, China, climo- climates. graph demonstrates this dry-winter tendency. The Before European settlement, forests covered the intruding cold of continental air is a significant winter humid continental hot-summer climatic region of the feature. United States as far west as the Indiana–Illinois border. Deep sod made farming difficult for the first settlers Beyond that approximate line, tall-grass prairies extended of the American prairies, as did the climate. However, westward to about the 98th meridian (98° W in central native grasses soon were replaced with domesticated M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:15 AM Page 298

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Cyclonic storm tracks Asian monsoon (summer convection) effects ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 35.0 38 (14) (100) (14) (100) 32.5 32 32.5 32 (13) (90) (13) (90) 30.0 27 30.0 27 (12) (80) (12) (80) 27.5 21 27.5 21 (11) (70) (11) (70) 25.0 16 25.0 16 (10) (60) (10) (60) 22.5 10 22.5 10 (9) (50) (9) (50) 20.0 4 20.0 4 (8) (40) (8) (40) 17.5 0(32) 17.5 0(32) (7) –1 (7) –1 (30) (30) 15.0 –7 15.0 –7 (6) (20) (6) (20) 12.5 –12 12.5 –12 (5) (10) (5) (10) Precipitation in centimeters (inches) Precipitation in centimeters (inches) Temperature ° C ( F) Temperature ° C ( F) 10.0 –18 10.0 –18 (4) (0) (4) (0) 7.5 –23 7.5 –23 (3) (–10) (3) (–10) 5.0 –29 5.0 –29 (2) (–20) (2) (–20) 2.5 –34 2.5 –34 (1) (–30) (1) (–30)

0 –40 0 –40 J FMAMJ J ASOND(–40) J FMAMJ J ASOND(–40) Month Month Station: New York, New York Elevation: 16 m (52.5 ft) Station: Dalian, China Elevation: 96 m (314.9 ft) Lat/long: 40°46' N 74°01' W Population: 8,092,000 Lat/long: 38°54' N 121°54' E Population: 5,550,000 Avg. Ann. Temp.: Ann. Temp. Range: Avg. Ann. Temp.: Ann. Temp. Range: 13°C (55.4°F) 24 C° (43.2 F°) 10°C (50°F) 29 C° (52.2 F°) Total Ann. Precip.: Ann. Hr of Sunshine: Total Ann. Precip.: Ann. Hr of Sunshine: 112.3 cm (44.2 in.) 2564 57.8 cm (22.8 in.) 2762 (a) (b)

40° 40° FIGURE 10.17 Humid continental hot-summer climates, New York Dalian City New York and China. ° 20° 20 Climographs for (a) New York City (humid continental hot 0° 0° summer that is moist all year) and (b) Dalian, China (humid continental hot summer that is dry in winter). (c) The “Literary 20° 20° Walk” with a canopy of American elms in New York City’s 40° 0 3,000 MILES Central Park emerging from winter just as spring and the return 160° 120° 80° 40° 0° 80° 120° 160° of leaves and warmth begin. (d) Dalian, China, cityscape and 0 3,000 KILOMETERS park in summer. [Photos (c) by Bobbé Christopherson; and (d) courtesy of the Paul Louis collection.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 299

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(a) (b) FIGURE 10.18 Central Indiana and Buffalo, NY, landscapes. (a) Typical humid continental deciduous forest and ready-to-harvest soybean field in central Indiana near Zelma in the American Midwest. (b) This forest near Buffalo, NY, with its characteristic mix of maple–beech–birch, with some elm and ash, is in transition as temperatures increase this century. [Photos by Bobbé Christopherson.]

wheat and barley. Various inventions (barbed wire, the in fields to create snowdrifts and thus more moisture self-scouring steel plow, well-drilling techniques, wind- retention on the soil. mills, railroads, and the six-shooter) aided nonnative peo- Characteristic cities are Duluth, Minnesota, and Saint ples’ expansion into the region. In the United States Petersburg, Russia. Figure 10.19 presents a climograph today, the humid continental hot-summer region is the loca- for Moscow, which is at 55° N, or about the same latitude tion of corn, soybean, hog, feed crop, dairy, and cattle as the southern shore of Hudson Bay in Canada. The production (Figure 10.18a). photos of landscapes near Moscow and Sebago Lake, in- The region around Buffalo, New York, is in a climat- land from Portland, Maine, show summer and late winter ic transition from milder to hotter summers. As the aver- scenes, respectively. age July temperature increases further above 22°C The dry-winter aspect of the mild-summer climate (71.6°F), Buffalo’s climatic designation will become more occurs only in Asia, in a far-eastern area poleward of the like that of New York and Chicago. The surrounding winter-dry mesothermal climates. A representative humid forest in the latter half of this century will shift from the continental mild-summer climate along Russia’s east coast is present maple–beech–birch, with some elm and ash, to a Vladivostok, usually one of only two ice-free ports in that dominant oak–hickory–hemlock mix (Figure 10.18b). country. Such shifting of climatic boundaries and their related ecosystems is occurring worldwide. Subarctic Climates Farther poleward, seasonal change becomes greater. The Humid Continental Mild-Summer short growing season is more intense during long summer days. The subarctic climates include vast stretches of Alaska, Climates Canada, northern Scandinavia with their cool summers, and Soils are thinner and less fertile in the cooler microther- Siberian Russia with its very cold winters. Discoveries of min- mal climates, yet agricultural activity is important and erals and petroleum reserves and the Arctic Ocean sea-ice includes dairy cattle, poultry, flax, sunflowers, sugar beets, losses have led to new interest in portions of these regions. wheat, and potatoes. Frost-free periods range from fewer Areas that receive 25 cm (10 in.) or more of precipita- than 90 days in the north to as many as 225 days in tion a year on the northern continental margins and are the south. Overall, precipitation is less than in the hot- covered by the so-called snow forests of fir, spruce, larch, summer regions to the south; however, notably heavier and birch are the boreal forests of Canada and the taiga of snowfall is important to soil-moisture recharge when it Russia. These forests are in transition to the more open melts. Various snow-capturing strategies are in use, in- northern woodlands and to the tundra region of the far cluding fences and tall stubble left standing after harvest north. Forests thin out to the north when the warmest M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 300

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Continental air mass (summer convection) ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 Station: Moscow, Russia Elevation: 156 m (511.8 ft) (14) (100) Lat/long: 55°45' N 37°34' E Population: 11,460,000 32.5 32 Avg. Ann. Temp.: 4°C (39.2°F) Ann. Temp. Range: (13) (90) Total Ann. Precip.: 29 C° (52.2 F°) 30.0 27 57.5 cm (22.6 in.) Ann. Hr of Sunshine: (12) (80) 1597

27.5 21 ° 180° (11) (70) 0 80° 25.0 16 (10) (60) 22.5 10 (9) (50) Moscow RUSSIA 20.0 4 (8) (40) 17.5 0(32) 0 1,200 MILES (7) –1 (30) 0 1,200 KILOMETERS 15.0 –7 (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) (b) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30) –40 0 J FMAMJ J ASOND(–40) Month (a)

(c) FIGURE 10.19 Humid continental mild-summer climate. (a) Climograph for Moscow, Russia (humid continental mild summer). (b) Fields near Saratov, Russia, during the short summer season. (c) Late-winter scene of Sebago Lake and forests inland from Portland, Maine. [(b) Photo by Wolfgang Kaehler/Liaison Agency, Inc.; (c) photo by Bobbé Christopherson.]

month drops below an average temperature of 10°C The subarctic climates that feature a dry and very cold (50°F). During the decades ahead, the boreal forests are winter occur only within Russia. The intense cold of shifting northward into the tundra in response to climate Siberia and north-central and eastern Asia is difficult to change with higher temperatures (Figure 10.20b). comprehend, for these areas experience an average Soils are thin in these lands once scoured by glaciers. temperature lower than freezing for 7 months; minimum Precipitation and potential evapotranspiration both are temperatures of below -68°C (–90°F) were recorded low, so soils are generally moist and either partially or to- there, as described in Chapter 5. Yet summer maximum tally frozen beneath the surface, a phenomenon known as temperatures in these same areas can exceed ϩ37°C permafrost (discussed in Chapter 17). (ϩ98°F). The Churchill, Manitoba, climograph (Figure 10.20) An example of this extreme subarctic climate with shows average monthly temperatures below freezing for very cold winters is Verkhoyansk, Siberia (Figure 10.21). 7 months of the year, during which time light snow cover For 4 months of the year, average temperatures and frozen ground persist. High pressure dominates fall below -34°C (–30°F). Verkhoyansk has probably Churchill during its cold winter—this is the source region the world’s greatest annual temperature range from for the continental polar air mass. Churchill is representa- winter to summer: a remarkable 63 C° (113.4 F°). Win- tive of the subarctic climate, with a cool summer: annual ters feature brittle metals and plastics, triple-thick win- temperature range of 40 C° (72 F°) and low precipitation dowpanes, and temperatures that render straight of 44.3 cm (17.4 in.). antifreeze a solid. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 301

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Continental air mass FIGURE 10.20 Subarctic cool summer climate. ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ (a) Climograph for Churchill, Manitoba (subarctic, cool summer). 35.0 38 (b) Winter scene on the edge of the boreal forest; young pioneer (14) (100) spruce trees move into the tundra. (c) Lone polar bear hunkered 32.5 32 down in a protective dugout next to a frozen pond. (d) Mom and two (13) (90) cubs-of-the-year in the tundra near Hudson Bay, west of Churchill; 30.0 27 (12) (80) characteristic willows in the background. (e) November street scene in Churchill. [All photos by Bobbé Christopherson.] 27.5 21 (11) (70) 25.0 16 Station: Churchill, Manitoba Elevation: 35 m (114.8 ft) (10) (60) Lat/long: 58°45' N 94°04' W Population: 1400 22.5 10 Avg. Ann. Temp.: –7°C (19.4°F) Ann. Temp. Range: (9) (50) Total Ann. Precip.: 40 C° (72 F°) Ann. Hr of Sunshine: 20.0 4 44.3 cm (17.4 in.) (8) (40) 1732 0(32) 17.5 0 1,000 MILES (7) –1 (30) 15.0 –7 0 1,000 KILOMETERS (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 Churchill (4) Polar Bear and (0) 50° 7.5 –23 CANADA High Latitude (3) (–10) Animals Photo 5.0 –29 40° (2) (–20) Galleries 30° 2.5 –34 30° (1) (–30) ° ° ° 0 –40 120 90 70 J FMAMJ J ASOND(–40) (a) Month

(b) (c)

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Continental air mass ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩

35.0 38 Station: Verkhoyansk, Russia Elevation: 137 m (449.5 ft) (14) (100) Lat/long: 67°35' N 133°27' E Population: 1500 32.5 32 Avg. Ann. Temp.: –15°C (5°F) Ann. Temp. Range: (13) (90) Total Ann. Precip.: 63 C° (113.4 F°) 15.5 cm (6.1 in.) 30.0 27 (12) (80) ° 0° 180

60° 27.5 21 80° (11) (70) 170° 25.0 16 (10) (60) Verkhoyansk 150 22.5 10 ° (9) (50) RUSSIA 20.0 4 (8) (40) 0 1,200 MILES 40° 17.5 0(32) (7) –1 (30) 0 1,200 KILOMETERS 15.0 –7 (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30)

0 –40 JF MAMJ J ASOND(–40) Month (a)

(b) FIGURE 10.21 Extreme subarctic cold winter climate. (a) Climograph for Verkhoyansk, Russia (subarctic, very cold winter). (b) Scene in the town of Verkhoyansk during the short summer. [Photo by Dean Conger/National Geographic Society.]

Polar and Highland Climates

The polar climates cover about 19% of Earth’s total surface and about 17% of its land area. These climates have no true summer like that in lower latitudes. Poleward of the Arctic and Antarctic Circles, daylength in summer becomes continuous, yet average monthly temperatures never rise above 10°C (50°F). These temperature conditions are intolerant to tree growth. Daylength, which in part determines the amount of insolation received, and low Sun altitude in the sky are the principal climatic factors in these frozen and barren regions. Yet, in winter, the Sun drops below the horizon poleward of 66.5° Antarctica latitude, producing continuous night. An extended dawn and twilight period eases this seasonal shock a little and reduces Tundra the time of true night. Ice cap and ice sheet Highland Principal climatic factors in these frozen and barren regions are the following: Polar climates have three regimes: tundra (high latitude, or el- • Extremes of daylength between winter and summer evation); ice caps and ice sheet (perpetually frozen); and polar determine the amount of insolation received. marine (oceanic association, slight moderation of extreme • Low Sun altitude even during the long summer days is cold). the principal climatic factor. Also in this climate category we include highland climates, • Extremely low humidity produces low precipitation for even at low latitudes the effects of elevation can produce amounts—these regions are Earth’s frozen deserts. tundra and polar conditions. Glaciers on tropical mountain • Light-colored surfaces of ice and snow reflect substantial summits attest to the cooling effects of elevation. Highland cli- energy away from the ground surface, thus reducing net mates on the map follow the pattern of Earth’s mountain radiation. ranges. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 303

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Tundra Climate Tundra climates are strictly in the Northern Hemi- In a tundra climate, land is under continuous snow cover sphere, except for elevated mountain locations in the South- for 8–10 months, with the warmest month above 0°C yet ern Hemisphere and a portion of the Antarctic Peninsula. never warming above 10°C (50°F). Because of elevation, the summit of Mount Washington in New Hampshire Ice-Cap and Ice-Sheet Climate (1914 m, or 6280 ft) statistically qualifies as a highland Most of Antarctica and central Greenland fall within the tundra climate on a small scale. ice-sheet climate, as does the North Pole, with all months In spring when the snow melts, numerous plants averaging below freezing. Both regions are dominated by appear—stunted sedges, mosses, flowering plants, and dry, frigid air masses, with vast expanses that never warm lichens. Some of the little (7.5-cm-, 3-in.-tall) willows can ex- above freezing. The area of the North Pole is actually a ceed 300 years in age. The September photo shows the sea covered by ice, whereas Antarctica is a substantial con- emerging fall colors of these small plants (Figure 10.22a). tinental landmass covered by Earth’s greatest ice sheet. Much of the area experiences permafrost and ground ice con- For comparison, winter minimums in central Antarctica ditions; these are Earth’s periglacial regions (see Chapter 17). (July) frequently drop below the temperature of solid Approximately 410,500 km2 (158,475 mi2) of Green- carbon dioxide or “dry ice” (–78°C, or -109°F). Ice caps land are ice-free, an area of tundra and rock about the size are smaller in extent than ice sheets, roughly less than of California. The rest of Greenland is ice sheet, covering 50,000 km2 (19,300 mi2), yet they completely bury the 1,756,00 km2 (677,900 mi2). Despite the severe climate, a landscape like an ice sheet. The Vatnajökull Ice Cap in permanent population of 56,500 lives in this province of southeastern Iceland is an example. Denmark. There are only a couple of towns along Green- Antarctica is constantly snow-covered but receives land’s east coast. Ittoqqortoormiit, or Scoresby Sund, has less than 8 cm (3 in.) of precipitation each year. However, 850 permanent residents (Figure 10.22b). Here is a village Antarctic ice has accumulated to several kilometers deep on the tundra. and is the largest repository of freshwater on Earth. Global warming is bringing dramatic changes to Earth’s two ice sheets cover the Antarctic continent and the tundra and its plants, animals, and permafrost ground most of the island of Greenland. Figure 10.23 shows two conditions. In parts of Canada and Alaska, registered tem- scenes of these repositories of multiyear ice. The status of peratures as much as 5 C° above average are a regular this ice is the focus of much attention during the present occurrence, setting many records. As organic peat deposits International Polar Year of scientific research. in the tundra thaw, vast stores of carbon are released to This ice contains a vast historical record of Earth’s at- the atmosphere, further adding to the greenhouse gas mosphere. Within it, evidence of thousands of past volcanic problem. Temperatures in the Arctic are warming at a rate eruptions from all over the world and ancient combinations twice that of the global average increase. of atmospheric gases lie trapped in frozen bubbles.

(b)

East Greenland Photos (a) FIGURE 10.22 Greenland tundra and a small town. (a) Tundra is marked by an uneven, hummocky surface of mounds resulting from an active layer that freezes and thaws with the seasons, as it is here in east Greenland. Large trees are absent in the tundra; however, relatively lush vegetation for the harsh conditions includes willow, dwarf birch and shrubs, sedges, moss, lichen, and cotton grass (white tufts). (b) A town in the tundra, Scoresby Sund fjord in the distance. In the foreground, sledge dogs rest to get ready for the winter’s work ahead. [Photos by Bobbé Christopherson.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 304

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(a) (b) FIGURE 10.23 Earth’s ice sheets—Antarctica and Greenland. High Latitude These are Earth’s frozen freshwater reservoirs. (a) On the Antarctic Peninsula, basaltic mountains Connection and glacial multiyear ice along the Graham Coast and Flandres Bay, Cape Renard in the distance. (b) Three outlet glaciers drain the Greenland ice sheet into the North Atlantic from southeastern Videos Greenland; the glacial front is in retreat. [Photos by Bobbé Christopherson.]

Chapter 17 presents analysis of ice cores taken from Green- Because of marine influences, annual temperature ranges land and the latest one from Antarctica, which pushed the are low. This climate exists along the Bering Sea, the climate record to 800,000 years before the present. southern tip of Greenland, northern Iceland, Norway, and in the Southern Hemisphere, generally over oceans between 50° S and 60° S. Macquarie Island at 54° S in Polar Marine Climate the Southern Ocean, south of New Zealand, is polar ma- Polar marine stations are more moderate than other rine. Precipitation, which frequently falls as sleet (ice polar climates in winter, with no month below pellets), is greater in these regions than in continental Ϫ7°C (20°F), yet they are not as warm as tundra climates. polar climates.

Arid and Semiarid Climates (permanent moisture deficits)

Dry climates are the world’s arid deserts and semiarid regions,

where we consider moisture efficiency along with temperature Lethbridge, Semey, Kazakstan Alberta for understanding the climate. These regions have unique plants, animals, and physical features. Arid and semiarid Albuquerque, NM Ar Riyad, regions occupy more than 35% of Earth’s land area and clearly Saudi Arabia are the most extensive climate over land. The mountains, long vistas, and resilient struggle for life are all magnified by the dryness. Sparse vegetation leaves the Walgett, landscape exposed; moisture demand exceeds moisture sup- NSW ply throughout, creating permanent water deficits (water bal- Australia ance is discussed in Chapter 9). The extent of this dryness distinguishes desert and steppe climatic regions. (In addition, Arid deserts Semiarid steppes refer to specific annual and daily desert temperature regimes, including the highest recorded temperatures, discussed in Chapter 5; surface energy budgets covered in Chapter 4; desert landscapes in Chapter 15; and desert environments in • Continental interiors, particularly central Asia, are far from Chapter 20.) moisture-bearing air masses. Important causal elements in these drylands include • Shifting subtropical high-pressure systems produce semi- • Dry, subsiding air in subtropical high-pressure systems arid steppe lands around the periphery of arid deserts. dominates. Dry climates are distributed by latitude and the amount of • Midlatitude deserts and steppes form in the rain shadow moisture deficits in four distinct regimes: arid deserts (tropical, of mountains, those regions to the lee of precipitation- subtropical hot, midlatitude cold) and semiarid steppes (tropi- intercepting mountains. cal, subtropical hot, midlatitude cold). M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 305

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Desert Characteristics seasonal change than the midlatitude deserts and The world climate map in Figure 10.5 reveals the steppes, where mean annual temperatures are below pattern of Earth’s dry climates, which cover broad 18°C (64.4°F) and freezing winter temperatures are regions between 15° and 30° N and S latitudes. In these possible. areas, subtropical high-pressure cells predominate, with subsiding, stable air and low relative humidity. Under Tropical, Subtropical Hot Desert generally cloudless skies, these subtropical deserts extend to western continental margins, where cool, sta- Climates bilizing ocean currents operate offshore and summer Tropical, subtropical hot desert climates are Earth’s true trop- advection fog forms. The Atacama Desert of Chile, the ical and subtropical deserts and feature annual average Namib Desert of Namibia, the Western Sahara of temperatures above 18°C (64.4°F). They generally reside Morocco, and the Australian Desert each lie adjacent to on the western sides of continents, although Egypt, So- such a coastline. malia, and Saudi Arabia also fall within this classification. Orographic lifting intercepts moisture-bearing Rainfall is from local summer convectional showers. weather systems to create rain shadows along mountain Some regions receive almost no rainfall, whereas others ranges that extend these dry regions into higher latitudes may receive up to 35 cm (14 in.) of precipitation a year. A (Figure 10.24). Note these rain shadows in North and representative subtropical hot desert city is Ar Riya-d¸ (Riyadh), South America on the climate map. The isolated Saudi Arabia (Figure 10.25). interior of Asia, far distant from any moisture-bearing Along the Sahara’s southern margin is a drought- air masses, falls within the dry arid and semiarid climates tortured region. Human populations suffered great hard- as well. ship as desert conditions gradually expanded over their Major subdivisions include: deserts (precipitation homelands. The sparse environment sets the stage for a supply roughly less than one-half of the natural moisture rugged lifestyle and subsistence economies, pictured demand) and semiarid steppes (precipitation supply here near Timbuktu, Mali (Figure 10.25c). Chapter 15 roughly more than one-half of natural moisture de- presents the process of desertification (expanding desert mand). Important is whether precipitation falls princi- conditions). pally in the winter with a dry summer, in the summer Death Valley, California, features such a hot desert with a dry winter, or is evenly distributed. Winter rains climate with an average annual temperature of 24.4°C are most effective because they fall at a time of lower (76°F). July and August average temperatures are 46°C moisture demand. Relative to temperature, the lower- and 45°C (115°F, 113°F), respectively. Temperatures over latitude deserts and steppes tend to be hotter with less 50°C (122°F) are not uncommon.

(a) (b) FIGURE 10.24 Desert landscapes. Desert vegetation is typically xerophytic: drought-resistant, waxy, hard-leafed, and adapted to aridity and low transpiration loss. (a) Ocotillo (to left) and creosote (to right) in the Anza-Borrego Desert, southern California; such plants are particularly well adapted to the harsh environment. (b) Colorful rock formations and view along a winding desert highway in Valley of Fire State Park, southern Nevada. [Photos by Bobbé Christopherson.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 306

306 Part II The Water, Weather, and Climate Systems

Subtropical high pressure ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩

35.0 40°C 38 Station: Ar Riyad- (Riyadh), Elevation: 609 m (1998 ft) (14) (100) Saudi Arabia Population: 5,024,000 ° ° 32.5 32 Lat/long: 24 42'N 46 43' E Ann. Temp. Range: (13) (90) Avg. Ann. Temp.: 26°C (78.8°F) 24 C° (43.2 F°) Total Ann. Precip.: 30.0 27 (12) (80) 8.2 cm (3.2 in.) 27.5 21 (11) (70) 25.0 16 (10) (60) 0 200 400 MILES 22.5 10 0 200 400 KILOMETERS (9) (50) 20.0 4 (8) (40) Baghdad 17.5 0(32) –1 (7) 25° (30) Ar Riyad¸ 15.0 –7 (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 15° (4) (0)

7.5 –23 ° (3) (–10) 45 55° 5.0 –29 (2) (–20) 2.5 –34 (1) (–30) 0 –40 J FMAMJ J ASOND(–40) Month (a)

(b) (c)

FIGURE 10.25 Tropical, subtropical hot desert climate. (a) Climograph for Ar Riy ¯ad¸(Riyadh), Saudi Arabia (tropical, subtropical hot desert). (b) The Arabian desert sand dunes near Ar Riy ¯ad¸. (c) Herders bring a few cattle to market near Timbuktu, Mali, in west Africa. Precipitation has been below normal in the region since 1966. [(b) Photos by Ray Ellis/Photo Researchers, Inc.; and (c) by Betty Press/Woodfin Camp & Associates.]

During this decade there has been much reporting during some days in July and August. Soldiers and civil- from Iraq on the war and related political events. What ians experience temperatures of 50°C (122°F) and higher seemed overlooked in many reports was the fact the in the city. Such readings broke records for Baghdad in air temperatures in Baghdad (located on the map in 2007. In January, averages for Death Valley (11°C; 52°F) Figure 10.25) were actually hotter than Death Valley and Baghdad (9.4°C; 49°F) are comparable. Death Valley M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 307

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Subtropical high; is drier with 5.9 cm of precipitation compared to 14 cm (summer continental tropical) in Baghdad (2.33 in.; 5.5 in.), both low amounts. Bagh- ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 dad’s May to September period is remarkable, with zero (14) (100) 32.5 32 precipitation, dominated as it is by an intense subtropical (13) (90) high-pressure system. (Baghdad is 34 m elevation at 30.0 27 33.3°N. Death Valley is at -54 m elevation at 36.5°N.) (12) (80) 27.5 21 Keep these hot desert climates in mind as you follow (11) (70) 25.0 16 events. (10) (60) 22.5 10 (9) (50) 20.0 4 Midlatitude Cold Desert Climates (8) (40) 17.5 0(32) Midlatitude cold desert climates cover only a small area: the (7) –1 (30) countries along the southern border of Russia, the Gobi 15.0 –7 Desert, and Mongolia in Asia; the central third of Nevada (6) (20) 12.5 –12 (5) (10)

and areas of the American Southwest, particularly at high Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 elevations; and Patagonia in Argentina. Because of lower (4) (0) temperatures and lower moisture-demand values, rainfall 7.5 –23 must be low for a station to qualify as a midlatitude cold (3) (–10) 5.0 –29 desert climate; consequently, total annual average rainfall (2) (–20) 2.5 –34 is only about 15 cm (6 in.). (1) (–30)

A representative station is Albuquerque, New Mexi- 0 –40 co, with 20.7 cm (8.1 in.) of precipitation and an annual JFMAMJJASOND(–40) average temperature of 14°C (57.2°F) (Figure 10.26). Month Note the summer convectional showers on the climo- (a) graph. Across central Nevada stretches a characteristic Station: Albuquerque, Elevation: 1620 m (5315 ft) New Mexico Population: 479,000 expanse of midlatitude cold desert, greatly modified by a Lat/long: 35°03′ N 106°37′ W Ann. Temp. Range: century of livestock grazing (Figure 10.26b). Avg. Ann. Temp.: 14°C (57.2°F) 24 C° (43.2 F°) Total Ann. Precip.: Ann. Hr of Sunshine: 20.7 cm (8.1 in.) 3420

0 1,000 MILES Tropical, Subtropical Hot Steppe 0 1,000 KILOMETERS Climates Tropical, subtropical hot steppe climates generally exist

around the periphery of hot deserts, where shifting sub- 50° tropical high-pressure cells create a distinct summer-dry

and winter-wet pattern. Average annual precipitation in Central Nevada 40°

subtropical hot steppe areas is usually below 60 cm (23.6 in.). Albuquerque 30° Walgett, in interior New South Wales, Australia, provides 30° 120° 70° a Southern Hemisphere example of this climate (Figure 10.27). 90° This climate is seen around the Sahara’s periphery and (b) in the Iran, Afghanistan, Turkmenistan, and Kazakstan region.

Midlatitude Cold Steppe Climates The midlatitude cold steppe climates occur poleward of about 30° latitude and the midlatitude cold desert climates. Such midlatitude steppes are not generally found in the Southern Hemisphere. As with other dry climate regions, rainfall in the steppes is widely variable and undependable, ranging from 20 to 40 cm (7.9 to 15.7 in.). Not all rainfall is convectional, for cyclonic storm tracks penetrate the continents; however, most storms produce little precipitation. Figure 10.28 presents a comparison between Asian and North American midlatitude cold steppe. Consider FIGURE 10.26 Midlatitude cold desert climate. Semey (Semipalatinsk) in Kazakstan (greater temperature (a) Climograph for Albuquerque, New Mexico (midlatitude cold desert). (b) Cold, high desert landscape of the Basin and range, precipitation evenly distributed) and Lethbridge, Range Province in Nevada, east of Ely along highway U.S. 50. Alberta (lesser temperature range, summer maximum This area is in the region shown in the chapter-opening conventional precipitation). photos. [Photo by Bobbé Christopherson.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 308

308 Part II The Water, Weather, and Climate Systems

Subtropical high ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ Global Climate Change 35.0 38 (14) (100) Significant climatic change has occurred on Earth in the 32.5 32 past and most certainly will occur in the future. There is (13) (90) nothing society can do about long-term influences that 30.0 27 (12) (80) cycle Earth through swings from ice ages to warmer peri- 27.5 21 ods. However, our global society must address short-term (11) (70) changes that are influencing global temperatures within 25.0 16 (10) (60) the life span of present generations. This is especially true 22.5 10 since these changes are due to human activities—an an- (9) (50) 20.0 4 thropogenic forcing of climate. (8) (40) Record-high global temperatures have dominated the 17.5 0(32) (7) –1 past two decades—for both land and ocean and for both (30) 15.0 –7 day and night. The record year for warmth was 2005, and (6) (20) all the years since 1995 were near this record. Air temper- 12.5 –12 (5) (10) atures are the highest since recordings began in earnest Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 more than 140 years ago and higher than at any time in (4) (0) the last 120,000 years, according to the ice-core record. 7.5 –23 (3) (–10) This warming trend is very likely* due to a buildup of 5.0 –29 greenhouse gases. Understanding this warming and all its (–20) (2) related impacts is an important applied topic of Earth sys- 2.5 –34 (1) (–30) tems science and an opportunity for spatial analysis in 0 –40 physical geography. J FMAMJ J ASOND(–40) Month (a) Global Warming Twenty years ago, climatologists Richard Houghton and Station: Walgett, New South Elevation: 133 m (436 ft) Wales, Australia Population: 8200 George Woodwell described the present climatic condition: Lat/long: 30°0′ S 148°07′ E Ann. Temp. Range: Avg. Ann. Temp.: 20°C (68°F) 17 C° (31 F°) The world is warming. Climatic zones are shifting. Total Ann. Precip.: 45.0 cm (17.7 in.) Glaciers are melting. Sea level is rising. These are not hypothetical events from a science fiction movie; these 130° changes and others are already taking place, and we expect them to accelerate over the next years as the amounts of carbon dioxide, methane, and other Australia 20° trace gases accumulating in the atmosphere through † Walgett human activities increase. 30° Your author knows this quote well because it has been in 0 600 1,200 MILES 40° every edition of Geosystems since the first edition in 1992.

0 600 1,200 KILOMETERS 150° During the intervening years, we watched global temperatures rise and climate-change science mature. There is a strong scientific consensus that global warming is occurring and that human activities are the cause, namely the burning of fossil fuels. The 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) concluded:

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea

*As a standard scientific reference on climate change, the IPCC uses the (b) following to indicate levels of confidence: Virtually certain Ͼ99% proba- FIGURE 10.27 Tropical, subtropical hot steppe climate. bility of occurrence; Extremely likely Ͼ95%; Very likely Ͼ90%; Likely (a) Climograph for Walgett, New South Wales, Australia Ͼ66%; More likely than not Ͼ50%; Unlikely Ͻ33%; Very unlikely (tropical, subtropical hot steppe). (b) Vast plains characteristic Ͻ10%; and Extremely unlikely Ͻ5%. of north-central New South Wales. [Photo by Otto Rogge/Stock †R. Houghton and G. Woodwell, “Global climate change,” Scientific Market.] American (April 1989): 36. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 309

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Continental air mass ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 35.0 38 Station: Semey (Semipalatinsk), Elevation: 206 m (675.9 ft) (14) (100) Kazakstan Population: 270,500 32.5 32 Lat/long: 50°21' N 80°15' E Ann. Temp. Range: (13) (90) Avg. Ann. Temp.: 3°C (37.4°F) 39 C° (70.2 F°) 30.0 27 Total Ann. Precip.: (12) (80) 26.4 cm (10.4 in.) 27.5 21 (11) (70) 25.0 16 (10) (60) 22.5 10 (9) (50) 20.0 4 (8) (40) 17.5 0(32) (7) –1 (30) 15.0 –7 (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) (b) 5.0 –29 (2) (–20) 2.5 –34 Lethbridge Semey (1) (–30) 40° 40° 0 –40 J FMAMJ J ASOND(–40) Month 0° 0° (a)

40° 0 3,000 MILES Continental air mass ° ° ° ° ° ° ° ° (summer convection) 160 120 80 40 0 80 120 160 (winter cP air mass) 0 3,000 KILOMETERS ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩

35.0 38 (14) (100) 32.5 32 (13) (90) Station: Lethbridge, Alberta Elevation: 910 m (2985 ft) Lat/long: 49°42' N 110°50' W Population: 73,000 30.0 27 ° ° (12) (80) Avg. Ann. Temp.: 2.9 C (37.3 F) Ann. Temp. Range: Total Ann. Precip.: 24.3 C° (43.7 F°) 27.5 21 25.8 cm (10.2 in.) (11) (70) 25.0 16 (10) (60) 22.5 10 (9) (50) 20.0 4 (8) (40) 17.5 0(32) (7) –1 (30) 15.0 –7 (6) (20) 12.5 –12 (5) (10) Precipitation in centimeters (inches) Temperature ° C ( F) 10.0 –18 (4) (0) 7.5 –23 (3) (–10) 5.0 –29 (2) (–20) 2.5 –34 (1) (–30)

0 –40 J FMAMJ J ASOND(–40) Month (c) (d) FIGURE 10.28 Midlatitude cold steppe climates, Kazakstan and Canada. Climograph for (a) Semey (Semipalatinsk) in Kazakstan. (b) Herders in the region near Semey. (c) Climograph for Lethbridge in Alberta. (d) Canadian prairies and grain elevators of southern Alberta. [(b) Photo by Sovfoto/Eastfoto; (d) photo by author.] M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 310

310 Part II The Water, Weather, and Climate Systems

News Report 10.2

Coordinating Global Climate Change Research

A cooperative global network of United released at the end of the year. The NASA agencies, such as Dr. James Nation members participate in the IPCC AR4 involved 2500 scientific ex- Hansen’s work at Goddard Institute United Nations Environment Pro- pert reviews, 800 contributing authors, for Space Studies (GISS, http://www. gramme (UNEP, http://www.unep. 450 lead authors from 130 countries, giss.nasa.gov/), Global Hydrology org) and the World Meteorological Or- and 6 years of work. You can download and Climate Center (GHCC, http:// ganization (WMO, http://www.wmo. their “Summary for Policy Makers” for www.ghcc.msfc.nasa.gov), and at ch/). The World Climate Research free from the www.ipcc.ch/ web site. NOAA agencies at the National Cli- Programme (WCRP, http://wcrp. The Arctic Council (at http:// mate Data Center (NCDC, http:// wmo.int/) and its network under the www.arctic-council.org/) initiated the www.ncdc.noaa.gov/) and the Na- supervision of the Global Climate Ob- Arctic Climate Impact Assessment tional Environmental Satellite, Data, serving System (GCOS, http://www. (ACIA, http://www.acia.uaf.edu/) in and Information Service (NESDIS, wmo.ch/web/gcos/gcoshome.html) 2000; its three working groups com- http://www.nesdis.noaa.gov/), among coordinate data gathering and research. pleted the research—Arctic Monitoring others. The Pew Center on Global The ongoing climate assessment and Assessment Program (AMAP, Climate Change offers credible analy- process within the UNEP is conducted http://www.amap.no/), the Conserva- sis and overview and has issued by the Intergovernmental Panel on tion of Flora and Fauna (CAFF, several policy reports at http://www. Climate Change (IPCC, http://www. http://www.caff.is/), the International pewclimate.org/. ipcc.ch/), whose three working groups Arctic Science Committee (IASC, The multiagency National Ice issued completed reports in 1990, 1992 http://www.iasc.no/), comprised of na- Center is at http://www.natice.noaa. (a supplementary report), 1995, and the tional scientific organizations, including gov/. Important research is done at the Third Assessment Report in 2001. The 18 national academies of science. National Center for Atmospheric latest is the Fourth Assessment Report In the United States, coordination Research (http://www.ncar.ucar.edu/). (AR4), with all three working groups is found at the U.S. Global Change For Canada, information and research reporting in 2007: Working Group I Research Program (http://www.usgcrp. is coordinated by Environment Canada “Climate Change 2007: The Physical gov/). An overall source for information (http://www.ec.gc.ca/climate/). The Basis,” WGII “Climate Change Im- is http://globalchange.gov, which pub- effect of global warming on permafrost, pacts, Adaptation, and Vulnerability,” lishes an on-line monthly summary of which involves half of Canadian and WGIII “Mitigation of Climate all related developments. Also impor- land area, is found at http://www. Change,” and a final Synthesis Report, tant are programs and services at socc.ca/.

level. ...Most of the observed increase in globally Peace Prize with former Vice-President Albert Gore averaged temperatures since the mid-20th century is for their two decades of work raising understanding very likely due to the observed increase in anthro- and awareness about global climate-change science. pogenic greenhouse gas concentrations. This is an The Nobel Committee said that Gore is responsible advance since the Third Assessment Report’s conclusion “. . . for convincing world governments that climate that “most of the observed warming over the last change was real, caused by human activity, and posed a 50 years is likely to have been due to the increase in threat to society.” Various organizations and agencies greenhouse gas concentrations.” Discernible human coordinate and conduct global climate-change research. influences now extend to other aspects of climate, News Report 10.2 offers an overview and contact infor- including ocean warming, continental-average temper- mation for climate-change science. atures, temperature extremes and wind patterns.‡ The Arctic Climate Impact Assessment (ACIA) Symposium met in 2004 and released a lengthy scientific The IPCC, formed in 1988, is an organization operating report. The ACIA summarized: under the United Nations Environment Programme (UNEP) and the World Meteorological Organization Human activities, primarily the burning of fossil fuels (WMO) and is the scientific organization coordinating (coal, oil, natural gas), and secondarily the clearing of global climate-change research, climate forecasts, and land, have increased the concentration of carbon diox- policy formulation. In 2007, the IPCC shared the Nobel ide, methane, and other heat-trapping (“greenhouse”) gases in the atmosphere . . . this is projected to lead ‡IPCC AR4, Working Group I, Climate Change 2007: The Physical Science to significant and persistent changes in climate . . . Basis (Geneva, Switzerland: IPCC Secretariat, 2007), pp. 5, 10. these changes are projected to lead to wide-ranging M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 311

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consequences including significant impact on coastal communities, animal and plant species, water resources, and human health and well being.‡‡

The American Association for the Advancement of Science (AAAS) reported in “The scientific consensus on climate change” (Science 306, December 3, 2004: 1686), the results of a survey of all 928 climate-change papers published in refereed scientific journals between 1993 and 2003. The papers were divided into six categories and analyzed. As study author Naomi Oreskes concluded, “Remarkably, none of the papers disagreed with the consensus position.” There is a consensus that human activities are heating Earth’s surface and lower atmosphere. The author concluded:

This analysis shows that scientists publishing in the peer-reviewed literature agree with IPCC, the National Academy of Sciences, and public statements of their professional societies. Politicians, economists, journalists, and others may have the impression of confusion, disagreement, or discord among climate scientists, but that impression is incorrect . . . there is a scientific consensus on the reality of anthropogenic climate change. FIGURE 10.29 A thousand years of record and the covariance of carbon dioxide and temperature. Carbon emissions, CO2 concentrations, and temperature In terms of paleoclimatology, the science that stud- change correlate over the past 1000 years. This graph was ies past climates (discussed in Chapter 17), proxy indica- prepared before the record-setting temperatures of 2005. By tors (ice-core data, sediments, coral reefs, ancient pollen, May 2007, with CO2 levels at 387 ppm, carbon emissions from tree-ring density, among others) point to the present time fossil-fuel burning were approaching 8 Gt (gigatons, or 8 as the warmest in the last 120,000 years, and further, that billion tons of carbon) annually. Earth systems are in record territory. [Illustration from ACIA, Impacts of a Warming Arctic the increase in temperature during the twentieth century (London: Cambridge University Press, 2004), p. 2. Used by is very likely the largest in any century over the past 1000 permission of ACIA.] years (Figure 10.29). Earth is less than 1 C° (1.8 F°) from equaling the highest average temperature over this time span. The latest Antarctic ice core at the Dome C location Scientists are working to determine the difference pushes this climatic information back 800,000 years between forced fluctuations (human-caused) and unforced (described in Chapter 17). fluctuations (natural) as a key to predicting future climate The rate of warming in the past 30 years exceeds any trends. Figure 10.31 from the IPCC Fourth Assessment comparable period in the entire measured temperature Report shows a comparison of climate models of forcing record, according to NASA scientists. Figure 10.30a plots from solar output changes and volcanoes (shaded blue observed annual temperatures and 5-year mean tempera- area) with anthropogenic (human) forcing (shaded red tures from 1880 through 2006: Worldwide, 2005 was the area) for global, all land, and all ocean regions. The black warmest year; 2006 was fifth warmest but warmest ever line on each graph plots observations from 1906 to 2005. for North America. Clearly, only those coupled climate models that include The map in 10.30b uses the same base period as the anthropogenic factors accurately simulate increasing tem- graph (1951–1980) to give you an idea of temperature peratures. Solar variability and volcanic output alone do anomalies across the globe in 2006. Note the Arctic not explain the increase. region, where new records for land and water tempera- Because the enhanced greenhouse gases are anthro- tures and sea-ice melt were set in 2006 and again broken pogenic in origin, various management strategies are pos- in 2007. Anomalies exceeding 2.5 C° (4.5 F°) are por- sible to reduce human-forced climatic changes. Let’s trayed on the map in the Canadian Arctic and portions of begin by examining the problem at its roots. Greenland, Siberia, and the Antarctic Peninsula. The fact that 2007–2009 is the International Polar Year under- Carbon Dioxide and Global Warming Carbon diox- scores the global scientific concerns about the polar ide and water vapor are the principal radiatively active climates and lands. gases causing Earth’s natural greenhouse effect. Radia- tively active gases include atmospheric gases, such as car- ‡‡ACIA, Impacts of a Warming Arctic (London: Cambridge University bon dioxide (CO2), methane (CH4), nitrous oxide (N2O), Press, 2004), p. 2. chlorofluorocarbons (CFCs), and water vapor, which M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 312

0.8 0.8 0.75

0.65 0.6 0.6

Observed Global Surface Air Temperature

0.4 0.4 Annual mean ) ° 5-year mean

0.2 0.2

Mount Pinatubo 0 effect 0 Temperature change (C

–0.2 –0.2

–0.4 –0.4

Source: J. Hansen 2005 2006 –0.6 –0.6 Global 1880 1900 1920 1940 1960 1980 2000 (a) Year Warming, GISS Surface Tem- 2006 Climate perature Analysis Surface Temperature Anomaly (C°) Change Movie, 1891 to 2006 2006 Annual Mean (b) FIGURE 10.30 Global temperature trends. (a) Global temperature trends from 1880 to 2006. The 0 baseline represents the 1951–1980 global average. Comparing annual temperatures and 5-year mean temperatures gives a sense of overall trends. (b) Temperature map shows temperature anomalies during 2006, fifth- warmest year on record. The coloration represents C° departures from the base period 1951–1980. On the CD-ROM that accompanies this text there is a movie of temperature anomalies from 1881 to 2006 in which you can see the warming patterns over this time span. [(a) and (b) Data courtesy of Dr. James Hansen, C° –3.0 –2.5 –1.5 –1 –0.5 –0.1 0.1 .5 1.0 1.5 2.5 3.8 GISS/NASA, and NCDC/NOAA.] F° –5.4 –4.5 –2.2 –1.8 –0.9 –0.18 0.18 0.9 1.8 2.2 4.5 6.8

FIGURE 10.31 Explaining global temperature changes. Computer models accurately track observed temperature change (black line) when they factor in human-forced influences on climate (red shading). Solar activity and volcanoes do not explain the increases (blue shading). [Graphs from Climate Change 2007: The Physical Science Basis, Working Group I, IPCC Fourth Assessment Report, February 2007: Fig. SPM-4, p. 11.] 312 M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 313

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absorb and radiate longwave energy. Figure 10.32 plots The present CO2 concentration tops anything over changes in three of these greenhouse gases over the past the last 800,000 years in the Dome C ice core. In fact, 10,000 years. over this ice-core record, changes of as much as 30 ppm in These gases are transparent to light but opaque to the CO2 took at least 1000 years, yet, the concentration has longer wavelengths radiated by Earth. Thus, they trans- changed 30 ppm in just the last 17 years. With 4.5% of mit light from the Sun to Earth but delay heat-energy loss the world’s population, the United States continues to to space. While detained, this heat energy is absorbed and produce 24% of global CO2 emissions. China, with 20% emitted over and over, warming the lower atmosphere. As of global population, is responsible for 18% of CO2 emis- concentrations of these greenhouse gases increase, more sions and is increasing its output. Clearly, per capita CO2 heat energy remains in the atmosphere and temperatures emissions in the United States are far above what an aver- increase. age person in China produces.

Methane and Global Warming Another radiatively active gas contributing to the overall greenhouse effect is methane (CH4), which, at more than 1% per year, is increasing in concentration even faster than carbon dioxide. In ice cores, methane levels never topped 750 ppb in the past 800,000 years, yet in Figure 10.32 we see present levels at 1780 ppb. We are at an atmospheric concentration of methane that is higher than at any time in the past 800 millennia. Methane is generated by such organic processes as digestion and rotting in the absence of oxygen (anaerobic processes). About 50% of the excess methane comes from bacterial action in the intestinal tracts of livestock and from organic activity in flooded rice fields. Burning of vegetation causes another 20% of the excess, and bacterial action inside the digestive systems of termite populations also is a significant source. Methane is thought responsible for at least 19% of the total atmospheric warming.

Other Greenhouse Gases Nitrous oxide (N2O) is the third most important greenhouse gas that is forced by human activity—up 17% in atmospheric concentration since 1750, higher than at any time in the past 10,000 years (Figure 10.32). Fertilizer use increases the processes in soil that emit nitrous oxide, although more research is needed to fully understand the relationships. Chlorofluo- rocarbons (CFCs) and other halocarbons also contribute to global warming. CFCs absorb longwave energy missed by carbon dioxide and water vapor in the lower troposphere. As radiatively active gases, CFCs enhance the greenhouse effect in the troposphere and are a cause of ozone depletion and slight cooling in the stratosphere.

Climate Models and Future Temperatures The scientific challenge in understanding climate change is to sense climatic trends in what is essentially a nonlin- FIGURE 10.32 Greenhouse gas changes over the last ear, chaotic natural system. Imagine the tremendous task 10,000 years. of building a computer model of all climatic components Ice-core and modern data show the trends in carbon dioxide, and programming these linkages (shown in Figure 10.1) methane, and nitrous oxide over the last 10,000 years. It is over different time frames and at various scales. immediately obvious that we are living in unique territory on Using mathematical models originally established for these graphs. During May 2007, CO2 passed the 387 ppm forecasting weather, scientists developed a complex com- level, CH4 was at 1780 ppb, and N2O approached 330 ppb. [Graphs from Climate Change 2007: The Physical Science Basis, puter climate model known as a general circulation Working Group I, IPCC Fourth Assessment Report, February model (GCM). There are at least a dozen established 2007: Fig. SPM-1, p. 3.] GCMs now operating around the world. Submodel M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 314

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programs for the atmosphere, ocean, land surface, cryo- Interaction with sphere, and biosphere operate within the GCM. The most adjoining boxes sophisticated models couple atmosphere and ocean sub- models and are known as Atmosphere-Ocean General Circu- Temperature lation Models (AOGCMs). Precipitation The first step in describing a climate is defining a Air pressure manageable portion of Earth’s climatic system for study. Relative humidity Wind Climatologists create dimensional “grid boxes” that extend Sunlight intensity Atmosphere from beneath the ocean to the tropopause, in multiple layers (Figure 10.33). Resolution of these boxes in the atmosphere is about 250 km (155 mi) in the horizontal and 1 km Ocean (0.6 mi) in the vertical; in the ocean the boxes use the same surface horizontal resolution and a vertical resolution of about 200 Ocean to 400 m (650–1300 ft). Analysts deal not only with the cli- Interaction with boxes matic components within each grid layer but also with the above and below interaction among the layers on all sides. A comparative benchmark among the operational GCMs is climatic sensitivity to doubling of carbon dioxide levels in the atmosphere. GCMs do not predict specific temperatures, but they do offer various scenarios of global warming. GCM-generated maps correlate well with the observed global warming patterns experienced since 1990. FIGURE 10.33 A general circulation model scheme. The 2007 IPCC Fourth Assessment Report, using a Temperature, precipitation, air pressure, relative humidity, wind, and sunlight intensity are sampled in myriad grid boxes. variety of GCM forecast scenarios, predicted a range of In the ocean, sampling is limited, but temperature, salinity, average surface warming for this century. Figure 10.34 and ocean current data are considered. The interactions illustrates six of these scenarios, each with its own assump- within a grid layer, and between layers on all six sides, are tions of economics, population, degree of global coopera- modeled in a general circulation model program. tion, and greenhouse gas emission levels. The orange line is the simulation experiment where greenhouse gas emissions are held at 2000 values with no increases. The gray other sources that summarize global impacts emerging from bars give you the best estimate and likely ranges of out- climate change. comes; for example, from a “low forecast” in B1 to a “high forecast” in A1Fl. Even the “B” scenario represents a sig- • The observed pattern of tropospheric warming and nificant increase in global land and ocean temperatures stratospheric cooling is very likely due to greenhouse and will produce consequences. Although regionally vari- gas increases and stratospheric ozone depletion. able and subject to revision, the IPCC temperature change • Widespread changes in extreme temperatures have forecasts for the twenty-first century are: been observed over the last 50 years. Cold days, cold nights, and frost are less frequent, while hot • High forecast: 6.4 C° (11.5 F°) days, hot nights, and heat waves are more frequent. • Middle forecast: 1.8 C°–4.0 C° (3.1 F°–7.2 F°) • Observations since 1961 show the average global • Low forecast: 1.1 C° (2.0 F°) ocean temperature increased to depths of 3000 m Figure 10.35 offers us a look at the world of and the ocean absorbed more than 80% of climate 2020–2029 and 2090–2099 using three scenarios from system heating. Such warming causes thermal several different AOGCMs. Find the three scenarios used expansion of seawater, contributing to sea level rise. for these three pairs of maps on the graph in Figure 10.34. • There is observational evidence of increased You can see from the maps why scientists are concerned intensity of tropical cyclones correlated with about temperature trends in the higher latitudes. increases of tropical sea-surface temperatures. Total “power dissipation” of these storms has Consequences of Global Warming doubled since 1970. Worldwide there are more The consequences of uncontrolled atmospheric warming category 3, 4, and 5 tropical storms than in the are complex. Regional climate responses are expected as previous record. temperature, precipitation, soil-moisture, and air mass char- • Mountain glaciers and snow cover declined on acteristics change. Although the ability to accurately fore- average in both hemispheres, contributing to sea- cast such regional changes is still evolving, some level rise. consequences of warming have been forecasted and in sev- • Mount Kilimanjaro in Africa, portions of the eral regions are already underway.The challenge for science South American Andes, and the Himalayas will is to analyze such effects on a global scale. very likely lose most of their glacial ice within the The following list is a brief overview from the IPCC next two decades, affecting local water resources. Fourth Assessment Report “Summary for Policy Makers” and Glacial ice continues its retreat in Alaska. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 315

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FIGURE 10.34 Model scenarios for surface warming. Ranging from business as usual, lack of international cooperation, and continuation of the use of fossil fuels (“A2Fl”) to a low-emission scenario (“B1”), each scenario spells climatic catastrophe of some degree. Holding emissions at the 2000 concentration (orange line plot) results in the least temperature impacts. [Graph from Climate Change 2007: The Physical Science Basis, Working Group I, IPCC Fourth Assessment Report, February 2007: Fig. SPM-5, p. 14.]

FIGURE 10.35 Model projections of surface temperature for three scenarios. Three pairs of model simulations for 2020–2029 and 2090–2099 for the B1, A1B, and A2 scenarios. The colors are defined in the temperature scale along the bottom. Note the severity of warming in the worst case. Correlate these three cases with the graph in Figure 10.34. [Maps from Climate Change 2007: The Physical Science Basis, Working Group I, IPCC Fourth Assessment Report, February 2007: Fig. SPM-6, p. 15.]

• The average atmospheric water vapor content has • Average Arctic temperatures increased at almost increased over land and ocean as well as in the upper twice the global average rate in the past 100 years. troposphere. The increase is consistent with the fact Wintertime lower atmosphere temperatures over that warmer air can absorb more water vapor. Antarctica are warming at nearly three times the • Flow speed accelerated for some Greenland and global average, first reported in 2006. Antarctic outlet glaciers as they drain ice from the • Temperatures in the permafrost active layer interior of the ice sheets. In Greenland this rate of increased overall since the 1980s in the Arctic up loss exceeds snowfall accumulation, with losses to 3 C°. The maximum area of seasonally frozen per year more than doubling between 1996 and ground decreased 7% in the Northern Hemi- 2005 (mass loses of 91 km3 compared to 224 km3). sphere, with a decrease in spring of up to 15%. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 316

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• Since 1978, annual average Arctic sea ice extent Unfortunately the new 2006–2007 measurements of Green- shrunk in summer by 7.4% per decade, according land’s ice-loss acceleration did not reach the IPCC in time to satellite measurements. September 2007 Arctic for its report. Scientists are considering at least a 1.2-m sea ice extent retreated to its lowest area coverage (3.94-ft) “high case” for estimates of sea-level rise this cen- in the record. tury as more realistic given Greenland’s present losses cou- • Changes in precipitation and evaporation over the pled with mountain glacial ice losses worldwide. Remember oceans and the melting of ice are freshening mid- that a 0.3-m rise in sea level would produce a shoreline and high-latitude oceans and seas, together with retreat of 30 m (98 ft) on average. Here is the concern: increased salinity in low-latitudes. Oceans are The data now available raise concerns that the climate acidifying (lower pH) in response to absorption of system, in particular sea level, may be responding more increasing atmospheric CO . 2 quickly than climate models indicate.... Therate of • Mid-latitude westerly winds strengthened in both sea-level rise for the past 20 years is 25% faster than hemispheres since the 1960s. the rate of rise in any 20-year period in the preceding • More intense and longer droughts have been 115 years. . . . Since 1990 the observed sea-level has observed over wider areas since the 1970s, partic- been rising faster than the rise projected by models.* ularly in the tropics and subtropics. Increased drying linked to higher temperatures and decreased These increases would continue beyond 2100 even if precipitation observed in the Sahel, the Mediter- greenhouse gas concentrations were stabilized. In ranean, southern Africa, parts of southern Asia, Chapter 16, maps present what coastlines will experience Australia, and the American West. in the event of a 1-m rise in sea level. • Higher spring and summer temperatures and A quick survey of world coastlines shows that even a earlier snowmelt are extending the wildfire season moderate rise could bring change of unparalleled propor- and increasing the intensity of wildfires in the tions. At stake are the river deltas, lowland coastal farming western U.S. and elsewhere. valleys, and low-lying mainland areas, all contending with • The frequency of heavy precipitation events increased high water, high tides, and higher storm surges. Particu- over most land areas, consistent with warming and larly tragic social and economic consequences will affect observed increases of atmospheric water vapor. Sig- small island states, which are unable to adjust within their nificantly increased precipitation has been observed in present country boundaries—disruption of biological eastern parts of North and South America, northern systems, loss of biodiversity, reduction in water resources, Europe, and northern and central Asia. and evacuation of residents are among the impacts. • Crop patterns, as well as natural habitats of plants There could be both internal and international migra- and animals, will shift to maintain preferred tion of affected human populations, spread over decades, temperatures. According to climate models, climatic as people move away from coastal flooding caused by the regions in the midlatitudes could shift poleward by sea-level rise—a 1-m rise will displace 130 million people. 150 to 550 km (90 to 350 mi) during this century. Presently, there is no body of world law that covers • Biosphere models predict that a global average of “environmental refugees.” 30% of the present forest cover (varying regionally from 15% to 65%) will undergo major species Political Action and “No Regrets” redistribution—greatest at high latitudes and least Reading through all this climate-change science must in the tropics. seem pretty “heavy.” Instead, think of this information as • Populations previously unaffected by malaria, empowering and as motivation to take action—personally, dengue fever, lymphatic filariasis, and yellow fever locally, regionally, nationally, and globally. (all mosquito vector), schistosomiasis (water snail A product of the 1992 Earth Summit in Rio de Janeiro vector), and sleeping sickness (tsetse fly vector) will was the United Nations Framework Convention on Cli- be at greater risk in subtropical and midlatitude mate Change (FCCC). The leading body of the Conven- areas as temperatures increase the vector ranges. tion is the Conference of the Parties (COP) operated by the countries that ratified the FCCC, 186 countries by 2000. Meetings were held in Berlin (COP-1, 1995) and Changes in Sea Level Sea-level rise must be ex- Geneva (COP-2, 1996). These meetings set the stage for pressed as a range of values that are under constant COP-3 in Kyoto, Japan, in December 1997, where 10,000 reassessment. During the last century, sea level rose participants adopted the Kyoto Protocol by consensus. Sev- 10–20 cm (4–8 in.), a rate 10 times higher than the aver- enteen national academies of science endorsed the Kyoto age rate during the last 3000 years. Protocol. (For updates on the status of the Kyoto Proto- The 2007 IPCC forecast scenarios for global mean col, see http://unfccc.int/2860.php.) The latest 2007 sea-level rise this century, given regional variations, are: gathering, COP-13, was in Bali, Indonesia. • Low forecast: 0.18 m (7.1 in.) • Middle forecast: 0.39 m (15.4 in.) *S. Rahmstorf, et al., “Recent climate observations compared to projec- • High forecast: 0.59 m (23.2 in.) tions,” AAAS Science 316 (May 4, 2007): 709. M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 317

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The Kyoto Protocol binds more-developed countries Benefits that equal or exceed their cost to society include to a collective 5.2% reduction in greenhouse gas emissions reduced energy cost, improved air quality and health, as measured at 1990 levels for the period 2008 to 2012. reduction in tanker spills and oil imports, and deployment Within this group goal, various countries promised cuts: of renewable and sustainable energy sources, among oth- Canada is to cut 6%, the European Union 8%, and Aus- ers. This holds true without even considering the benefits tralia 8%, among many others. The Group of 77 countries of slowing the rate of climate change. For Europe, scien- plus China favor a 15% reduction by 2010. With Russian tists determined that carbon emissions could be reduced ratification in November 2004, the Kyoto Protocol is now to less than half the 1990 level by 2030, at a negative cost. international law, with nearly 140 national signatories; this One key to “no regrets” is the untapped energy-efficiency is without United States participation. potential. The Intergovernmental Panel on Climate Change In the United States, five Department of Energy na- (IPCC) declared that “no regrets” opportunities to reduce tional laboratories (Oak Ridge, Lawrence Berkeley, Pacif- carbon dioxide emissions are available in most countries. ic Northwest, National Renewable Energy, and Argonne) The IPCC Working Group III defines this as follows: reported that the United States can meet the Kyoto carbon emission reduction targets with negative overall costs No regrets options are by definition greenhouse gas (cash benefit savings) ranging from -$7 to -$34 billion. emissions reduction options that have negative net (For more, see Working Group III, Climate Change 2001, costs, because they generate direct and indirect bene- Mitigation, London: Cambridge University Press, 2001, fits that are large enough to offset the costs of imple- pp. 21, 474–76 and 506–507.) menting the options.

Summary and Review—Global Climate Systems

᭿ Define climate and climatology, and explain the differ- ᭿ Review the development of climate classification sys- ence between climate and weather. tems, and compare genetic and empirical systems as ways of classifying climate. Climate is dynamic, not static. Climate is a synthesis of weather phenomena at many scales, from planetary to local, in contrast to Classification is the process of ordering or grouping data in re- weather, which is the condition of the atmosphere at any given lated categories. A genetic classification is based on causative time and place. Earth experiences a wide variety of climatic con- factors, such as the interaction of air masses. An empirical clas- ditions that can be grouped by general similarities into climatic sification is one based on statistical data, such as temperature or regions. Climatology is the study of climate and attempts to dis- precipitation. This text analyzes climate using aspects of both cern similar weather statistics and identify climatic regions. approaches, with a map based on climatological elements. climate (p. 277) classification (p. 280) climatology (p. 278) genetic classification (p. 280) climatic regions (p. 278) empirical classification (p. 280) 1. Define climate and compare it with weather. What is 6. What are the differences between a genetic and an climatology? empirical classification system? 2. Explain how a climatic region synthesizes climate statistics. 7. What are some of the climatological elements used in 3. How does the El Niño phenomenon produce the largest classifying climates? Why each of these? interannual variability in climate? What are some of the changes and effects that occur worldwide? ᭿ Describe the principal climate classification categories ᭿ Review the role of temperature, precipitation, air pressure, other than deserts, and locate these regions on a world map. and air mass patterns used to establish climatic regions. Here we focus on temperature and precipitation measures. Keep Climatic inputs include insolation (pattern of solar energy in the in mind these are measurable results produced by interacting Earth–atmosphere environment), temperature (sensible heat energy elements of weather and climate. These data are plotted on a content of the air), precipitation (rain, sleet, snow, and hail; the supply climograph to display the characteristics of the climate. of moisture), air pressure (varying patterns of atmospheric density), There are six basic climate categories. Temperature and and air masses (regional-sized homogeneous units of air). Climate is precipitation considerations form the basis of five climate the basic element in ecosystems, the natural, self-regulating commu- categories and their regional types: nities of plants and animals that thrive in specific environments. • Tropical (equatorial and tropical latitudes) 4. How do radiation receipts, temperature, air-pressure rain forest (rainy all year) inputs, and precipitation patterns interact to produce monsoon (6 to 12 months rainy) climate types? Give an example from a humid environment and one from an arid environment. savanna (less than 6 months rainy) 5. Evaluate the relationships among a climatic region, • Mesothermal (midlatitudes, mild winters) ecosystem, and biome. humid subtropical (hot summers) M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 318

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marine west coast (warm to cool summers) semiarid regions, with their unique plants, animals, and physical Mediterranean (dry summers) features. The arid and semiarid climates occupy more than 35% of • Microthermal (mid- and high latitudes, cold winters) Earth’s land area, clearly the most extensive climate over land. Major subdivisions are arid deserts in tropical and mid- humid continental (hot to warm summers) latitude areas (precipitation—natural water supply—less than subarctic (cool summers to very cold winters) one-half of natural water demand) and semiarid steppes in tropical • Polar (high latitudes and polar regions) and midlatitude areas (precipitation more than one-half of tundra (high latitude or high altitude) natural water demand). ice caps and ice sheets (perpetually frozen) 19. In general terms, what are the differences among the four polar marine desert classifications? How are moisture and temperature • Highland (compared to lowlands at the same latitude, highlands distributions used to differentiate these subtypes? have lower temperatures—recall the normal lapse rate) 20. Relative to the distribution of arid and semiarid climates, describe at least three locations where they occur across the Only one climate category is based on moisture efficiency globe and the reasons for their presence in these locations. as well as temperature: • Desert (permanent moisture deficits) ᭿ Outline future climate patterns from forecasts presented, arid deserts (tropical, subtropical hot and midlatitude cold) and explain the causes and potential consequences of climate change. semiarid steppes (tropical, subtropical hot and midlatitude cold) climograph (p. 285) Various activities of present-day society are producing climatic changes, particularly a global warming trend. The highest average 8. List and discuss each of the principal climate categories. annual temperatures experienced since the advent of instrumental In which one of these general types do you live? Which measurements have dominated the last 25 years. There is a scien- category is the only type associated with the annual tific consensus building that global warming is related to the distribution and amount of precipitation? anthropogenic impacts on the natural greenhouse effect. 9. What is a climograph, and how is it used to display climatic The 2007 Fourth Assessment Report from the Intergovern- information? mental Panel on Climate Change affirms this consensus. The 10. Which of the major climate types occupies the most land IPCC has predicted surface temperature response to a doubling and ocean area on Earth? of carbon dioxide ranging from an increase of 1.1 C° (2.0 F°) to 11. Characterize the tropical climates in terms of temperature, 6.4 C° (11.5 F°) between the present and 2100. Natural climatic moisture, and location. variability over the span of Earth’s history is the subject of 12. Using Africa’s tropical climates as an example, characterize paleoclimatology. A general circulation model (GCM) the climates produced by the seasonal shifting of the ITCZ forecasts climate patterns and is evolving to greater capability with the high Sun. and accuracy than in the past. People and their political institu- 13. Mesothermal (subtropical and midlatitude, mild winter) tions can use GCM forecasts to form policies aimed at reducing climates occupy the second-largest portion of Earth’s unwanted climate change. entire surface. Describe their temperature, moisture, and precipitation characteristics. paleoclimatology (p. 311) 14. Explain the distribution of the humid subtropical hot-summer general circulation model (GCM) (p. 314) and Mediterranean dry-summer climates at similar latitudes 21. Explain climate forecasts. How do general circulation and the difference in precipitation patterns between the two models (GCMs) produce such forecasts? types. Describe the difference in vegetation associated with 22. Describe the potential climatic effects of global warming on these two climate types. polar and high-latitude regions. What are the implications 15. Which climates are characteristic of the Asian monsoon of these climatic changes for persons living at lower region? latitudes? 16. Explain how a marine west coast climate type can occur in the 23. How is climatic change affecting agricultural and food Appalachian region of the eastern United States. production? Natural environments? Forests? The possible 17. What role do offshore ocean currents play in the spread of disease? distribution of the marine west coast climates? What type of 24. What are the actions being taken at present to delay the fog is formed in these regions? effects of global climate change? What is the Kyoto 18. Discuss the climatic conditions for the coldest places on Protocol? What is the current status of U.S. and Canadian Earth outside the poles. government action on the protocol?

᭿ Explain the precipitation and moisture efficiency criteria used to determine the arid and semiarid climates, and locate them on a world map. The dry and semiarid climates are described by precipitation rather than temperature. Dry climates are the world’s arid deserts and M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:16 AM Page 319

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NetWork

The Geosystems Student Learning Center provides on-line re- for items in the chapter, and in “Destinations” many links to sources for this chapter on the World Wide Web. To begin: interesting related pathways on the Internet. Geosystems Stu- Once at the Center, click on the cover of this textbook, scroll dent Learning Center is found at http://www.prenhall.com/ the Table of Contents menu, and select this chapter. You will christopherson/. find self-tests that are graded, review exercises, specific updates

Critical Thinking

A. The text asked that you find the climate conditions for your (horizontal axis), arranged from “high” to “very low.” campus and your birthplace and locate these two places on Those columns above the “0” value (in red) indicate positive Figures 10.3, 10.4, and 10.5. Briefly describe the informa- forcing, such as the greenhouse gases grouped in the far-left tion sources you used: library, Internet, teacher, and phone column. Columns that fall below the “0” value (in blue) in- calls to state and provincial climatologists. Now, refer to dicate negative forcing, such as the haze from sulfate Appendix B to refine your assessment of climate for the aerosols, fourth column from the left. The vertical line be- two locations. Briefly show how you worked through the tween the markers on each column is an estimate of the un- Köppen climate criteria given in the appendix that estab- certainty range. Where no column appears but there is lished the climate classification for your two cities. instead a line denoting a range, there is no central estimate given present uncertainties, such as for mineral dust. B. Many external factors force climate. The chart “Global and Assume you are a policymaker with a goal of reducing the annual mean radiative forcing for the year 2000, relative to rate of global warming, that is, reducing positive radiative forc- 1750” is presented here (from IPCC Climate Change 2001, ing of the climate system. What strategies do you suggest to The Scientific Basis, Washington: Cambridge University alter the height of the columns and adjust the mix of elements Press, 2001, Figure 3, p. 8, and Figure 6.6, p. 392). that cause warming? Assign priorities to each suggested strate- The estimates of radiative forcing in Watts per square gy to denote most-to-least effective in moderating climate meter units are given on the y-axis (vertical axis). The level change. Brainstorm and discuss your strategies with others. of scientific understanding is noted along the x-axis

The Global Mean Radiative Forcing of the Climate System for the Year 2000, Relative to 1750 3

Halocarbons

2 N2O Aerosols CH4 ⎧ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎩ Black

Warming CO carbon from 2 Tropospheric 1 fossil ozone Mineral fuel Aviation-induced Solar

Dust ⎧ ⎪ ⎨ ⎪ ⎪ ⎩ burning Contrails Cirrus 0

Stratospheric Organic Land- ozone carbon use Aerosol from Biomass (albedo) –1 Sulphate indirect fossil burning ony fuel effect

Cooling burning

Radiative forcing (Watts per square meter) –2

High MediumMedium Low Very Very Very Very Very Very Very Very Low Low Low Low Low Low Low Low

Level of Scientific Understanding