Featuring a Mixed Hardwood Forest. There Are Bromeliads (Epiphytes) Growing on the Live Oak Trees and a Few on the Cabbage, Or Sabal, Palms
Total Page：16
File Type：pdf, Size：1020Kb
M10_CHRI5988_07_SE_C10.QXD 12/18/07 4:21 AM Page 276 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.] 276 M10_CHRI5988_07_SE_C10.QXD 12/18/07 4:21 AM Page 277 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 ex- tremes, a pattern emerges that constitutes climate. Think of climatic pat- terns 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. 277 M10_CHRI5988_07_SE_C10.QXD 12/15/07 1:14 AM Page 278 278 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 con- ditions, 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 classifica- tion 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,