Environmental Problems, Their Causes, and Sustainability 1

6-2 CLIMATE: A BRIEFINTRODUCTIONWhat Is Climate? Long-Term Weatherand Global Air CirculationClimate is the average temperature and averageprecipitation of an area over long periods of time,which in turn are affected by global air circulation.Climate is a region’s long-term atmospheric conditions—typicallyover decades. Average temperature andaverage precipitation are the two main factors determininga region’s climate and its effects on people, asshown in Figure 6-5.Figure 6-6 (p. 106) is a generalized map of theearth’s major climate zones. In what type of climatezone do you live?The temperature and precipitation patterns thatlead to different climates are caused primarily by theClimateisthe average weather patterns for an area overa long period of time (30–1,000,000 years).Average PrecipitationIt is determined byandwhich are influenced byAverage Temperatureamount of incoming solar energy per unit area of land,air circulation over the earth’s surface, and water circulation.Solar energy heats the atmosphere, evaporateswater, helps create seasons, and causes air to circulate.Four major factors determine global air circulationpatterns. One is the uneven heating of the earth’s surface.Air is heated much more at the equator, where thesun’s rays strike directly throughout the year, than atthe poles, where sunlight strikes at an angle and thusis spread out over a much greater area. You can observethis effect by shining a flashlight in a darkenedroom on the middle of a spherical object such as abasketball. These differences in the amount of incomingsolar energy help explain why tropical regionsnear the equator are hot, polar regions are cold, andtemperate regions in between generally have intermediateaverage temperatures.Asecond factor is seasonal changes in temperature andprecipitation. The earth’s axis—an imaginary line connectingthe north and south poles—is tilted. Asaresult, various regions are tipped toward oraway from the sun as the earth makes its yearlongrevolution around the sun (Figure 6-7,p. 106). This creates opposite seasons in thenorthern and southern hemispheres.A third factor is rotation of the earth on itsaxis. As the earth rotates, its surface turns fasterbeneath air masses at the equator and slowerbeneath those at the poles. This deflects airmasses moving north and south to the west oreast over different parts of the earth’s surface(Figure 6-8, p. 107). The direction of air movementin these different areas sets upbelts of prevailing winds—major surfacewinds that blow almost continuallyand distribute air and moisture over theearth’s surface.Fourth, properties of air, water, andland affect global air circulation. Heatfrom the sun evaporates ocean waterand transfers heat from the oceans tothe atmosphere, especially nearthe hot equator.latitudealtitudeocean currentsand affectswhere people livehow people livewhat theygrow and eatFigure 6-5 Climate and its effects. (Datafrom National Oceanic and AtmosphericAdministration)http://biology.brookscole.com/miller14105