Environmental Problems, Their Causes, and Sustainability 1

ArcticCircleTropic ofCancerNorth PacificAlaskacurrentdriftc urrentCaliforniaGulfstreamLabrador currentCanaries currentNorth Atlantic driftNorthKuroshio currentequatorialOyashiocurrentcurrentEquatorial countercurrentCaribbeancurrentGuinea currentMonsoon driftTropic ofCapricornWest wind driftSouth equatorial currentcurrentPeruBrazilcurrentSouthequatorialcurrentcurrentBenguelaWest wind driftSouth equatorial currentcurrentWest AustralianWest wind driftralianEast AustcurrentAntarcticCirclePolar (ice)Warm temperateHighlandWarm ocean currentSubarctic (snow)DryMajor upwelling zonesCold ocean currentCool temperateTropicalRiverFigure 6-6 Natural capital: generalized map of the earth’s current climate zones, showing the major contributingocean currents and drifts.This evaporation of water creates cyclical convectioncells that circulate air, heat, and moisture both verticallyand from place to place in the troposphere, asshown in Figure 6-9. Trace the flows in this diagram. Tounderstand this cycle, remember two things. First, hotair tends to rise, cool, and release moisture as precipitation.Second, cool air tends to sink, get warmer, and loseits moisture by evaporation (not precipitation).The earth’s air and water circulation patterns andits mixture of continents and oceans lead to an irregulardistribution of climates and patterns of vegetation,as shown in Figure 6-10.Figure 6-7 Seasons in the northern and southern hemispheresare caused by the tilt of the earth’s axis. As the planet makes itsannual revolution around the sun on an axis tilted about 23.5°,various regions are tipped toward or away from the sun. The resultingvariations in the amount of solar energy reaching theearth create the seasons.Spring(sun aims directlyat equator)Summer(northern hemispheretilts toward sun)SolarradiationWinter(northern hemispheretilts away from sun) 23.5 °Fall(sun aims directly at equator)106 CHAPTER 6 Climate and Terrestrial Biodiversity