Environmental Problems, Their Causes, and Sustainability 1

WesterliesNortheast tradesCold deserts 60°NForests30°NHot desertsForests0°EquatorCold,dry airfallsPolar capCell 3 NorthArctic tundraEvergreen60° coniferous forestTemperate deciduousforest and grasslandDesert30°Moist air rises — rainCell 2 NorthCool, dryair fallsCell 1 NorthSoutheast tradesWesterliesForestsCold desertsHot deserts60°S30°SFigure 6-8 The earth’s rotation deflects the movement of the airover different parts of the earth and creates global patterns ofprevailing winds.0°30°60°Polar capTropical deciduous forestEquatorDesertTemperate deciduousforest and grasslandTropicalrain forestTropical deciduous forestCool, dryair fallsCell 2 SouthMoistair rises,cools, andreleasesmoistureas rainCell 1 SouthCold,dry airfallsCell 3 SouthMoist air rises — rainLOWPRESSURECool, dryairFalls, is compressed, warmsHeat releasedradiates to spaceHIGHPRESSURECondensationandprecipitationRises, expands, coolsFigure 6-10 Natural capital: global air circulation and biomes.Heat and moisture are distributed over the earth’s surface byvertical currents that form six large convection cells (Hadleycells) at different latitudes. The direction of airflow and the ascentand descent of air masses in these convection cells determinethe earth’s general climatic zones. The resulting unevendistribution of heat and moisture over the planet’s surface leadsto the forests, grasslands, and deserts that make up the earth’sbiomes.Warm,dry airHIGHPRESSUREFlows toward low pressure,picks up moisture and heatMoist surface warmed by sunHot, wetairLOWPRESSUREFigure 6-9 Transfer of energy by convection in the atmosphere.Convection occurs when matter warms, becomes less dense,and rises within its surroundings. This efficient means of heattransfer occurs in the planet’s interior, oceans, and atmosphere(as shown here). Distribution of heat and water occurs in the atmospherebecause vertical convection currents stir up air in thetroposphere and transport heat and water from one area to anotherin circular convection cells called Hadley cells.How Do Ocean Currents and WindsAffect Regional Climates? Moving Heat andAir AroundOcean currents and winds influence climate byredistributing heat received from the sun from oneplace to another.The oceans absorb heat from the air circulation patternsjust described, with the bulk of this heat absorbednear the warm tropical areas. This heat plusdifferences in water density create warm and coldocean currents (Figure 6-6). These currents, driven bywinds and the earth’s rotation, redistribute heat receivedfrom the sun from one place to another andthus influence climate and vegetation, especially nearcoastal areas. They also help mix ocean waters and distributenutrients and dissolved oxygen needed byaquatic organisms.http://biology.brookscole.com/miller14107