Environmental Problems, Their Causes, and Sustainability 1

FPO(a) Rays of sunlight penetratethe lower atmosphere andwarm the earth's surface.(b) The earth's surface absorbs much of the incoming (c) As concentrations of greenhousesolar radiation and degrades it to longer-wavelength gases rise, their molecules absorb andinfrared (IR) radiation, which rises into the loweremit more infrared radiation, which addsatmosphere. Some of this IR radiation escapes into space more heat to the lower atmosphere.as heat and some is absorbed by molecules ofgreenhouse gases and emitted as even longerwavelength IR radiation, which warms thelower atmosphere.Figure 6-14 Natural capital: the natural greenhouse effect. Without the atmospheric warming provided bythis natural effect, the earth would be a cold and mostly lifeless planet. According to the widely accepted greenhousetheory, when concentrations of greenhouse gases in the atmosphere rise, the average temperature of thetroposphere rises. (Modified by permission from Cecie Starr, Biology: Concepts and Applications, 4th ed.,Brooks/Cole [Wadsworth] 2000)on the leeward side of high mountains are called therain shadow effect, (Figure 6-15). This is one waysome deserts form.Cities also create distinct microclimates. Bricks,concrete, asphalt, and other building materials absorband hold heat, and buildings block wind flow. Motorvehicles and the climate control systems of buildingsrelease large quantities of heat and pollutants. As a result,cities tend to have more haze and smog, highertemperatures, and lower wind speeds than the surroundingcountryside.Now that you have the basics of climate we canexamine how it applies to ecology.6-3 BIOMES: CLIMATE AND LIFEON LANDWhy Do Different Organisms Livein Different Places? Think ClimateDifferent climates lead to different communitiesof organisms, especially vegetation.Why is one area of the earth’s land surface a desert, anothera grassland, and another a forest? Why do differenttypes of deserts, grasslands, and forests exist? Thegeneral answer to these questions is differences inclimate (Figure 6-6), caused mostly by differences inPrevailing windspick up moisturefrom an ocean.On the windwardside of a mountain range,air rises, cools, andreleases moisture.On the leeward side ofthe mountain range, airdescends, warms, and releaseslittle moisture.Dry habitatsMoist habitatsFigure 6-15 The rain shadow effect is a reduction of rainfall on the side of high mountains facing away fromprevailing surface winds. It occurs when warm, moist air in prevailing onshore winds loses most of its moistureas rain and snow on the windward (wind-facing) slopes of a mountain range. This leads to semiarid and aridconditions on the leeward side of the mountain range and the land beyond. The Mojave Desert (east of theSierra Nevada in California) and Asia’s Gobi Desert are produced by this effect.110 CHAPTER 6 Climate and Terrestrial Biodiversity