Environmental Problems, Their Causes, and Sustainability 1

DroughtUnusually high rainfallUnusually warm periodsEl NiñoFigure 6-13 Typical global climatic effects of anEl Niño–Southern Oscillation. During the 1996–98 ENSO,huge waves battered the California coast, and torrential rainscaused widespread flooding and mudslides. In Peru, floodsand mudslides killed hundreds of people, left about 250,000people homeless, and ruined harvests. Drought in Brazil, Indonesia,and Australia led to massive wildfires in tinder-dryforests. India and parts of Africa also experienced severedrought. A catastrophic ice storm hit Canada and the northeasternUnited States, but the southeastern United States had fewerhurricanes. (Data from United Nations Food and AgricultureOrganization)In an ENSO, often called El Niño, prevailing tropicaltrade winds blowing westward weaken or reversedirection. This warms up surface water along theSouth and North American coasts, which suppressesthe normal upwellings of cold, nutrient-rich water.The decrease in nutrients reduces primary productivityand causes a sharp decline in the populations ofsome fish species.A strong ENSO can trigger extreme weatherchanges over at least two-thirds of the globe (Figure6-13)—especially in lands along the Pacific andIndian Oceans—and distorts the fast-moving jetstream that flows high above North America.La Niña, the reverse of El Niño, cools some coastalsurface waters, and brings back upwellings. TypicallyLa Niña means more Atlantic Ocean hurricanes, colderwinters in Canada and the northeastern United States,and warmer and drier winters in the southeastern andsouthwestern United States. It also usually leads towetter winters in the Pacific Northwest, torrential rainsin Southeast Asia, lower wheat yields in Argentina,and more wildfires in Florida.How Do Gases in the AtmosphereAffect Climate? The Natural GreenhouseEffectWater vapor, carbon dioxide, and other gasesinfluence climate by warming the lower troposphereand the earth’s surface.Small amounts of certain gases play a key role in determiningthe earth’s average temperatures and thusits climates. These gases include water vapor (H 2 O),carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide(N 2 O).Together these gases, known as greenhouse gases,allow mostly visible light and some infrared radiationand ultraviolet (UV) radiation from the sun to passthrough the troposphere. The earth’s surface absorbsmuch of this solar energy. This transforms it to longerwavelengthinfrared radiation, which rises into thetroposphere.Some of this infrared radiation escapes into spaceand some is absorbed by molecules of greenhousegases and emitted into the troposphere in all directionsas even longer wavelength infrared radiation.Some of this released energy is radiated into spaceand some warms the troposphere and the earth’s surface.This natural warming effect of the troposphereis called the greenhouse effect, diagrammed in Figure6-14 (p. 110).The basic principle behind the natural greenhouseeffect is well established. Indeed, without itscurrent concentrations of greenhouse gases (especiallywater vapor, which is found in the largest concentration),the earth would be a cold and mostly lifelessplanet.Human activities such as burning fossil fuels,clearing forests, and growing crops release carbondioxide, methane, and nitrous oxide into the troposphere.There is concern that these large inputs ofgreenhouse gases can enhance the earth’s naturalgreenhouse effect and lead to global warming—more onthis in Chapter 21. This could alter precipitation patterns,shift areas where we can grow crops, raise averagesea levels, and shift areas where some types ofplants and animals can live.How Does Topography of the Earth’s SurfaceAffect Local Climate? Creating Deserts andWarming CitiesMountains and cities affect local and regionalclimates.Various topographic features of the earth’s surface cancreate local and regional climatic conditions that differfrom the general climate of a region. For example,mountains interrupt the flow of prevailing surfacewinds and the movement of storms. When moist airblowing inland from an ocean reaches a mountainrange, it cools as it is forced to rise and expand. Thiscauses the air to lose most of its moisture as rain andsnow on the windward (wind-facing) slopes.As the drier air mass flows down the leeward(away from the wind) slopes, it draws moisture out ofthe plants and soil over which it passes. The lower precipitationand the resulting semiarid or arid conditionshttp://biology.brookscole.com/miller14109