Environmental Problems, Their Causes, and Sustainability 1

InputsOutputsEnergyFoodWaterRawmaterialsManufacturedgoodsMoneyInformationSolid wastesWaste heatAir pollutantsWater pollutantsGreenhouse gasesManufactured goodsNoiseWealthIdeasFigure 25-8 Natural capital degradation: Urban areas rarely are sustainable systems. The typical citydepends on large nonurban areas of land and water for huge inputs of matter and energy resources and forlarge outputs of waste matter and heat. For example, according to an analysis by Mathis Wackernagel andWilliam Rees, an area 58 times as large as that of London is needed to supply its residents with resources.They estimate that meeting the needs of all the world’s people at the same rate of resource use as that ofLondon would take at least three more earths.fle noise, provide wildlife habitats, and give aestheticpleasure. As one observer remarked, “Most cities areplaces where they cut down all or most of the trees andthen name the streets after them.”As cities grow and water demands increase, expensivereservoirs and canals must be built and deeperwells drilled. This can deprive rural and wild areas ofsurface water and deplete groundwater faster than it isreplenished.Flooding also tends to be greater in cities, in somecases because they are built on floodplains or in lowlyingcoastal areas subject to natural flooding. Anotherreason is that covering land with buildings, asphalt,and concrete causes precipitation to run off quicklyand overload storm drains. In addition, urban developmentoften destroys or degrades wetlands that actas natural sponges to help absorb excess water.Another threat is that many of the world’s largestcities are in coastal areas (Figure 25-2) that could beflooded sometime in this century if sea levels rise dueto projected global warming.Because of their high population and resource consumption,urban dwellers produce most of the world’sair pollution, water pollution, and solid and hazardouswastes. Also, pollutant levels are generally higher inurban areas because they are produced in a smallerarea and cannot be as readily dispersed and diluted asare those produced in most rural areas.Most urban dwellers are subjected to noise pollution:any unwanted, disturbing, or harmful sound thatimpairs or interferes with hearing, causes stress, hampersconcentration and work efficiency, or causes accidents.Noise levels (Figure 25-9, p. 570) above 65 dBAare considered unacceptable, and prolonged exposureto levels above 85 dBA can cause permanent hearingdamage.In addition, high population densities in urban areascan increase the spread of infectious diseases, especiallyif adequate drinking water and sewage systemsare not available.Cities generally are warmer, rainier, foggier, andcloudier than suburbs and nearby rural areas mostlybecause of their buildings, pavement, and lack ofgreen space. The enormous amounts of heat generatedby cars, factories, furnaces, lights, air conditioners, andheat-absorbing dark roofs and roads in cities create anurban heat island surrounded by cooler suburban andrural areas.Higher CO 2 and soot concentrations from fossilfuel–burning, cars, factories, and buildings intensifythis heat-island effect. The higher CO 2 levels can increaseplant growth, expecially opportunistic speciessuch as ragweed, that can worsen asthma. Also, tinysoot and other particles help deliver pollen, mold, andother allergens deep into the lungs. This may helpexplain why childhood asthma rates have climbedhttp://biology.brookscole.com/miller14569