Environmental Problems, Their Causes, and Sustainability 1

Despite joblessness, squalor, overcrowding, andenvironmental and health hazards, most squatters andslum residents are better off than the rural poor. Withbetter access to family planning programs, they tendto have fewer children and better access to schools.They work, raise families, educate their children, andoften have to care for their parents. Some work togetherto establish water supplies, sewer, and healthcare facilities, and schools. Many squatter settlementsprovide a sense of community and a vital safety net ofneighbors, friends, and relatives.Mexico City is an example of an urban area in crisis.About 18.3 million people—roughly one of everysix Mexicans—live there (Figure 25-2). It is the world’ssecond most populous city, and each year, about210,000 new residents arrive.Mexico City suffers from severe air pollution, closeto 50% unemployment, deafening noise, overcrowding,traffic congestion, inadequate public transportation,and a soaring crime rate. More than one-third ofits residents live in slums called barrios or in squattersettlements without running water or electricity.At least 3 million people have no sewer facilities.This means huge amounts of human waste are depositedin gutters, vacant lots, and open sewers everyday, attracting armies of rats and swarms of flies. Whenthe winds pick up dried excrement, a fecal snow oftenfalls on parts of the city. Open garbage dumps also contributedust and bacteria to the atmosphere. This bacteria-ladenfallout leads to widespread salmonella andhepatitis infections, especially among children.Mexico City has one of the world’s worst photochemicalsmog problems because of a combination oftoo many cars and polluting industries, a sunny climate,and topographical bad luck. The city lies in ahigh-elevation bowl-shaped valley surrounded onthree sides by mountains—ideal conditions for thermalinversions that trap pollutants at ground level(Figure 20-7, top, p. 443). Since 1982, the amount ofcontamination in the city’s air has more than tripled,and breathing that air is said to be roughly equivalentto smoking three packs of cigarettes a day.The city’s air and water pollution cause an estimated100,000 premature deaths per year. Writer CarlosFuentes has nicknamed this megacity “MakesickoCity.”Water demands are pushing the city’s aquifer beyondits limits. Energy costs to extract water havesoared as wells have become much deeper. Withdrawalfrom aquifers caused parts of the city to subsideby 9 meters (30 feet) during the twentieth century.Some areas now subside as much as 30 centimeters(1 foot) a year.The city government has banned cars from a 50-block central zone, required catalytic converters on allcars made after 1991, phased out use of leaded gasoline,and replaced old buses, taxis, and delivery vehicleswith cleaner vehicles running mostly on liquefiedpetroleum gas. The city also planted more than 25 milliontrees to help absorb pollutants and bought someland for use as green space.Some progress has been made. The percentage ofdays each year in which air pollution standards are violatedhas fallen from 50% to 20%. But the city still hasan inadequate mass transportation system and weak,poorly enforced air pollution standards for industriesand motor vehicles. If you were in charge of MexicoCity, what are the three most important things youwould do?xHOW WOULD YOU VOTE? Should squatters around citiesof developing countries be given title to land they live on?Cast your vote online at http://biology.brookscole.com/miller14.25-3 TRANSPORTATION AND URBANDEVELOPMENTHow Do Land Availability and TransportationSystems Affect Urban Development? Stackor SprawlLand availability determines whether a city growsvertically or spreads out horizontally and whetherit relies mostly on mass transportation or theautomobile.The two main types of ground transportation are individual(such as cars, motor scooters, bicycles, andwalking) and mass (mostly buses and rail systems).About 90% of all travel in the world is by foot, bicycle,motor scooter, or bus—mostly because only about 10%of the world’s people can afford a car.Land availability is a key factor determining thetypes of transportation people use. If a city cannotspread outward, it must grow vertically—upwardand downward (below ground)—so it occupies asmall land area with a high population density. Mostpeople living in such compact cities like Hong Kongand Tokyo walk, ride bicycles, or use energy-efficientmass transit.A combination of cheap gasoline, plentiful land,and a network of highways produces dispersed cities.They are found in countries such the United States,Canada, and Australia, where ample land often isavailable for outward expansion. Sprawling cities dependon the automobile; motor vehicles are increasingin both compact and dispersed cities. Today there areabout 700 million cars, trucks, and buses in the world.By 2050, the number of motor vehicles is projected toincrease sevenfold to 3.5 billion—2.5 billion of them intoday’s developing countries.Is this sustainable? No one knows. Some analystsbelieve that phasing in motor vehicles with cleanburninghybrid and fuel cell engines would allow thehttp://biology.brookscole.com/miller14571