Environmental Problems, Their Causes, and Sustainability 1

ter temperatures in the Sierra Nevada and the Rockieswould cause most precipitation to fall as rain ratherthan snow. This would increase flooding during thewinter months and sharply reduce the summer supplyof water for central and southern California.Even larger effects would occur if snow mass in theHimalayas decreased. Such a change could reduce wateravailable in summer for irrigation from the Yellow,Indus, and Ganges Rivers. Irrigation water from theserivers is vital. It is currently used to produce theworld’s two largest wheat harvests in China and inIndia. Also, reduced water flow in the summer fromthe Yangtze River in China would harm the world’slargest rice harvest.Crop and fish production in some areas could be reducedby rising sea levels that would flood river deltas,which are home to some of the world’s most productiveagricultural lands and coastal aquaculture ponds.What Are Some Possible Effects of RisingSea Levels? Seek Higher GroundRising sea levels could flood low-lying coastalwetlands and islands, coral reefs, and parts ofsome of the world’s coastal cities.Another problem with a warmer world is a rise inglobal sea level caused by runoff from melting snowand ice and by the fact that water expands slightlywhen heated. In their 2001 IPCC report, climate scientistsprojected that global sea levels are very likely to riseduring this century (Figure 21-16).The high projected rise in sea level of about 88centimeters (35 inches) would have a number of harmfuleffects. They include the following:■ Threatening half of the world’s coastal estuaries,wetlands (one-third of those in the United States, especiallyin southern Louisiana and southern Florida),and coral reefs■ Disrupting many of the world’s coastal fisheries■ Flooding low-lying barrier islands and causinggently sloping coastlines (especially along the U.S.East Coast) to erode and retreat inland by about1.3 kilometers (0.8 mile)■ Flooding agricultural lowlands and deltas in partsof Bangladesh, India, and China, where much of theworld’s rice is grown■ Contaminating freshwater coastal aquifers withsalt water■ Submerging some low-lying islands in the PacificOcean (the Marshall Islands) and the Indian Ocean(the Maldives, a chain of 1,200 small islands)One comedian jokes that he plans to buy land in Kansasbecause it will probably become valuable beachfrontMean Sea-Level Rises (centimeters)1009080706050403020High ProjectionShanghai, New Orleans,and other low-lying citieslargely underwaterMedium ProjectionMore than a third of U.S.wetlands underwater10Low Projection02010 2020 2030 2040 2050 2060 2070 2080 2090 2100YearFigure 21-16 It is very likely that global sea levels will risefrom 9–88 centimeters (4–35 inches) during this century. If thisoccurs, flooding and coastal erosion would be especially severein heavily populated coastal areas of the tropics and warmtemperate regions. (Data from Intergovernmental Panel onClimate Change, 2000)property. Another boasts that she is not worried becauseshe lives in a houseboat—the “Noah strategy.”On a more serious note, a Netherlands architecturalfirm has designed a prototype for an energy-efficient,floating home for use in areas subject to flooding.21-7 DEALING WITH THE THREATOF GLOBAL WARMINGWhat Are Our Options? The GreatClimate DebateThere is disagreement over what we should doabout the threat of global warming.As we have seen, nearly all climate scientists agree thatthe earth’s temperature is very likely to increase duringthis century and that human activities play a partin this change. Despite this scientific consensus, thereis debate among scientists over the causes of thesechanges (natural or human), how rapidly they mightoccur, the effects on humans and ecosystems, and howwe should respond to this potentially serious longtermglobal threat.Economists and policymakers also disagree overhow we should respond to the threat of climate change.They disagree on whether■ the economic costs of reducing greenhouse gasemissions are higher than the economic benefits.http://biology.brookscole.com/miller14477