Environmental Problems, Their Causes, and Sustainability 1

could reach 6 million (Figure 1-15, p. 17) or more. Someanalysts say these estimates are exaggerated. But evenwith a lower toll this is a serious and largely preventablehuman tragedy.BeechHow Might a Warmer Troposphere AffectOrganisms and Ecosystems? Change isupon Them.A warmer troposphere will change thedistribution and population sizes of wild species,shift locations of some of the world’s ecosystems,and threaten some protected reserves and coralreefs.According to the IPCC, projected change in the temperatureof the troposphere during this century willhave a significant effect on the “distributions, populationsizes, population density, and behavior ofwildlife.” A warmer climate could expand ranges andpopulations of some plant and animal species that canadapt to warmer climates. This should lead to increasedtree and plant growth in parts of the northernUnited States, Canada, Russia, central Asia, and northernEurope. In parts of Scandinavia, for example, birchtrees are taking over traditional reindeer lichen pastures.And the reindeer are having to compete forlichen with elk and red deer moving north.There is also bad news from the IPCC. A warmertroposphere would threaten plant and animal speciesthat could not migrate rapidly enough to new areas(Figure 21-15), species with specialized niches,and those with a narrow tolerance for temperaturechange. And shifts in regional climate would threatenmany parks, wildlife reserves, wilderness areas, wetlands,and coral reefs—thwarting some current effortsto stem the loss of biodiversity. Also, species likelyto do better in a warmer world include certain rapidlymultiplying weeds, insect pests, and disease-carryingorganisms such as mosquitoes and water-bornebacteria.The IPCC says it is very likely that tree deaths willincrease from more disease and higher pest populationsthat would thrive in areas with a warmer climate.It is also very likely that wildfires in forest and grasslandareas with drier climates will increase, destroyingwildlife habitats and, as a result, releasing largeamounts of CO 2 into the troposphere.A 2004 report by the UN Environment Programmeestimated that at least 1 million species (especiallyplant, mammal, butterfly, and bird species) could facepremature extinction by 2050 unless greenhouse gasemissions are drastically reduced. According to theIPCC, ecosystems most likely to be disrupted and losespecies are coral reefs, polar seas, coastal wetlands,arctic and alpine tundra, and high-elevation mountaintops.FuturerangeOverlapPresentrangeFigure 21-15 Possible effects of global warming on thegeographic range of beech trees based on ecologicalevidence and computer models. According to one projection,if CO 2 emissions doubled between 1990 and 2050, beechtrees (now common throughout the eastern United States)would survive only in a greatly reduced range in northernMaine and southeastern Canada. This is only one of anumber tree species whose geographic ranges could bechanged drastically by increased atmospheric warming. Forexample, native sugar maples are likely to disappear in thenortheastern United States. On the other hand, ranges of sometree species adapted to a warm climate would spread. (Datafrom Margaret B. Davis and Catherine Zabinski, University ofMinnesota)How Might a Warmer Troposphere AffectAgriculture? Winners and LosersFood production may increase in some areas anddecrease in others.In a warmer world, agricultural productivity may increasein some areas and decrease in others. For example,some analysts project that warmer temperaturesand increased precipitation at northern latitudes maylead to a northward shift of some agricultural productionfrom the midwestern United States to Canada. Butoverall food production could decrease because soilsin these areas of Canada are generally less fertile thanthose in the midwestern United States.Adecrease in high-elevation snow packs could leadto a sharp decline in agricultural productivity in someheavily irrigated areas. For example, water experts projectincreasing water shortages in areas such as centraland southern California that receive most of their waterin summer months from snow melting on the SierraNevada as well as snowmelt in the Rockies that feedsthe Colorado River (Figure 15-10, p. 314). Warmer win-476 CHAPTER 21 Climate Change and Ozone Loss