Environmental Problems, Their Causes, and Sustainability 1

SunTroposphereAerosolsGreenhousegasesWarmingfromdecreaseCoolingfromincreaseCO 2 removalby plants andsoil organismsCO 2 emissions fromland clearing,fires, and decayHeat andCO 2 removalHeat andCO 2 emissionsIce and snow coverShallow oceanNatural and human emissionsLand and soil biotoaLong-termstorageDeep oceanFigure 21-9 Natural capital: simplified model of some of the major processes that interact to determine theaverage temperature and greenhouse gas content of the troposphere and thus the earth’s climate.A 2001 report by the National Academy of Sciencesand a 2002 Bush administration report, preparedby various U.S. government agencies for the UnitedNations, reached similar conclusions. In 2004, theAmerican Geophysical Union released a positionstatement that said, “Scientific evidence strongly indicatesthat humans have played a role in the rapidwarming of the past half century.” And it is “virtuallycertain” that increasing greenhouse gases will warmthe planet.IPCC and other climate scientists holding the consensusview agree that current climate models need tobe improved. This is why the very likely projectedrange of average atmospheric temperature during thiscentury is quite broad (Figure 21-11). Scientists arehard at work trying to develop better models and narrowdown such uncertainties.A few climate scientists disagree with the consensusview about future temperature changes in theearth’s atmosphere. They say we know too little abouthow the earth’s climate works to make reliable projectionsabout such changes. They also point out thatsome of the projected climate changes can be beneficialto some regions. And they believe we can use our inge-470 CHAPTER 21 Climate Change and Ozone Loss