Environmental Problems, Their Causes, and Sustainability 1

Table 21-2 Major Characteristics of Global Warming and Ozone DepletionCharacteristic Global Warming Ozone DepletionRegion of atmosphere involved Troposphere. Stratosphere.Major substances involved CO 2 , CH 4 , N 2 O (greenhouse gases). O 3 , O 2 , chlorofluorocarbons (CFCs).Interaction with radiation Molecules of greenhouse gases absorb About 95% of incoming ultraviolet (UV)infared (IR) radiation from the earth’s sur- radiation from the sun is absorbed by O 3face, vibrate, and release longer-wavelength molecules in the stratosphere and does notIR radiation (heat) into the lower troposphere. reach the earth’s surface.This natural greenhouse effect helps warmthe lower troposphere.Nature of problem There is a high (90–99%) probability that CFCs and other ozone-depleting chemicalsincreasing concentrations of greenhouse released into the troposphere by humangases in the troposphere from burningactivities have made their way to the stratofossilfuels,deforestation, and agriculture sphere, where they decrease O 3 concentraareenhancingthe natural greenhouse effect tion. This can allow more harmful UV radiaandraisingthe earth’s average surfacetion to reach the earth’s surface.temperature (Figure 21-2, bottom right, andFigure 21-11, p. 471).Possible consequences Changes in climate, agricultural productivity, Increased incidence of skin cancer, eyewater supplies, and sea level.cataracts, and immune system suppressionand damage to crops and phytoplankton.Possible responses Decrease fossil fuel use and deforestation; Eliminate or find acceptable substitutes forprepare for climate change.CFCs and other ozone-depleting chemicals.South Pole is covered by Antarctica, which containsabout 70% of the earth’s ice.As the atmosphere warms, it causes more convectionthat transfers surplus heat from equatorial topolar areas (Figure 6-10, p. 107). Thus, temperature increasestend to be greater in polar regions. This explainswhy scientists regard the ice- and snow-coveredareas at or near the earth’s poles and as early warningsentinels of changes in the average temperature ofearth’s troposphere. Measurements from the ArcticSea, Greenland, and the northwestern shores of Alaska(Figure 17-9, p. 357) show that floating sea ice aroundthe North Pole (Arctic) and Greenland is melting andthinning faster than it is being formed. For example,less ice covered the Arctic Ocean at the end of 2003than in any year since 1979 when satellites began keepingtrack of such ice (Figure 21-6).Why should we care if there is less ice in the Arctic?The answers lies in the albedo or reflectivity of differentparts of the earth’s surface (Figure 21-7, p. 467).Light-colored surfaces of ice and snow help cool theearth by reflecting 80–90% of incoming sunlight backData collected by Defense Satellite Program (DMSP) Special SensorMicrowave Imager (SSMI), Image: NASAFigure 21-6 Satellite data showing Arctic sea ice in 1979 (left) and in 2003 (right). according to NASA, the icecover shrunk by 9% during this period. [Defense Meteorological Satellite Program (DMSP) Special SensorMicrowave Imager (SSMI)]http://biology.brookscole.com/miller14467