Conservationreducespetroleumimports, savesmoney, and reduces air pollution. In short, conservation is responsiblestewardship of the environment and it makespracticalsense. But its effect on globalwarming is lesscertain. Although a
growingnumber of scientistsbelieve the increasingamount of CO2 in the atmosphere is the majorimpetusbehindglobalwarming, the issue is not yet settled. For example, recentfindingspublished in Natureconcludethat the sun is moreactive now
than at any time in the past 8,000 years. Othernaturalcycles may also be playing a role. Deforestation and otherland use
changescontribute to warming. Towns and cities and the roadsthatconnectthemformheatislandsthatcausesignificantlocal
Scientists are especiallyuncertainabout the globalwarmingroles of watervapor, clouds and particles in the atmosphere.
Watervapor is a muchmorepotentgreenhouse gas thancarbondioxide. If the atmosphereweredevoid of the warm air trapped
by watervapor, the Earthwould be so coldthat the oceanswould be frozen. Warm air can holdmorewatervaporthancool air.
Increasing the watervapor in the atmosphere can trapmoreheat, thusincreasingtemperature. On the otherhand, increasing the
watervapor can alsoincreasecloudcover, whichreduces the solarirradiancethatincreases the temperature. The interactions of
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thesepoorlyunderstoodmechanismscontribute to the uncertainty of globalwarmingmodels. So does the presence of particles
in the atmosphere, which can eitherreflectsunlight (a coolingeffect) or absorb it (a warmingeffect).
The melting of glaciers is powerfulevidencethat the Earth is indeedwarming. Or is it? ConsiderAlaska’s BeringGlacier,
the largest in NorthAmerica. According to NASA’s EarthObservatorywebsite, warmertemperatures and changes in
precipitationover the pastcenturyhavethinned the BeringGlacier by severalhundredmeters. Since 1900 the glacier has
retreatedsome 7.5 miles. It seemsonlylogical to blame the retreat of a massiveglacier on globalwarming, but checking the
temperaturerecordsuggestssomethingelsemust be at work. The temperature has beenmeasured on eitherside of the BeringGlaciersince 1909, and the temperaturerecord at bothsitesdoes not showobviouswarming or coolingtrendsthat are foundelsewherearound the Earth. So why is the giantglacierreceding?
JamesHansen, NASA’s primaryglobalwarmingadvocate, has shownthatsoot may be causingsignificantmelting of
global ice and snow. Majorsources of sootincludeagriculturalfiresaround the world, coal-burningpowerplants in China,
cookingfires in India, and massiveforestfires in Alaska, Canada, and Russia. The smokefromthesefires is clearlyvisible in
NASAsatelliteimages. The possiblerole of soot in meltingglaciersmightsomeday be viewed as a majordiscovery,
particularly if it explains the melting of glaciers, such as BeringGlacier, in the absence of any warmingtrends. Meanwhile,
globalwarmingadvocatescontinue to claimthatwarmingalone is meltingglaciers.
Thisbrings us to the issue of the magnitude of globalwarming, for there is greatcontroversyover the accuracy of
measurementsused to determinetemperaturetrends. The centralissue is thatmanystationsthatmeasuretemperaturearound
the worldhavebecomesurrounded by developmentthatcauses an artificialwarmingeffect. Climatemodelershaveattempted
to removethisheatislandeffect, but there is controversyovertheirsuccess.
【題組】48. According to the passage, which of the following is NOT true?
(A)The vagueunderstanding of naturalcycles and interactionsresults in the uncertainty of warmingeffect.
(B) The role of particles in effecting the atmosphereremainsdebatable in thatthey can raise as well as lower the
(C) The controversialestimations of temperaturetrends may resultfromwarmingeffectsgenerated by artificialdevelopment.
(D) The role of soot in meltingglaciersproves the irrelevance of globalwarming to glacialreceding.
【題組】49. Which of the following is closest to the word “soot” in the fourthparagraph?
(A) Dustproducedwhenbranches are chopped.
(B) Liquidwasteoriginatedwhencoal is mined.
(C) Powdersgeneratedwhencoal or wood is burnt.
(D) Fumesexhaledwhenengines or motors are operating.