如果你看过动画片《冰河时代》，一定对那番冰天雪地的场景记忆犹新。最新研究显示，数万年之后，地球又将进入冰川期，整个北半球都将被厚厚的冰雪覆盖。那么现在最让人们头疼的
温室效应
能阻止下一个冰川期的来临吗？
Emissionsofgreenhousegases—suchasthecarbondioxide,orCO2,thatcomesfrompowerplantsandcars—areheatingtheatmospheretosuchanextentthatthenexticeage,predictedtobethedeepestinmillionsofyears,
may
bepostponedindefinitely.
Inabout10,000to100,000years,thestudysuggests,Antarctic-like"permanent"icesheetswouldshroudmuchofCanada,Europe,andAsia."Ithinkthepresentcarbondioxidelevelsareprobablysufficienttopreventthatfromeverhappening,"saidCrowley,whosestudywillappeartomorrowinthejournalNature.
Forthepastthreemillionyears,Earth'sclimatehaswobbledthroughdozensoficeages,withthickicesheetsgrowing
from
thepolesandthenshrinkingbackagain.Theseiceagesusedtolastroughly41,000years.Butinthepasthalfamillionyears,thesebigfreezeseachstretchedtoaboutahundredthousandyearslong.Meanwhile,thetemperatureswingsduringandbetweentheseiceagesbecamemoreextreme,soaringtonewhighsandlows.Theseextremeclimateswingsdon'tappeartobeeasinganytimesoon,accordingtoevidencerecordedinEarth'srocks,Crowleysaid."Thelatesttwoglaciationsweretwoofthebiggestwe'veseen."
Theresearchersfoundthatbetween10,000and100,000years
from
now,Earthwouldenterintoaperiodofpermanenticesheets—moreseverethananyseeninmillionsofyears.Thoughthisextremeiceagewouldbeunusual,soistheclimatethatpeoplearecreatingbyemittinghugeamountsofgreenhouse
gas
es,Crowleysaid(
global
warmingfastfacts)."It'shardtosaywhat'sgoingtohappen,"Crowleysaid."The
very
factthatyouhavethisnon-glacialatmospherewithpolaricecaps,presentsabizarrescenario.Prehistoric-climateexpertLorraineLisieckisaid,"Thisisthe
only
studyofwhichIamawarethatsuggeststhenexticeagecouldbemuchmoreextremethanthoseofthepreviousonemillionyears."
Manymoretestsareneededtoseeifthestudy'spredictionseemscorrect,saidLisiecki,oftheUniversityofCalifornia,SantaBarbara.Butsheagreedthatwemightneverfindoutwhatwouldhavehappenednaturally,duetohuman-caused
global
warming."Currentgreenhouse
gas
concentrationsareprobablysimilartothosethatoccurredthreemillionyearsagoandarehighenoughtopreventaniceageforhundredsofthousandsofyears,"shesaid.
