第1章 现代气候变化

现代气候变化全球气候变暖气候系统的相关变化近百年全球降水变化近百年中国气温变化近百年中国降水变化非洲Sahel干旱(Jonesetal.1999)GISSTemperatureStatisticsfortheglobalmeantemperatureLandairtemperatureor/andSSTGlobalsurfacetemperatureshaveincreasedby0.6Csincethelate19thcentury,with95%confidencelimitsofnear0.4and0.8C.Mostofthisincreasehasoccurredintwoperiods,about1910-45andsince1976,andthelargestrecentwarmingisinthewinterextratropicalNorthernHemisphere.Therateoftemperatureincreasein1976-99is0.19C/decade,slightlyhigherthantherateofwarmingbetween1910-45.Intheavailabledata,the1910-1945warmingwasconcentratedintheNorthAtlanticandnearbyregions.Bycontrast,theperiod1946-1975showscoolinginmuchoftheNorthernHemisphere.Duringthemostrecentwarming,1976-1999,strongerwarmingoccurredinthemidandhighlatitudesofNorthernHemispherecontinentsduringwinterandspring,withyear-roundcoolinginthenorthwestNorthAtlanticandtheCentralNorthPacific.TheNorthAtlanticcoolingmayhaverecentlyreversed.AmultidecadalfluctuationofSSTintheNorthAtlantichasbeeninarisingphasesinceaboutthemid-1980s.Warminginmanyregionsofthisoceanhasacceleratedoverthelastfiveyearsandislikelytohavecontributedtoquiterapidparallelincreasesofnear-surfaceairtemperatureinmuchofEurope.Thereisnewevidenceofsubstantialsubsurfaceoceantemperatureincreasessincethe1940sinmostoceanbasinsbutsuperimposedglobaldecadalvariabilityisverypronounced.Fewchangeshavebeenmeasuredforlongenoughtoestimatecenturytimescaletrendsbutnominaloverallwarminginthefirst300moftheglobaloceanaveraged0.37Cfromthelate1940sto1998.Snow,ice,glacier...NewanalysesofNorthernHemispherelake-iceandriver-iceoverthepastcenturyormoreshowwidespreaddecreasesinthedurationoflakeandriverice.AFrozenLake

Magnusonetal,2000,ScienceFreezeandbreakupdatesoficeonlakesandriversaroundtheNorthernHemispherefrom1846to1995(150yr).

Changesinfreezedatesaveraged5.8daysper100yearslater.Changesinbreakupdatesaveraged6.5daysper100yearsearlier.Thesetranslatetoincreasingairtemperaturesofabout1.2oC/100years.Thereisahighlysignificantinterannual(-0.6)andmultidecadalcorrelationbetweenchangesinspringNorthernHemispherelandtemperaturesandareductioninspringsnowcoverextentthroughthe20thCentury.Aerialviewoftypicalpolarseaice.

SeaiceretreatintheArcticspringandsummeroverthelastfewdecadesisconsistentwithanincreaseinspring,andtoalesserextent,summertemperaturesinthehighlatitudes.ThereislittleindicationofreducedArcticseaiceextentduringwinterwhentemperatureshaveincreasedinthesurroundingregion.USSSkateduringanArcticsurfacingin1959.(USNavyPhoto)

USSPargoattheNorthPolein1993.(USNavyPhoto)Newdatafromsubmarinesindicatethattherehasbeenabouta40%declineinArcticseaicethicknessinsummerorearlyautumnbetweenthemid1990sandtheperiod1958-1976.Substantialinterannualvariabilityandinterdecadalvariabilitymaybeinfluencingthechangesthatcannotbeassessedbecauseofrestrictedsampling.Bycontrast,thereisnoreadilyapparentrelationshipbetweendecadalchangesofAntarctictemperaturesandseaiceextentsincethe1970s.Satellitedataindicatethatafteraninitialdecreaseinthe1970s,Antarcticseaiceextenthasstayedalmoststableorevenincreased.DiurnalTemperatureRange(DTR)

Trendsinannualdiurnaltemperaturerange(DTR,Cperdecade),1950-1993,fornonurbanstationsonlyupdatedfromEastering

etal(1997).Reductionsareinblueandincreasesinred.Plotofcloudcover(dashedline)andDTR(Csolidline)forEurope,USA,Canada,Australia,theformerSovietUnion,andeasternChina.(fromDaietal.1997a).Newanalysesofmeandailymaximumandminimumtemperaturescontinuetosupportareductioninthediurnaltemperaturerangeinmanypartsoftheworld,with,globally,minimumtemperaturesincreasingatabouttwicetherateofmaximumtemperaturessince1950.Temperaturechangesinhighaltitude...青藏高原及其邻近地区178站根据高度分级的年平均气温变化趋势,LiuandChen,2001

Analysisofglobaltemperaturetrendssince1958inthelow-tomid-tropospherefromballoonsshowawarmingofabout+0.10°C/decade,whichisquiteclosetothewarminginthesurfacelayer.Since1979,usingbothsatellitesandballoons,thelowertropospherictrendisabout+0.05°C/decade.Since1965therehasbeenlittlechangeofglobalmeantemperatureintheuppermosttroposphere.Inthepre-satelliteera(1958-1979)thetropospherictemperaturelikelywarmedrelativetothesurfaceby0.05to+0.20C/decade.Since1979,itisverylikelythatthesurfacewarmedrelativetothetroposphereby+0.05°Cto+0.20°C/decade,reflectingarealdifferenceintemperaturetrendbetweenthesetwolevelsoverthisperiod.Throughoutthestratospheresince1979,negativetemperaturetrendsareobserved,rangingfrom-0.5C/decadeinthelowerstratosphereto-0.5C/decadeintheupperstratosphere.平流层低层温度(100-50hPa)(a:北半球，b:南半球，c:全球)(Angell1999)Cloud,Watervapour...Trendsinannualmeanwatervapourpressure,1975-1995,expressedasapercentageofthe1975-1995mean.Areaswithoutdotshavenodata.Blueshadedareashavesignificantincreasingtrendsandbrownshadedareashavesignificantdecreasingtrends,bothatthe5%confidencelevel.FromNewetal(2000)Annually-averagedtrendsinsurfaceto500hPaprecipitablewaterat0000UTCfortheperiod1973-1995.Positivetrendsareindicatedbytrianglesandnegativetrendsbycircles.Filledsymbolsindicatethetrendswerestatisticallysignificantatthe5%levelaccordingtotheSpearmantest.Thetwosizesofsymbolsgiveanindicationofthemagnitudeofthetrend.(RossandElliott,2000).Changesintheplants...Trendsinthebeginningof“latespring”whenflowersfirstbegintoopen.(Red,earlierbymorethan–0.3days/year;yellow,earlierbylessthan–0.3butstillsignificant;pink,increasing(later)andsignificant;blue,nosignificantchange.)Schwartz&Bernhard,2000.Leafemergencedate,basedonanetworkofindicatorplantsacrossNorthAmerica.Springisarrivingfivedaysearlier.Schwartz&Bernhard,2000Analysesofboreholetemperaturesindicateagloballyaveragedwarmingofsurfaceairtemperatureoverlandof1.0±0.3oCoverthelast500years,thoughtheremaybeadditionaluncertaintiesduetodetailsofthistechnique.Changesintheglobalseaheatcontent...Timeseriesfor1948-1998ofoceanheatcontentanomaliesintheupper300mforthetwohemispheresandtheglobalocean.Notethat1.5x1022Jequals1watt-year-m-2averagedovertheentiresurfaceoftheearth.Verticallinesthrougheachyearlyestimateare+-onestandarderror.(Levitus

etal,2000)Changesinsealevel...Globalmeansea-levelvariations(lightline)computedfromtheTOPEX/POSEIDONsatellitealtimeterdatacomparedwiththeglobalaveragedseasurfacetemperaturevariations(darkline)for1993to1998(Cazenaveetal.,1998,updated).Theseasonalcomponentshavebeenremovedfrombothtimeseries.Basedontidegaugedata,therateofglobalmeansea-levelriseduringthe20thcenturyisintherange1.0to2.0mm/yr,withacentralvalueof1.5mm/yr.Basedonthefewverylongtide-gaugerecords,theaveragerateofsea-levelrisehasbeenlargerduringthe20thcenturythanthe19thcentury.Factorsthataffectthesealevel...Componentcontributions

LowMiddleHigh

Thermalexpansion24

7Glaciers/icecaps23.55Greenlandicesheet-404Antarcticicesheet-14

0

14Surfacewaterandgroundwaterstorage

-50.57Totalfromabove-19837Totalbasedontidegauges101520

Estimatedcontributionstosealevelriseoverthelast100years.cm.Oceanthermalexpansionleadstoanincreaseinoceanvolumeatconstantmass.Observationalestimatesofabout1mm/yroverrecentdecadesaresimilartovaluesof0.7to1.1mm/yrobtainedfromAOGCMsoveracomparableperiod.Averagedoverthe20thcentury,AOGCMsimulationsresultinratesofthermalexpansionof0.3to0.7mm/yr.Themassoftheocean,andthussealevel,changesaswaterisexchangedwithglaciers,icecapsandicesheets.Observationalandmodellingstudiesofglaciersandice-capsindicateacontributiontosea-levelriseof0.1to0.4mm/yraveragedoverthe20thcentury.Climatechangesduringthe20thcenturyareestimatedfrommodellingstudiestohaveledtocontributionsofbetween-0.2and0.0mm/yrfromAntarctic(theresultsofincreasingprecipitation)and0.0to0.1mm/yrfromGreenland(fromchangesinbothprecipitationandrunoff).Geologicalsea-leveldataandice-sheetmodellingindicatethatGreenlandandAntarcticahavecontributed0.0to0.5mm/yroverthe20thcenturyasaresultoflongtermadjustmenttopastclimatechanges.Changesinterrestrialstorageofwaterovertheperiod1900to1990areestimatedtohavecontributedbetween-0.25to+0.05mm/yrofsea-levelrise.Estimatedsea-levelrisefrom1910to1990.(a)Thethermalexpansion,glacierandicecap,GreenlandandAntarcticcontributionsresultingfromclimatechangeinthe20thcenturycalculatedfromarangeofAOGCMs.Theestimatedterrestrialstoragetermsarealsoshown.(b)Themid-rangeandupperandlowerboundsforthecomputedresponseofsealeveltoclimatechange(thesumofthetermsin(a)excludingtheterrestrialstoragetermsbutincludingthepermafrostcontribution).Thesecurvesrepresentourestimateoftheimpactofanthropologicclimatechangeonsealevelduringthe20thcentury.

GlobalaveragesealevelchangesfromthermalexpansionsimulatedinAOGCMexperimentswithhistoricalconcentrationsinthe20thcentury,thenfollowingtheIS92ascenarioforthe21stcentury.GSdenotesthesimulationsincludingthedirecteffectofsulphateaerosols,Gthosewithgreenhousegasesonly.(IPCC,2001)全球平均年降水量?最近30多年来，有许多全球降水的估计，对全球平均降水这个基本量的估计都有较大出入，最少的估计只有784mm，最多的有1130mm，取1960年以来近20位作者估计值的平均，是977mm。Hulme2000全球降水量的变化Seasonality1937-1994,Yeetal,2001Overall,globallandprecipitationhasincreasedabout1%sincethebeginningofthe20thCenturyTheincreaseisstatisticallysignificantbuthasneitherbeenspatiallynortemporallyuniform.Duringthe20thCentury,annual-zonallyaveragedprecipitationincreasedbetween7%and12%forthezones30°Nto85°Nandabout2to3%between0°Sto55°S.

Theexactrateofincreasedependsonthemethodofcalculatingthechanges.Thisunsteady,butneverthelesshighlystatisticallysignificant,trendtowardmoreprecipitationintheseregionsiscontinuing.In1998theNorthernHemispherehighlatitudes(55°Nandhigher)hadtheirwettestyearonrecordandthemidlatitudeshavehadprecipitationtotalsexceedingthe1961-90meaneveryyearsince1995.Theincreaseofprecipitationinthemiddleandhighlatitudescontrastswithdecreasesinthenorthernsubtropics(withmarginalstatisticalsignificance)whichwerelargelyresponsibleforthedecade-longreductionofgloballandprecipitationfromthemid-1980sthroughthemid-1990’s.SinceIPCC(1996),recordlowprecipitationhasbeenobservedinequatorialregions,whilethesubtropicshaverecoveredfromtheiranomalouslylowvaluesofthe1980s.InstrumentalrecordsoflandsurfaceprecipitationcontinuetoshowanincreaseinmuchoftheNorthernHemispheremidandhighlatitudes,butovermuchofthetropicallandareasconditionshavebecomedrier.However,otherindicatorssuggestthatlargepartsofthetropicaloceanshavebecomewetterinrecentdecades.公元800～1999年中国年平均气温

●20世纪是千年来最暖的一个世纪

1880～1999年中国年平气温距平

●应用了冰芯、年轮、史料及所可能得到的观测资料●包括了新疆、西藏、台湾等过去研究中未包括的地区●新的序列变暖～0.5℃/百年

●1998年是近百年最暖的1年，1990s是最暖的10年1998年全球各地区年平均温度距平分布(据CRU/UEA全球5

5

格点温度资料，空白地区缺数据,单位:

C)中国年平均气温变化趋势（%/10a）分布图（1960—1999）翟盘茂,20011951－1998年不同降水量序列比较a:165站平均，b:35站平均,c:384站平均,为距平,d:旱减涝站数

●

用35个站对中国东部有较好的代表性

长沙站夏季降水序列(a.夏季降水级别,b.6月降水级别c.7月降水级别d.8月降水级别e.夏季降水量序列)1880－1999年中国四季及年降水量●冬季降水量变化不尽相同●全年降水量主要决定于夏季●20－30年波动为主●

与气温变化不一致

a:春季,b:夏季c:秋季d:冬季e:年降水量,距平为对1961-1990年平均Interdecadalchanges中国平均年降水量的功率谱分析Changesintheextremeconditions1953-1997年中国年降水频率（日降水量大于0.1mm的日数）变化趋势（%/10a）翟盘茂,2001Mostseveredroughtoverglobeinthe20thcenturySahel地区雨季降水量,(a)20-10

N,15

W-30

E平均6-9月降水量,据Hulme(1992)；(b)是20-8

N，20

W-10

E区域14个站平均6-9月降水量,据Janowiak(1988)；(c)为10-20

N,18

W-20

E平均7-9月降水指数，据Thiaw和Bell(1999)。标准化处理，对19