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Polar meteorology Understanding global impacts

WMO - No. 1013

Polar meteorology Understanding global impacts

WMO-No. 1013© 2007, World Meteorological OrganizationISBN 92-63-11013-1

NOTEThe designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitations of its frontiers or boundaries.

Photo credits

We would like to thank the following individuals and organizations for their generosity in sharing their photos and figures with WMO:

Cover, pages 3, 27, 28, 29 and 31 to 37: Christian MorelPages 12, 15, 16, 21 and 22: International Polar FoundationPages 4, 6, 8 and 11: G. Dargaud (International Polar Foundation)Pages 19 and 20: NASAPage 5: University of Wisconsin-MadisonPage 7: Scottish Association for Marine SciencePage 17: Columbia UniversityPage 18: UNEPPages 14 (2) and 24: Mathieu QuétuPage 25: EUMETSATPage 26: ESA/AOES MEDIALAB (left); http:www.Firstpeople.US (right)

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CONTENTSForeword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....3

Polar meteorology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....5

Observingthepolarregions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..5

High-latitudeweathersystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..8

Weatherforecastinginthepolarregions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..11

The role of the polar regions in the global climate system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..17

ThePoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..17

Linkswithlowerlatitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..17

Recenthigh-latitudeenvironmentalchanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..22

Howwillthepolarregionschangeinthefuture?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..30

International Polar Year 2007-2008 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..37

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FOREWORDInrecentdecades,greatadvanceshavebeenmadeinourunderstandingoftheroleofthepolarregionsintheglobalclimatesystem.Shrinkingsea-ice,meltingicesheets,thedis-chargeofglaciersandthawingofpermafrostarealldramaticchangesthathavebeentakingplaceinthoseregionsowingtoanincreaseinglobalaveragetemperature.Itisevidentthattheincreasedaveragerateofsea-levelriseresultingfromthemeltingoficeoflandoriginwouldbedangerousforlowlandsandsomeislandswhatevertheirgeographicallocation.Oceancirculationchangesmayhaveanimpactonthedistributionoftemperature,salinityandorganicsubstancesintropicalareas.Thiswouldhaveacrucialimpactonfishstocksandthereforeonnationaleconomiesandlivelihoodsandoureatinghabits.Thatiswhyevencountriesgeographically farremovedfromthePoleshavearealconcernregardingchangesinthepolarenvironmentandareparticipatingintheInternationalPolarYear(IPY)2007-2008.

WMO,throughtheNationalMeteorologicalandHydrologicalServices(NMHSs)of itsMembers,willbeofferingsubstantialcon-tributionstothe IPY in theareasofpolarmeteorology,oceanography,glaciologyandhydrology, in termsofscientificresearchandobservations.Ultimately,thescientificandoperationalresultsof the IPYwillbeofferingbenefitstoallWMOprogrammesbygeneratingcomprehensivedatasetsandauthoritativescientificknowledgetoensurethefurtherdevelopmentofenvironmentalmonitoringandforecastingsystems,includ-ingsevereweatherprediction.Moreover,theIPYwillprovidevaluablecontributionsto theassessmentofclimatechangeandits impacts,sotheobservingnetworkstobeestablishedorimprovedduringtheIPYperiodwillbekeptinoperationalmodeformanyyears.ThiswillbeanimportantpartoftheIPYlegacytotheworld.

Thisbooklethighlightsthe importanceofthepolarregionsintheentireEarthsystem,particularlyinclimate.Itdescribessomeofthemajorenvironmentalchangesthathavetakenplace in theArcticandAntarctic inrecentyearsandconsiderspossiblechanges

overthenextcentury.Iwishtoexpressmyappreciation to theauthor, JohnTurner,ProjectLeaderwith theBritishAntarcticSurvey,andothercontributors.

Iurge theNMHSsofallWMOMembershavingan interest inpolar researchandobservationstoparticipateactivelyinimple-mentingtheIPY.IwouldalsowelcometheNMHSs, internationalorganizations,non-governmentalorganizationsandindeedallwhoareinterestedintheseuniquepartsoftheglobetoseizethisidealopportunitytoprovideinputtotheIPYandsosecurearichscientificoutputforthebenefitofall—nowandinthefuture.

(M.Jarraud)Secretary-General

M. Jarraud, Secretary-General

WorldMeteorologicalDay(23March)celebratesthedateoftheentryintoforceoftheConventionwhichcreatedtheOrganizationin1950.

TheWMOExecutiveCouncildecidedthatthethemeforWorldMeteorologicalDayin2007wouldbe“Polarmeteorology:understandingglobalimpacts”,inrecognitionoftheimportanceof,andasacontributionto,theInternationalPolarYear(IPY)2007-2008,whichisbeingco-sponsoredbyWMOandtheInternationalCouncilforScience(ICSU).

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FOREWORD INTRODUCTIONInrecentyears,therehasbeenanunprec-edented level of interest in the climateandenvironmentalconditionsofthepolarregions.ThediscoveryoftheAntarcticozonehole, record low levelsofArcticsea ice,lossof ice fromtheGreenland icesheet,thedisintegrationofanumberoffloatingiceshelvesaroundtheAntarcticPeninsulaand thehigh levelsofaerosols reachingtheArctic,haveallbeenreportedby themedia.Moreover,climatemodelpredictionsindicatethathigh-latitudeareaswillwarmmorethananyotherregionoverthenextcenturyasaresultof increasinglevelsofgreenhousegases. It remainstobeseen,however,whethertherapidclimaticfluctua-tionsinthepolarregionsoverthelastfewcenturiesandmillenniaareinfactaresultofnaturalclimatevariability.Itisimportant,therefore,totrytoseparatetheimpactsofnaturalclimatevariability from thoseofhumanactivity.

Althoughthepolarregionsareremotefrommajorpopulatedareas, theyareofgreatsignificance intheglobalclimatesystem;changesathighlatitudescanhaveanimpactonecosystemsandhumansocietythrough

factorssuchassea-levelriseandvariationsinatmosphericandoceaniccirculations.

TheGreenlandandAntarctic icesheetscontain9and90percent,respectively,oftheworld’sglacierice.Ifboththeseicesheetsmeltedcompletely, theywouldcontribute7mand70m, respectively, tosea-levelrise.Whilesuchadramaticoccurrence isnotexpected,evenonthe time-scalesofhundredsofyearsormillennia,themeltingofasmallfractionofthisicewouldnonethelesshaveseriousimplicationsforglobalsea-levelriseandoceancirculation.

Thepolar regionsarealsocharacterizedby largeareasof sea ice—theAntarcticeffectivelydoublesinsizeovertheyearastheoceanaroundthecontinentfreezes.Theseaiceprovidesaneffectivethermalcaponthetopoftheoceanandtheexpulsionofsaltthattakesplaceasitformsisimportantfortheglobalcirculationoftheocean.

Polarmeteorologyinthiscontextisconsid-eredinabroadsensewithrespectbothtothebehaviourofweathersystemsanditsroleintheglobalclimatesystem.

Thepolarregionshavewarmedmoresignificantlythanotherregions.

Globalimpactsincludesea-levelrise,withtheriskoffloodingandeventhecontinuedexistenceofsomelow-lyingareasandislands.

Localimpacts—whichareofglobalinterestandimportance—includethreatstobiodiversity—thesurvivalofanimalandplantspecies.AtriskalsoisthetraditionalwayoflifeofindigenouspeoplesoftheArctic,whodependonthoseanimalsandplantsfortheirfood,clothing,settlements,huntingandfishingweapons,etc.

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POLAR METEOROLOGY ObservIng The POlar regIOns

ThepolarregionsaresomeoftheleastwellobservedareasonEarth,asfaras insitumeteorologicalobservationsareconcerned.Forexample,acrosstheAntarctic,whichistwiceas largeastheUSA,thereareonly44stationsmakingsurfacemeteorologicalobservationsandsome14stationslaunch-ingradiosondes(instrumentscarriedaloft,chieflybyballoon, togatherandtransmitmeteorologicaldata).ThemoresoutherlypartsoftheArcticarebetterservedbyobserv-ingstationsbecauseofthelargenumberofhumansettlementsthere.Overhigherlatitudeareas,however,fewdataareavailablefromhumanobserversbecauseofthelackofislandobservingstations.

ThroughitsAntarcticActivitiesProgramme,WMOcoordinatesmeteorologicalactivitiescarriedoutbynationsandgroupsofnations.

WithintheframeworkoftheAntarcticTreaty,itfocusesontheinterfacesbetweentheseactivities and other WMO Programmes,notablytheWorldWeatherWatch(WWW),andaimsatmeetingtherequirementsformeteorologicalservicesaswellasforenvi-ronmentalmonitoringandclimateresearch,inparticular, theupper-air soundingsofmeteorologicalvariablesgeneratedbytheWMOAntarcticBasicSynopticNetwork.Theseprovideverticalprofilesfromthesur-facetoaltitudesofabout25kmandevenoccasionally35km(thelowerstratosphere).Thesurfaceandupper-airstationsroutinelyprovidecodedreportsthatareessentialforglobalweatherforecasting.Theobservationsaretodaysent fromthepolarregionsviasatellitecommunicationsystemsandtotheWMOGlobalTelecommunicationSystemfortransfertothemainforecastingcentres.Specializeddataandproductsforvarioususersaregeneratedby regional centresof theWMOGlobalData-processingandForecastingSystem.

DespitetheharshenvironmentalconditionsintheAntarcticandtheproblemoflogistics,theAntarcticBasicSynopticNetworkiswellimplemented,thankstotheeffortsofNationalMeteorologicalandHydrologicalServices

A mosaic of infra-red satellite imagery of the Antarctic and Southern Ocean on 21 August 2006

A 48-hour forecast from the Antarctic Mesoscale Prediction System

TheAntarctic’smassiveicecapandisolationfromtherestoftheplanetbytheSouthernOceanpreventedanypermanenthumansettlementpriortotheestablishmentofscientificstationsintheearly20thcentury.

ThecontinentssurroundingtheArcticOceanhavebeentemperateenoughtobehometotheirindigenouspopulationsformillennia.

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(NMHSs)and theAntarcticprogrammesof thecountrieswhichareParties to theAntarcticTreaty.AssessmentoftheAntarcticmeteorologicalreportsarrivingatthemaincentresofWMO’sGlobalTelecommunicationSystemsuggests that thepercentageofreportsreceivedisclosetotheglobalaver-age.MostoftheobservationsfromstaffedstationsintheArcticandAntarcticprovideasignificantcontributiontotheupper–airandsurfacenetworksanddatabaseoftheGlobalClimateObservingSystem.

Becauseof the lackof insitudata,polarmeteorologistshavealwaysmadeextensiveuseofdatafromautonomoussystemsandpolar-orbitingsatellites.Since the1960s,satelliteimageryhasbeenanimportanttoolinidentifyingthelocationsofsynopticandmesoscale (less than1000kmdiameter)weathersystemsoveroceanandremotelandareas.Althoughtheearlyimagerywasofpoorqualitywithcoarsehorizontalresolutionandfewgreyscales,manystationstodayhavedigitalreceiverscapableofprovidinghigh-resolutionimagesatseveralwavelengths.

Theearliestsatellitedataforthepolarregionsconsistedofvisibleandinfra-redimagery.Inrecentyears,however,avastrangeofproductshasbeenproducedfromactiveandpassivemicrowaveinstrumentsthatallowthedeterminationoftemperatureandhumidity

profiles(throughtheatmosphereincloudyconditions),theextentandconcentrationofseaiceandwindsovertheice-freeocean.

The lackof insituobservations fromthepolarregionsledtotheearlydeploymentofautomaticweatherstations(AWSs),whichprovidefrequentobservationsandrequireonly infrequentmaintenance.AWSswerefirstinstalledintheAntarcticinthemid-1980sandhaveprovedtheirworth;moreobserva-tionsarenowobtained fromAWSs thanfromstaffedstations.IntheAntarctic,mostresearchstationsarelocatedonthecoast,soAWSsareessential formeteorologicalanalysis inthe interior. IntheArctic, theyareinstalledonthelandareassurroundingtheArcticOceanintheRussianFederation,Fenno-Scandinavia, North America andGreenland.TheyhaveprovedparticularlyvaluableinGreenland,wheretemperatureshaverisenmarkedlyinrecentyears.

AnAWSisastand-alonesystemthattypicallymeasuressurfacemeteorologicalvariables,suchaswindspeedanddirection,airtem-peratureandairpressureandmaymeasureadditionalvariablessuchasrelativehumidityorverticalairtemperaturedifference.MostpolarAWSstransmitdata intheblindforreceptionby theArgosSystemonboardpolar-orbitingsatellitesoftheUSNationalOceanicandAtmosphericAdministration

An automatic weather station in the Antarctic

TheAntarcticTreatywasopenedforsignatureon1December1959andenteredintoforceon23June1961.

TheGlobalClimateObservingSystemisco-sponsoredbyWMO,theIntergovernmentalOceanographicCommissionofUNESCO,theUnitedNationsEnvironmentProgrammeandtheInternationalCouncilforScience.

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(NOAA)seriesorstoredonamemorymoduleforretrievalatalaterdate.IntheAntarctic,some70AWSscurrentlysupplement thedatafromstaffedstations.

ToobtaindataovertheArcticOceanorinthesea-icezonearoundtheAntarctic,driftingbuoysaredeployedontheice.ThemajoradvanceinthedevelopmentanddeploymentofdriftingbuoyscamewiththeFirstGARP(GlobalAtmosphericResearchProgramme)GlobalExperiment (FGGE) in1978/1979,whenover300systemsweredeployedintheSouthernOceantoinvestigateatmosphericpredictabilityandtherequirementsforanoptimumobservingsystem.Sincethen,manydifferenttypesofdriftingbuoyhavebeendeployedintheArcticbytheInternationalArctic Buoy Programme (IABP) and intheSouthernOceanby the InternationalProgramme for Antarctic Buoys (WorldClimate Research Programme/ScientificCommitteeonAntarcticResearch(WCRP/SCAR)).Currently,anumberofcommercialcompaniesandresearchinstitutesmanufac-turebuoys.Theseareofvaryingdegreesofsophistication,fromlow-costoceandrifterswithnometeorologicalsensorstoadvancedsystemsmakingawiderangeofatmosphericandoceanographicmeasurements.

Variousinstrumentscanbeattachedtothebasicbuoyplatform,dependingonthedata

requirementsandexperimentstobecarriedout.Measurements includeatmosphericpressure,windspeedanddirection,airtem-peratureandhumidityatvariouslevelsabovethesurfaceand,inthecaseofbuoysonicefloes,thesurfacetemperatureofthesnoworiceandsnowthickness.UsingtheIABPdata,significantwarmingoftheArcticinthe1980sand1990swasdetected.

Althoughsomesurfacesynopticweatherchartswerepreparedintheearlypartofthe20thcentury,theycoveredmainlythemorepopulousregionsand lackedaccuracyathighlatitudes.Inparticular,therewereveryfewobservationsoveroceanareasof theAntarctic;Arcticanalysesweresomewhatbetter.Anincreasingnumberofobserva-tionsbecameavailablefrompolar-orbitingmeteorologicalsatellites inthe1970sthatallowedmorereliableatmosphericanaly-sesinhigh-latitudeareas.Theatmospherictemperature sounders flown on polar-orbitingsatellitessincethemid-1970swereofparticularimportance.Similarinnaturetoradiosondeascents,theyprovidedprofilesoftemperatureandhumidityfromthesur-faceuptothestratospherewiththebroadcoverageprovidedbyasatellitesystem.

Overthelastfewyears,thehistoricalarchiveof insituandsatelliteobservationshavebeenre-processedusingdata-assimilation

A drifting buoy on an ice floe in the Weddell Sea, Antarctic

TheWorldClimateResearchProgrammeisco-sponsoredbyWMO,theIntergovernmentalOceanographicCommission(UNESCO)andtheInternationalCouncilforScience.

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techniquestoproduceso-called“re-analysis”datasets,whichprovideaparticularlyvaluablesourceforinvestigationofclimatevariabilityoverthelastthreedecadesorso.There-analysisfieldsforthesouthernhemispherepriorto1974,whensatellitesounderdatabecameavailable,werepoor,however,andcannotbeusedtoinvestigateatmosphericcirculationchange.

hIgh-laTITude weaTher sYsTems

TheArcticandAntarcticarepolewardofthemainstormtracksinthenorthernandsouthernhemispheresandmeansea-levelsurface-pressurechartsshowclimatologicalanticyclonesintheseareas.Nevertheless,careneedstobeexercised incalculatingatmosphericpressureatmeansea-levelusing

measurementstakenatelevatedareasoftheAntarcticandGreenland.MeteorologicalconditionsatthePolesaredifferent,astheNorthPoleislocatedovertheArcticOcean,whiletheSouthPoleisonthehighAntarcticplateau.

Inthenorthernhemisphere,becauseofthemajormountainrangesoftheHimalayasandtheRockies,thetroposphericflowishighlymeridionalwithmanyweathersystemsreach-inghighlatitudesandoccasionallycrossingtheArcticOcean.Ontheotherhand, thesouthernhemispherehasfewlarge,highlandmassessothedepressionsmoveinamuchmorezonaltrack,spirallingonlygraduallytowardstheAntarcticcoastalregion.ThefactthattheAntarcticconsistsofalarge,highmassoficecentredneartheSouthPolehasalargeimpactontheatmosphericcirculationof

MeteorologicalconditionsatthePolesaredifferent.TheNorthPoleislocatedovertheArcticOcean,whiletheSouthPoleisonthehighAntarcticplateau.

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thesouthernhemisphere.Depressionsmov-ingsouthwardsfrommid-latitudestendtobecomeslowmovingorstarttotracktowardstheeast intheAntarcticcoastalregionastheyencountersteepmountains.Thereare,therefore,fewactivedepressionsovertheAntarcticinterior,althoughsomedepressionsdopenetratetoDomeC,SouthPoleorevenVostok,wherethemid-troposphericflowismoremeridional.Thisappearstohappenaspartofnaturalclimatevariabilityandcanbedetectedatinteriorstationsbyasudden,rapidriseoftemperature,thepresenceofcloudandoccasionallymoderateprecipitationfallinginwhatisacolddesert.

TheAntarcticcoastalregionbetween60°Sand70°Sishometomanyactivedepressionsandsmaller-scalelows.Theoccurrenceofsomanystormsmeansthatatmosphericpres-suresarelowandthezoneisknownasthecircumpolartrough.ThereisnocomparablefeaturearoundtheArctic,whereorographicconditionsaredifferent.

Polar lowsThemostviolentweathersystemsfoundintheArcticareshort-lived(usuallylessthan24hours),mesoscalepolarlows,whichareactivedepressionsoccurringovercertainice-free,maritimeareaspolewardof thepolar front—themainboundarybetweenpolarandtropicalairmasses.Polar lows

intheArcticareprimarilyawinterseasonphenomenon.Mostactivepolarlowshaveahorizontalscaleof400-600km,althoughconvectivesystemscanhavesmallervorticesembeddedwithinthem.Polarlowsarepartofthebroadcategoryofdisturbancesknownaspolarmesocyclones,whichincludesthemanyminorvorticesobservedonsatelliteimageryof thepolar regions.Thedefini-tionofapolarlowisthatitshouldhaveasurfacewindspeedof17m/sorstronger.Observationshaveindicatedthattheycanhavewindspeedsashighas33m/s.TheybringsomeoftheworstweathertoArcticcoastalandislandlocationsandcanbeamajorhazardtomaritimeoperations,aswellasgasandoilexplorationandproductionplatforms.

IntheAntarctic,theair-seatemperaturedif-ferencesaremuchlessthan intheArcticanddeepconvectionisnotfoundclosetothecoastofthecontinentoratthelatitudeofthecircumpolartrough.Hence,thepolarlowsthatoccurtendtobefoundonshallowhorizontaltemperaturegradients,althoughmanyminorpolarmesocyclonesappearonsatelliteimagery.

Individualpolarlowsareobviouslyimpor-tantinweatherforecastingforthetwopolarregionsbutitisstillunclearwhethertheyareimportantclimatologically.Withthe large

A polar low off the north coast of Norway with extensive convective cloud

An active polar low with a spiral cloud pattern

Thebranchofphysicalgeographywhichdealswiththeformationandfeaturesofmountainsiscalledorography.

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Polarlowswerefirst investigatedinthelate1960swhensatelliteimagerybecameavailable,butstudieswerehamperedbythelackofinsituobservationssincethelowsrarelycrossedsynopticobservingstations.Earlymodellingstudiesfrequentlyfailedtorepresentthesystemsbecauseof theirsmallhorizontalscaleand thepoorparameterizationofsomekeyphysi-calprocesses,suchasdeepconvection.Recently,majoradvanceshavebeenmadeinourunderstandingof thesesystemsasaresultofcampaignsinwhichdedi-catedaircraftflythroughthelows,studiesusingmultiplesourcesofsatellitedata,andexperimentswithhigh-resolution,limited-areamodels.

Inthelate1960s/early1970s,therewasdebateastowhetherpolarlowsformedanddeepenedinthesamewayasmid-latitudedepressionsonhorizontaltemperaturegra-dientsorwhethertheyweremainlyassoci-atedwithdeepCumulonimbusclouds,ratherlikehurricanes.Today,weknowthatthereisaspectrumofdisturbancesrangingfromtheratherraresmall-scaledepres-sions,whichformonshallowtemperaturegradientswitha frontalstructure thatresemblesasmallmid-latitudecyclone,to thesystemscharacterizedbymanydeepCumulonimbusclouds.

Polarlowswerefirst investigatedintheNorwegianandBarentsSeasareas,where

thesystemsaffectedcoastalcommunitiesofNorwayandproducedsomeof themostsignificantsnowfallsovertheUnitedKingdom.Assatellite imagerybecamemorereadilyavailable,however,polarlowswereidentifiedinotherpartsoftheArcticwheretheair-seatemperaturedif-ferencesare large, includingtheDavisStrait/LabradorSea, theGulfofAlaskaand theBeringSea, theBeaufortSea,northoftheRussianFederationcoast,theNorth-WestPacific,theSeaofJapan,andsurroundingareas.

WhilesomepolarlowsarefoundintheAntarctic,theydevelopprimarilyonshal-lowhorizontaltemperaturegradients,asthereisnodeepconvectionathighsouth-ernlatitudes.Thissituationarisesbecausetheoceaniccirculationof thesouthernhemisphereismuchmorezonalthannorthoftheEquator,andwarmwatermassesdonotreachtheAntarcticcoastline.Largeair-seatemperaturedifferencescanexistinthecoastalpolynyas(ice-freeareasofwaterwithin thepack ice) (seeboxonpage14),butthetrackofairacrosstheseareasisquiteshortsopolarlowsdonothavetimetodevelop.

air-seatemperaturedifferencesassociatedwithpolarlows,coupledwiththehighnear-surfacewindspeeds,surfaceheatfluxesofupto1000W/m2havebeenrecorded,althoughtherearerelativelyfewsuchsys-temseachseasonataparticularlocation.Thequestionhasbeenposedastowhether

themanyminorvorticesathighlatitudescantogethergeneratesufficientheat lossfromthesurfaceof theocean to triggerdownwardconvection,whichmayaffectthethermohalinecirculation,whichisdrivenbydifferencesinoceanwaterdensityarisingfromtemperatureandsalinitygradients.

Polar lowsMesoscalepolarlowsarereferredtobyawidevarietyofnames,includingArctichurricane,Arcticbomb,Arcticinstabilitylow,coldairdepression,commacloudandpolarmesocyclone.

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Thisquestioncanonlybeansweredusingmodellingexperimentswhicharecurrentlybeingcarriedout.

weaTher FOrecasTIng In The POlar regIOns

Althoughmostpartsofthepolarregionsareremotefromthemajorpopulationcentres,thereisstillaneedforreliableweatherfore-casts.IntheArctic,forecastsareneededfortheindigenouscommunitiesandinsupportofmaritimeoperationsandoilandgasexplora-tionandproduction.IntheAntarctic,reliableforecastsareneededforthecomplexairandsealogisticaloperationsthatsupportresearchprogrammesandforthegrowingtourismindustry.Forecastsarealsoneededforfieldpartiesworkinginremotelocations.

ForecastsoftheweatherovertheArcticandAntarctichavebeenmadesince the firstexpeditions,althoughtheywerepoorintheearlyyearsowingtothefewobservationsavailableandarudimentaryunderstandingoftheworkingsofhigh-latitudeclimates.

This situation remained more or lessunchangeduntiltheInternationalGeophysicalYear(IGY)of1957-1958,whenanumberofresearchstationswereestablishedathighlatitudes,especiallyacrosstheAntarctic,withmanyofthesemakingroutineradiosondeascents.Theseadditionaldataallowedmorereliablesurfaceandupper-airanalysestobeprepared,althoughtherewerestill fewobservationsovertheoceanareas.

Satellite imageryhasbeenusedasanaidtoweatherforecastingsincethe1960s.Formanyyears,theanalyseswerepoorathighlatitudesand imageryprovided theonlymeansofdeterminingthe“truth”regardingatmosphericconditions.Theimageswereusedtoprovideearlywarningofapproachingweathersystems,frontsandisolatedcloud-banks,aswellassupplementaryinformationonsea-iceextent.

Sincethelate1970s,ithasbeenpossibletodetermineupper-leveltemperatureandhumid-ityprofilesthroughtheatmosphereusingdatacollectedbypolar-orbitingsatellites.Suchobjectivedataallowedtheimplementationof

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globalnumericalweatherprediction(NWP)systems thatcouldprovide forecasts forseveraldaysahead.Duringthe1980s,theaccuracyofpolarforecastsfromsuchNWPsystemswasmuch lower than those fortropicalandmid-latitudeareasbut,duringthe1990s,thereweremarkedimprovementsasaresultofbetteranalysistechniques,highermodelhorizontalresolutionandadditionaldatafromnewsatellite-borneinstruments,suchasthewindscatterometer.

Today,theforecastingproblemintheAntarcticisquitedifferentovertheoceanareasandthecontinentitself.Overtheocean,theNWPmodelshavegreateraccuracythaninthenorthernhemispherebecausetheorographyofthesouthernhemisphereislesscomplex.However,overthecontinent,andespeciallyinthecoastalregion,sitesareaffectedbylocalwindsystemsthatmanyglobalmodelscannotcapture.Forecastersthereforetendtoadoptanowcastingapproachbasedonsatelliteimagerytopredictthewindsupto24hoursahead.Highhorizontalresolution,

limited-areanumericalweatherpredictionmodels(suchastheUSAntarcticMesoscalePredictionSystem)arestartingtopredictsurfacewindsinareasofcomplexorographywithmoresuccess.

Theforecastingproblemissomewhateasierin theArctic,sincemuchof theregion isringedby land fromwhichmany in situmeteorologicalobservationsareprovided.These,coupledwithsatellitesounderdata,allowhigh-qualitynumericalanalysesandforecaststobeprepared.Therelativelyloworographyof theArcticalsoaidspredict-ability.ThemainexceptionistheinteriorofGreenland,wherethesameproblemsapplyasarefoundontheAntarcticplateau.

The forecasting processWeatherforecastingintheArcticandAntarcticpresentsanumberofuniquechallengescomparedtotheextra-polarregions(seeboxonpage23).Thegreatadvancesinobservingsystemsandnumericalweatherpredictiondescribedabove,however,haveconsiderably

Thewindscatterometerisasatellite-borneinstrumentwhichprovidessurfacewindobservationsfrommeasurementsofradarbackscatterfromtheocean.

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improvedthequalityoftheforecasts,butthetasksofforecastingoverlandandoceanareasarequitedifferent.

Overoceanareas,thelargeamountsofsatel-litesounderdatathatarenowavailablemeanthatthemeteorologicalanalysesareofhighquality,despitethelackofradiosondedata.ThisisturnmeansthattheNWPfieldscanbeusedwithconfidenceovertwoorthreedays,andgiveareasonableindicationofthebroadscaledevelopmentstobeexpecteduptoaboutsixdaysahead.AcrosstheAntarcticcontinentandintheinteriorofGreenland,thelackofinsitudata,theproblemsofderivingsatellitetemperaturesoundingsoverahigh,ice-coveredsurfaceandthecomplexlocalwindandcloudsystemsmeanthatthequalityof theNWPfieldsdropsoff rapidlyawayfromthecoast.

Arecentdevelopmenthasbeenthatlimited-areaNWPmodelswithhighhorizontalresolu-tionarebeingrunoperationallyacrosscertainpartsoftheAntarctic.Althoughnoadditional

dataareasyet includedinthesemodels,thehighhorizontalresolutionandthemorerealisticorographythatcanbeincludedhasthepotentialtogivebettershort-termweatherforecasts.

ThOrPeXTHORPEX(TheObservingSystemResearchandPredictabilityExperiment) ispartofWMO’sWorldWeatherResearchProgramme.Itprovidesanorganizationalframeworkthataddressesweatherforecastproblems,includ-ingthoseinpolarareas,whosesolutionswillbeacceleratedthroughinternationalcollabo-rationamongoperationalforecastcentresofNationalMeteorologicalandHydrologicalServices,academic institutionsandusersofforecastproducts.

InthecontextoftheInternationalPolarYear2007-2008,THORPEXhasspecificresearchgoals(seeboxbelow).Inordertoassistinaccomplishingtheseresearchgoals,fieldcampaignswillbecarriedoutduringanIPYintensiveobservingperiod.

Aradiosondeisaunitforuseinweatherballoonsthatmeasuresvariousatmosphericparametersandtransmitsthemtoafixedreceiver.

Radiosondesmeasureorcalculatethefollowingvariables:•Atmosphericpressure•Altitude•Geographicalposition(latitude/longitude)•Temperature•Relativehumidity•Windspeedanddirection

THORPEX and the International Polar Year 2007-2008InthecontextoftheIPY,THORPEXseeksto:

• Addressthetwo-wayinteractionsofpolarandsub-polarweatherregimes• Assessandimprovethequalityofoperationalanalysesandresearchreanalysis productsinthepolarregions• Addresstheimprovementofdata-assimilationtechniquesforthepolarregions• Assesstheskillinthepredictionofpolar-to-globalhigh-impactweatherevents fordifferentobservingstrategiesinhigherlatitudes• Demonstratetheutilityof improvedutilizationofensembleweatherforecast productsforhigh-impactweathereventsandforIPYoperations,whenapplicable• DeveloprecommendationsonthedesignoftheGlobalObservingSystemin polarregionsforweatherprediction

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MuchoftheplannedIPY-THORPEXresearchisalignedwiththeTHORPEXfocusonglobal-to-regionalinfluencesontheevolutionandpredictabilityofweathersystemsandtheIPYobjectiveofunderstandingpolar-globaltele-connectionsonallscales,andtheprocessescontrollingtheseinteractions.IPY-THORPEXwilladdresshigh-impactweatherforecasts,thepredictability,andincreasedknowledgeofrelatedphysicalanddynamicalprocesses

associatedwithpolarandsub-polarinterac-tions.ExamplesofresearchinvestigationsincludetheroleofGreenland’sorographyonEuropeanandAfricancyclonicstormsystems,theinteractionsbetweentropical,middlelatitudeandpolarprocesses,RossbywavetrainsexcitedbyintensecyclogenesisoffthecoastofAsiaandwhetheranomalousopenwaterinthevicinityoftheArcticandAntarcticcanleadtomodificationstostorm

THORPEXisakeycomponentoftheWMONaturalDisasterReductionandMitigationProgramme.ItwillcontributetoWMO’sgoaltohalvethenumberofdeathsduetonaturaldisastersofmeteorological,hydrologicalandclimaticoriginoverthenext15years.

WhenAntarcticglaciersreachthecoastofthecontinent,theybegintofloatandbecomeiceshelves,fromwhichicebergsarethencalved.Since1974,atotalof13500km2oficeshelveshavedisintegratedintheAntarcticPeninsula,aphenomenonlinkedtotheregionaltemperatureriseofmorethan2°Cinthepast50years.

Similarbreak-upsinotherareascouldleadtoincreasesiniceflowandcausesea-leveltorisedramatically.ThefinalcollapseoftheLarsenBplatforminFebruary2002freedanadditional3250km2ofseabottomofanicecoverthathasbeenestimatedtohavebeenthereforatleast5000years.

Glaciers, ice shelves and icebergs

Thevanishingiceallowsvegetalandanimalplanktontoinvadeandthrive.Studieswillbecarriedouttodeterminethechangesinecosystemsstructuredlargelybyiceintheseareas.ResearcherswillmonitorpreviouslyfishedareaslocatedinthewesternpartoftheAntarcticPeninsulatodeterminethestateofstockrecovery.

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tracks,stormintensityandtheFerrel/Walkercirculations.

TheIPY-THORPEXwillalsoaddressothercoreTHORPEXgoalsinordertocontributetothedevelopmentofadvanceddata-assimilationandensemblepredictionsystemsandtocontributetothedesignanddemonstrationof interactiveforecastingsystems.TheseeffortsincludeafocusedcampaignovertheAntarcticaimedatevaluatingandimprovingsatellitedata-assimilationtechniques,which

willcontributetotheIPYcoreobjectiveofdeterminingthepresentenvironmentalstatusof thepolar regionsbyquantifying theirspatialandtemporalvariability.

The improvement insatelliteassimilationoverthepolesaffordedbythisstudywillbeanobservational legacyof improvingourabilitytopredictpolarweathersystems,theinteractionsofpolarprocesseswithlowerlatitudesandourabilitytomonitortheclimateoverthepoles.

THORPEX:acceleratingimprovementsintheaccuracyofone-daytotwo-weekhigh-impactweatherforecastsforthebenefitofsociety,theeconomyandtheenvironment

Changes in Arctic sea-ice conditions impact navigation.

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Many animals are at risk from global warming in the polar regions, such as penguins. It behoves all nations to preserve these unique communities for the benefit of future generations.

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The POles

TheglobalclimatesystemisdrivenbyenergyfromtheSun,mostofwhich,atanyonetime,arrivesatlowlatitudes.Overtheyear,theEquator receivesabout five timesasmuchheatas thePoles,creatinga largeEquator-to-Poletemperaturedifference.Theatmosphericandoceaniccirculationsrespondtothislargehorizontaltemperaturegradientbytransportingheatpolewards.Infact,theclimatesystemcanberegardedasanengine,withthelowlatitudeareasbeingtheheatsourceandthepolarregionstheheatsink.

Boththeatmosphereandtheoceansplaymajorrolesinthepolewardtransferofheat,withtheatmospherebeingresponsiblefor60percentof theheattransport,andtheocean the remaining 40 per cent. In theatmosphere,heatistransportedbyboththedepressionsandthemeanflow.Thedepres-sionscarrywarmairpolewardontheireasternsidesandcoldairtowardslowerlatitudesontheirwesternflanks.Theatmosphereisabletorespondrelativelyquicklytochangesinthehigh-orlow-latitudeheatingrates,withstormtracksandthemeanflowchangingonscalesfromdaystoyears.Oceanicchangetakesplaceonmuchlongertime-scales.

Thedifferentdistributionof landmassesinthenorthernandsouthernhemisphereshasamajorimpactontheatmosphericandoceaniccirculations,withthemeanoceanandatmosphericflowsinthesouthbeingmuchmorezonalthaninthenorth.

Virtuallyeverywhereinthesouthernhemi-sphere, the atmospheric heat transportisgreater than thecontribution fromtheoceanwhile,northoftheEquator,theoceantransportdominates fromtheEquator to17°N.Thepeakoftransportisfoundinbothhemispherescloseto35°fromtheEquator.Atthoselatitudes,theatmosphericcomponentisabout78percentofthetotalinthenorthernhemisphereand92percentinthesouthernhemisphere.

Afurtherconsequenceofthedifferentland/seaconditionsinthetwohemispheresisthat

theEquator-Poletemperaturedifferenceinthesouthisalmost40percentgreaterthaninthenorth,producingstrongermid-latitudewesterlies.

Thepolewardatmospherictransportofheatislargestduringwinter,whenthereisstrongheat lossathighlatitudesandthelargesttemperaturedifferencebetweenequatorialandtropicallatitudes.

lInks wITh lOwer laTITudes

ThepolarregionsarelinkedtotherestoftheEarth’sclimatesystembycomplexpathsthroughtheatmosphericflowandtheoceancirculation.Thecirculationoftheupperlay-ersoftheoceancanchangeovermonthstoyears,butthedeepoceanandtheglobalthermohalinecirculationrequiredecades

THE ROLE OF THE POLAR REGIONS IN THE GLOBAL CLIMATE SYSTEM

Theclimatesystemcanberegardedasanengine,withthelowlatitudeareasbeingtheheatsourceandthepolarregionstheheatsink.

Theprincipalmodesofvariabilityintheatmosphericcirculationoftheextra-tropicsandhighlatitudesarereferredtoastheNorthernHemisphereAnnularMode,whichiscloselyrelatedtotheNorthAtlanticOscillationandtheSouthernHemisphereAnnularMode(alsoknownasthehighlatitudemodeortheAntarcticOscillation).

Atmospheric conditions during the positive phase (top) and negative phase (bottom) of the North Atlantic Oscillation (see pages 18-20 for more details).

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highlatitudes,suchassurfacepressureandtemperature,geopotentialheightandzonalwind.NAMandSAMshowlittlevariabilitywithheight.Observationalandmodellingstudieshaveshownthat theycontributea largeproportionof thehigh-andmid-latitudeclimatevariabilityonalargerangeoftime-scales,withSAMbeinglikelytodrivethelarge-scalecirculationoftheSouthernOcean.SAMandNAMareusuallydefinedasthemeansea-levelpressuredifferencebetween40°and65°.

TheNorthAtlanticOscillation(NAO)iscloselylinkedtotheArcticOscillationanditsvari-abilityhasamajorinfluenceontheArcticclimate.NAOisthedominantmodeofwinterclimatevariabilityintheNorthAtlanticregion

The thermohalinecirculation links themajor oceans. It plays an extremelyimportantpartinlinkingthehigh-latituderegionswiththerestoftheEarthsystemandprovidesadirect linkbetweentheArcticandAntarctic.

Itisdrivenbydifferencesinthedensityofseawater,which,inturn,arecontrol-ledbytemperatureandsalinity.Wind-drivensurfacecurrents(suchastheGulf

Stream)headpolewardsfromtheequato-rialAtlanticOcean,coolingallthewhileandeventuallysinkingathighlatitudes(formingNorthAtlanticDeepWater).Thisdensewater thenflows into theoceanbasins.While thebulkof itupwells intheSouthernOcean, theoldestwaters(withatransittimeofaround1600years)upwell in theNorthPacific.Extensivemixing therefore takesplacebetweentheoceanbasins,reducingdifferencesbetween themandmaking theEarth’soceanaglobalsystem.

Ontheirjourney,thewatermassestrans-portbothenergy(intheformofheat)andmatter(solids,dissolvedsubstancesandgases)around theglobe.Assuch, thestateofthecirculationhasalargeimpactontheclimateofourplanet.

ThewordthermohalineisderivedfromtheGreekwordsforheat(therme)andsalt(hals),which,together,determinethedensityofseawater.

Thethermohalinecirculationisvariouslycalledtheoceanconveyorbelt,theglobalconveyorbelt,orthemeridionaloverturningcirculation.

tocenturies torespond(seeboxabove).Themostrapidlinksbetweenhighandlowlatitudesthereforetendtobethroughtheatmosphere.

Overthelastfewyears,therehasbeenagreatdealofinterestinthemodesofvariabilityofhigh-latitudeareas.Thesereflectthemeansbywhichhigh-andmid-latitudeareasinteractandcoverbroadscalechangesinatmosphericpressureandthemajorstormtracks.

TheNorthernHemisphereAnnularMode(NAM)andtheSouthernHemisphereAnnularMode(SAM)havezonallysymmetricorannu-larstructures,withsynchronousanomaliesofoppositesigninhighandmid-latitudes.Theycanbeseeninmanyparametersmeasuredat

Thermohaline circulation

Sea-to-airheat transfer

Cold and saltydeep current

Warm shallowcurrent

IndianOcean

PacificOcean

AtlanticOcean

Gulf S

tream

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ElNiño-SouthernOscillation(ENSO)isamajorfluctuationofmassacrossthetropicalPacificassociatedwithperiodsof“warm”,“cold”andintermediateconditionsinthesea-surfacetemperatures(SSTs)of theeasternPacificOcean.Duringthemorefrequent“cold”periods,thetropicalPacificischaracterizedbystrongeasterlytradewindsandameansea-levelpressuredis-tributionofhighpressureovertheeasternPacificoffSouthAmericaandlowpressurearoundIndonesia.Thisisaccompaniedbygeneralascent(descent)overthewestern(eastern)Pacificandawest-to-eastreturnflowatupper levels intheatmosphere,knownastheWalkerCirculation.

SuchascenariotendstogiveextensiveconvectiveprecipitationoverAustralasiaand Indonesia (whereSSTsarehigh),andmoresettledanticyclonicconditionsovertheeasternPacific.Thestrongeast-to-westtradewindsinduceawestward-movingoceancurrent,knownastheSouthEquatorialCurrent,withaneastward-moving return current (theEquatorial

Undercurrent)atlowerlevels.Whenthese“cold”conditionsarepronounced, thesystemisreferredtoasbeingintheLaNiñaphaseofthecycle,whentheAustralasianconvectioncanbemarkedwithfloodinginareassuchasAustraliaandIndonesia.Intheocean,theupwellingofnutrient-richwaterovertheeasternPacificcanbeextensive,withconsequentbenefitstothefisheriesofSouthAmerica.

Duringthe“warm”phaseof theENSOcycle,knowasElNiño,thereisareductioninthesurfacepressuregradientacrossthePacificandaweakeningofthetradewinds.ConvectionoverthewesternPacificdecreasesand,inextremeElNiñocondi-tions, therecanbedrought inpartsofAustralia.Themainareaoftropicalconvec-tionmoveseastwardstowardsthedatelineandSSTsriseacrossthecentralandeasternPacific.OceancurrentsarereducedinstrengthandthereisamarkedreductionintheupwellingoffSouthAmerica,withconsequenteffectsonthefishingindustryinthearea.

El Niño-Southern Oscillation

Visualization of an El Niño-Southern Oscillation event (June 1997)

Teleconnectionsarestatisticallysignificantlinksbetweenclimatesofdifferentgeographicalareaswhichcanbegreatdistancesapart.

ElNiño-SouthernOscillation(ENSO)isthelargestclimaticcycleonEarthondecadalandsub-decadaltime-scales.IthasaprofoundeffectnotonlyontheweatherandoceanicconditionsacrossthetropicalPacific,whereENSOhasitsorigins,butalsoinregionsfarremovedfromthePacificbasin.

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ThepolarregionsarekeepersoftheEarth’sclimatearchives.Theyalsoactasakindofearlywarningsystemofwhatcouldbeexpectedbytheplanetasawhole...

ClimatechangesintheAntarcticthataffecttheiceshelves,sea-iceproductionortheflowofcold,Antarcticairmassescouldhaveimplicationsfortheglobaloceansystem.

anditsinfluenceextendsintotheArcticbasin.NAOisalarge-scaleoscillationinatmosphericmassbetweenthesubtropicalhighclosetotheAzoresandthelow-pressurecentreclosetoIceland.Theindexvariesfromyeartoyearbutalsoexhibitsatendencytoremaininonephaseforintervalslastingseveralyears.

DuringthepositivephaseofNAO,thesub-tropicalhigh-pressurecentre isstrongerthanusual,whiletheIcelandiclowisdeeper.Thestrongerpressuregradientresults inmore frequentanddeeperwinterstormscrossingtheAtlanticOceanandreachingthenorthernpartsofEurope.Europegetswarm,wetwinters,butwarmairisalsocarriedintotheNorwegianandBarentsSeas,resultinginlessseaicethannormal.Ontheotherhand,thedeepIcelandiclowgivesstrongnortherly

flowdowntheLabradorSea,resultinginmoreseaicethanusualaroundGreenland.

In the negative phase of NAO, both thesubtropicalhighandtheIcelandiclowareweak,givingareducedpressuregradientandfewerandweakerwinterstormsacrosstheNorthAtlantic.ThereiscoldairacrossnorthernEuropeandinthewesternsectoroftheArctic,causingmoreextensiveseaice.Ontheotherhand,Greenlandhasmilderwintertemperatures.

DuringElNiñoevents,theintensestormactiv-ityinthetropicalPacificisclosetothedatelinewithdeepconvectiongivingdivergenceintheupperatmosphere.Thisresultsinlongmeteorologicalwavetrains(Rossbywaves)thattravelpolewardsinbothhemispheres

A new polynya formed in the Beaufort Sea in August 2006 and continued to grow. By 11 September 2006, the area of open water had grown to some 100 000 km2.

Polynyas“Polynya” isaRussianwordmeaning“anenclosedareaofunfrozenwatersur-roundedbyice”.Althoughpolynyascanbehundredsofkilometreswide,theirsurfaceareaisfar lessthantheareaofseaicewhichsurroundsthem.Somepolynyasoccurat thesametimeandplaceeachyearandcertainanimalsadapttheirlifestrategiestothisregularity.

Polynyasteemwithanimalandplantlife.Itisonlyhere,wheretheseaiceisabsent,thattheSun’senergydirectlyreachesthewaters.SnowandiceordinarilyreflectmuchoftheSun’slightenergy,buttheopenwatersofpolynyasabsorbit.

Phytoplankton in thepolynyause thisenergytoproduceanutrient-richgrazingareaforzooplankton.Feedingonthesesmallanimalsarewhalesandfishesthatin turn feedseals,walrusesandpolarbears.

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andprovideameansfortheestablishmentofteleconnectionsbetweenENSOandtheclimatesofmid-andhigh-latitudeareas.IntheNorthPacific,aclearsignalofENSOwarmeventsistransmittednorthwardsviaRossbywave trainsknownas thePacificNorthAmericanpattern.ThenorthernmostlimitofthiswavetraincanaffecttheclimateofAlaska,USA.

ThemostpronouncedsignalsofENSOinhighsouthernlatitudesarefoundovertheSouth-EastPacificasaresultofaRossbywavetraingivingpositiveheightanomaliesovertheAmundsen-BellingshausenSeaduringElNiñoeventsandnegativeanomaliesintheLaNiñaphaseofthecycle.Theextra-tropicalsignaturecansometimesshowahighdegreeofvariabilitybetweenevents inthisarea,however.

Thethermohalinecirculationisthesystemthatlinksthemajoroceans(seeboxonpage18).

TheseasaroundtheAntarcticareparticu-larlyimportantbecauseoftheproductionofAntarcticbottomwater—thedensestwatermassfoundintheoceans.AntarcticbottomwaterisformedbydeepwinterconvectionintheAntarcticcoastalregion,particularlyintheWeddellandRossSeas,butalsoinassociationwithothericeshelves.

ThewatermassisformedascoldairfromtheAntarcticrapidlycoolsthesurfacewaters,openingnear-coastalpolynyas(seeboxonpage20)andpromotingdownwardconvec-tion.Brinerejectionduringtheformationofseaiceontheoceansurfaceisalsoveryimportant,asismeltingundertheiceshelves.Antarcticbottomwaterflowsout intotheworld’soceansandisfoundbelow4000minalltheoceanbasins.

ItflowsnorthwardsintheAtlanticOcean,reachingtheArctic,whereheatisreleasedintotheatmosphere.Itcanbeappreciated,

Evidenceofwidespreadsea-icemeltingiscorroboratedbyarecentthree-foldincreaseinfreshwatercontentoftheArcticOcean.

Sea-iceareaattheendofsummer(September)hasdeclinedabout17percentoverthelast25years.Regionally,thisisseenasaretreatintheiceedgeof300-500kmintheBeaufortSeaortheeastSiberianSea,dependingontheyear.

Sea ice is important for walruses during feeding as it provides a resting place between dives and enables them to fish over a wider area.

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Taiga:theswampyconiferousforestofhighnorthernlatitudes

Tundra:avast,nearlylevel,treelessArcticregion,usuallywithamarshysurfaceandunderlyingpermafrost

ThefrozenareasoftheArctictundraandtaigacontainone-thirdoftheworld’ssoil-boundcarbon.Whenthepermafrostmelts,itreleasescarbonandmethaneintotheatmosphereandcancontributetoincreasinggreenhouse-gasconcentrations.

therefore,thatclimatechangesintheAntarcticthataffecttheiceshelves,sea-iceproductionor the flowofcold,Antarcticairmassescouldhaveimplicationsfortheglobaloceansystem.

ChangesinoceanconditionsintheArcticcanalsohavewidespreadimplications.Forexample,oceansalinityanomalies in thecentralArctichavebeenshowntopropagateintotheGreenlandSea,wheretheycancausemajormodificationstooceanstratification.

SignificantadvancesintheunderstandingoftheroleoftheArcticintheglobalclimatesys-temweremadeduringtheyears1994-2003,thedecadeoftheWorldClimateResearchProgramme’sArcticClimateSystemStudy(ACSYS).TheArctic(andtoamuchlesserextent thesub-Antarctic islands)playsafurtherimportantpartintheglobalclimate

systemasasourceandsinkof importantgreenhousegases,whichareheld in thepermafrostorseasonallyfrozenground.ThefrozengroundoftheArctictundraandtaigacontainsmethane,ozoneandcarbondioxide.Infact,theseareascontainone-thirdoftheworld’ssoil-boundcarbon.Whenpermafrostmelts,itreleasescarbonintotheatmosphereandcancontributetoincreasinggreenhouse-gasconcentrations.

recenT hIgh-laTITude envIrOnmenTal changes

Inrecentdecades,therehavebeenmajorchangesinthepolarenvironments,withrisingnear-surfaceairtemperaturescausinglargedecreasesinperennialsea-iceextentintheArctic,areductionintheamountofsnowcover,meltingofpermafrostanddecreases

The polar bear is emblematic of the Arctic region. Climate warming puts at risk his habitat, his food supply and ultimately his survival — as well as that of the indigenous human population.

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ThewindfieldoftheAntarcticisoneofthemostmarkedcharacteristicsof thecontinent,withthepersistentdownslope(katabatic)windsinpartsofthecoastalregionbeingthemostdirectionallyconstantonEarth.Thewindsarestrongestduringthewinterwhenstrongradiationalcoolingproducesalargepoolofcoldairontheplateautofeedthekatabaticwindsystem.Strongkatabaticwindsarenotfoundallaroundthecoastalregionbutareconcen-tratedinthemainglacialvalleys,particularlyaroundthecoastoftheeasternAntarctic.Climatologyprovidesagoodguidetowherethestrongestkatabaticwindsarefound,butexcellentforecastsareprovidedforthecoastalregionbynumericalweatherpredictiontechniques.

KatabaticwindsarelessofafeatureoftheArcticbecausethemountainsarelower.StrongkatabaticwindsarefoundinthecoastalregionsofGreenland,however,wheretheycanaffectlocalcommunities.

Anumberofmeteorological elementsareofparticularimportanceinthepolarregions.Oneoftheseissurfacecontrast.Thisistheeasewithwhichfeaturesonasnow-coveredsurfacecanbedistinguished,eitherfromtheairorbyasurfaceobserver.Foraviation,knowledgeofsurfacecontrastisvitalsothatsafetake-offsandlandingscanbemade.Surfacecontrastisdictatedprimarilybycloudcover; incloud-freeconditions,thesurfacecontrastisusuallyexcellentbecauseofthesmallamountsofaerosol thatarepresent inthepolaratmosphereandverygoodvisibility.Thegreatestproblemsareencounteredwithdeep,opaquelayersofcloud,oftenintheformoffeaturelessStratus,Altostratusor

Nimbostratus.Undersuchconditions,itisoftenimpossibleforanobservertoseesmallmoundsorcrevassesonthesurfacewhenonlyafewmetresaway.Aforecastofsurfacecontrastisthereforeessentiallyoneofthetypeanddepthofcloudtobeexpectedatagivenlocation.

Arelatedquantityishorizontaldefinition,whichistheeasewithwhichtheboundarybetweenthegroundandtheskycanbedetermined.Theparameterisextremelyimportantforflyingoperationsontheiceshelvesandinfeaturelesspartsofthepolarregions,suchastheinteriorAntarcticpla-teauorthecentreofGreenland.Inasimilarwaytosurfacecontrast,horizontaldefinitionisdeterminedprimarilybythetypeandnatureof thecloudpresent.TheworstconditionsareexperiencedwhenthereisathicklayerofStratus,AltostratusorNimbostratus.Aswithsurfacecontrast,theforecastingofhorizontaldefinitioniscarriedoutonceaforecasthasbeenmadeofthecloudtobeexpected.Thekeyelementsrequiredarepredictionsoftypeanddepthofcloud,plusknowledgeoflocalorography.Together,theseallowasubjectiveforecastofthehorizontaldefinitiontobemade.

Weather forecasting problems specific to the polar regions

Akatabaticwindisawindthatblowsdownatopographicinclinesuchasahill,mountainorglacier.

Therehavebeencontrastingtrendsinpolarseaiceoverthelastcoupleofdecades,withalargelossoficeintheArcticandaslightincreaseintheAntarctic.

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Satelliteshaverevolutionizedmeteorologicalscienceandclimateandenvironmentmonitoring.Theyenablescientiststoobserveandmonitortheextentofpackice,thevolumeoficecaps,theproductivityofoceanwatersandlevelsofstratosphericozone.

Someofthelargestenvironmentalchangeshavetakenplaceathighlatitudes.

inriverandlakeice.MeltingglaciersinmanypartsoftheArcticarecontributingtorisingsea-levelworldwide.InareassuchasAlaska,meltingglacierscanhavepronouncedregionaleffectsthroughthecontributionoftheirrunofftooceancurrentsandmarineecosystemsintheGulfofAlaskaandBeringSea.Changeis lessevidentandlesswidespreadintheAntarcticthanintheArctic.

Investigatinghigh-latitudeclimatechangepresentsanumberofproblems.Thepeoplesof theArctichave reportedwarmerandincreasinglyvariableweather,aswellaschangesinterrestrialandmarineecosys-tems,whichhavehadanimpactontheirtraditionalwayoflife.

Thelengthoftherecords,however,israthershortcomparedtowhatisavailableinthemorepopulouspartsoftheworld.AroundtheArctic,theclimaterecordsextendback

overacenturyinsomeareas,butonlyabout50yearsintheAntarctic.Theseobserva-tionsprovideuswith themostaccuratemeasurementsofatmosphericconditions,yettheobservationsarewidelyseparatedinmany regions,with fewobservationsfromovertheoceans.

TemperatureAnalysesofsurfacemeteorologicalobser-vationssuggest that thenear-surfaceairtemperature of the Earth increased byapproximately0.6°Coverthelastcentury.However,thepatternofsurfacechangeacrosstheEarthintheinstrumentaleraiscomplexandsensitivetotheperiodthatisexamined.Manystudieshighlightthatsomeofthelarg-estenvironmentalchangeshavetakenplaceathighlatitudes.

ThemapoflineartrendsofannualsurfacetemperatureacrosstheEarthoverthelast

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50years indicatesthree“hotspots”overAlaska/northernCanada,centralSiberiaandtheAntarcticPeninsula.Theseareashaveallexperiencedannualmeantemperaturerisesofmorethan1.5°Coverthepast50years.

IntheArctic,thespatialandtemporalpatternoftemperaturechangehasbeencomplex.Time-seriesofseasonalsurfacetemperatureanomaliesfrom59weatherstationsshowmanywarmandcoldperiodsthatwereoftenfoundonlyinlimitedsectors.

Oneofthemostpronouncedwarmperiodshaditspeakaround1940asevidencedbytemperaturerecordsandbythelimitedareaofseaicearoundIceland.Experimentswithclimatemodelsforcedbyincreasinglevelsofgreenhousegaseshavenotbeenabletoreproducethiswarmperiod,suggestingthatitmayhaveoccurredbecauseofnaturalclimateinterdecadalvariability.

ThewarmingtrendacrossAlaskaandnorth-ernCanadaisprimarilyassociatedwithasuddenwarmingaroundthemid-1970s.TheclimateofAlaskaisstronglyinfluencedbytheclimatological low-pressurecentrelocatedovertheAleutianIslands.Whenthislowisdeep,Alaskacomesundertheinfluenceofwarm,southerlyairmasses.Whenthelowisweak,thencold,northerlyairmassesbecome

morecommonandtemperaturesarelower.Inthemid-1970stheshiftedphaseofthePacificDecadalOscillation(amajorclimatecycleofthePacificregion)resultedinadeepeningoftheAleutianLow,andwarmerconditionsintheAlaskanarea.

TheSiberianwarmingontheotherhandseemstobeassociatedwiththeshiftoftheNorthAtlanticOscillation/ArcticOscillationintoitspositivephaseoverrecentdecades,resultinginthegreatertransportofwarmAtlanticairacrossEuropeandintocentralAsia.

Whilethereweremoreregional/temporalepisodicwarmevents fromthe1930s tothe1950s,warmtemperaturesweremoregeneralacrosstheArcticduringthe1990s.Surfacedatafor1979-1995fromthecentralArcticshowlargewarmingtrendsforspringfollowedbywinter,whiletrendsaresmallforsummerandautumn.Surfaceair-temperaturewarmingtrendsaregreaterforinlandregionsthancoastal/oceanregions.Siberiahadwarmanomaliesaround1980andtheregionfromeastSiberiatoCanadahasbeenwarmsince1989.ManyArcticstationsshowpositivespringanomaliesfor2002–2005andwestGreenlandhasbeenwarmsince1999. Inadditiontochangesinmeantemperatures,Alaskashowsasubstantialdecreaseinthenumberofextremelycolddays.

IntheAntarctic,thepictureofrecentclimatechangeisquitedifferent,withfewsignificanttemperaturechangesbeyondtheAntarcticPeninsula.TemperaturesattheSouthPolehavedroppedsincethe1950sasthewester-liesincreasedaroundthecontinentwiththeSouthernHemisphereAnnularModeshiftingintoitspositivephase.TherehavebeennosignificantchangesattheVostokstationontheeasternAntarcticplateau,however.

AcrosstheAntarcticpeninsula,temperaturechangeshavebeenquitedifferentontheeasternandwesternsides.Theeasternwarm-inghasbeenmostpronouncedduringthesummerandautumnseasons,andhasbeenlinkedtothestrongerwesterlies,whichareaconsequenceofthechangesintheSouthern

Overthenextcentury,near-surfaceairtemperaturesareexpectedtorisemoreinthepolarregionsthaninanyotherpartsoftheEarth.Thiswillhaveseriousimplicationsforthecryosphere,oceanicandatmosphericcirculations,theterrestrialenvironmentandtheindigenouspeoplesoftheArctic.

Satellites provide invaluable environmental data, especially over areas where surface observations are sparse.

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HemisphereAnnularMode.Duringtheseseasons,morewarmairmassesarecrossingthepeninsulacomparedtoearlierdecades,raisingtemperaturesbyseveraldegrees.Sincetemperatureswerepreviouslyclosetofreezingpoint,thishashadamajorimpactontheenvironment,includingcontributingtothebreak-upofseveraliceshelves.Ofcourse,thelossoftheiceshelvesdoesnotdirectlyaffectsea-levelsincetheywerealreadyfloatingontheoceanbuttheirdisintegrationmayresultinglaciersontheeasternsideofthepeninsulaflowingmorequickly.

Temperatureson thewesternsideof theAntarcticpeninsulahaverisenbymorethananywhereelseinthesouthernhemisphere,withinsitudataindicatingwarmingsof3°Cintheannualmeanand5°Cinwintertem-peraturesoverthelast50years.Inthisarea,thereisacloseassociationbetweenwinterseasontemperaturesandtheextentofseaiceoffthecoast,withyearsofextensiveiceresultingincoldtemperaturesandyearsoflittleiceyieldinghightemperatures.Thelargewarmingtrendintheareasuggestsmoreextensivesea ice inthe1950sand1960s,althoughthereasons for thisarenotyetunderstood.Thehighertemperatureshavebeenaccompaniedbyagreaternumberofprecipitationevents,withalargeincreaseinthenumberofreportsofsummerrainfall.

sea icePrior tothe1970s,ourknowledgeofsea-iceextentandconcentrationwasmostlybasedonshipandaircraftobservations,withsomeinformationfromcoastalstations.ThemajorityofthesedataarefromtheArctic,whereithasprovedpossibletoprepareice

analysesfortheEurasianArcticthatextendbackto1930.SomeNorwegianicechartsalsoexistfortheNorthAtlanticgoingbacktothe1500s,althoughthedataonwhichtheyarebasedareextremelysparseintheearlyyears.Drawinglargelyonthissource,theWCRPACSYSprojectwasabletoproduceaclimatologyofArcticOceansea-iceedgedatingbackasfaras1553.

Reliable,highhorizontalresolutionsea-iceextentandconcentrationdataareavailableforthepolarregionsfrom1978,whenthescanningmultichannelmicrowaveradiometerinstrumentwasfirstflownontheNimbus-7polar-orbitingsatellite.Suchdatashowedthat,overtheperiod1978-1996,Arcticseaicedecreasedby2.8percentperdecadeor34300km2peryear.Thesereductionstookplaceinallseasonsandovertheyearasawhole,butthelossesweregreatest inthespringandsmallestintheautumn.Thegreat-estlosseswereintheKaraandBarentsSeaswithdecreasesof10.5percentperdecade.SmallerlevelsoficelosshavetakenplaceintheSeasofOkhotskandJapan(greatestinwinter)andtheArcticOcean.LessericelossoccurredintheGreenlandSea,HudsonBayandtheCanadianArchipelago.

Sincethemid-1990s,therehavebeenseveralyearswithrecordlowsummer-iceextents.DatafromtheUSNationalSnowandIceDataCenterindicateaSeptemberdeclineofmorethan8percentperdecadefrom1979to2005.Basedonthefrequencyofnear-recordlowice

ShrinkingpackiceintheArctichascausedareductioninthenumberofsealswhicharetheprincipalfoodforpolarbears.

Polar ice cover as seen by satellite

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extents,itislikelythattheArcticSeaisonanaccelerating,long-termdecline.Inaddition,therecenticeminimumwasbelievedtobelowerthantheArcticiceminimaofthe1930sand1940s.

Thewinterof2004/2005wasremarkableinthatsea-icerecoveryduringtheseasonwas the smallest in the satellite record.Astemperaturesdroppedoverthewinter,sea iceformedbut,withtheexceptionofMay2005, everymonth fromDecember2004setanewrecord low iceextent forthatmonth.September2005sawanewrecordminimuminArcticsea-iceextentsurpassingthepreviousrecordlowin2002.On21September2005,thefive-dayrunningmeansea-iceextentdroppedto5.32mil-lionkm2, the lowesteverobserved in thesatelliterecord,startingin1978.Allfouryears2002-2005had iceextentsapproximately20percentlessthanthe1978-2000mean,withthelossofseaiceamountingtoapproxi-mately1.3millionkm2.

TheextentandconcentrationofAntarcticseaiceareknownwithconfidenceonlysince

the1970s,whenreliablesatellitepassivemicrowaveobservationsbecameavailable.Thesedatashowthat,fortheperiod1979-1998,Antarcticseaiceasawholeincreasedby11180km2peryearor0.98percentperdecade.Regionally,thetrendsinextentwerepositiveintheWeddellSea,PacificOceanandRossSeasectors,slightlynegativeintheIndianOceansectorandstronglynegativeintheBellingshausen-AmundsenSeas.ThisisconsistentwiththeongoingwarmingonthewesternsideoftheAntarcticPeninsula,whichiscloselycoupledwiththeoceanicconditionsoftheAmundsen-BellingshausenSea.Forallsectors,thesea-iceincreasesoccurredinallseasons,withthelargestincreaseduringtheautumn.Fromregiontoregion,thetrendsaredifferentacrosstheseasons.

Thereareonlylimiteddataavailableonsea-icethickness,butdatafroma1000kmtransectintwosummercruisesin1958and1970sug-gestedthatthedrafthaddecreasedby0.2minthetranspolardriftstreamandtheEurasianbasinandby0.7mintheCanadianBasin.Thereisalsoevidenceofsea-icethinningof0.8mover1976-1987betweenFramStrait

TheAntarctichasnopermanenthumanresidentsandhasneverhadanindigenouspopulation.Onlycertainplantsandanimalscansurvivethere,includingpenguins,furseals,mosses,lichensandalgae.

TheArcticismostlyavast,ice-coveredocean,surroundedbytreeless,frozenground.Itteemswithlife,includingorganismslivingintheice,fishandmarinemammals,birds,landanimalsandhumansocieties.

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andthePoleandof2.2mnorthofGreenland.Upward-lookingsonarmeasurementsofsea-icedraft fromsubmarinesprovidearecordextendingbackintothe1950s.Thesehaveprovidedthefirstpersuasiveevidenceoflarge-scalethinningovertheentireArcticbasin.Suchdatashowedthat,between1958and1976andbetween1993and1997,themeanicedraftattheendofthemeltseasonhaddecreasedinmostdeepwaterpartsoftheArcticOcean, from3.1min theearlyperiodto1.8minthe1990s, i.e.byabout1.3mor40percent.

PermafrostLossofpermafrostintheArcticisalreadyhavingaprofoundeffectontheenvironmentbecauseoftheseveredamagethatcanbecausedtobuildingsreliantonpermafrostforsolidfoundations.Thetrans-Arcticpipeline,whichrunsforsome1287kmacrossAlaska,wasahugelyexpensiveenterprise,butbreaksinthepipelineandotherrepaircostsduetomeltingpermafrostcouldbecomesignificant.Thenear-termriskofdisruptiontoopera-tionsofthepipelineisjudgedtobesmall,althoughcostlyincreasesinmaintenanceduetoincreasedgroundinstabilityarelikely.Wecanexpecttoseeincreasesinsuchpotentiallydamagingslumpingof landinthecomingdecades.

The ice sheets and sea-levelThealtimetersthathavebeenflownsincetheearly1990sonpolar-orbitingsatellitesallowustodeterminetheheightofmajoricesheetsandthereforetoinvestigatethequestionofmassbalance—whethertheicesheetsaregrowingorshrinking.Themassbalanceofanicesheet isdependentonanumberoffactors,includingthesnowthatfallsonit,theamountofsnowthatisblownintotheocean,thelossofmassviaicebergcalvingandtheisostaticadjustment.

Between1992and2002,theGreenlandicesheetshowedamixedpatternofthickeningandthinning.Above1200melevation,therehasbeenthickeningof4cmperyearandicegrowthof53gigatonnes(Gt)peryear.Belowthatelevation, therehasbeenthinningof21cmperyearandashrinkageof42Gtper

year.Thishasresultedinasmalloverallmassgainof11Gtperyear,whichisequivalenttoadropof-0.03mmperyearinsea-level.

ThewestAntarcticicesheetislosingmassatarateof-47Gtperyear,whiletheicesheetintheeasternAntarcticshowsasmallmassgainof+16Gtperyear.Thecombinednetchangehasbeen-31Gtperyearoranincreaseinsea-levelof+0.08mmperyear.

Thisisofparticularinterest,sincemuchofitisgroundedbelowsea-level.AcompletelossofthewestAntarcticicesheetwouldresultina5msea-levelrisesothereisobviousconcernoverthedisintegrationofevenasmallsection.SatellitedatahaverecentlyrevealedathinningofpartoftheicesheetinthevicinityofPineIslandglacier.ThisisthelargestglacierinthewesternAntarctic.Itisupto2500mthickandisgroundedover1500mbelowsea-level.Intheeightyearsfrom1992,theglacierretreatedinlandbyover5kmwiththelossof31km3ofice.ThelossoficefromthePineIslandandThwaitesglacierbasinsareprobablyice-dynamicresponsestolong-termclimatechangeandmaybealsotopastremovaloftheiradjacenticeshelves.Ifthepresentrateofthinningcontinues,itisthoughtthatthewholePineIslandglaciercouldbelosttotheoceanwithinafewhun-dredyears.An importantresearchtargetmustbetounderstandwhythisglacier iscurrentlyshrinking,whetherthisisaresultofanthropogenicactivityandwhether,ina

Risingtemperaturesareaffectingpenguinpopulationswithgrowthoccurringinsomepartsanddeclineinothers,especiallywherethefoodsupply—krill—isdisappearing.

Oilpipelinesacrossareasofpermafrosthavefractured,resultinginsignificantpollutionandenvironmentaldamage.

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warmingworld,thethinningofotherglacierscouldstart toaccelerateanddrainmoreicefromthe interiorof the icesheetwithconsequentimpactsonsea-level.

Since1992,globalmeansea-levelhasbeenrisingatarateof3.2±0.4mmperyear,comparedto1.7±0.3mmperyear inthepreviouscentury.Thisisfasterthantherateof1mmperyearthathascharacterizedthelast5000years.Sea-levelriseisaresultofthermalexpansionoftheocean,increasedriverflowintotheocean,changesinprecipita-tion/evaporationandlossoficefromtheicesheets.Theexactreasonsforthecurrentriseinsea-levelarenotknownandareamajortopicofresearch.

The antarctic ozone holeOzoneisanextremelyimportantgasinthestratosphereasitabsorbssolarultraviolet(UV)light,protectinghumansandotherele-mentsofthebiosphere.ThetotalamountofozonethroughthedepthoftheatmospherewasfirstmeasuredintheAntarcticduringtheIGY(1957-1958)bysurface-basedinstru-ments.Theseshowedthat typicalvaluesforthetotalozoneamountwerearound300DobsonUnits(DU),whichcorrespondstoalayerofozone3mmthickatthesurface.

TheseasonalcycleofozoneintheAntarcticislinkedtothedevelopmentandbreakdownofthewintercircumpolarvortex,whichisthestrongcirculationaroundhighsouthernlatitudes.Historically,ozonevalueswithinthevortexwerearound300DUatthebegin-ningof thewinterandsimilarat theend.Duringthewinter,ozoneamountsbuildupinacircumpolarbelt justoutsidethevor-tex,duetotransportofozonefromsourceregionsinthetropics.Sincethemid-1970s,anincreasinglydifferentpatternofbehaviourhasbeenobserved—theAntarcticozonehole.Attheendofwinter,valueswerefoundtobearound10percent lowerthantheywere inthe1970sandtheythendroppedabout1percentperdaytoreacharound100DUattheendofSeptember.Valuesthenslowlybegantorecoverasthestratospherewarmed.Becausethespringwarminginthestratosphereisoftendelayedtotheendof

NovemberorintoDecember,theozoneholecanlastseveralmonths.

TheAntarcticozoneholedevelopedbecauseofemissions,mainlyinthenorthernhemi-sphere,ofchlorofluorocarbons(CFCs)andhalons.Thesegaseswerewidelyused inrefrigeration,asindustrialsolventsandforfirecontrol.IftheprovisionsoftheMontrealProtocolonSubstances thatDeplete theOzoneLayerof1987arestrengthenedandfollowed,andaccordingtotheUNEP/WMO“ScientificAssessmentofOzoneDepletion:2006”,theozonelayeroverthemid-latitudesshouldrecoverbyapproximatelythemiddleofthiscentury.OvertheAntarctic,therecoverywouldtakeapproximately15yearslonger.Currently,itseemstohavestabilized,withsomevariationfromyeartoyear,dependingonatmosphericconditions.

WhiletheAntarcticozoneholeispresent,there are increased levels of ultravioletradiationat thesurfaceof thecontinent,whichcanbeahazardtohumansandbiota.Reducedlevelsofozonecanalsohaveanimpactonlowerlatitudes.ThepolarvortexcanfrequentlybecomeelongatedandextendoverthesouthernpartofSouthAmericaandAustralia,resultinginincreasedUVatthesurfacethere.Manynewspapers intheseregionsprovidereportsandpredictionsofUV levels toalert thecommunity to takeprecautionsandusesunblock.

FourmillionindigenouspeoplesliveoneightmillionsquarekilometresofthehabitableArcticlandmass.

ManystudieshighlightthevulnerabilityoftheGreenlandicesheetinaworldofincreasingairtemperatures.

Ifsea-levelcontinuestoriseatitspresentrateormore,itwillposeaverysignificantproblemforlow-lyingareasacrosstheworld.

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hOw wIll The POlar regIOns change In The FuTure?

Possible consequences for the rest of the globeThemaintoolswehaveforpredictinghowtheclimateoftheEarthwillevolvearecoupledatmosphere-oceanclimatemodels.Yetcur-rentclimatemodelsdonotworkwellinthepolarregionsintryingtosimulatetheclimateofthe20thcentury.Forexample,theyfailed

topredictatmosphericconditionsthat ledinrecentyearstothedramaticbreak-upofAntarcticiceshelves.Furthermore,thevari-ousmodelshaveahighdegreeofvariabilityintheirpredictions.Researchisneededtorefinetheiroutputs.

atmospheric circulationModelpredictionssuggestthat,withincreas-inglevelsofgreenhousegases,theSouthernHemisphereAnnularModeandtheNorthern

From21to30September2006,theaverageareaoftheAntarcticozoneholewasthelargesteverobserved,breakingrecordsforbothareaanddepth.A littleoveraweekaftertheozoneholesustaineditsnewrecordhighforaveragearea,satellitesandballoon-basedinstrumentsrecordedthelowestconcentrationsofozoneeverobservedovertheAntarctic,makingtheozoneholethedeepestithadeverbeen.

Thenewrecordsetin2006,bycontrast,wasforthelargestaverageareaoveran11-dayperiod, indicating that theholestayedlargerforlongerthaniteverhasbefore.

Whilehuman-producedcompoundsbreakdowntheozoneholebyreleasingchlorineandbrominegasesintotheatmosphere,thetemperatureoftheAntarcticstratospherecausestheseverityoftheozoneholetovaryfromyeartoyear.Colder-than-averagetemperaturesresultinlargeranddeeperozoneholes,whilewarmertemperaturesleadtosmallerones.In2006,temperaturesplungedwellbelowaverage,hoveringnearordippingbelowrecord-lows.Theseunusuallycoldtemperaturesincreasedthesizeoftheozonehole.

DepletionoftheArcticozonelayerhasalsobeenobserved,albeittoalesserextent,becausethetemperatures in the lowerstratospherethereusuallyremainhigherthanthoseovertheAntarctic.Ozonedeple-tionisaconcernintheArctic,however,becauseofthehumansettlementsthereandtherisktothefishandanimallifewhichistheirtraditionalsourceoffood.

The Antarctic ozone hole in 2006

The Antarctic ozone hole on 24 September 2006. The blues and purples indicate low ozone levels, while greens, yellows and red point to higher ozone levels.

TheozonelayerprotectslifeonEarthbyblockingharmfulultravioletraysfromtheSun.The“ozonehole”isaseveredepletionoftheozonelayerhighabovetheAntarctic.

The1987MontrealProtocoltotheViennaConventionfortheProtectionoftheOzoneLayer(1985)bannedozone-depletingchemicals,butthelonglifetimeofthosechemicalsmeansthattheozonelayerwillnotrecoverforseveraldecades.

TheannualassessmentsofthestateoftheozonelayerovertheAntarcticandArcticarebasedondatacollectedbyWMO’sGlobalAtmosphereWatch.DuringtheAntarcticozoneholeseasonfromlateAugustthroughNovember,WMOissuesbi-weeklybulletinsonthestateoftheozonelayer.Moreinformationcanbefoundat:http://www.wmo.int/web/arep/ozone.html.

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HemisphereAnnularModemaybeintheirpositivephaseforagreaterlengthoftime.Thiswillresult inloweratmosphericpres-suresovertheArcticandAntarcticandhigherpressuresatmid-latitudes.Withthegreaterpressuregradientbetweenthemid-latitudesandthePoles,therewillbeanincreaseinthestrengthofmid-latitudewesterlywinds.

TemperatureThe IntergovernmentalPanelonClimateChange (IPCC)ThirdAssessmentReport(2001)estimatedthat,overtheperiod1990-2100,globallyaveragedsurfacetemperatureswillriseby1.4-5.8°C.Thisrangeofestimatescomesfromtheoutputsof35greenhouse-gasemissionscenariosandanumberofclimatemodels.

The model runs for the IPCC’s FourthAssessmentReportsuggest that,withanincreaseingreenhousegasesof1percentperyear,annualmeansurfacetemperaturesintheAntarcticsea-icezoneoverthe21stcenturywould increaseby0.2-0.3°Cperdecade.Therewouldbeacorrespondingdecreaseintheextentofseaice.LargepartsofthehighinterioroftheAntarcticwouldexperiencesurfacetemperaturerisesofmorethan0.3°Cperdecade.Thiswouldweakenthekatabaticwinds,especiallyinthesummerseason.

FortheArctic,amajorfocusofresearchhasbeentheArcticClimateImpactAssessment,whichinvolvedhundredsofresearchscien-tists.Basedontheresultsfromanaverageoftheoutputfromfiveclimatemodels,whichwerealsousedfor the IPCC,temperatureprojectionswereproducedforthenextcen-tury.Themodelsallpredictedasteadyriseinannualmeantemperaturewith,onaverage,temperaturesbeing4°Chigherby2100.

ThemodelssuggestthelargesttemperatureincreaseswillbeinautumnandwinteraftermuchoftheArctic’sseaicehaseithergoneorthinned.Thealbedofeedbackassociatedwithretreatingseaicedominatesthesignalofhigh-latitudeclimatewarming.

Withrising temperatures, therewillbeanorthwardshiftoftheArcticclimaticzoneswithapolewardextensionof theborealforestsandthetreeline.ThiswillresultinatransformationofArcticlandscapes,withthenorthernedgeoftheborealforestadvancingintotheareanowcoveredbytundra.InareassuchasAlaskatherearefearsthattherewillbealossofthemoistureneededforforestgrowth,ariseintreemortalitycausedbyinva-sionsofinsects,increasedriskoflargefiresanddetrimentalchangestothereproductionofsometrees,suchaswhitespruce.

TheIPCChasestimatedthat,overtheperiod1990-2100,globallyaveragedsurfacetemperatureswillriseby1.4-5.8°C.

Ithasalsoestimatedthat,by2100,sea-levelmayhaverisenbybetween0.09and0.88m.

Albedo:theratiooftheoutgoingsolarradiationreflectedbyanobjecttotheincomingsolarradiationincidentuponit.

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TheArcticCouncilisagroupingoftheeightcountriesthathaveterritoryintheArctic:Canada,Denmark(Greenland,FaeroeIslands),Finland,Iceland,Norway,theRussianFederation,SwedenandtheUSA.

ThefocusoftheArcticCouncilistheenvironmentandsustainabledevelopment.

http://www.arctic-council.org/

AcrosstheAntarctic,manymammalsandplantspeciesrequirespecificclimaticcondi-tionsinwhichtoflourish,withtemperatureandtheamountofliquidprecipitationbeingparticularlyimportant,althoughthelevelofUV-Bradiationisalsoasignificantfactor.TheamountofUV-BradiationreceivedinthespringhasincreasedmarkedlyinrecentyearswiththeappearanceoftheAntarcticozonehole,withconsequentimpactonthebiota.Increasingtemperatureswouldextendtheactiveseason,boostdevelopmentratesandreducethelifecycleduration.Inaddition,therewouldbereducedstresstolerance,altereddistributionofspeciesandexoticcoloniza-tion.Anincreaseinwateravailabilitywouldcreateanextendedactiveseason,furtherthelocaldistributionofspeciesandexposenewgroundforcolonization.Meanwhile,anincreaseinUV-Bradiationcouldalterresourceallocation,damagecellularstructuresandimpactthefoodchain.

sea iceBecause sea-surface temperatures areincreasing, theextentofbothArcticandAntarcticseaisexpectedtodecreaseoverthenextcentury.ItisthoughtthatthisprocesswillbeamplifiedbyfeedbacksintheArctic,withsomeclimatemodelspredictingthatallsummerseasonseaicewilldisappearbythesecondhalfofthe21stcentury.

Sea-iceretreatwillallowlargerstormsurgestodevelop in largerareasofopenwater,increasingerosion throughgreaterwaveactivity.Therewouldalsobesedimentationandtheriskoffloodingincoastalareas.

AlthoughlossofArcticseaicecouldhaveseriousimplicationsfortheoceancirculation,therecouldbesomebenefits in termsofnavigationaroundthenorthernpartsoftheRussianFederationandCanada.Alongerice-freesummerseasoncouldprovidesubstantial

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IndigenouspeoplesoftheArcticincludetheAleut,Athabaskan,Gwich’in,InuitandSaami.

IndigenousleadershavecalledontheArcticCounciltodevelopanimpactsandadaptationprogrammethatwouldincludecommunity-basedpilotprojectsonadaptation,andthatwouldstressworkoneducation,outreachandcommunications,andcapacity-building.

Salekhard(RussianFederation)istheonlycityintheworldsituatedonthepolarcircle.

benefitsformarinetransportandoffshoregasandoiloperations,whichcouldhavemajorimplicationsforinternationaltrade.

LossofseaicearoundtheAntarcticthreatenslarge-scalechangesinmarineecosystems,includingthreatstopopulationsofmarinemammals,suchaspenguinsandseals.OfthesixspeciesofAntarcticseal,fourbreedontheseaiceduringspringandmaybeaffectedbymajorreductionsinsea-iceextent.Atpresent,theAntarcticseaicesheltersthelarvaeofthevastkrillpopulationthatfeedscountlessseabirds,sealsandwhales;seriousreductionsintheextentofseaicewoulddiminishthekrillpopulation,withsubsequenteffectsonhigherpredators.

PermafrostPermafrostishighlysensitivetolong-termatmosphericwarming,so therewillbeaprogressivethawof thepermanentlyandseasonallyfrozengroundaroundtheArctic.TheIPCChasestimatedthat,undersomegreenhouse-gasemissionscenarios,90percentoftheupperlayerofArcticpermafrostmaythaw.

Thelossofpermafrostwillbringdestructionoftreesandlossofborealforests,therelease

of thawwaterandtheexpansionof thawlakes,grasslandsandwetlands.Thiswillresultinchangestohabitatsandecosystems,suchaslossofhabitatforcaribouandter-restrialbirdsandmammals—buttherewillbeadditionalhabitatforaquaticbirdsandmammals.

Lossofpermafrostwillalsoresultinincreasederosionandsoilinstability,especiallyonthecoastandalongthebanksofrivers.Thiscouldresult in theblockingofstreamsthatareimportantforsalmonspawning.Therecouldalsobeincreasedoccurrenceoflandslidesanddevelopmentoftalik(ayear-roundthawedlayerofwhatwasformerlypermafrost)andincreasedwatertabledepth.Someofthemajorimpactsonthecommunitycouldbethroughdamagetobuildings,roadsandotherinfrastructure.

ThemeltingofArcticpermafrosthasseriousimplicationsfor thecarboncycleandthelevelsofgreenhousegasesintheatmosphere.Inthepast,permafrosthasbeenasinkofcar-bon,whichislockedintothefrozenground.However,withmeltingand the resultingwarmersoils, therewillbean increase inspeedofdecompositionandthereleaseofthegreenhousegasescarbondioxideandmethaneintotheatmosphere.

TheWCRPClimateandCryosphere(CliC)Project, the International PermafrostAssociation,andtheGlobalCarbonProjectof theEarthSystemSciencePartnershiparecurrentlyundertakingastudyaimedatassessingmoreexactlythecarbonpoolsinpermafrostandthepotentialimpactsoftheirrelease into theatmosphere inawarmerclimate.

The oceansPredictinghowtheoceancirculationwillevolveinthenextcenturyisextremelydif-ficult.Becausetheoceanisseriouslyunder-sampledcomparedwith theatmosphere,westillhaveapoorunderstandingofrecentoceanvariability.Nevertheless,somerea-sonablepredictionscanbemade. In theAntarctic,with theSouthernHemisphereAnnularModebeing in itsmorepositive

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InOctober2006,theRussianAssociationofIndigenousPeoplesoftheNorthtoldtheArcticCouncilthatdevelopmentpressuresandpollutionwerethreateningreindeerpastures,huntingandfishingactivitiesandsacredsites.

phaseandthewesterliesbeingstronger,itisexpectedthattheAntarcticcircumpolarcurrentwillstrengthen.

TheAntarcticcoastalregionisoneoftheprimaryareasfortheproductionofbottomwaterby thesinkingofcolddensewateroncontinentalshelves.Thesedensecoldwaterscarryabundantoxygenintotheoceandeeps,therebycoolingandventilatingdeepoceanspace.Withtheproductionof lessseaicebeinglikelyoverthenextcentury,itseemsprobablethatlessbottomwaterwillbeproduced,raisingtheconcernthatthedeepoceansmaywarm.

IntheArcticthelossofseaice,increasedriverrunoff,precipitation,meltingoftheGreenlandicesheetandtheattendantfresheningofthewatersintheupperlayeroftheoceanwillsimilarlymeanlessproductionoftheNorthAtlanticdeepwater that feeds theAntarcticregionthroughtheglobalthermo-halineconveyorbelt.ThusbothArcticandAntarcticprocesseswillcombinetoreducetheintensityofthethermohalinecirculation.Thatreductionmay,inturn,weakentheGulfStreamandNorthAtlanticDrift.ThishasthepotentialtoseriouslyaffecttheclimateofnorthernEurope,possiblyloweringsurfacetemperaturesbyseveraldegrees.

The ice sheets and sea-levelWithrisingsurfacetemperaturesoverthenextcentury,itisestimatedthatglaciers,icecapsandsnowcoverwillallcontract.Theextenttowhichtheywilldoso,andhowfastitwillhappenindifferentregions,isstillamatterforcalculationanddebate.ItisveryunlikelythattherewillbeamajordisintegrationofthemainAntarcticicesheetduringthenextfewcenturiesbutsomepartsoftheAntarctichaveshownrapidglaciologicalchangesoverthelastfewyears,indicatingasensitivitytoclimaticfactors.MostofthemainAntarcticicesheetistoocoldforwidespreadsurfacemeltingandit isexpectedthat itwillgainicethroughincreasedsnowfalloverthenextcentury,whichwillacttoreduceglobalsea-levelbyabout10cm.Inresponsetofurtherlossoftheiceshelvesbyoceanwarmingortosurfacemeltingatthemargins,however,therecouldbeanaccelerationof the iceflowfromthe interior,which iscurrentlydammedbycoastaliceshelves.Theimpactofsucheffectscouldoffsetoroutweighgreatersnowfallacrossthecontinent.

ThelossoficeshelvesaroundtheAntarcticpeninsula inrecentyearshasoftenbeenreportedandattributedtoanthropogenicactivity.Thereiscertainlyevidencethatthewarmingduringthesummerontheeastern

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ThepeoplesoftheArctichavereportedwarmerandincreasinglyvariableweather,aswellaschangesinterrestrialandmarineecosystems,whichhavehadanimpactontheirtraditionalwayoflife.

sideofthepeninsulais,atleastinpart,aresultofatmosphericcirculationchangesassociatedwith“globalwarming”. Ifgreenhousegaslevelscontinuetoincrease,wemaywellseefurtherlossoficeshelvesinthisregion.Ofcourse,iceshelvesarealreadyfloatingontheoceanandtheirlossdoesnotcontributetosea-levelrise.Itisatpresentunclearwhethertheicestreamsthatflowintotheiceshelveswillaccelerateoncetheshelveshavedisap-peared,soleadingtoamorerapiddrainingoficefromtheinterioroftheAntarctic.Thereisevidencefromthepeninsulathatsome87percentoftheglacierstherehaveshownsignsofretreatingoverthepast50years.Thispatternseemslikelytocontinuewithcontinuedwarming.

Overthenextcentury,majorchangesintheGreenlandicesheetareexpected.Higherairtemperaturesarelikelytotriggergreatersnowfalloverthehigh,interiorparts,increas-ingsurfaceelevations.Atlowerlevels,onthefringesofGreenland,warmerconditionswillmelttheiceandpromptincreasedrunoff.In

addition,therecouldbeagreateramountof icebergcalving.At theedgeof the icesheet it isexpectedthat the lossofmassthroughrunoffwillexceedthegain fromgreaterprecipitation.Expertsalsopredictanoveralllossofice,whichwillresultinachangeofsea-levelof-0.02to0.09m.Thiscomparestothecontributiontosea-levelrisefromtheAntarctic,whichisestimatedat-0.17to+0.02m.

Asnear-surfaceairtemperaturesincreaseworldwide,athermalexpansionoftheoceanswill leadtoariseinsea-levelestimatedat0.11-0.43m.Thiswillbeaugmentedormiti-gatedbycontributionsfromtheicecaps,asdiscussedabove.Therewillalsobecontribu-tionsfrommeltingglaciers,whichhavebeenestimatedat0.01-0.23m.Overall,theIPCChasestimatedthat,by2100,sea-levelmayhaverisenbybetween0.09and0.88m.

Ifsea-levelcontinuestoriseatitspresentrateormore,itwillposeaverysignificantproblemforlow-lyingareasacrosstheworld.

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INTERNATIONAL POLAR YEAR 2007-2008TheInternationalPolar2007-2008willemphasizethecentralimportanceofthepolarregionsasintegralandsensitivecomponentsoftheEarthsystem.

TheIPYwillalsoaddresshistoricalweatherandclimaterecords,humanhealthimpactsandcommunitysustainability;andhumanandecosystemvulnerabilitytoextremeweathereventsandnaturaldisasters.

Despiteagreatdealof research into thepolarregionsoverrecentdecades,therearestilllargegapsinourknowledgeabouthowpolarclimateoperatesand its interactionwithecosystems,polarenvironmentsandsocieties.Wethereforeneedabetterpic-tureofconditionsatthePolesandhowtheyinteractwithandinfluencetheatmosphere,oceansandlandmasses.Thiswillbeobtainedduring the InternationalPolarYear (IPY),2007-2008,amajor international focusedresearchprogrammethatwasinitiatedbytheInternationalCouncilforScience(ICSU)andtheWorldMeteorologicalOrganization.

ThefundamentalconceptoftheIPY2007-2008isasanintensiveburstofinternation-allycoordinated,interdisciplinary,scientificresearchandobservation in theEarth’spolarregions.Themaingeographicfocus

willbeconcentratedonthehighlatitudes,butstudiesinanyEarthregionrelevanttotheunderstandingofpolarprocessesorphenomenawillalsobeencouraged.Toensurethatresearchershavetheopportunitytowork inbothpolarregions insummerandwinteriftheywish,thePolarYearwillactuallyrunfortwoyearsfromMarch2007toMarch2009.

ThefirstInternationalPolarYeartookplacein1882/1883.Sincethattime,therehavebeenanumberofmajorinternationalscienceinitia-tivesathighlatitudes,includingthesecondInternationalPolarYear(1932/1933),allofwhichhavehadamajorinfluenceinimprov-ingourunderstandingofglobalprocessesintheseimportantareas.Theseinitiativeshaveallinvolvedintenseperiodsofdatacollection,interdisciplinaryresearchandtheestablish-mentofarchivesthat indicatethestateofthepolarregions.ThelastmajorinitiativewastheInternationalGeophysicalYear(IGY)in1957/1958,inthepre-satelliteera,whichinvolved80000scientistsfrom67countries.TheIGYinvolvedunprecedentedexplorationandproducedunexpecteddiscoveries inmanyfieldsofresearch.ItwasduringthisperiodthatmanyoftheAntarcticresearchstationsthatexisttodaywereestablished.TheIGYalsogaverisetotheformulationoftheAntarcticTreatyin1959anditsratificationin1961.

Today,technologicaldevelopments,suchaspolar-orbitingsatellites,automaticweatherstations and autonomous vehicles offergreatopportunitiesforfurther increaseinourunderstandingofpolarsystems.Theupcoming IPY 2007-2008 also offers anopportunitytoengagethenextgenerationofyoungEarthsystemscientistsandtoraisetheprofileofresearchinthepolarregionswiththepublic.

IPY2007-2008hasattractedgreat interestfromscientistsworkinginmanydisciplinesandnationalities. Inresponsetoacallbythe ICSU/WMOJointCommittee for IPY,scientistshavealreadyplannedandproposedmorethan200complex,international,inter-disciplinaryprojectsaddressingawiderange

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African involvement in International Polar Year (IPY) 2007-2008

“Remoteandharsh,polarregionsarenonethelessthebarometersofglobalwarmingandthewaterstoredintheirvastamountsoficehassignificantimplicationsfortheentireplanet.ThelaunchofInternationalPolarYear2007–2008comesatapropitioustimeandwillprovideavitalheritageofscientificknowledgeforgenerationstocome.”

(MichelJarraud,Secretary-General,WMO)

“Thescientificcommunitystandsready...togatherasmuchdataabouttheeffectsofglobalwarmingonpolarareasasquicklyaspossible—changesintheseregionswillhaveamassiveinfluenceonthewell-beingoftherestoftheplanet.”

(DavidCarlson,DirectoroftheInternationalPolarProgrammeOffice(IPO)forIPY)

ofphysical,biologicalandsocialresearchtopicsinthepolarregions.

TheNationalMeteorologicalandHydrologicalServicesofcountrieshavinganinterestintheArcticandtheAntarcticareactivelyinvolvedintheIPYpreparationandimplementation.ItisenvisagedthattheIPYwillinvolvemorethan50000individualsfrommorethan60nations.Climatechangeresearch,weatherforecastingandestablishingbetterobservingsystemsaresomeofthepriorities.Moreover,IPYwilldevelopauniquelegacyofdiscovery,data,observingsystemsandinternationalcoopera-tionamongthegeophysical,biologicalandsocialsciences.

Theurgencyandcomplexityofchangesinthepolarregionsdemandabroadandintegratedscientificapproach.Thesecollaborationsandcoalitionswillstimulatenewdataaccessandexchangepractices,newacademiccoursesandnewformsand forums forscientificdiscourse.Initstotalscienceandoutreacheffort,IPYwillrepresentalargestepforwardinmakingscienceavailableandaccessibletothegeneralpublic.

TheRegionalWorkshoponAfricanInvolvementinIPY2007-2008andInternationalHeliophysicalYearwasheldinCapeTown,SouthAfrica,inOctober2006withthesupportoftheICSURegionalOfficeandtheSouthAfricanNationalFoundationforResearch.TherepresentativeoftheInternationalProgrammeOfficeforIPYmadeapresentationonInternationalOpportunitiesfromtheIPY.

TheaudiencewasprimarilySouthAfricanscientistsandresearchcouncilrepre-sentativesbutalsoincludedrepresentationfromseveralotherAfricancountries,includingKenya,Nigeria,Malawi,theUnitedRepublicofTanzaniaandZambia.TherewasobviousenthusiasmfortheIPYandoutcomesfromthemeetingincludedtheintentiontoestablishaWebsiteforIPYthatcouldrepresenttheinterestsofAfricancountries.

(IPYIPONewsletter,November2006,IssueNo.2)

For more information, please contact:

World Meteorological Organization

7 bis, avenue de la Paix – P.O. Box 2300 – CH 1211 Geneva 2 – Switzerland

Tel.: +41 (0) 22 730 83 14 – Fax: +41 (0) 22 730 80 27

E-mail: cpa@wmo.int – Website: www.wmo.int