ClimateDataChallengesInThe21stCentury

PERSPECTIVE

ciatedwithourunderstandingofhowtheclimatesystembehaves.

ClimateDataChallengesInadditiontothealreadylargebodyofdigitalinstrumentaldataavailableindiverseholdingsinthe21stCentury

aroundtheglobe,asubstantialnumberofcriticalobservations,suchasmanyearlytemperatureob-servations,arenotyetwidelyavailableasdigitalJonathanT.Overpeck,1*GeraldA.Meehl,2SandrineBony,3DavidR.Easterling4

records.ItisimportanttocreateandmaintaincentralrepositoriesofthesedatainamannerthatClimatedataaredramaticallyincreasinginvolumeandcomplexity,justastheusersofthesefirmlydefinestheoriginandnatureofthedataanddatainthescientificcommunityandthepublicarerapidlyincreasinginnumber.Anewparadigmalsoensuresthattheyarefreelyavailable(1,2).Inofmoreopen,user-friendlydataaccessisneededtoensurethatsocietycanreducevulnerabilityaddition,anincreasingarrayofpaleoclimaticproxytoclimatevariabilityandchange,whileatthesametimeexploitingopportunitiesthatwilloccur.recordsfromhumanandnaturalarchives,suchasC

historicaldocuments,trees,sediments,caves,corals,limatevariabilityandchange,bothnaturalevolutionofclimate.Inevitably,thereareuncer-andicecores,arebeinggenerated.Theserecordsandanthropogenic,exertconsiderablein-taintiesintheobservationalrecordsthatneedtoareparticularlyhelpfulinunderstandingclimatefluencesonhumanandnaturalsystems.betranslatedintothedegreeofconfidenceasso-

variabilitybeforetheperiodofinstrumentaldata,

Theseinfluencesdrivethescientificquestforanunderstandingofhowclimatebehavedinthepastandwillbehaveinthefuture.Thisunderstandingiscriticalforsupportingtheneedsofanever-broadeningspectrumofsociety’sdecision-makersastheystrivetodealwiththeinfluencesofEarth’sclimateatglobaltolocalscales.Ourunderstand-ingofhowtheclimatesystemfunctionsisbuiltonafoundationofclimatedata,bothobservedandsimulated(Fig.1).Althoughresearchscientistshavebeenthemainusersofthesedata,anincreasingnumberofresourcemanagers(workinginfieldssuchaswater,publiclands,health,andmarineresources)needandareseekingaccesstoclimatedatatoinformtheirdecisions,justasagrowingrangeofpolicy-makersrelyonclimatedatatodevelopclimatechangestrategies.Quiteliterally,climatedataprovidethebackboneforbillion-dollardecisions.Withthisgravitycomesthere-sponsibilitytocurateclimatedataandshareitmorefreely,usefully,andreadilythaneverbefore.TheExplodingVolumeofClimateData

Documentingthepastbehavioroftheclimatesystem,aswellasdetectingchangesandtheircauses,requirestheuseofdatafrominstrumental,paleoclimatic,satellite,andmodel-basedsources.Theearliestinstrumental(thermometerandba-rometer)recordsstretchbacktothemid-tolate1600s,althoughwidespreadland-andship-basedobservationswerenotinitiateduntiltheearlytoFig.1.Climatedatafromobservationsandclimatemodelsimulationsarecriticalforunderstandingthepastmid-1800s,mostlyinsupportofweatherfore-andpredictingthefuture.Increasingly,theclimatedataenterprisemustservebothscientistandnonscientistcastingandanalysis.Changesinobservationsequallywellintermofobserved(left)andfuture(right)climatevariabilityandchange.Observations,models,throughtime,duetoshiftsinobservingprac-research,andunderstandingareallunderpinnedbyclimatedata,andallinturninformusesinsocietysuchtices,instrumentation,andlanduse,havemadeitasthoseshownsurroundingthearrow.Theglobeatleftshowsobservedannualmeansurfacetemperaturenecessarytodevelopandapplyadvanceddata-anomalies(2006–2010)fromthe1951–1980baseperiodaverage[NASAdataaredescribedin(20)].Arcticprocessingalgorithmsinordertodescribethetime

sea-iceextentisthe5-year(2006–2010)June-July-Augustaverage,excludingsea-iceconcentrationslessthan10%[NOAAdataaredescribedin(21)].Theglobeatrightdepictsprojectedsurfacetemperature1

anomaliesforanexamplefive-memberannualmeanensembleaveragefromaclimatemodel(CCSM4),InstituteoftheEnvironment,845NorthParkAvenue,Suite532,UniversityofArizona,Tucson,AZ85721,USA.2National2081–2100minusthe1986–2005average,forthefuturegreenhousegasandaerosolemissionscenarioCenterforAtmosphericResearch,Boulder,CO,USA.3CNRS,RCP8.5(22).Thesea-iceextentfromthemodelisa5-year(2096–2100)June-July-Augustensembleaverage,LaboratoiredeMétéorologieDynamique,InstitutPierre-Simonexcludingsea-iceconcentrationslessthan10%.TheleftsideofthetimeseriesatbottomisannualmeanLaplace,observedgloballyaveragedsurfacetemperatures(20),andtherightsidedepictsfutureprojectionsforfive-4

UniversitéPierreetMarieCurie,Paris,France.NationalOceanicandAtmosphericAdministration(NOAA)/memberensembleaveragesfromCCSM4forthreeemissionscenarios(RCP2.6,RCP4.5,andRCP8.5).TheNationalClimaticDataCenter,Asheville,NC,USA.magnitudeoffutureclimatechangedependsonwhatsocietydecidestodonowintermsofemissions*Towhomcorrespondenceshouldbeaddressed.E-mail:

reductions.TakinglittleactionproducesthegreatestwarmingasreflectedbytheRCP8.5trajectory,whereasjto@email.arizona.edu

aggressivereductionsasrepresentedbyRCP2.6resultinstabilizedwarmingatamuchlowerlevel.

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SPECIALSECTION

overcenturytomillennialtimescales,throughperiodsofpastabruptclimatechange,andduringtimeswhenclimateforcingwassubstantiallydif-ferentfromthatoftoday(3)—allcriticalforunder-standingwhattheclimateofthefutureislikelytobe.Someoftheserecordshavebeencentrallyarchived(4),butmanyhavenotoraredescribedonlyinisolatedreferences.

Anotherkeysourceofclimatedataisspace-borneinstruments.Thedevelopmentoflong-term,high-qualityclimateobservationsfromsatellitesismoredifficultthanfromsurface-basedinstru-mentaldata,becauseindividualsatellitesandtheirinstrumentshaveshortlifespans(typicallyafewyears),overwhichtheirorbitsandsensitiv-itiescanchange.Theseproblemsrequiretheuseofadvanceddata-processingtechniques,andtheresultingdataarepronetobeingreprocessedaspreviouslyunknownproblemsarediscoveredovertime.Inaddition,gapsintherecordsandsystem-aticerrorsbetweensatellites(oralackofoverlap-pingcalibrationperiods)maketheincreasinglyimportantconstructionofcoherentclimatedatarecordsmoreofachallenge(5).

Athirdbroadtypeofdataismodel-based“reanalyses”:hybridmodel-observationaldatasetscreatedbyassimilatingobservationsintoaglobalorregionalforecastmodelforagiventimeperiod(suchas1958tothepresent).Theseprovidephysicallyconsistentandexpandeddepictionsoftheobservedtime-evolvingclimatesystemandhavebecomeindispensableinclimatesystemresearch.Thefutureofreanalysisrestsinthees-tablishmentofdedicatedeffortsthatincludefrozenmodelversionsandallowreprocessingofallobservationaldatafieldsasmodelsandinputdatasetsimprove.Futurereanalysismeth-odswillincludemorediverseobservationaldatatypes(suchasatmosphericchemistry,bio-spheric,oceanographic,andcryosphericdata)andlongertimescales(includingpaleoclimatictimescales).

Finally,therehasbeenanexplosionindatafromnumericalclimatemodelsimulations,whichhaveincreasedgreatlyincomplexityandsize.Datafromthesemodelsareexpectedtobecomethelargestandthefastest-growingsegmentoftheglobalarchive(Fig.2).Thearchivingandsharingofoutputfromclimatemodels,particularlythoserunwithacommonexperimentalframework,beganinthemid-1990s,startingwithoutputfromtheearlyglobalcoupledatmosphere-oceangeneralcirculationmodels(AOGCMs)usedformakingfutureclimatechangeprojections(6).ThisledtotheCoupledModelIntercomparisonProject(CMIP),organizedbytheWorldClimateResearchProgram(WCRP),invitingallthemodelinggroupstomakeincreasinglyrealisticsimulationsof20th-centuryandpossiblefuture21st-centuryclimates(7–9).Recently,CMIP3involved16internationalmodelinggroupsfrom11countries,using23modelsandsubmitting36terabytesofmodeldata,allarchivedbythe

atmosphericdynamicsandregionalprecipitation,aswellaspredictingnat-uralclimatevariabilityandhowmuchEarth,andlocalpartsofit,couldwarmforagivenamountofgreenhousegasforcing.Newhigh-resolutionactivere-motesensingobservationsfromsatel-liteinstruments(suchasCALIPSOlidarorCloudSatradar)arerevealingtheverticaldistributionofcloudsforthefirsttime.However,tofacilitatethecom-parisonofmodeloutputswiththesecomplexnewobservationseffectively,ithasbeennecessarytodevelopanddistributenewdiagnostictools(re-ferredtoas“observationsimulators”)visualizingwhatthesesatelliteswouldseeiftheywereflyingabovethesim-ulatedatmosphereofamodel(11,12).Thankstothesedevelopments,itwill

Fig.2.Thevolumeofworldwideclimatedataisexpandingsoonbepossibletorigorouslyassessrapidly,creatingchallengesforbothphysicalarchivingandsharing,therealismofcloudsimulationsintheaswellasforeaseofaccessandfindingwhat’sneeded,partic-latestgenerationofmodels;fortheularlyifyouarenotaclimatescientist.Thefigureshowsthepriceofanadditional6%[160tera-projectedincreaseinglobalclimatedataholdingsforclimatebytes(TB)]ofCMIP5-relatedclimatemodels,remotelysenseddata,andinsituinstrumental/proxy

datathatmustbeshared.

data.

Climatechangemodelinghasevolvedinjust5yearsfromrunning

ProgramforClimateModelDiagnosisandIn-afewAOGCMexperimentswithasinglecategorytercomparison(PCMDI),signalinga“newerainofmodel,torunningmanymoreexperimentswithclimatechangeresearch”(10).Thisactivityhasamuchlargerprofusionofmodelsofincreasingmadeitpossibleforanyonetoopenlyaccesstheseresolutionandcomplexity.First-generationEarthstate-of-the-artclimatemodeloutputsforanalysissystemmodels(ESMs)arenowbeingrunaspart

ofthecurrentCMIP5exercise(13,14).ESMsandresearch.

Climatemodeldatahavebeenarchivedandincludeatleastaninteractivecarboncyclecoupledaccessed,exchanged,andsharedprimarilywithintothetraditionalAOGCMs,whichhaveatmo-thephysicalclimatescienceresearchcommunity,sphere,ocean,land,andsea-icecomponents.Also,althoughtherehasbeengrowinginterestinthehigh-resolutionclimatemodels(suchasthosewithuseoftheseclimatemodeldatabyothercom-20-kmgridspacing)arerunfortimeslices,pastmunitiesofresearchers.CMIPwasdesignedtoandfuture,forintegrationsofadecadeortwoinprovidethisbroaderaccesstoclimatemodeloutputordertoobtainabetterquantificationofregionalforresearchersfromawiderangeofcommunities.climatechangeandsmaller-scalephenomenasuchTheIntergovernmentalPanelonClimateChangeashurricanes[forexample,see(15)].Thenetresult(IPCC)wasalsoabletouseCMIPmultimodeldataisahugeincreaseindatavolume(Fig.2).Earlysetstoprovidestate-of-the-artassessmentsofwhatphasesoftheCMIPprojectinvolvedlessthanthemodelsasagroupindicateaboutpossible1TBofmodeldata,whereasCMIP3archivedfutureclimatechange(10).Nowclimatemodels36TB,andCMIP5isexpectedtomakeavail-arebeginningtobeusedformuchmorethanable2.5petabytes(PB).Newcapabilitiesoftheclimateresearch.Inparticular,theyareexpectedtoEarthSystemGridportalwillprovidedistributedinformdecisionsthatsocietymusttakeatglobaltoaccesstoalargepartofthisnewmodeloutputlocalscalestoadapttonaturalclimatevariationsas(16),makingitpossibleformodelinggroupstowellastoanthropogenicclimatechange,andtosharedatafromdistributedlocalserverswithguidetheimplementationofpossiblemitigationWeb-basedaccesstools.Modeldatathusdonotmeasures.Thisputsnewdemandsonthevariety,needtobecentrallyarchivedbutcanbeaccessedscale,andavailabilityofobservationaldataneededinadistributedfashion.Clearly,thisisanformodelevaluationanddevelopment,andex-exampletobefollowedmorebroadly,withthepands,yetagain,thevolumeofclimatedatathatcaveatthatthesafetyandreliabilityoflong-term

archivesofthesedatamustnotbejeopardized.mustbesharedopenlyandefficiently(Fig.2).

Anillustrationofthechallengesandpossi-bilitiesposedbythefutureinteractionoffine-MeetingtheNeedsofaWideRangeofUsersscaleobservationaldatawithmorecomplexmodelsTheburgeoningtypesandvolumeofclimatedataistheevaluationofcloudsandthehydrologicaloneconstituteamajorchallengetothecli-cycle.Theseprocessesarecriticalforsimulatingmateresearchcommunityanditsfundingbodies.

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Institutionalcapacitymustexisttoproduce,format,document,andshareallthesedata,while,atthesametime,amuchlargercommunityofdiverseusersclamorstoaccess,understand,andusecli-matedata.Theseincludeanever-increasingrangeofscientists(ecologists,hydrologists,socialsci-entists,etc.)anddecision-makersinsocietywhohaverealmoney,livelihoods,andevenlivesatstake(resourcemanagers,farmers,publichealthofficials,andothers).Keyusersalsoincludethosewithpublicresponsibilities,aswellastheirconstituentsinthegeneralpublicwhomustsup-portandunderstanddecisionsbeingmadeontheirbehalf.Asaresult,climatescientistsmustnotonlysharedataamongthemselves,buttheymustalsomeetagrowingobligationtofacilitateaccesstodataforthoseoutsidetheircommu-nityand,indoingso,respondtothisbroaderusercommunitytoensurethatthedataareasusefulaspossible.

InadditiontothelatestIPCCassessment,variousongoingnationalclimateassessmentandclimateservicesactivitiesarebeinginitiatedthatwillneedtoaccessanduseclimatedata,justasagrowingnumberofclimateadaptationandmiti-gationeffortsaroundtheglobewillneedtobebetterinformedbyclimatedata.Theseeffortswillsucceedonlyifclimatedataaremadereadilyac-cessibleinformsusefultoscientistsandnon-scientistsalike.

TheFutureofClimateData:AnEmergingParadigm

Thus,twomajorchallengesforclimatesciencerevolvearounddata:ensuringthattheever-expandingvolumesofdata(Fig.2)areeasilyandfreelyavailabletoenablenewscientificresearch,andmakingsurethatthesedataandtheresultsthatdependonthemareusefultoandunder-standablebyabroadinterdisciplinaryaudience.Anewparadigmthatjoinstraditionalclimatere-searchwithresearchonclimateadaptation,ser-vices,assessment,andapplicationswillrequirestrengthenedfundingforthedevelopmentandanalysisofclimatemodels,aswellasforthebroaderclimatedataenterprise.Increasedsupportfromthefundingagenciesisneededtoenhancedataaccess,manipulation,andmodelingtools;improveclimatesystemunderstanding;articu-latemodellimitations;andensurethattheob-servationsnecessarytounderpinitallaremade.Otherwise,climatesciencewillsuffer,andtheclimateinformationneededbysociety—climateassessment,services,andadaptationcapability—willnotonlyfallshortofitspotentialtoreducethevulnerabilityofhumanandnaturalsystemstoclimatevariabilityandchange,butwillalsocausesocietytomissoutonopportunitiesthatwillinevitablyariseinthefaceofchangingconditions.

Atpresent,abouthalfoftheinternationalmod-elinggroupsarerestrictedfromsharingdigitalclimatemodeldatabeyondtheresearchcom-munitybecauseofgovernmentalinterestinthesaleofintellectualpropertyforcommercialap-plications;thesameholdstrueforsomeobser-vationaldata.Openandfreeavailabilityofmodeldata,observations,andthesoftwareusedforpro-cessingiscrucialtoallaspectsofthenewpar-adigm.Governmentsthatcurrentlyrestricteithermodeloutputorobserveddatadistributionmustbeconvincedthatitisinthebestinterestsofeveryonethatallclimatedatabemadeopenlyavailabletoallusers,includingthoseengagedinresearchandapplications.Internationalagree-mentsmusteliminatedatarestrictions,justasjour-nalsandfundingagenciesshouldrequireeasyaccesstoalldataassociatedwiththepaperstheypublishandtheworktheyfund.

Theoptimaluseofclimatedatarequiresamoreeffectiveinterdisciplinarycommunicationofdatalimitationswithregardto,forexample,spatialandtemporalsamplinguncertainties;in-strumentchanges;quality-controlprocedures;and,inparticular,whatmodel-basedclimatepre-dictionsorprojectionsdowellandnotsowell.Thefirststepistoincreasetheaccessibilityofobservationsandhigh-resolutionsimulationstoawiderangeofusers,eitherviaafewcentralizedportals(suchasPCMDI)withbroaderrespon-sibilities,orusingamoredecentralizedapproach.Asecondstepistodevelopaninternationalde-positorysiteformodeldiagnostictools(suchassatellitesimulators)andevaluationmetricsthatwouldhelpusersassessthereliabilityofspe-cificaspectsofmodelsimulations(suchasseaice,ElNiño–SouthernOscillation,ormonsoons,droughts,andotherclimateextremes).Thekeyisthatnewdata-sharingsystemshavetobeeval-uatedandimproveduntilalltypesofinterdis-ciplinaryusersareabletobeeffectivepartnersintheuseofclimatedata.

Anincreasinglydauntingaspectofhavingtensandeventuallyhundredsofpetabytesofclimatedataopenlyavailableforanalysis(Fig.2)ishowtoactuallylookatandusethedata,allthewhileunderstandinguncertainties.Moreresourcesneedtobededicatedtothedevelopmentofso-phisticatedsoftwaretoolsforsiftingthrough,accessing,andvisualizingthemanymodelversions,experiments,andmodelfields(temperature,pre-cipitation,etc.),aswellasalloftheobserveddatathatisonline.Inparallel,itisbecomingincreas-inglyimportanttounderstandcomplexmodelresultsthroughahierarchyofmodels,includingsimpleorconceptualmodels(17).Withoutthisstep,itwillbeextremelydifficulttomakesenseofsuchhugearchivedclimatedatasetsandtoassesstherobustnessofthemodelresultsandtheconfidencethatmaybeputinthem.Again,ful-fillingtheneedsofalltypesofinterdisciplinaryusersneedstobethemetricofsuccess.

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edge,withclimatestakeholdersinsociety(18,19).Thesestakeholders,alongwiththeinterdisciplinarysciencecommunitythatsupportsthem,aretheusersthatmustdrivetheclimatedataenterpriseofthefuture.

ReferencesandNotes

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Climate Data Challenges in the 21st CenturyJonathan T. Overpeck et al.Science 331, 700 (2011);

DOI: 10.1126/science.1197869

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