WMO Global Annual to Decadal Climate Update 2025-2029（WMO 2025-2029年全球年度至十年期气候更新）

WEATHERCLIMATEWATER

WMOGlobalAnnualtoDecadalClimateUpdate

2025-2029

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WORLDMETEOROLOGICALORGANIZATION

GlobalAnnualtoDecadalClimateUpdate2025

KeyMessages

TheGlobalAnnualtoDecadalClimateUpdateisissuedannuallybytheWorldMeteorologicalOrganization(WMO).Itprovidesasynthesisoftheglobalannualtodecadalpredictionsproducedbythe

WMOdesignatedGlobalProducingCentresandothercontributingcentres

.Thelatestpredictionsshowthat:

Globalmeantemperaturesarelikelytocontinueatornearrecordlevelsinthefive-yearperiod2025-2029.Theannuallyaveragedglobalmeannear-surfacetemperatureforeachyearbetween2025and2029ispredictedtobebetween1.2°Cand1.9°Chigherthantheaverageovertheyears1850-1900.

Itislikely(86%chance)thatglobalmeannear-surfacetemperaturewillexceed1.5°Cabovethe1850-1900averagelevelsforatleastoneyearbetween2025and2029.Itisalsolikely(70%chance)thatthe2025-2029five-yearmeanwillexceed1.5°Cabovethe1850-1900average.

Itislikely(80%chance)thatatleastoneyearbetween2025and2029willbewarmerthanthewarmestyearonrecord(currently2024)andalthoughexceptionallyunlikely,thereisnowalsoachance(1%)ofatleastoneyearexceeding2°Cofwarminginthenextfiveyears.

Long-termwarming(averagedoverdecades)remainsbelow1.5°C.

Thefive-yearaveragetemperatureintheNiño3.4regionrelativetothewholetropicsindicatesmixedormainlyneutralENSOconditionsinthisperiod.

TheaverageArctictemperatureanomalyoverthenextfiveextendedwinters(NovembertoMarch),relativetotherecentclimatologicalnormal(theaverageoftheyears1991-2020),ispredictedtobe2.4°C,morethanthreeandahalftimesaslargeastheanomalyinglobalmeantemperature.

PredictionsofArcticsea-iceforMarch2025-2029suggestfurtherreductionsinsea-iceconcentrationintheBarentsSea,BeringSea,andSeaofOkhotsk.

PredictedprecipitationpatternsforMay-September2025-2029,relativetothe1991-2020average,suggestanomalouslywetconditionsintheSahel,northernEurope,AlaskaandnorthernSiberia,andanomalouslydryconditionsforthisseasonovertheAmazon.

Recentyears,apartfrom2023,intheSouthAsianregionhavebeenanomalouslywetandtheforecastsuggeststhiswillcontinueforthe2025-2029period.Thismaynotbethecaseforallindividualseasonsinthisperiod.

ObservedClimateoftheLastFiveYears

Thissectionprovidesabriefsummaryoftheobservedclimateofthelastfiveyearstogivecontextforthepredictionsshownlaterinthisreport.Pleaserefertothe

WMOStateoftheGlobalClimatereport

foramorecompletediscussion.Figure1showstheglobalpatternsofsurfaceairtemperature,sea-levelpressureandprecipitationanomaliesoverthelastyear(2024)andthelastfive-year(2020-2024)periodwithrespecttothemostrecentclimatologicalnormal,theaverageovertheyears1991-2020.

Lastyear,2024,wasthewarmestyearonrecord,withthegloballyaveragednear-surfacetemperatureestimatedat1.55°C±0.13°Cabovethe1850–1900baseline.Near-surfacetemperaturesin2024werewarmerthanthelong-termaveragealmosteverywhereoverlandwithparticularlylargewarmanomaliesinthetropics,NorthAmerica,NorthAfrica,EuropeandpartsofAsia.

Over2020-2024,positiveanomalieswerewidespread,exceptovertheeasterntropicalPacificandpartsofSouthAmerica,AustraliaandIndia.TheseweregreatestathighlatitudesintheNorthernHemisphere,especiallytheArctic,andgenerallylargeroverlandthanocean,apartfromintheNorthPacific.ThisperiodhadLaNiñaconditionsinthreeconsecutiveyears.

Sea-levelpressurein2024andinthelastfiveyearswasanomalouslylowoverAntarctica.TheAleutianLowfor2020-2024wasanomalouslyweak,consistentwiththeextendedLaNiñaconditionsthatprevailed.

Precipitationpatternsin2024showthatpartsofcentralandsouthernAfricaandSouthAmericawereparticularlydry.During2020-2024,partsofAsiaandtheAfricanSahelwerewetterthanaverage,andsouthernAfrica,westernAustralia,centralandsouthernSouthAmerica,southwesternEuropeandpartsofNorthAmericaweredrierthanaverage.

Figure1:Observedannualmeannear-surfacetemperature(°C,top),pressure(hPa,middle)andprecipitation(mm/day,bottom)anomaliesrelativeto1991-2020.Theleftcolumnshowstheyear2024,therightcolumnreferstotheaverageofthefive-yearperiod2020-2024.Near-surfacetemperatureisERA52mtemperaturefromECMWF(Belletal,2021).Meansea-levelpressureisalsofromERA5.PrecipitationisfromGPCP(Adleretal,2003,updated).

Tohighlightsummerandwinterdifferences,Figure2showsaverageanomaliesoverthelastfiveyearsfortwoextendedseasons,MaytoSeptemberandNovembertoMarch.Bothseasonshadgenerallyhighertemperaturesthanthe1991-2020average,apartfromthetropicaleasternPacific,andSouthPacific.WesternNorthAmericawasanomalouslycoldinNovembertoMarch.

Thesea-levelpressureanomaliesseeninthefive-yearmeaninFigure1overAntarcticaandtheAleutianLowwerelargestinNovembertoMarch.PrecipitationpatternsshowthatEastAsiaandSouthAsiawerewetterthanaverageinMaytoSeptember,butthishideslargeinter-annualvariabilityinthe

monsoons.TheAfricanSahelalsoshowswetanomaliesforthisseason.WesternAustraliaandmostofSouthAmericaweredrierthanaverageoverthefiveyearsinbothseasons.

Figure2:Observedfive-yearseasonalmeannear-surfacetemperature(°C,top),pressure(hPa,middle)andprecipitation(mm/day,bottom)anomaliesrelativeto1991-2020.TheleftcolumnshowsanomaliesforMaytoSeptemberaveragedover2020-2024,therightcolumnshowsanomaliesforNovembertoMarchaveragedover2019/2020-2023/2024.

ObservationaldatasetsarethesameasthoseinFigure1.

Annuallyaveragedglobal(landandsea)meannear-surfacetemperaturehasincreasedsincethe1960s(Figure3).Lastyear,2024,brokemanyrecordsincludingthewarmestyear(asdid2023).TheWMOStateoftheGlobalClimatereportnotesthateachofthelasttenyears(2015-2024)wereindividuallythewarmesttenyearsonrecordprimarilyduetotheatmosphericconcentrationofcarbondioxidebeingatthehighestlevelin800,000years.AtlanticMultidecadalVariability(AMV)anomaliesinthelastfouryearsarepositivesincenear-surfacetemperaturesintheNorthAtlantichavebeenwarmerthantherestoftheoceans.Afterastringofthreenegative(LaNiña)DecembertoFebruaryseasons,thetropicalEastPacifichadwarmanomaliesatthebeginningof2024(ElNiño).In2025,theanomaliesarenegativeagain.

Figure3:Observedclimateindicators.Globalannualmeannear-surfacetemperatureanomaly(top),annualmeanAtlanticMultidecadalVariability(AMV)definedasthedifferencebetweentworegions:45°N-60°N,60°W-0°Eminus45°S-0°S,30°W-10°EasinRobertsetal,2013(middle)andDecembertoFebruaryNiño3.4definedastheaverageover5°S-5°N,170°W-120°Wwiththetropicalaverage20°S-20°NremovedasinvanOldenborghetal,2021(bottom).Sixdatasetsareusedinthecalculationofglobalnear-surfacetemperatureandarethesameasintheWMOStateofGlobalClimate2024report.Anomaliesarewithrespectto1850-1900.Theothertwoindicesarebasedon2mtemperaturefromERA5asinFigure1andanomaliesarerelativetothe1991-2020referenceperiod.

PredictionsfromtheWMOLeadCentre

Predictionsofclimateindicesandglobalfieldsareobtainedfrommulti-modelinitialisedannual-to-decadalclimatepredictionscontributedtothe

WMOLeadCentreforAnnualtoDecadalClimate

Prediction.

Forthisyear’supdatethereare220ensemblemembersfrommodelscontributedby14differentinstitutes,includingfourGlobalProducingCentres:BarcelonaSupercomputerCentre,CanadianCentreforClimateModellingandAnalysis,DeutscherWetterdienst,andtheMetOffice.Predictionsareeitherstartedfromtheconditionson1November2024or1January2025,dependingonthedecadalpredictionsystem.Retrospectiveforecasts,orhindcasts,coveringtheperiod1960-2018areusedtoestimateforecastskill.AlsoshownfortheclimateindicatorsareuninitialisedhistoricalsimulationsandprojectionsfromtheWorldClimateResearchProgramme’sCoupledModelIntercomparisonProjectphase6(CMIP6).Pleaseconsultthe

“HowtoUsetheGlobalAnnualto

DecadalClimateUpdate”

sectionofthisreportforinformationonforecastconfidenceandsee

Hermansonetal(2022)

forbackgroundinformation.

PredictionsofGlobalClimateIndicators

Annuallyaveragedglobaltemperaturesarelikelytocontinueatornearrecordlevelsinthefive-yearperiod2025-2029andstaywellaboveannualmeantemperaturesseeninthelast60years(Figure4).Annuallyaveragedglobalmeannear-surfacetemperatureforeachyearinthisfive-yearperiodispredictedtobebetween1.2°Cand1.9°C(90%confidenceinterval)higherthantheaveragefortheperiod1850-1900

1.

Thechanceoftheannuallyaveragedglobalnear-surfacetemperaturein2025-2029exceeding1.5°Cabove1850-1900levelsforatleastoneyearhasbeenincreasingwithtimeandisnow86%(brownhistogramandright-handaxisinFigure4).Itislikely(70%)thatthefive-yearmeanwillalsoexceedthisthreshold.Notethatthe1.5°ClevelspecifiedintheParisAgreementreferstolong-termlevelofwarminginferredfromglobaltemperatures,typicallyover20years.Temporaryexceedancesofthe

1.5°Clevelareexpectedtooccurwithincreasingfrequencyastheunderlyingriseinglobaltemperatureapproachesthislevel.Thereisnowalsoanon-zerochance(1%)ofatleastoneyearexceeding2°Cin2025-2029.

Thechanceofatleastoneyearexceedingthewarmestyearonrecord,2024,inthenextfiveyearsis80%.Thechanceofthefive-yearmeanfor2025-2029beinghigherthanthelastfiveyearsis89%.Confidenceinforecastsofannuallyaveragedglobalmeannear-surfacetemperatureishighsincehindcastsshowveryhighskillinallmeasures(right-handpanelsofFigure4).

Estimatesofthecurrentglobalwarminglevelfor2024werepresentedintheWMOStateoftheGlobalClimate2024reportearlierthisyearusingthreeapproaches,withcentralestimatesrangingfrom

1.34°Cto1.41°C,andthe90%confidencerangesforhuman-inducedwarmingspanning1.1–1.7°C.Oneofthoseapproachescombinesthemostrecent10yearsofobservedhistoricaltemperaturewithclimatemodelprojectionsforthenext10yearstogivea20-yearaverageasthecurrentglobalwarminglevel.Adoptingthisapproachusingthedecadalforecastsfeaturedheretoreplacetheprojectionsgivesanestimateof1.44°Cabovethe1850-1900average,witha90%confidencerangeof1.22–1.54°C.SeveralapproachesareunderconsiderationbyWMOandtheinternationalscientific

1Forecastsareproducedrelativeto1991-2020andthenthedifferencebetweenthisperiodand1850-1900derivedfromobservationsisadded.Thisdifferenceismostlikely0.88°C,butisuncertainduetotheincompleteobservationalnetworkinthe19thcenturyandcouldbeaslowas0.72°Coraslargeas0.99°C.

communitytoenablemoretimelyreportingofwarminginthecontextoftheParisAgreement.FurtherdetailscanbefoundintheWMOStateoftheGlobalClimateReport2024.

Figure4:Multi-annualpredictionsofglobalmeannear-surfacetemperaturerelativeto1850-1900.Annualglobalmeanobservations(seeFigure3)inblack,forecastinblue,hindcastsingreen.Theextentofshadingindicatesthe90%confidenceinterval,withtheintensityofshadingindicatingtheleveloflikelihoodattheindicatedanomalyvalue.Thegreyshadingshowsthe90%confidenceintervalofunininitialisedsimulations,indicatingthedegreetowhichforecastsreducetheuncertaintycomparedtoclimateprojections.Thecalibratedprobabilityforaboveaverage(comparedto1991-2020)ofthefive-year-meanforecastisgivenatthebottomofthemainpanel.Hindcastskillscoresareshownintheupperrightpanel;thesquareandthecrossshowthecorrelationskillandMeanSquareSkillScore(MSSS)forfive-yearmeans,respectively.Statisticallysignificantcorrelationskill(atthe5%confidencelevel)isindicatedbysolidcircles/square.Thecontingencytableforthepredictionofabove-averagefive-yearmeans(comparedto1991-2020)isshowninthebottomrightpanel.Alsoinsetinthemainpanel,inbrown,referringtotherighthandaxis,istheprobabilityofglobaltemperatureexceeding1.5°Cabove1850-1900levelsforatleastoneofthefivefollowingyears,startingwiththeyearindicated.ThisprobabilityiscalculatedasinSmithetal(2018)bycountingtheproportionofensemblemembersthatpredictatleastoneyearabove1.5°C.

Predictionsindicatean87%calibratedprobability(Bettetal,2022)thatAtlanticMultidecadalVariability(AMV)indexwillbepositiveonaverageoverthenextfiveyears(Figure5).Thehindcastshavemediumskillinbothmeasuresandamediumhitrate,givingmediumconfidenceinthisprediction.TheNorthAtlanticsubpolargyre,themaincentreofactionoftheAMV,hashadpositivenear-surfacetemperatureanomaliesinthelastfiveyears(Figure1).Somepredictionsfromthecontributingcentresindicateareturntocooltemperaturesinthenextfiveyears,butmostpredictcontinuedwarmingoftheregion(individualcentrecontributionscanbe

seenonthewebsite

).PredictionsfortheAtlanticMeridionalOverturningCirculation(AMOC),whichisrelatedtoAMVandshowsanincrease,canbefoundintheAppendix.

Figure5:Multi-annualpredictionsofAtlanticMultidecadalVariability(AMV)relativetoits1991-2020average,definedastheanomalydifferencebetweentworegions:45°N-60°N,60°W-0°Eminus45°S-0°S,30°W-10°EasinRobertsetal(2013).Annualmeanobservations(seeFigure3)inblack,forecastinblue,hindcastsingreen.Theextentofshadingindicatesthe90%confidenceinterval,withtheintensityofshadingindicatingtheleveloflikelihoodattheindicatedanomalyvalue.Thegreyshadingshowsthe90%confidenceintervalofunininitialisedsimulations,indicatingthedegreetowhichforecastsreducetheuncertaintycomparedtoprojections.Thecalibratedprobability(asinBettetal,2022)forthemostlikelycategory(aboveorbelowclimatology)ofthefive-year-meanforecastisgivenatthebottomofthemainpanel.Hindcastskillscoresareshownintheupperrightpanel;thesquareandthecrossshowthecorrelationskillandMeanSquareSkillScore(MSSS)forfive-yearmeans,respectively.Statisticallysignificantcorrelationskill(atthe5%confidencelevel)isindicatedbysolidcircles/square.Thecontingencytableforthepredictionofabove/belowaveragefiveyearmeansisshowninthebottomrightpanel.

Thisyear,2025,startedwithweakLaNiñaconditionsinthetropicalEastPacific.Theseanomaliesarepredictedtodecline,andthemulti-modelensemble-meantemperatureanomaliesintheNiño3.4regionarepredictedtobenearzeroforDecember2025–February2026.Thereisalargeensemblespread(±0.5°C)andskillismediumforyear1(Figure6).Thefive-yearaveragetemperatureintheNiño3.4regionrelativetothewholetropicshasa55%calibratedprobabilityofbeingaboveaverage,indicatinglittlesignalforpredominanceofeitherElNiñoorLaNiñainthisperiod.Skillismedium,givingmediumconfidenceinthisforecast.

Figure6:AsFigure5,butforDecember-FebruaryaveragedNiño3.4relativetothetropicalmeandefinedastheaverageover5°S-5°N,170°W-120°Wwithaverageover20°S-20°Nremoved.Thisindexissuitableforawarmingclimate(vanOldenborghetal,2021).

RegionalPredictionsfor2025

Near-surfacetemperaturesin2025arepredictedtobehigherthanthe1991-2020averageinalmostallregionsacrosstheglobe,exceptforpartsoftheSouthPacificandSouthernOcean(Figure7).ThestippledregionsinFigure7indicatewherethedifferentpredictionsystemsdisagreeonthesignoftheanomaly.Theregionsshowingbelow-averagetemperaturesarestippled,whichimplieslowconfidenceinwhethertheforecastsfortheseregionswillbeaboveorbelownormal.Skillisestimatedfromhindcaststobemediumorhighinmostotherregions(Figure8),givingmediumtohighconfidenceintheforecastthere.

Sea-levelpressureforecastssuggesttheAleutianLowwillremainweakandanomaloushighpressureislikelyovertheSouthPacific.Theskillgivesmediumconfidenceinthisprediction.ThepatternoflowpressureoverAntarcticaandhighpressureoverthesouthernhemispheremid-latitudesisconsistentwithapositiveAntarcticOscillationindex(seealsoFigure21).Theskillfortheseregionsgivemediumtolowconfidence.

PredictedprecipitationpatternsshowanincreasedchanceofwetterconditionsintheAfricanSahelduetoanorthwardshiftedIntertropicalConvergeZone(ITCZ)intheAtlantic,possiblyduetothe

relativelywarmNorthAtlantic.Northernhighlatitudesarelikelytohaveaboveaverageprecipitationasexpectedfromclimatechange.PartsofAustraliaarelikelytobewetterthanusual.Correlationskillforprecipitationinhindcastsislowdespitebeingsignificantintheseregions,givinglowconfidenceintheforecast.

Figure7:Annualmeananomalypredictionsfor2025relativeto1991-2020.Ensemblemean(leftcolumn)fortemperature(top,°C),sealevelpressure(middle,hPa),precipitation(bottom,mm/day),stippledwheremorethan1/3ofmodelsdisagreeonthesignoftheanomaly,andprobabilityofaboveaverage(rightcolumn).Asthisisanuncalibratedtwo-categoryforecast,theprobabilityforbelowaverageisoneminustheprobabilityshownintherightcolumn.

Figure8:Predictionskillofannualmeansevaluatedusinghindcastexperiments.Pearsoncorrelation(left)andROCscoreforpredictionsofaboveaverageconditions(right).Forcorrelationstipplingshowswhereskillisinsignificant(atthe5%level).

RegionalPredictionsfor2025-2029

ThissectionshowspredictionsfortheaverageofthenextfiveextendedseasonsforMaytoSeptemberandNovembertoMarch.

FortheMaytoSeptemberaverage,predictedtemperaturepatternsovertheyears2025-2029showahighprobabilityoftemperaturesabovethe1991-2020averagealmosteverywhere,withenhancedwarmingoverlandinthenorthernhemisphere(Figure9).Skillisveryhighinmostregions,givinghighconfidenceinthisprediction(Figure10).

Forthesameseason,sea-levelpressureispredictedtobeanomalouslylowovertheMediterraneanandsurroundingcountries.AnomalouslyhighpressureispredictedovertheSouthPacificandthemid-latitudesoftheotheroceansintheSouthernHemisphere.Thereislowtomediumskillformostoftheseregions,givinglowtomediumconfidence.PredictionsofprecipitationshowwetanomaliesintheSahel,northernEurope,AlaskaandSiberia,anddryanomaliesforthisseasonovertheAmazon.Skillgiveslowtomediumconfidence.

FortheNovembertoMarchaverageovertheyears2025/26-2029/30(Figure11),thepredictionsshowthatwarmanomaliesarelikelyalmosteverywhere,withlandtemperaturesshowinglargeranomaliesthanthoseovertheocean.TheArctic(northof60°N)near-surfacetemperatureanomalyforthisseasonispredictedtobe2.4°Cabove1991-2020average,whichismorethanthreeandhalftimeslargerthantheglobalmeananomaly.TheNorthAtlanticsubpolargyre,thelocationoftheso-called“warminghole”,whichhasbeenlinkedtoareductionintheAMOCandchangestoregionalwinds,isanareawherethemodelsdisagreeonthesignoftheanomaly.SkillishighinmostregionsexceptforpartsoftheNorthPacific,someareasinAsia,Australia,andtheSouthernOcean(Figure12),givingmediumtohighconfidence.

TherewilllikelybeapositivepressureanomalyoverthetropicalwestandcentralPacific.IntheArctic,thereisanegativepressureanomalypredictedandapositiveanomalyintheNorthAtlantic(thoughmodelsdisagreeonthelatterregion)implyingincreasedlikelihoodofpositiveNorthAtlanticOscillation(NAO)conditionsinthisperiod.TheskilloverthetropicalPacificgivesmediumconfidenceforthisprediction,butthereislowconfidenceintheNAOpredictionduetolowerskillintheseregions.

Precipitationpredictionsfavourwetterthanaverageconditionsathighlatitudesinthenorthernhemisphereforthenextfiveextendedwinterseasons(NovembertoMarch).Thepatternofincreasedprecipitationinthetropicsandhighlatitudescomparedtothe1991-2020referenceperiod,andreducedprecipitationinthesubtropics,particularlyinthesouthernhemisphere,isconsistentwithexpectationsofawarmingclimate.SkillismoderateoverlargepartsofnorthernEurasia,Greenland,andtheCanadianArcticArchipelagogivinglowtomediumconfidenceintheforecastforanincreasedchanceofprecipitationintheseregions.

Figure9:Predictionsfor2025-2029MaytoSeptemberanomaliesrelativeto1991-2020.Ensemblemean(leftcolumn)fortemperature(top,°C),sealevelpressure(middle,hPa),precipitation(bottom,mm/day),stippledwheremorethan1/3ofmodelsdisagreeonthesignoftheanomaly,andprobabilityofaboveaverage(rightcolumn).Asthisisanuncalibratedtwo-categoryforecast,theprobabilityforbelowaverageisoneminustheprobabilityshownintherightcolumn.

Figure10:Predictionskilloffive-yearmeanMaytoSeptemberanomaliesevaluatedusinghindcastexperiments.Pearsoncorrelation(left)andROCscoreforpredictionsofaboveaverageconditions(right).Forcorrelationstipplingshowswhereskillisnotsignificantlypositive(atthe5%level).

Figure11:Predictionsfor2025/2026-2029/2030NovembertoMarchanomaliesrelativeto1991-2020.Ensemblemean(leftcolumn)fortemperature(top,°C),sealevelpressure(middle,hPa),precipitation(bottom,mm/day),stippledwheremorethan1/3ofmodelsdisagreeonthesignoftheanomaly,andprobabilityofaboveaverage(rightcolumn).Asthisisanuncalibratedtwo-categoryforecast,theprobabilityforbelowaverageisoneminustheprobabilityshownintherightcolumn.

Figure12:Predictionskilloffive-yearmeansNovembertoMarchanomaliesevaluatedusinghindcastexperiments.Correlation(left)andROCscoreforpredictionsofaboveaverageconditions(right).Forcorrelationstipplingshowswhereskillisnotsignificantlypositive(atthe5%level).

RegionalForecastIndices

Thissectionshowsanexampleofaregionalforecastindexbasedonnotableforecastsignalsfoundintheprevioussectionandwherethereisskillinthemulti-modelensemble.Thefullsetofregionalforecastsandhindcastscanbe

foundonthewebsite

onthe“Regional”tab.TheregionsarebasedontheWMO

RegionalClimateOutlookForums

(RCOFs)andRegionalAssociations.Theseasonusedfortheindicesistherelevantseasonforthatregion,usuallythewetseasonormonsoonseason.

TheSouthernAsian(SASCOF)region,consideredhereasanexampletoshowcaseregionalforecastindices,hasdecadalvariabilityinitsMaytoSeptembermonsoonseason.Recentyears,apartfrom2023,havebeenanomalouslywetandtheforecastsuggeststhiswillcontinueforthe2025-2029period(Figure13).Thecalibratedprobabilityofaboveaverageis82%.Predictionsforthisregionare

skilful,butskillismedium,soconfidenceismediuminthisprediction.Notethatalthoughthefive-year-meanmaybepositive,thismaynotbethecaseforallindividualmonsoonseasonsinthisperiod.

Figure13:AsFigure5,butforMaytoSeptember(MJJAS)averagedprecipitationovertheSouthernAsian(SASCOF)region.

SeaiceForecasts

Seaiceforecastsarechallengingforcurrentdecadalpredictionsystems.Thiscanbeseenbyinspectingthesea-iceconcentrationmapswhichareshown(underthe“Forecasts”tab)andsea-iceextenttimeseries(underthe“Timeseries”tab)

onthewebsite.

Althoughthereisawiderangeofmeanstatesandforecastskill,themulti-modelensemblemeanisskilful,andtheseforecastsareissuedtostimulateconversationstofurtherimprovethisaspectofannual-to-decadalpredictions.

Thesea-iceconcentrationanomalies(Figure14)fortheArcticinMarch(thetimeofmaximumiceextent)showlargepredictedreductionsfor2025-2029intheBarentsSea,BeringSea,andSeaofOkhotsk.ThereisalsomodelagreementforreductionsintheGreenlandSeaandLabradorSea.SkillishighintheNorthAtlanticandmediuminthePacificforthesepredictions(Figure15).ForArcticseaiceinSeptember(minimumextent)2025-2029,largereductionsarepredictedforallregionsthatnormallyhavesea-iceatthistimeofyear.Thereishighskillinpredictinganomaliesatthesea-iceedge,sothereishighconfidenceforthesereductions,exceptintheArcticArchipelagowherethereislowconfidence.

ForAntarcticSeptember(maximumextent)thepredictionsshowahighprobabilityofbelownormalseaicealongtheclimatologicalsea-iceedge.Correlationskillgivesislow-to-mediumconfidenceinthisprediction.ManypredictionsystemshaveunrealisticallylowseaiceinAntarcticainMarchandsothereislittleagreementonanomalies(stippling),butthereisasignalforreductionsintheeasternRossSeathathasincreasedsincelastyear’sforecast.Confidenceismediumforthisforecast.

Figure14:Predictionsfor2025-2029MarchandSeptembersea-iceconcentrationanomaliesrelativeto1991-2020.Ensemblemean(leftcolumn)forMarch(top,%)andSeptember(bottom,%),stippledwheremorethan1/3ofmodelsdisagreeonthesignoftheanomaly,andprobabilityofaboveaverage(rightcolumn).Asthisisanuncalibratedtwo-categoryforecast,theprobabilityforbelowaverageisoneminustheprobabilityshownintherightcolumn.

Figure15:Predictionskilloffive-yearmeansofMarchandSeptembersea-iceanomaliesevaluatedusinghindcastexperiments.Correlation(left)andROCscoreforpredictionsofaboveaverageconditions(right).Forcorrelationstipplingshowswhereskillisnotsignificantlypositive(atthe5%level).

EvaluationofPreviousForecasts

Thissectionassessesforecaststhatwereissuedinrealtimeforthemostrecentlycompletedone-andfive-yearperiods.Theforecastfor2024,whichwasproducedusingsimulationsinitialisedattheendof2023,isshowninFigure16.S