世界气象组织-2023全球气候状况报告 Provisional State of the Global Climate 2023

ProvisionalStateofthe

GlobalClimate2023

Keymessages

.

Theglobalmeannear-surfacetemperaturein2023(toOctober)wasaround1.40±0.12°C

abovethe1850–1900average.BasedonthedatatoOctober,itisvirtuallycertainthat2023

willbethewarmestyearinthe174-yearobserva甘onalrecord,surpassingthepreviousjoint

warmestyears,2016at1.29±0.12°Cabovethe1850–1900averageand2020at1.27±0.13°C.

.

Thepastnineyears,2015–2023,willbetheninewarmestyearsonrecord.

.

Recordmonthlyglobaltemperatureshavebeenobservedfortheocean–fromAprilthrough

toSeptember–and,star甘ngslightlylater,theland–fromJulythroughtoSeptember.

.

Theten-yearaverage2014–2023(toOctober)globaltemperatureis1.19±0.12°Cabovethe

1850–1900average,thewarmest10-yearperiodonrecord.

.

Observedconcentra甘onsofthethreemaingreenhousegases–carbondioxide,methane,and

nitrousoxide–reachedrecordhighlevelsin2022,thelatestyearforwhichconsolidated

globalvaluesareavailable(1984–2022).Real-甘medatafromspecificloca甘onsshowthatlevels

ofthethreegreenhousegasescon甘nuedtoincreasein2023.

.

Oceanheatcontentreacheditshighestlevelin2022,thelatestavailablefullyearofdatain

the65-yearobserva甘onalrecord.

.

In2023,globalmeansealevelreachedarecordhighinthesatelliterecord(1993topresent),

reflec甘ngcon甘nuedoceanwarmingaswellasthemel甘ngofglaciersandicesheets.Therate

ofglobalmeansealevelinriseinthepasttenyears(2013–2022)ismorethantwicetherate

ofsealevelriseinthefirstdecadeofthesatelliterecord(1993–2002).

.

Antarc甘csea-iceextentreachedanabsoluterecordlowforthesatelliteera(1979topresent)

inFebruary.IceextentwasatarecordlowfromJuneonwards,andtheannualmaximumin

Septemberwasfarbelowthepreviousrecordlowmaximum.

.

GlaciersinwesternNorthAmericaandtheEuropeanAlpsexperiencedanextrememelt

season.InSwitzerland,glacierslostaround10%oftheirremainingvolumeinthepasttwo

years.

.

Extremeweathercon甘nuestoleadtoseveresocio-economicimpacts.Extremeheataffected

manypartsoftheworld.WildfiresinHawaii,CanadaandEuropeledtolossoflife,the

destruc甘onofhomesandlarge-scaleairpollu甘on.Floodingassociatedwithextremerainfall

fromMediterraneanCycloneDanielaffectedGreece,Bulgaria,Türkiye,andLibyawith

par甘cularlyheavylossoflifeinLibya.

.

Foodsecurity,popula甘ondisplacementsandimpactsonvulnerablepopula甘onscon甘nuetobe

ofconcernin2023,withweatherandclimatehazardsexacerba甘ngthesitua甘oninmanyparts

oftheworld.

.

Extremeweatherandclimatecondi甘onscon甘nuedtotriggernew,prolonged,andsecondary

displacementin2023andincreasedthevulnerabilityofmanywhowerealreadyuprootedby

complexmul甘-causalsitua甘onsofconflictandviolence.

Globalclimateindicators

Theglobalclimateindicatorsprovideanoverviewofchangesintheclimatesystem

1

.Thesetof

interlinkedphysicalindicatorspresentedhereconnectthechangingcomposi甘onoftheatmospherewithchangesinenergyintheclimatesystemandtheresponseofland,ocean,andice.

Theglobalindicatorsarebasedonawiderangeofdatasetswhichcomprisedatafrommul甘ple

observingsystemsincludingsatellitesandinsitunetworks(fordetailsondatasetsusedinthereport,see

Datasetsandmethods)

.

Changestothephysicalclimate,measuredherebykeyindicators,canhavecascadingimpactsonna甘onaldevelopmentandprogresstowardtheSustainableDevelopmentGoals(SDGs)

2

.For

example,changesintheacidityortemperatureoftheoceancanaffectmarinelife,poten甘allyimpac甘ngcoastalcommuni甘esthatmaydependonthelocalcatchfortheirlivelihoodorfoodsecurity.Ontheotherhand,climatesciencehasacri甘calroletoplayinfacilita甘ngsustainable

development.Asdemonstratedbythe2023UnitedinSciencereport,weather,climate,andwater-relatedsciencessupporttheachievementofmanyoftheSDGs

3

.Recognizingtheinterconnec甘onsbetweenclimateanddevelopmentcanthereforeleadtosynergis甘cac甘on—anincreasingnecessityastheworldgetsfurtheroff-trackfromachievingboththeSDGsandParisAgreement

4

.

Baselines

Baselinesareperiodsof甘me,usuallyspanningthreedecadesormore,thatareusedasafixed

benchmarkagainstwhichcurrentcondi甘onscanbecompared.Forscien甘fic,policyandprac甘cal

reasons,severaldifferentbaselinesareusedinthisreport,andthesearespecifiedinthetextandfigures.Wherepossible,themostrecentWMOclimatologicalstandardnormal,1991–2020,isusedforconsistentrepor甘ng.

Forsomeindicators,however,itisnotpossibletousethestandardnormalowingtoalackof

measurementsduringtheearlypartoftheperiod.Therearealsotwospecificexcep甘ons.First,fortheglobalmeantemperature甘meseries–andonlyfortheglobalmeanseries–areferenceperiod

of1850–1900isused.ThisisthebaselineusedinIPCCAR6WGIasareferenceperiodforpre-industrialcondi甘onsandisrelevantforunderstandingprogressinthecontextoftheParis

Agreement.Second,greenhousegasconcentra甘onscanbees甘matedmuchfurtherbackin甘meusinggasbubblestrappedinicecores.Therefore,theyear1750isusedinthisreporttorepresentpre-industrialgreenhousegasconcentra甘ons.

Greenhousegases

Keymessage:

.Observedconcentra甘onsofthethreemaingreenhousegases–carbondioxide,methane,andnitrousoxide–reachedrecordhighlevelsin2022,thelatestyearforwhichconsolidated

globalvaluesareavailable(1984–2022).Real-甘medatafromspecificloca甘onsshowthatlevelsofthethreegreenhousegasescon甘nuedtoincreasein2023.

Atmosphericconcentra甘onsofgreenhousegasesreflectabalancebetweenemissionsfromhumanac甘vi甘es,naturalsources,andsinks.Increasinglevelsofgreenhousegasesintheatmosphereduetohumanac甘vi甘eshavebeenthemajordriverofclimatechangesincetheindustrialrevolu甘on.Global

1/view/journals/bams/102/1/BAMS-D-19–0196.1.xml

2ClimateIndicatorsandSustainableDevelopment:DemonstratingtheInterconnections()

/records/item/56276-climate-indicators-and-sustainable-development-demonstrating-the-interconnections

3UnitedInScience2023()

/records/item/68235-united-in-science-2023

4/sites/default/files/2023–09/UN%20Climate%20SDG%20Synergies%20Report-091223B_1.pdf

averagemolefrac甘onsofgreenhousegases–referredtohereforsimplicityasthe“concentra甘on”intheatmosphere–arecalculatedfrominsituobserva甘onsmadeatmul甘plesitesthroughtheGlobalAtmosphereWatch(GAW)ProgrammeofWMOandpartnernetworks.

In2022–thelatestyearforwhichconsolidatedglobalfiguresareavailable–atmosphericlevelsof

greenhousegasesreachednewhighs

(Figure1)

,withgloballyaveragedconcentra甘onsforcarbon

dioxide(CO2)at417.9±0.2partspermillion(ppm),methane(CH4)at1923±2partsperbillion(ppb)andnitrousoxide(N2O)at335.8±0.1ppb,respec甘vely150%,266%and124%ofpre-industrial

(1750)levels.TherateofincreaseofCH4wasthesecondhighestonrecord,aier2021andtherate

ofincreaseofN2Owasthehighestonrecord.TherateofincreaseofCO2at2.2ppmwasslightly

belowthe10-yearaverageof2.46ppm·yr-1.CO2growthrateistypicallylowerinyearswhichstart

withLaNiñaas2022did,andhigherinyearswhichstartwithElNiñoas2016did

5

.Real-甘medata

fromspecificloca甘ons,includingMaunaLoa

6

(Hawaii,UnitedStatesofAmerica)andKennaook/CapeGrim

7

(Tasmania,Australia)indicatethatlevelsofCO2,CH4andN2Ocon甘nuedtoincreasein2023.

(acarbonDioxideconcentration

420

400

380

360

340

1990200020102020

(b)Methaneconcentration(ppb)

1950

1900

1850

1750

1700

1650

1990200020102020

cNitrousoxideconcentrationppb)

340

330

320

310

300

1990200020102020

4

3

Q

(d)carbonDioxidegrowthrate(ppm/year)

1990200020102020

(e)Methanegrowthrate(ppbyear)

20

15

5

-5

2010

1990

2020

2000

(f)Nitrousoxidegrowthrate(ppbyear)

1.5

0.5

1990200020102020

Figure1:Toprow:Monthlygloballyaveragedmolefraction(measureofatmosphericconcentration),from1984to2022,of

(a)CO2inpartspermillion,(b)CH4inpartsperbillionand(c)N2Oinpartsperbillion.Bottomrow:thegrowthrates

representingincreasesinsuccessiveannualmeansofmolefractionsfor(d)CO2inpartspermillionperyear,(e)CH4inparts

perbillionperyearand(f)N2Oinpartsperbillionperyear.

Temperature

Keymessages:

.Theglobalmeannear-surfacetemperaturein2023(toOctober)wasaround1.40±0.12°C

abovethe1850–1900average.BasedonthedatatoOctober,itisvirtuallycertainthat2023

willbethewarmestyearinthe174-yearobserva甘onalrecord,surpassingthepreviousjoint

warmestyears,2016at1.29±0.12°Cabovethe1850–1900averageand2020at1.27±0.13°C.

.Thepastnineyears,2015–2023,willbetheninewarmestyearsonrecord.

5Betts,R.,Jones,C.,Knight,J.etal.ElNiñoandarecordCO2rise.NatureClimateChange6,806–810(2016).

/10.1038/nclimate3063

6/ccgg/trends/mlo.html

MeasurementsatMaunaLoawereinterruptedbyavolcaniceruptionandthemeasurementsitewastemporarilyrelocatedtoMaunakeaobservatories21milestothenorth.

7https://www.csiro.au/greenhouse-gases/

.Recordmonthlyglobaltemperatureshavebeenobservedfortheocean–fromAprilthroughtoSeptember–and,star甘ngslightlylater,theland–fromJulythroughtoSeptember.

.Theten-yearaverage2014–2023(toOctober)globaltemperatureis1.19±0.12°Cabovethe1850–1900average,thewarmest10-yearperiodonrecord.

Globalmeannear-surfacetemperaturein2023(datatoOctober)was1.40±0.12°Cabovethe1850–1900average

8

(Figure2)

.Theanalysisisbasedonasynthesisoffiveglobaltemperaturedatasets(see

Datasetsandmethods)

.BasedonthedatatoOctober,itisvirtuallycertainthat2023willbethe

warmestyearinthe174-yearinstrumentalrecordineachofthefivedatasets.Themostrecentnineyears–2015to2023–willbetheninewarmestyearsonrecord.Thetwopreviousjointwarmest

yearswere2016withananomalyof1.29±0.12°C,and2020withananomalyof1.27±0.13°C.

Thereweresomenoteworthyindividualmonths,withJune,July,August,andSeptember2023eachsurpassingthepreviousrecordfortherespec甘vemonthbyawidemargininalldatasets.Themarginincreasedfrombetween0.14and0.20°CinJunetobetween0.46and0.51°CinSeptember.The

second-highestmarginbywhichaSeptemberrecordwasbrokeninthepast60years(theperiod

coveredbyalldatasets)was0.02to0.17°Cin1983.Octoberwasalsorecordwarm.Julyistypicallythewarmestmonthoftheyearglobally,andthusJuly2023becametheall-甘mewarmestmonthonrecord.

Thelong-termincreaseinglobaltemperatureisduetoincreasedconcentra甘onsofgreenhousegases

intheatmosphere.TheshiifromLaNiña,whichlastedfrommid-2020toearly2023,tofully

developedElNiñocondi甘onsbySeptember2023(see

Short-termClimateDrivers)

likelyexplainssomeoftheriseintemperaturefrom2022to2023.However,someareasofunusualwarmingsuchastheNortheastAtlan甘c

(Figure3)

donotcorrespondtotypicalpaternsofwarmingorcooling

associatedwithElNiño.Otherfactors,whichares甘llbeinginves甘gated,mayalsohavecontributedtotheexcep甘onalwarmingfrom2022to2023.

Theaverageglobaltemperatureoverthepasttenyears,2014to2023(datatoOctober),was

1.19±0.12°Cabovethe1850–1900average,makingthepasttenyearsthewarmestamongallten-yearperiodsonrecordinallfivedatasets.The2014to2023averageisslightlyhigherthanthetotalobservedwarming(1.15[1.00to1.25]°C)fortheperiod2013to2022es甘matedbyForsteretal.

(2023)

9

,consistentwithcon甘nuedwarming.

Globalaveragesea-surfacetemperatures(SSTs)wereatarecordobservedhighforthe甘meofyear,star甘nginthelateNorthernHemispherespring.AprilthroughtoSeptember(thelatestmonthfor

whichwehavedata)wereallatarecordwarmhigh,andtherecordsforJuly,AugustandSeptemberwereeachbrokenbyalargemargin(around0.21to0.27°C).Excep甘onalwarmthrela甘vetothe

1991–2020baseline,wasrecordedintheeasternNorthAtlan甘c,theGulfofMexicoandthe

Caribbean,andlargeareasoftheSouthernOcean

(Figure3,

seealso

Marineheatwavesandcold-

spells)

.

GloballandtemperatureanomaliesreachedrecordobservedlevelsinJulyandAugust,somewhat

laterthanfortheSSTs,andtheSeptemberaveragewasarecordbyalargemarginof0.53to0.72°C.Thesecondhighestmargininthepast60yearswas0.21to0.27°Cin2002.Fortheyear2023to

date,mostlandareaswerewarmerthanthe1991–2020average

(Figure3)

.UnusualwarmthwasreportedacrosslargeareasoftheeasternU.S.,Mexico,andCentralAmerica,aswellaswesternand

8Foranomaliesrelativetootherbaselinessee

Globalmeantemperatureanomaliesfor2023relativetootherperiods.

9Forsteretal.usedanupdateoftheIPCCmethodologybasedonfourdatasets,twoofwhichareusedinthecurrentreport.Forsteretal.(2023)IndicatorsofGlobalClimateChange2022:annualupdateoflarge-scaleindicatorsofthestateoftheclimatesystemandhuman

influence,EarthSyst.Sci.Data,15,2295–2327,

/10.5194/essd-15–2295–2023.

created:2023-11-2321:37:04

southernareasofSouthAmerica.WesternEuropeandwesternpartsofNorthAfrica,westernEurasia,areasofCentralandsoutheastAsia,andJapan,werealsounusuallywarm.

GlobalMeanTemperatureDifference(°C)

comparedto1850-1900average

1.4

1.2

0.4

0.2

-0.2

HadcRUT5(1850-2023)

NOAAGlobalTemp(1850-2023)

GISTEMP(1880-2023)

JRA-55(1958-2023)

ERA5(1940-2023)

186018801900192019401960198020002020

year

C01d：202311-2322:22

Figure2:Annualglobalmeantemperatureanomalies(relativeto1850–1900)from1850to2023.The2023averageis

basedondatatoOctober.Dataarefromfivedatasets,see

Datasetsandmethodsf

ordetails.

AnnualTemperatureAnomalies2023

-5-3-2-1-0.5-0.2500.250.51235

Temperaturedifferencefrom1991-2020average(°C)

ERA5to2023-10GISTEMpto2023-10HadcRUT5to2023-10，JRA-55to2023-10，NOAAGlobalTempto2023-10

Figure3:Meannear-surfacetemperatureanomalies(differencefromthe1991–2020average)for2023toOctober.Dataare

themedianoffivedatasetsasindicatedinthelegend,see

Datasetsandmethodsf

ordetails.

Ocean

IncreasinghumanemissionsofCO2andothergreenhousegasescauseaposi甘veradia甘veimbalanceatthetopoftheatmosphere,meaningenergyisbeingtrappedwithintheclimatesystem.The

imbalanceleadstoanaccumula甘onofenergyintheEarthsystemintheformofheatthatisdriving

globalwarming

10

,

11

.Theocean,whichcoversaround70%oftheEarth’ssurface,absorbsheatandCO2,whichcanacttoslowtherateofwarmingintheatmosphere.However,theheatabsorbedbytheoceanleadstooceanwarmingwhich,togetherwiththemel甘ngoficeonland,raisessealevels.TheoceanalsoabsorbsCO2leadingtooceanacidifica甘on

12

.Warmingwaters,sealevelriseand

oceanacidifica甘onallhavesignificanteffectsontheocean,aswellastheplantsandanimalsthatliveinitandthepeoplewhorelyuponitfortheirlivelihoods.

Oceanheatcontent

Keymessage:

.Oceanheatcontentreacheditshighestlevelin2022,thelatestavailablefullyearofdatainthe65-yearobserva甘onalrecord.

Around90%oftheenergythataccumulatedintheEarthsystemsince1971wasstoredintheocean.Asenergyhasaccumulatedintheocean,ithaswarmedandtheheatcontentoftheocean(Ocean

HeatContent,

Figure4)

hasincreased.

Accordingtoaconsolidatedanalysisbasedonsevenindividualdatasets,theupper2000moftheoceancon甘nuedtowarmin2022(thelatestfullyearforwhichwehavedata)

13

.Itisexpectedthatwarmingwillcon甘nue–achangewhichisirreversibleoncentennialtomillennial甘mescales

14

,

15

.

Oceanheatcontentin2022wasthehighestonrecord,exceedingthe2021valueby17±9ZJ

(Figure4)

.Alldatasetsagreethatoceanwarmingratesshowapar甘cularlystrongincreaseinthe

pasttwodecades.Therateofoceanwarmingforthe0–2000mlayerwas0.7±0.1W·m-2from1971–

2022,but1.2±0.2W·m-2from2006–2022(theperiodcoveredbytheArgoprogramme).Deep-

oceanglobalwarmingbelow2000mdepthises甘matedtobe0.07±0.1W·m-2from1992–2022

16

.

Althoughoceanheatcontent(OHC)hasincreasedstronglythroughtheen甘rewatercolumn,therateofwarminghasnotbeenthesameeverywhere

17

.Thestrongestwarmingintheupper2000m

occurredintheSouthernOcean(60°S-35°S),NorthAtlan甘c(20°N-50°N)andSouthAtlan甘c(60°S-0°S)

(Figure5)

.TheSouthernOceandomainisthelargestreservoirofheat,accoun甘ngforaround36%of

theglobalOHCincreaseintheupper2000msince1958.TheAtlan甘cOceanaccountsforapproximately33%oftheglobal0-2000mOHCincrease;thePacificOceanaround20%.

Somerela甘velysmallregionsarecooling,includingthesubpolarNorthAtlan甘cOceanextending

fromnearthesurfacedowntoadepthofover800m(alsotheonlyareatoshowcentennialcoolingatthesurface).Thecontras甘ngpaternofcooling(50°N-70°N)andwarming(20°N-50°N)inthe

NorthAtlan甘chasbeenassociatedwithaslowingoftheAtlan甘cMeridionalOverturningCircula甘on

10Hansen,J.etal.(2011).Earth’senergyimbalanceandimplications.AtmosphericChemistryandPhysics

/10.5194/acp-11–

13421–2011

11vonSchuckmann,K.etal.(2016).AnimperativetomonitorEarth’senergyimbalance.InNatureClimateChange.

/10.1038/nclimate2876

12StateoftheOceanReport2022|UNESCO

/en/articles/state-ocean-report-2022

13vonSchuckmannetal.(2020).HeatstoredintheEarthsystem:wheredoestheenergygo?EarthSyst.Sci.Data,12(3),2013–2041.

/10.5194/essd-12–2013–2020

14Cheng,L.;Trenberth,K.E.;Fasullo,J.etal.Improvedestimatesofoceanheatcontentfrom1960to2015,ScienceAdvances2017,3(3),e1601545

./10.1126/sciadv.1601545.

15IPCC,2019:SummaryforPolicymakers.In:IPCCSpecialReportontheOceanandCryosphereinaChangingClimate[H.-O.Pörtner,D.C.Roberts,V.Masson-Delmotte,P.Zhai,M.Tignor,E.Poloczanska,K.Mintenbeck,A.Alegría,M.Nicolai,A.Okem,J.Petzold,B.Rama,N.M.Weyer(eds.)].Inpress

/10.1175/2010JCLI3682.1.

16Purkey,S.G.,&Johnson,G.C.(2010).WarmingofGlobalAbyssalandDeepSouthernOceanWatersbetweenthe1990sand2000s:

ContributionstoGlobalHeatandSeaLevelRiseBudgets.JournalofClimate,23(23),6336–6351.

/10.1175/2010JCLI3682.1

17Cheng,L.,Abraham,J.,Trenberth,K.E.etal.AnotherYearofRecordHeatfortheOceans.Adv.Atmos.Sci.(2023).

/10.1007/s00376–023–2385–2

andCheng,L.,vonSchuckmann,K.,Abraham,J.P.etal.Pastandfutureoceanwarming.NatRevEarthEnviron3,776–794(2022).

/10.1038/s43017–022–00345–1.

andlocalinterac甘onsbetweentheairandsea

18

.OthercoolingregionsincludethenorthwestPacific,southwestPacificandsouthwestIndianOceans.

Figure4:1960–2021ensemblemeantimeseriesandensemblestandarddeviation(2-standarddeviations,shaded)ofglobal

oceanheatcontent(OHC)anomaliesrelativetothe2005–2021averageforthe0–300m(grey),0–700m(blue),0–2000m

(yellow)and700–2000mdepthlayer(green).TheensemblemeansOHCanomaliesfortheyear2022hasbeenaddedas

separatepoints,togetherwiththeirensemblespread,andisbasedonasubsetof7datasets.Source:MercatorOcean

international.UpdatedfromvonSchuckmannetal.(2020)

19

Figure5:Observedupper2000mOHCtrendfrom1958to2022.Units:W·m–2.DataupdatedfromChengetal.(2017)

20

.

18Cheng,L.,vonSchuckmann,K.,Abraham,J.P.etal:Pastandfutureoceanwarming.NatureReviewsEarth&Environment.2022,

/10.1038/s43017–022–00345–1.

19vonSchuckmannetal.(2020).HeatstoredintheEarthsystem:wheredoestheenergygo?EarthSyst.Sci.Data,12(3),2013–2041.

/10.5194/essd-12–2013–2020

20Cheng,L.;Trenberth,K.E.;Fasullo,J.etal.Improvedestimatesofoceanheatcontentfrom1960to2015,ScienceAdvances2017,3(3),e1601545

./10.1126/sciadv.1601545

Sealevel

Keymessage:

.In2023,globalmeansealevelreachedarecordhighinthesatelliterecord(1993topresent),reflec甘ngcon甘nuedoceanwarmingaswellasthemel甘ngofglaciersandicesheets.

.Therateofglobalmeansealevelinriseinthepasttenyears(2013–2022)ismorethantwicetherateofsealevelriseinthefirstdecadeofthesatelliterecord(1993–2002).

In2023,globalmeansealevel(GMSL)hascon甘nuedtorise

(Figure6)

.TheLaNiñacondi甘ons

betweenmid-2020andearly2023hadonlyasmallapparenteffectonGMSL,unlikethe2011LaNiñathatledtoatemporarydecreaseintheGMSLofseveralmillimetres.Therapidriseobservedin2023

islikelydueinparttothenascentElNiñoandislikelytoincreasefurtherasthe2023ElNiño

develops.Thelong-termrateofsealevelrisehasmorethandoubledsincethestartofthesatelliterecord,increasingfrom2.14mm·yr-1between1993and2002to4.72mm·yr-1between2013and2022.

FromJanuarytoMarch2023,sealevels

(Figure7)

werehigherthanthelong-termaverage(1993–

2012)inthewesterntropicalPacific.Thisischaracteris甘cofwarmseawaterintheregionassociatedwithENSO-neutralcondi甘ons.SealevelsintheNorthAtlan甘candeasterntropicalPacificwerelowerthanthelong-termaverage.WarmingofthesurfacewatersintheeasternTropicalpacificduringtheearlystagesofthe2023ElNiño(see

Short-termClimateDrivers)

ledtoanincreaseinsealevel

rela甘vetothelong-termmeaninthemosteasternpartoftheTropicalPacificbetweenApriland

June.ByJulytoSeptember,theElNiñosignaturewasclearlyvisible,withsealevelbeingabove

averagefromthemid-tropicalPacifictothecoastsofcentralandSouthAmerica.Aboveaveragesealevelswerealsoobservedinthetropicalandnorth-eastAtlan甘c,associatedwiththeanomalous

warmingintheseareasduringNorthernHemispheresummer.

Figure6:GMSLevolutionbetweenJanuary1993andOctober2023basedonsatellitealtimetry.Theblacklineisthebest

estimate,andthegreyshadedareaindicatestheuncertainty.Near-real-timeupdatesareindicatedbyadottedline.Redandblueannotationsindicatetheaveragerateofsealevelriseduringthreedecadesoftherecordasindicated.(SourceAVISO)

Figure7:3-monthaveragesofaltimetry-basedsealevelanomalies(relativetothe1993–2012average,whichistheproduct

climatology)for(topleft)JanuarytoMarch,(topright)ApriltoJune,and(bottomleft)JulytoSeptember.Datadownloaded

fromtheCopernicusMarineService(CMEMS,

https://marine.copernicus.eu)

.

Marineheatwavesandcoldspells

Aswithheatwavesandcold-spellsonland,marineheatwaves(MHW)andmarinecold-spells(MCS)areprolongedperiodsofextremehighorlowtemperaturesintheseasandoceanthatcanhavearangeofconsequencesformarinelifeanddependentcommuni甘es

21

.MHWshavebecomemore

frequent,intense,andlongerlas甘ngsincethelate20thcentury,whileMCSshavebeendecreasingbythosesamemeasures.Satelliteretrievalsofsea-surfacetemperatureareusedtomonitorMHWs

andMCSsglobally,categorizedhereasmoderate,strong,severe,extreme,orice(fordefini甘ons,see

Datasetsandmethods)

.

ElNiñoeventstendtocausewide-spreadMHWsintheeasternTropicalPacific.Thisregiondid

experience'strong'MHWsin2023

(Figure8a

,tolateAugust),butyet,theyhavecoveredasmallerareathanduringpreviousElNiñoevents.TheareaislikelytoincreaseastheElNiñocon甘nuestodevelop.Ofpar甘cularconcern,in2023werethepersistentandwide-spreadMHWsintheNorth

Atlan甘cthroughoutNorthernHemispheresummerandearlyautumn.TheMediterraneanSeawasalsounusuallywarmrela甘vetothebaselineperiodandexperiencednearcompletecoverageof

'strong'and'severe'MHWsforthetwelihconsecu甘veyear.Inthesouthernhemisphere,thewaters

surroundingNewZealandremained1to2°Cabovethelong-termaveragethroughJanuarytoSeptember(~270days).

Incontrast,therewerealmostnooccurrencesofMCSswithin60°NorthorSouthoftheequatorin2023todate

(Figure9a

).TheglobaloceanexperiencedanaveragedailyMHWcoverageof20%(to

21Smale,D.A.,Wernberg,T.,Oliver,E.C.J.etal.Marineheatwavesthreatenglobalbiodiversityandtheprovisionofecosystemservices.Nat.Clim.Chang.9,306–312(2019).

/10.1038/s41558–019–0412–1

date,

Figure8b

),wellabovethepreviousrecordof17%in2016.Incontrast,theaveragedailycoverageofMCS

(Figure9b

)wasonly2%,farbelow2022(5%).

Figure8:(a)GlobalmapshowingthehighestMHWcategory(fordefinitions,see

Datasetsandmethods)

experiencedat

eachpixelover2023(throughSeptember;referenceperiod1982–2011).LightgreyindicatesthatnoMHWoccurredina

pixelovertheentireyear;(b)StackedbarplotshowingthepercentageofthesurfaceoftheoceanexperiencinganMHWon

anygivendayoftheyear;(c)StackedbarplotshowingthecumulativenumberofMHWdaysaveragedoverthesurfaceof

theocean.Note:ThisaverageiscalculatedbydividingthecumulativesumofMHWdaysperpixelweightedbythesurface

areaofthosepixels.(d)StackedbarplotshowingthetotalpercentageofthesurfaceoftheoceanthatexperiencedanMHW

from1982topresent.DataarefromNationalOceanicandAtmosphericAdmi