世界气象组织-2023全球气候状况报告（英）

Provisional

State

oftheGlobalClimate

2023Key

messages•Theglobalmeannear-surface

temperature

in

2023

(toOctober)wasaround1.40±0.12°Cabove

the

1850–1900

average.Based

onthedata

to

October,

itis

virtuallycertainthat2023willbethe

warmestyearin

the174-yearobserva�onalrecord,

surpassing

thepreviousjointwarmestyears,2016

at1.29

±0.12

°Cabovethe1850–1900averageand2020

at1.27±0.13

°C.Thepast

nine

years,2015–2023,willbetheninewarmestyearsonrecord.Recordmonthly

globaltemperatures

have

been

observedfor

theocean

–fromAprilthroughto

September–

and,star�ngslightly

later,

theland

–from

July

throughto

September.Theten-yearaverage2014–2023(to

October)globaltemperature

is1.19±0.12°Cabove

the1850–1900average,

thewarmest10-yearperiodonrecord.Observedconcentra�onsofthethreemaingreenhouse

gases–carbon

dioxide,methane,andnitrousoxide–reachedrecordhighlevelsin2022,thelatestyearfor

which

consolidatedglobalvaluesareavailable(1984–2022).Real-�medata

fromspecificloca�onsshow

thatlevelsofthethree

greenhousegases

con�nuedtoincrease

in

2023.••••••Oceanheat

content

reacheditshighestlevelin

2022,the

latest

available

full

yearofdatainthe65-yearobserva�onalrecord.In2023,globalmean

sealevelreachedarecordhighin

thesatelliterecord(1993to

present),reflec�ngcon�nuedocean

warmingaswellasthe

mel�ngofglaciersandice

sheets.

Therateofglobal

meansealevelinriseinthepasttenyears

(2013–2022)ismorethantwicetherateofsealevelriseinthefirstdecadeof

thesatellite

record

(1993–2002).•••Antarc�c

sea-iceextentreachedanabsoluterecordlow

forthesatellite

era(1979

to

present)inFebruary.

Iceextentwasat

arecordlow

fromJune

onwards,andtheannualmaximuminSeptemberwasfarbelowthe

previousrecordlow

maximum.GlaciersinwesternNorthAmericaandtheEuropeanAlps

experiencedanextreme

meltseason.InSwitzerland,glacierslostaround10%of

theirremainingvolume

inthe

pasttwoyears.Extremeweathercon�nuestoleadto

severe

socio-economicimpacts.Extremeheataffectedmany

partsoftheworld.WildfiresinHawaii,CanadaandEuropeledto

lossoflife,

thedestruc�on

ofhomesandlarge-scale

airpollu�on.Floodingassociatedwithextreme

rainfallfrom

MediterraneanCyclone

Daniel

affectedGreece,

Bulgaria,Türkiye,andLibyawithpar�cularlyheavy

lossof

life

inLibya.••Food

security,

popula�ondisplacementsandimpactsonvulnerable

popula�ons

con�nue

tobeofconcernin

2023,withweatherandclimate

hazardsexacerba�ngthesitua�oninmany

partsoftheworld.Extremeweatherandclimate

condi�onscon�nuedtotrigger

new,

prolonged,andsecondarydisplacementin2023

andincreasedthevulnerability

ofmanywhowere

alreadyuprootedbycomplex

mul�-causalsitua�onsofconflict

andviolence.GlobalclimateindicatorsTheglobal

climate

indicators

provideanoverviewofchangesintheclimate

system1.Thesetofinterlinkedphysicalindicatorspresentedhere

connectthechangingcomposi�on

oftheatmospherewithchangesin

energy

inthe

climate

system

and

theresponseofland,ocean,

andice.Theglobalindicators

are

basedonawiderange

of

data

setswhichcomprise

datafrom

mul�pleobservingsystems

includingsatellites

andinsitunetworks

(for

detailsondata

sets

usedinthereport,seeDatasetsandmethods).Changesto

thephysicalclimate,measuredhere

by

key

indicators,canhave

cascadingimpactsonna�onaldevelopmentand

progresstowardtheSustainable

DevelopmentGoals(SDGs)2.Forexample,

changesintheacidityortemperatureof

theoceancan

affect

marinelife,

poten�allyimpac�ngcoastalcommuni�esthatmay

depend

onthe

localcatchfortheirlivelihoodorfoodsecurity.Onthe

otherhand,climate

sciencehasacri�calrole

to

playinfacilita�ngsustainabledevelopment.Asdemonstratedby

the2023

Unitedin

Sciencereport,weather,

climate,andwater-relatedsciencessupportthe

achievementofmanyofthe

SDGs3.Recognizingtheinterconnec�onsbetweenclimate

anddevelopment

canthereforelead

to

synergis�c

ac�on—anincreasingnecessityastheworld

getsfurtheroff-track

fromachievingboththeSDGsand

ParisAgreement4.BaselinesBaselinesare

periodsof�me,usuallyspanningthreedecadesormore,thatareusedasa

fixedbenchmarkagainst

which

current

condi�onscanbecompared.Forscien�fic,policy

andprac�calreasons,several

different

baselinesare

usedinthisreport,and

thesearespecifiedinthetextandfigures.Wherepossible,the

most

recentWMOclimatological

standardnormal,1991–2020,is

usedfor

consistentrepor�ng.Forsomeindicators,

however,

itisnotpossibleto

usethe

standardnormalowingto

alackofmeasurementsduringtheearlypart

of

theperiod.

There

are

alsotwo

specificexcep�ons.First,

fortheglobalmeantemperature

�meseries–andonlyfor

theglobalmeanseries–areference

periodof1850–1900

isused.Thisisthebaselineused

inIPCCAR6WG

Ias

areferenceperiodfor

pre-industrialcondi�onsandisrelevant

forunderstandingprogressinthe

contextofthe

ParisAgreement.Second,greenhousegas

concentra�ons

can

bees�matedmuchfurtherbackin�meusinggas

bubblestrappedinicecores.Therefore,

theyear

1750

isusedinthisreportto

representpre-industrialgreenhouse

gas

concentra�ons.Greenhouse

gasesKey

message:•Observedconcentra�onsof

thethreemaingreenhouse

gases–carbon

dioxide,methane,andnitrousoxide–reachedrecordhighlevels

in2022,thelatestyearfor

which

consolidatedglobalvaluesareavailable(1984–2022).Real-�medata

fromspecificloca�onsshow

thatlevelsofthethree

greenhousegases

con�nuedtoincrease

in

2023.Atmosphericconcentra�ons

ofgreenhousegasesreflect

abalancebetweenemissionsfromhumanac�vi�es,naturalsources,andsinks.Increasinglevelsofgreenhouse

gasesin

theatmospheredue

tohumanac�vi�eshavebeen

themajordriverofclimatechangesincetheindustrialrevolu�on.Global1/view/journals/bams/102/1/BAMS-D-19–0196.1.xml2

ClimateIndicatorsandSustainableDevelopment:DemonstratingtheInterconnections()/records/item/56276-climate-indicators-and-sustainable-development-demonstrating-the-interconnections3

UnitedInScience2023()/records/item/68235-united-in-science-20234

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

frac�onsofgreenhousegases–referredto

hereforsimplicityas

the

“concentra�on”intheatmosphere–are

calculatedfrominsitu

observa�onsmadeatmul�plesitesthroughthe

GlobalAtmosphereWatch

(GAW)ProgrammeofWMOandpartnernetworks.In2022–the

latestyearfor

whichconsolidatedglobal

figuresareavailable–atmosphericlevelsofgreenhousegasesreachednew

highs(Figure1),withgloballyaveraged

concentra�ons

forcarbondioxide

(CO

)at

417.9

±0.2partspermillion(ppm),methane

(CH

)at1923±2

partsperbillion(ppb)24andnitrousoxide(N

O)at335.8±0.1

ppb,respec�vely

150%,266%and124%of

pre-industrial2(1750)levels.Therate

ofincreaseof

CH

wasthesecondhigheston

record,a�er

2021andtherate4ofincreaseofN

Owasthehigheston

record.

TherateofincreaseofCO

at

2.2

ppmwasslightly22belowthe10-yearaverageof2.46ppm·yr-1.CO

growthrate

istypicallylowerinyearswhichstart2withLa

Niñaas2022did,andhigherinyearswhichstart

with

ElNiñoas2016did5.Real-�medatafromspecificloca�ons,includingMaunaLoa6(Hawaii,UnitedStatesofAmerica)andKennaook/CapeGrim7(Tasmania,

Australia)

indicate

thatlevelsofCO

,CH

andN

Ocon�nuedto

increasein2023.242Figure1:Top

row:Monthlygloballyaveragedmolefrac1984to2022,of(a)CO

inpartspermillion,(b)CH

inpartsperbillionand(c)N

Oinpartsper

billion.Bo242represeninsuccessiveannualmeansofmolefracCO

inpartspermillionperyear,

(e)CH

inparts24perbillionper

yearand(f)N

Oinpartsperbillionper

year.2TemperatureKey

messages:•Theglobalmeannear-surface

temperature

in

2023

(toOctober)wasaround1.40±0.12°Cabove

the

1850–1900

average.Based

onthedata

to

October,

itis

virtuallycertain

that

2023willbethe

warmestyearin

the174-yearobserva�onalrecord,surpassing

thepreviousjointwarmestyears,2016

at1.29

±0.12

°Cabovethe1850–1900averageand2020

at

1.27±0.13

°C.Thepast

nine

years,2015–2023,willbetheninewarmestyearsonrecord.•5Betts,R.,Jones,C.,Knight,J.etal.ElNiñoandarecordCO

rise.NatureClimateChange6,

806–810(2016).2/10.1038/nclimate30636/ccgg/trends/mlo.html

MeasurementsatMaunaLoa

wereinterruptedby

avolcaniceruptionandthemeasurementsitewastemporarilyrelocated

toMaunakeaobservatories

21milestothenorth.7https://www.csiro.au/greenhouse-gases/••Recordmonthly

globaltemperatures

have

been

observedfor

theocean

–fromAprilthroughto

September–

and,star�ngslightly

later,

theland

–from

July

throughto

September.Theten-yearaverage2014–2023(to

October)globaltemperature

is1.19±0.12°Cabove

the1850–1900average,

thewarmest10-yearperiodonrecord.Globalmeannear-surfacetemperature

in

2023(datato

October)was1.40

±0.12°Cabovethe1850–1900average8(Figure

2).

The

analysisisbased

onasynthesisoffiveglobal

temperature

datasets(seeDatasetsandmethods).Basedon

thedatato

October,itisvirtuallycertainthat2023

will

be

thewarmestyearinthe

174-yearinstrumentalrecord

ineachof

thefive

datasets.The

most

recent

nineyears

–2015

to

2023–will

be

theninewarmestyearsonrecord.Thetwoprevious

jointwarmestyears

were2016withananomalyof

1.29±0.12°C,and2020with

ananomalyof1.27±0.13°C.Therewere

somenoteworthy

individualmonths,with

June,July,

August,andSeptember2023

eachsurpassingthepreviousrecord

for

therespec�ve

monthby

awidemargin

inalldatasets.The

marginincreasedfrom

between0.14and

0.20°Cin

June

to

between

0.46

and0.51

°Cin

September.Thesecond-highestmarginby

whicha

Septemberrecordwasbroken

inthepast60years(theperiodcoveredbyalldatasets)was

0.02

to

0.17°Cin

1983.

Octoberwasalsorecordwarm.July

istypicallythewarmest

monthofthe

yearglobally,

andthusJuly2023became

the

all-�mewarmestmonth

onrecord.Thelong-termincreaseinglobaltemperature

isdueto

increasedconcentra�onsofgreenhousegasesintheatmosphere.Theshi�

fromLaNiña,whichlastedfrommid-2020

to

early2023,to

fullydeveloped

ElNiñocondi�onsby

September2023

(seeShort-termClimateDrivers)likely

explainssomeofthe

rise

intemperature

from

2022to2023.However,

someareasof

unusualwarmingsuchastheNortheastAtlan�c

(Figure

3)

do

not

correspondto

typicalpat

ernsof

warmingorcoolingassociatedwithElNiño.Otherfactors,whichare

s�ll

beinginves�gated,

may

also

havecontributedto

the

excep�onalwarmingfrom

2022

to

2023.Theaverageglobaltemperature

overthepastten

years,2014to2023

(data

to

October),was1.19±0.12

°Cabovethe1850–1900average,makingthe

past

tenyears

the

warmest

amongallten-yearperiodson

recordinallfive

datasets.The2014

to

2023average

isslightly

higherthanthetotalobservedwarming(1.15

[1.00to1.25]°C)fortheperiod2013to2022

es�matedby

Forster

et

al.(2023)9,consistentwithcon�nuedwarming.Global

averagesea-surfacetemperatures(SSTs)

wereat

arecordobservedhighfor

the�meof

year,star�nginthelate

NorthernHemispherespring.April

throughto

September(the

latest

monthforwhichwehave

data)

wereallat

arecord

warmhigh,andtherecordsfor

July,

August

andSeptemberwereeachbroken

by

alarge

margin(around0.21to

0.27°C).Excep�onalwarmthrela�ve

to

the1991–2020baseline,was

recordedintheeasternNorthAtlan�c,theGulfof

Mexico

andtheCaribbean,andlarge

areasoftheSouthernOcean(Figure

3,

see

alsoMarineheatwaves

andcold-spells).Globallandtemperatureanomaliesreached

recordobservedlevelsinJulyandAugust,somewhatlaterthanfor

the

SSTs,

andtheSeptemberaveragewas

arecordbyalargemarginof

0.53

to

0.72

°C.Thesecondhighestmargininthepast60years

was0.21to0.27

°Cin2002.For

the

year2023todate,most

landareaswerewarmerthanthe1991–2020average

(Figure3).

Unusualwarmthwasreportedacrosslargeareasof

theeasternU.S.,Mexico,

andCentralAmerica,aswellaswesternand8Foranomaliesrelativeto

otherbaselinesseeGlobalmeantemperatureanomaliesfor2023relativeto

other

periods.9Forsteret

al.usedanupdateoftheIPCC

methodologybasedonfourdatasets,twoofwhichareused

inthecurrentreport.Forsteretal.(2023)IndicatorsofGlobalClimateChange2022:annualupdateoflarge-scaleindicators

ofthe

state

oftheclimatesystemandhumaninfluence,EarthSyst.Sci.Data,15,2295–2327,/10.5194/essd-15–2295–2023.southernareasofSouthAmerica.WesternEurope

andwesternpartsofNorthAfrica,westernEurasia,areasofCentralandsoutheastAsia,andJapan,were

also

unusuallywarm.Figure2:Annualglobalmeantemperatureanomalies(rel–1900)from1850to2023.The2023averageisbasedondata

to

October.

Dataarefromfivedatasets,seeData

setsandmethodsfordetails.Figure3:Meannear-surfacetemperatureanomalies(differencefromthe1991–2020average)for

2023to

October.

Dataarethemedianoffivedatasetsasindicatedinthelegend,seeData

setsandmethodsfordetails.OceanIncreasinghumanemissionsofCO

andothergreenhouse

gasescause

aposi�ve

radia�ve

imbalance2at

thetopofthe

atmosphere,meaningenergyisbeing

trappedwithintheclimatesystem.

Theimbalanceleadsto

an

accumula�onof

energyintheEarthsystem

intheformof

heatthat

isdrivingglobalwarming10,11.Theocean,whichcovers

around70%oftheEarth’s

surface,absorbsheatandCO

,whichcanactto

slow

therate

of

warminginthe

atmosphere.However,

the

heatabsorbed

by2theoceanleadsto

ocean

warmingwhich,togetherwiththemel�ng

oficeonland,raisessealevels.TheoceanalsoabsorbsCO

leadingtoocean

acidifica�on12.Warmingwaters,

sealevelriseand2ocean

acidifica�onallhavesignificanteffectsontheocean,aswellastheplantsandanimalsthatliveinitandthepeoplewho

rely

uponitfortheirlivelihoods.Ocean

heat

contentKey

message:•Oceanheat

content

reacheditshighestlevelin

2022,the

latest

available

full

yearofdatainthe65-yearobserva�onalrecord.Around90%of

theenergythataccumulatedin

theEarthsystemsince1971was

storedintheocean.Asenergy

hasaccumulatedintheocean,ithaswarmedandtheheatcontentofthe

ocean(OceanHeatContent,Figure4)

hasincreased.Accordingto

aconsolidatedanalysisbased

onsevenindividualdatasets,theupper2000

m

oftheoceancon�nuedto

warmin

2022(thelatest

fullyearfor

which

wehave

data)13.Itis

expectedthatwarmingwillcon�nue

–achange

whichisirreversibleoncentennialto

millennial�mescales14,15.Oceanheatcontent

in

2022

was

thehighestonrecord,

exceedingthe

2021

value

by17

±9ZJ(Figure

4).

Alldata

sets

agree

thatocean

warmingrates

showapar�cularlystrongincreaseinthepast

two

decades.The

rateof

ocean

warmingforthe0–2000mlayer

was

0.7

±0.1

W·m-2from1971–2022,

but1.2

±0.2

W·m-2from2006–2022(theperiod

coveredbytheArgo

programme).Deep-oceanglobalwarmingbelow

2000

mdepthises�matedtobe0.07

±0.1W·m-2from1992–202216.Althoughoceanheatcontent

(OHC)hasincreasedstrongly

throughtheen�rewater

column,the

rateofwarminghasnotbeen

the

sameeverywhere17.Thestrongestwarmingintheupper2000moccurredintheSouthernOcean(60°S-35°S),NorthAtlan�c

(20°N-50°N)andSouthAtlan�c

(60°S-0°S)(Figure

5).

TheSouthern

Oceandomainisthelargestreservoirof

heat,accoun�ngfor

around36%oftheglobal

OHCincreasein

theupper2000

m

since1958.

TheAtlan�c

Oceanaccountsforapproximately33%oftheglobal0-2000mOHCincrease;thePacificOceanaround20%.Somerela�vely

smallregionsare

cooling,includingthesubpolarNorthAtlan�c

Oceanextendingfromnearthesurface

downto

adepthofover800m

(alsotheonlyareatoshowcentennialcoolingat

thesurface).

Thecontras�ngpat

ernofcooling(50°N-70°N)and

warming(20°N-50°N)intheNorthAtlan�c

hasbeenassociated

withaslowingof

the

Atlan�cMeridionalOverturningCircula�on10Hansen,J.etal.(2011).Earth’senergyimbalanceandimplications.AtmosphericChemistryandPhysics/10.5194/acp-11–13421–201111

vonSchuckmann,K.etal.(2016).An

imperativetomonitorEarth’senergyimbalance.InNatureClimateChange./10.1038/nclimate287612

StateoftheOceanReport2022|UNESCO/en/articles/state-ocean-report-202213

vonSchuckmannetal.(2020).Heatstoredin

theEarthsystem:wheredoestheenergygo?EarthSyst.Sci.Data,

12(3),2013–2041./10.5194/essd-12–2013–202014

Cheng,L.;

Trenberth,K.E.;Fasullo,J.etal.Improvedestimatesof

oceanheat

contentfrom

1960to2015,ScienceAdvances2017,3(3),e1601545./10.1126/sciadv.1601545.15

IPCC,2019:SummaryforPolicymakers.In:IPCCSpecialReporton

theOceanandCryosphereinaChangingClimate[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/10.1175/2010JCLI3682.1.16

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

LevelRiseBudgets.JournalofClimate,23(23),6336–6351./10.1175/2010JCLI3682.117

Cheng,L.,Abraham,J.,Trenberth,K.E.etal.AnotherYearofRecordHeatforthe

Oceans.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�ons

betweentheairandsea18.Other

coolingregionsincludethe

northwestPacific,southwest

Pacificandsouthwest

IndianOceans.Figure4:1960–2021ensemblemean-standarddevioceanheatcontent(OHC)anomaliesrel–2021averagefor

the0–300m(grey),0–700m(blue),0–2000m(yellow)and700–2000mdepthlayer(green).TheensemblemeansOHCanomaliesfor

theyear2022hasbeenaddedasseparatepoints,togetherwiththeirensemblespread,andisbasedonasubsetof7datasets.Source:MercatorOceaninter19Figure5:Observedupper2000m

OHCtrendfrom1958to2022.Units:W·m–2.DataupdatedfromChengetal.(2017)20.18

Cheng,L.,vonSchuckmann,K.,Abraham,J.P.etal:Pastandfutureoceanwarming.NatureReviewsEarth&Environment.2022,/10.1038/s43017–022–00345–1.19

vonSchuckmannetal.(2020).Heatstoredin

theEarthsystem:wheredoestheenergygo?EarthSyst.Sci.Data,

12(3),2013–2041./10.5194/essd-12–2013–202020

Cheng,L.;Trenberth,K.E.;Fasullo,J.etal.Improvedestimatesof

oceanheat

contentfrom1960to2015,ScienceAdvances2017,3(3),e1601545./10.1126/sciadv.1601545Sea

levelKey

message:••In2023,

globalmean

sealevelreachedarecordhighin

thesatelliterecord(1993to

present),reflec�ngcon�nuedocean

warmingaswellasthe

mel�ngofglaciersandice

sheets.Therate

of

globalmean

sealevelinrise

inthepasttenyears

(2013–2022)ismore

thantwicetherate

of

sealevelrise

in

thefirstdecadeof

thesatellite

record(1993–2002).In2023,globalmean

sealevel(GMSL)hascon�nuedto

rise(Figure6).

TheLaNiñacondi�onsbetweenmid-2020

and

early

2023

had

onlyasmallapparent

effectonGMSL,unlike

the2011LaNiñathatledto

atemporary

decreaseintheGMSLof

several

millimetres.Therapidrise

observedin2023islikelydue

inparttothenascentEl

Niño

andislikelyto

increasefurtheras

the2023

ElNiñodevelops.Thelong-term

rate

ofsealevelrisehasmore

thandoubled

sincethestart

of

thesatelliterecord,

increasingfrom2.14

mm·yr-1between1993

and2002to4.72

mm·yr-1between

2013

and2022.FromJanuary

to

March2023,sealevels(Figure7)

were

higherthanthe

long-termaverage

(1993–2012)inthewesterntropicalPacific.Thisischaracteris�c

of

warmseawaterintheregion

associatedwithENSO-neutralcondi�ons.SealevelsintheNorth

Atlan�c

andeasterntropicalPacificwere

lowerthanthelong-term

average.Warmingof

thesurfacewatersintheeasternTropical

pacificduringtheearlystagesof

the2023El

Niño

(seeShort-termClimateDrivers)ledto

anincrease

insea

levelrela�vetothelong-term

meaninthemosteasternpart

of

theTropical

PacificbetweenAprilandJune.By

July

to

September,theEl

Niño

signature

was

clearlyvisible,withsealevelbeingaboveaveragefromthe

mid-tropicalPacific

to

thecoastsof

centralandSouthAmerica.Aboveaveragesealevelswerealsoobservedin

thetropicalandnorth-east

Atlan�c,associated

with

theanomalouswarmingintheseareasduringNorthernHemisphere

summer.Figure6:GMSLevoles

andthe

greyshadedarea

indicatestheuncertainty.Near-real-blueannotOctober2023basedon

satelliteal.Theblacklineisthebest.Redand(SourceAVISO)Figure7:3-month

averagesofal-climatology)for

(top

lebasedsealevelanomalies(rela1993–2012average,whichisthe

producttop

right)ApriltoJune,and(b)JulytoSeptember.DatadownloadedfromtheCopernicusMarineService(CMEMS,h).Marine

heatwaves

and

cold

spellsAswithheatwaves

andcold-spellsonland,marineheatwaves(MHW)andmarine

cold-spells(MCS)are

prolongedperiodsof

extreme

highorlow

temperatures

intheseasand

oceanthatcanhavearangeofconsequencesformarinelife

anddependentcommuni�es21.MHWs

havebecomemorefrequent,intense,andlongerlas�ngsincethelate20thcentury,whileMCSshavebeendecreasingby

thosesamemeasures.Satelliteretrievalsofsea-surface

temperature

are

usedto

monitorMHWsandMCSsglobally,

categorizedhereasmoderate,strong,severe,extreme,orice(fordefini�ons,seeDatasetsandmethods).ElNiño

events

tendto

cause

wide-spreadMHWs

inthe

easternTropicalPacific.This

regiondidexperience'strong'MHWs

in

2023(Figure8a,to

late

August),but

yet,

they

havecoveredasmallerareathanduringpreviousEl

Niño

events.Theareaislikelytoincrease

astheElNiño

con�nuestodevelop.Of

par�cularconcern,in2023

werethepersistent

and

wide-spread

MHWs

inthe

NorthAtlan�c

throughoutNorthernHemispheresummer

andearlyautumn.TheMediterraneanSea

wasalso

unusuallywarmrela�ve

to

thebaselineperiod

andexperiencednearcomplete

coverageof'strong'and'severe'MHWsfor

the

twel�h

consecu�veyear.Inthesouthernhemisphere,thewaterssurroundingNewZealandremained1to2°Cabovethe

long-termaveragethroughJanuarytoSeptember(~270

days).Incontrast,there

werealmostno

occurrences

of

MCSswithin

60°North

orSouth

of

theequatorin2023todate

(Figure

9a).The

global

ocean

experiencedanaverage

dailyMHW

coverageof

20%(to21

Smale,D.A.,Wernberg,T.,Oliver,E.C.J.etal.Marineheatwavesthreatenglobalbiodiversityand

theprovisionofecosystem

services.Nat.Clim.Chang.9,306–312(2019).

/10.1038/s41558–019–0412–1date,Figure8b),

wellabove

thepreviousrecordof

17%

in2016.Incontrast,theaveragedailycoverageof

MCS(Figure9b)wasonly2%,far

below2022(5%).Figure8:(a)GlobalmapshowingthehighestMHWcategory(fordefiniData

setsandmethods)experiencedateachpixelover2023(throughSeptember;referenceperiod1982–2011).Light

greyindicatesthatnoMHWoccurredin

apixelovertheenany

givenday

oftheyear;(c)Stacked

barplotshowingthecumulatheocean.Note:ThisaverageiscalculatedbydividingthecumulaMHWdaysaveragedoverthesurfaceofareaofthosepixels.(d)Stackedbarplotshowingthetotalpercentageofthesurfaceoftheocean

thatexperiencedan

MHWfrom1982topresent.DataarefromN

OpSurfaceTemperature

(OISST).Source:RobertSchlegel-Figure9:AsforFigure8butshowingmarine

cold-spellsratherthanmarineheatwaves.DataarefromNOAAOISST.

Source:RobertSchlegel.Ocean

acidificTheoceanabsorbsaroundonequarteroftheannualemissionsofanthropogenic

CO

tothe2atmosphere22,23.CO

reactswithseawaterandaltersthe

carbonatechemistry,

resul�nginadecrease2inpHreferredto

as