世界氣象組織-2023全球氣候狀況報告（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

fromspeci?cloca?onsshow

thatlevelsofthethree

greenhousegases

con?nuedtoincrease

in

2023.??????Oceanheat

content

reacheditshighestlevelin

2022,the

latest

available

full

yearofdatainthe65-yearobserva?onalrecord.In2023,globalmean

sealevelreachedarecordhighin

thesatelliterecord(1993to

present),re?ec?ngcon?nuedocean

warmingaswellasthe

mel?ngofglaciersandice

sheets.

Therateofglobal

meansealevelinriseinthepasttenyears

(2013–2022)ismorethantwicetherateofsealevelriseinthe?rstdecadeof

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.Extremeheata?ectedmany

partsoftheworld.Wild?resinHawaii,CanadaandEuropeledto

lossoflife,

thedestruc?on

ofhomesandlarge-scale

airpollu?on.Floodingassociatedwithextreme

rainfallfrom

MediterraneanCyclone

Daniel

a?ectedGreece,

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?onsofcon?ict

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

a?ect

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

getsfurthero?-track

fromachievingboththeSDGsand

ParisAgreement4.BaselinesBaselinesare

periodsof?me,usuallyspanningthreedecadesormore,thatareusedasa

?xedbenchmarkagainst

which

current

condi?onscanbecompared.Forscien??c,policy

andprac?calreasons,several

di?erent

baselinesare

usedinthisreport,and

thesearespeci?edinthetextand?gures.Wherepossible,the

most

recentWMOclimatological

standardnormal,1991–2020,is

usedfor

consistentrepor?ng.Forsomeindicators,

however,

itisnotpossibleto

usethe

standardnormalowingto

alackofmeasurementsduringtheearlypart

of

theperiod.

There

are

alsotwo

speci?cexcep?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

fromspeci?cloca?onsshow

thatlevelsofthethree

greenhousegases

con?nuedtoincrease

in

2023.Atmosphericconcentra?ons

ofgreenhousegasesre?ect

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

?guresareavailable–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

Ni?aas2022did,andhigherinyearswhichstart

with

ElNi?oas2016did5.Real-?medatafromspeci?cloca?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.ElNi?oandarecordCO

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

onasynthesisof?veglobal

temperature

datasets(seeDatasetsandmethods).Basedon

thedatato

October,itisvirtuallycertainthat2023

will

be

thewarmestyearinthe

174-yearinstrumentalrecord

ineachof

the?ve

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?

fromLaNi?a,whichlastedfrommid-2020

to

early2023,to

fullydeveloped

ElNi?ocondi?onsby

September2023

(seeShort-termClimateDrivers)likely

explainssomeofthe

rise

intemperature

from

2022to2023.However,

someareasof

unusualwarmingsuchastheNortheastAtlan?c

(Figure

3)

do

not

correspondto

typicalpat

ernsof

warmingorcoolingassociatedwithElNi?o.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

recordinall?ve

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.

Dataarefrom?vedatasets,seeData

setsandmethodsfordetails.Figure3:Meannear-surfacetemperatureanomalies(di?erencefromthe1991–2020average)for

2023to

October.

Dataarethemedianof?vedatasetsasindicatedinthelegend,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

acidi?ca?on12.Warmingwaters,

sealevelriseand2ocean

acidi?ca?onallhavesigni?cante?ectsontheocean,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;thePaci?cOceanaround20%.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.

P?rtner,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

northwestPaci?c,southwest

Paci?candsouthwest

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),re?ec?ngcon?nuedocean

warmingaswellasthe

mel?ngofglaciersandice

sheets.Therate

of

globalmean

sealevelinrise

inthepasttenyears

(2013–2022)ismore

thantwicetherate

of

sealevelrise

in

the?rstdecadeof

thesatellite

record(1993–2002).In2023,globalmean

sealevel(GMSL)hascon?nuedto

rise(Figure6).

TheLaNi?acondi?onsbetweenmid-2020

and

early

2023

had

onlyasmallapparent

e?ectonGMSL,unlike

the2011LaNi?athatledto

atemporary

decreaseintheGMSLof

several

millimetres.Therapidrise

observedin2023islikelydue

inparttothenascentEl

Ni?o

andislikelyto

increasefurtheras

the2023

ElNi?odevelops.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)inthewesterntropicalPaci?c.Thisischaracteris?c

of

warmseawaterintheregion

associatedwithENSO-neutralcondi?ons.SealevelsintheNorth

Atlan?c

andeasterntropicalPaci?cwere

lowerthanthelong-term

average.Warmingof

thesurfacewatersintheeasternTropical

paci?cduringtheearlystagesof

the2023El

Ni?o

(seeShort-termClimateDrivers)ledto

anincrease

insea

levelrela?vetothelong-term

meaninthemosteasternpart

of

theTropical

Paci?cbetweenAprilandJune.By

July

to

September,theEl

Ni?o

signature

was

clearlyvisible,withsealevelbeingaboveaveragefromthe

mid-tropicalPaci?c

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(forde?ni?ons,seeDatasetsandmethods).ElNi?o

events

tendto

cause

wide-spreadMHWs

inthe

easternTropicalPaci?c.This

regiondidexperience'strong'MHWs

in

2023(Figure8a,to

late

August),but

yet,

they

havecoveredasmallerareathanduringpreviousEl

Ni?o

events.Theareaislikelytoincrease

astheElNi?o

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(forde?niData

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

acidi?cTheoceanabsorbsaroundonequarteroftheannualemissionsofanthropogenic

CO

tothe2atmosphere22,23.CO

reactswithseawaterandaltersthe

carbonatechemistry,

resul?nginadecrease2inpHreferredto

as