early warning of climate tipping points - cnr · 2016-07-05 · • early warning methods exist for...

EarlyWarningofClimateTippingPoints

TimLentont.m.lenton@exeter.ac.uk

EarthSystemScience,CollegeofLifeandEnvironmentalSciences,UniversityofExeter,UK

Outline

Whatareclimatetippingpoints?

Dotheycarryearlywarningsignals?

Whatshouldwedoaboutthem?

1.Tippingpoints

Typesoftipping‘Bifurcation’tipping

Typesoftipping‘Bifurcation’tipping ‘Noise-induced’tipping

Iceageabruptclimatechanges

Deplazes etal.(2013)NatureGeoscience 6:213-217

Age (ka)

Time

Temperature

inGreenlandMonsooninIndia

Monsoonin

Am

azon

Holoceneabruptclimatechanges

Wangetal.(2013)ChineseGeographical Science 23:1-12

Collapse of Neolithic Culture of China

Time

Littlethingscanmakeabigdifference

• Tippingelement– AcomponentoftheEarthsystem,atleastsub-continentalinscale(~1000km),thatcanbeswitched–undercertaincircumstances– intoaqualitativelydifferentstatebyasmallperturbation.

• Tippingpoint– Thecorrespondingcriticalpoint– inforcingandafeatureofthesystem– atwhichthefuturestateofthesystemisqualitativelyaltered.

Lentonetal.(2008)PNAS105(6):1786-1793

Policyrelevant tippingelements• Humanactivitiesareinterferingwiththesystemsuchthat

decisionstakenwithina“politicaltimehorizon”(~100years)candeterminewhetherthetippingpointisreached.

• Thetimetoobserveaqualitativechangeplusthetimetotriggeritliewithinan“ethicaltimehorizon”(~1000years).

• Asignificantnumberofpeoplecareaboutthefateofthesystem.

Lentonetal.(2008)PNAS105(6):1786-1793

Tippingelementsintheclimatesystem

UpdatedfromLentonetal.(2008)PNAS105(6):1786-1793

Estimatesofproximity

Lenton&Schellnhuber (2007)NatureReportsClimateChange

ThethermohalinecirculationAtlanticMeridionalOverturning Circulation(AMOC) =theAtlanticbranchofthethermohaline circulation

ProbabilitiesunderdifferentscenariosThreedifferentwarmingscenarios:

Impreciseprobability statementselicitedfromexperts.

ExampleofcollapseofAtlanticmeridional overturning circulation:

Kriegleretal.(2009)PNAS 106(13):5041-5046

Amazonrainforest

Malhi etal. (2009)PNAS 106:20610-5;Jonesetal. (2009)NatureGeosci.2:484-487

Expertelicitationforfuturewarmingscenarios:

Low Medium High

Greenland

Atlantic

Antarctica

Amazon

ElNiño

Kriegleretal.(2009)PNAS 106(13):5041-5046

Likelihood• Impreciseprobability

statementsfromexpertsformallycombined.

• Under2-4°Cwarming:>16%probabilityofpassingatleastoneoffivetippingpoints

• Under >4°Cwarming:>56%probabilityofpassingatleastoneoffivetippingpoints

2.Earlywarningprospects

One of the consequences of the Japanese 2011 tsunami (for which there were advanced early warning systems)

Earlywarningprospects

Systembeingforcedpastabifurcationtippingpoint

Held&Kleinen (2004)GRL31:L23207;Lentonetal.(2008)PNAS105(6):1786-1793

ThankstoChris Boultonfortheanimation

Earlywarningindicators• Autocorrelation

– Simplestmeasureisatlag-1(α inxt+1 =αxt +σηt)

• Variance– Should increaseduetocriticalslowingdown

• Skewness– Timeseries‘lean’towardsnewbasinofattraction

• Sensitivityanalysis– Varyde-trendingbandwidthandslidingwindowlength

• TrendsmeasuredwithKendallτ rankcorrelationcoefficient

Abruptclimatechangeearlywarning

Earlywarningindicator

GRIPice-coreδ18Oproxytemperature

Detrendeddata

Lenton,Livina,Dakos,Scheffer(2012)ClimateofthePast8:1127-1139

Modeltestsofearlywarning:CollapseofAtlanticMeridionalOverturningCirculation(AMOC)

GENIE-1intermediatecomplexitymodel GENIE-2atmosphere-oceanGCM

Ove

rturn

ing

(Sv)

Ove

rturn

ing

(Sv)

Lenton (2011)NatureClimateChange 1:201-209

GENIE-1intermediatecomplexitymodel GENIE-2atmosphere-oceanGCM

Ove

rturn

ing

(Sv)

Ove

rturn

ing

(Sv)

Lenton (2011)NatureClimateChange 1:201-209

Modeltestsofearlywarning:CollapseofAtlanticMeridionalOverturningCirculation(AMOC)

Boulton, Allison, Lenton(2014)NatureComms.5:5752

Earlywarninginamorecomplexmodel

• TheAtlanticMeridional overturningcirculation(AMOC)iscurrentlymonitoredat26oN

• Freshwaterforcingofthe‘FAMOUS’ocean-atmosphereGCMcausescollapseoftheAMOC

• Thereareearlywarningsignalse.g.at26oN

Earlywarningsignalsatalllatitudes

Boulton,Allison, Lenton(2014)NatureComms.5:5752

Wherearethebestearlywarningsignals?Howearlyarethey?

Boulton,Allison, Lenton(2014)NatureComms.5:5752

Redareasindicateearlywarningsignalsthataresignificantatp<0.05fromtestingagainst10,000instancesofanullmodelwheretheoriginaldataare

bootstrapped todestroytheirmemory

TrendsinautocorrelationofSSTdata

Red=slowingdownBlue=speedingup

Boulton&Lenton (2015)PNAS112(37):11496-11501

Pacificdecadaloscillation(PDO)

SlowingdowninthePacificDecadalOscillation(PDO)indexn = 1343

Boulton&Lenton (2015)PNAS112(37):11496-11501

Implicationsformarineecosystems

Boulton&Lenton (2015)PNAS112:11496-11501, adaptingthemodel ofDiLorenzo&Ohman (2013)PNAS 110:2496-2499

• Marineecosystemsactasintegratorsofoceanvariabilitywiththeirowncharacteristicdampingtimescale

• Thesurfaceoceantypicallyhasafasterdampingtimescale(~6months)thane.g.zooplanktonpopulations(~2years)

• Ifoceanvariabilityslowsdownthenwecanexpectmarineecosystemstobecomemorecorrelatedwithit,morevariable,andmorelikelytopasstippingpointsiftheyhavethem

AR(1)ofoceanvariability

Ecosystem

correlationwith

ocean

Ecosystem

standarddeviatio

n

Population-levelearlywarning• Severalexperimentshave

demonstratedearlywarningsignalsofpopulationcollapse,e.g.photo-inhibitionbyalgaeinachemostat

• Experimentsspandifferentspeciesanddifferentpositivefeedbackmechanisms

• Inlatestspatialexperiments‘recoverylength’providesthebestearlywarningsignal

Wissel (1984)Oecologia 65:101-107;Veraart etal.(2012)Nature 481:357-359;Daietal.(2013)Nature 496:355-358.

Ecosystem-levelearlywarning

Carpenteretal. (2011)Science 332:1079-82;Wangetal. (2012)Nature 492:419-22;Streeter&Dugmore (2013)PNAS 110:5779-84.

• Experimentalmanipulationofalakeecosystemhasrevealedearlywarningofatrophiccascade

• Thereisdebatedevidenceof‘flickering’priortolakeeutrophication

• Earlywarningoflandsurfacechangehasalsobeenarguedforintephralayers

Biome-levelearlywarning?• Evidenceformultiplestablestatesof

forest-savannah-grasslandintropicsandborealregions

• Debateoverhowlocalisedthemechanismsofbi-stabilityare– firefeedbacksorvegetation-climatefeedbacksorboth?

• Somemodelsshowabruptbiometransitionsinfuturescenarios,e.g.Amazonrainforestdieback…

Hirota etal. (2011)Science 334:232-5;Staver etal. (2011)Science 334:230-2;Schefferetal.(2012)PNAS 109:21384-9.

Amazondiebackcasestudy• Non-zeroequilibriumV*,ishighlynon-

linearwithrespecttoproductivityP, whichcausesdieback.

• AsP isreduced,atranscriticalbifurcationisapproachedaseigenvalueG-P tendstowardszero.

• Thisshouldgiveanearlywarningsignalintheformofcriticalslowingdown

Boultonetal. (2013)TheoreticalEcology 6:373-384;Jonesetal. (2009)NatureGeosci.2:484-487.

Amazondiebackcasestudy• ‘Generic’earlywarningsignals

arenotrobustlyfound• AR(1)generallyappearsto

decreaseovertimedespiteapproachingabifurcation

• Increasingvarianceisthemostrobustsignal,butitispresentinclimatedriversoftheforest

• Abruptforcingdestroysexpectedearlywarningsignals

Boultonetal. (2013)TheoreticalEcology 6:373-384.

Different locations in one model

Different models, spatially averagedKendall τ for indicator trends

Kendall τ for indicator trends

System-specificearlywarning• SensitivityofNEPtotemperature

robustlybecomesmorenegativeastemperatureincreases

• SensitivityofCO2 anomaliestotemperaturealsofairlyrobustlyincreases

• Theseareobservablevariables• Thereisn’taparticularthreshold

valueforeitherindicatorrelatedtoonsetofdieback

Respiration

T

GPP

T

Boultonetal. (2013)TheoreticalEcology 6:373-384.

Interactionsacrossscales• Globalclimatemodelsdonotyet

includelocalpositivefeedbackbetweenvegetationstateandfirescreatingbi-stability

• Firesthemselvescandisplaycriticaltransitionsfromlocalisedtomega-fireregimes

• ThereisevidenceforacriticaltransitioninthefireregimeunderextremedroughtintheAmazon

Lenton(2013)Ann.Rev.Env.Res.38:1-29;Pueyo etal. (2010)EcologyLetters13:793-802.

From William A. Hoffmann

Howusefulisearlywarning?• Itdependsonwhetherafast

interventionmechanismisavailabletoavoidatippingpoint

• Evenwhenatippingpointremainsunavoidable,earlywarningcouldstillbeausefulaidtoadaptation

• Successfulearlywarningsystemsrequireriskknowledge,warningservice,effectivecommunicationandresponsecapability

Biggsetal. (2009)PNAS 106:826-831;Basher(2006)PhilTransA364:2167-82;Lenton(2012)Env Sci &Policy27:S60-S75.

3.Whatshouldwedoaboutit?

Conventionalcost-benefitanalysis

Global temperature change

Pric

e

Cost of mitigation Cost of climate damages

Butwhatifthereareuncertaintippingpoints?

Optimum (?)

Addinguncertaintippingpointstoawidely-usedintegratedassessmentmodel

Lontzek,Cai, Judd, Lenton(2015)NatureClimateChange5(4):441–444

TheDSICEmodel– basedonNordhaus’DICE-2013modelasused inUSFederalSocialCostofCarbon estimates

Tippingeventsandtheircausalinteractions

Diebackof Amazonrainforest

Shift to a (more) persistent

El Ninoregime

Disintegration of West Antarctic Ice Sheet

Collapse ofAtlantic

thermohalinecirculation

Melt ofGreenland Ice Sheet

+

+

++

+

-

+ +

+/-

+/-

+/-

ReducedwarmingofGreenland

Cooling ofNEtropicalPacific,thermoclineshoaling,weakeningofannualcycleinEEP

Enhancedwatervapourexportfrom

Atlantic

-

HeataccumulationinSouthernOcean

SouthwardshiftofInter-tropicalConvergence

Zone

DryingoverAmazonia

Tropicalmoisturesupplychanges

Increase inmeridionalsalinitygradient

FastadvectionofsalinityanomalytoNorth

Atlantic

Sealevelrisecausinggroundinglineretreat

Freshwaterinput

WarmingofRossandAmundsenseas

Increase inprobability

Decreaseinprobability

Uncertain directionofchange

+

-

+/-TippingeventsareconnectedA→Bifatleast5expertsjudgedthattriggeringAhadadirecteffectontheprobability oftriggeringBthereafter

Fromexpertelicitation:Kriegler etal.(2009)PNAS 106(13):5041-5046

RepresentationoftippingpointsinDSICE

Lontzek,Cai, Judd, Lenton(2015)NatureClimateChange5:441–444;Cai,Lenton,Lontzek(2016)NatureClimateChange

Tippingelement

Hazardrate(%/yr/K)

Transitiontime(years)

Finaldamages(%worldGDP)

AMOC 0.063 10-50-250 10-15-20GIS 0.188 300-1500-7500 5-10-15WAIS 0.104 100-500-2500 2.5-5-7.5AMAZ 0.163 10-50-250 2.5-5-7.5ENSO 0.053 10-50-250 5-10-15

Cai,Lenton,Lontzek(2016)NatureClimateChange

Examplecascadeoftippingpoints

Cai,Lenton,Lontzek(2016)NatureClimateChange

Solid line=withinteractionsDashedline=withoutinteractions

Tippingmindsets• Theory:Humansholdcoherent

worldviewssowhenwechangeourmindithappensabruptly

• Oneworldviewiscoherentfrompurelyevidencebasedthinking

• Analternativeworldviewiscoherentifweincludevaluesandemotions

PaulThagard &ScottFindlay (2011)‘Changingmindsaboutclimatechange:Beliefrevision, coherenceandemotion’

Solid lines are coherent relations,Dashed lines are incoherent relations

Tippingcollectiveaction• Uncertaintyaboutthelocation

ofatippingpointcanleadtofailuretocoordinatetoavoidit

• Belowacriticallevelofuncertainty,socialdynamicsaretippedfromfreeridingtocoordinatingtoavoidcatastrophe

• Experimentalresultssupportthisgametheoreticalprediction

Barrett&Dannenberg(2014)NatureClimateChange4:36-39

Tippingtheenergysystem• Controlvariable: Increase

thecarbonprice• Interventions: Technology

transfer• Tippingpoint:Shiftin

backstopenergysource• Response:Renewable

energyshareincreasesdespitecarbonpricedeclining

Edenhofer etal. (2006)TheEnergyJournalSpecialIssue:57-108

Conclusion• Ifbusiness-as-usualcontinuesthenclimatetippingpointsareexpectedto

becomehighimpacthigh probabilityevents

• Earlywarningmethodsexistfortippingpointsandhavebeensuccessfullytestedagainstpastclimatedataandmodels,butwillrequireadvancesinpastclimatereconstructionaswellascontemporaryclimatemonitoring

• Aclimatetippingpointearlywarningsystemcouldreducetherisktheyposebyhelpingusadaptinadvanceifnotavoidthem

• Thethreatofmultiple,interacting,uncertainclimatetippingpointsshouldbetriggeringstrongmitigationactivitynowtoreducetheirlikelihood

• Theoptimalpolicyresponsefromastandardcost-benefitmodelwitharealisticspecificationofriskaversionisacarbonpricetodayof>$100/tCO2

Somesynthesischallenges• Joiningdata,statisticalmodelsandprocess-basedmodels:

• Canwe‘recalibrate’thedynamicalbehaviourofourprocess-basedmodelsbasedonthekindofstabilityindicatorsexploredhere?

• Combiningapproachestodiagnosingsystemstability:– Dynamicalapproachfromdynamicalsystemstheory– Structuralapproachfromnetworktheory

• Canweformulateatheorythatcanassessthepotentialfor‘tippingcascades’acrossscales?

Publications• Lenton,T.M.,andH.J.Schellnhuber(2007),Tippingthescales,NatureReportsClimateChange,1,97-98.• Livina,V.N.,andT.M.Lenton(2007),Amodifiedmethodfordetectingincipientbifurcationsinadynamicalsystem,GRL,34,L03712.• Lenton,T.M.,etal.(2008),TippingElementsintheEarth'sClimateSystem,PNAS,105,1786-1793.• Livina,V.N.,etal.(2010),Potentialanalysisrevealschangingnumberofclimatestatesduringthelast60kyr,ClimateofthePast,6,77-82.• Livina,V.N.,etal.(2011),Changingclimatestatesandstability:fromPliocenetopresent,ClimateDynamics,37,2437-2453.• Lenton,T.M.(2011),Beyond2°C:Redefiningdangerousclimatechangeforphysicalsystems,WIRes:ClimateChange,2,451-461.• Lenton,T.M.(2011),Earlywarningofclimatetippingpoints,NatureClimateChange,1,201-209.• Lenton,T.M.(2011),2°Cornot2°C?Thatistheclimatequestion,Nature,473,7.• Livina,V.N.,etal.(2012),Anindependent testofmethodsofdetectingandanticipatingbifurcations…,PhysicaA,391,485-496.• Lenton,T.M.(2012),Arcticclimatetippingpoints,AMBIO,41,10-22.• Lenton,T.M.,etal.(2012),Climatebifurcationduringthelastdeglaciation?,ClimateofthePast,8,1127-1139.• Lenton,T.M.,etal.(2012),Earlywarningofclimatetippingpointsfromcriticalslowingdown,PhilTransA,370,1185-1204.• Lenton,T.M.(2012),Whatearlywarningsystemsarethereforenvironmentalshocks?,EnvironmentalScienceandPolicy,27,S60-S75• Scheffer,M.,Carpenter,S.R.,Lenton,T.M.,etal.(2012),AnticipatingCriticalTransitions.Science,338,344-348.• Lenton,T.M.,andJ.C.Ciscar(2013),Integratingtippingpointsintoclimateimpactassessments,ClimaticChange,117,585-597.• Livina,V.N.,andT.M.Lenton(2013),ArecenttippingpointinArcticsea-icecover,TheCryosphere,7,275-286.• Livina,V.N.,etal.(2013),Forecastingtheunderlyingpotentialgoverningthetimeseriesofadynamicalsystem.PhysicaA392,3891-3902.• Lenton,T.M.(2013),EnvironmentalTippingPoints.AnnualReviewofEnvironmentandResources,38,1-29.• Lenton,T.M.(2014),Gametheory:Tippingclimatecooperation.NatureClimateChange,4,14-15.• Barrett,S.,Lenton,T.M.,etal.(2014),Climateengineeringreconsidered.NatureClimateChange,4,527-529.• Lontzek,T.S.,Cai,Y.,Judd,K.,Lenton,T.M.(2015)NatureClimateChange,5,441–444.• Boulton,C.andT.M.Lenton(2015)SlowingdownofNorthPacificclimatevariabilityanditsimplicationsforabruptecosystemchange.

PNAS112,11496-11501.• Cai,Y.,Lenton,T.M.,Lontzek,T.S.(2016)Riskofmultipleinteractingtippingpointsshouldtriggerrapidemissionsreduction.Nature

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