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Early Warning of Climate Tipping Points Tim Lenton [email protected] Earth System Science, College of Life and Environmental Sciences, University of Exeter, UK
EarlyWarningofClimateTippingPoints
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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