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AnAbruptClimateChangeScenarioandItsImplicationsforUnitedStatesNationalSecurityOctober2003ByPeterSchwartzandDougRandallImaginingtheUnthinkableThepurposeofthisreportistoimaginetheunthinkable–topushtheboundariesofcurrentresearchonclimatechangesowemaybetterunderstandthepotentialimplicationsonUnitedStatesnationalsecurity.Wehaveinterviewedleadingclimatechangescientists,conductedadditionalresearch,andreviewedseveraliterationsofthescenariowiththeseexperts.Thescientistssupportthisproject,butcautionthatthescenariodepictedisextremeintwofundamentalways.First,theysuggesttheoccurrencesweoutlinewouldmostlikelyhappeninafewregions,ratherthanonglobally.Second,theysaythemagnitudeoftheeventmaybeconsiderablysmaller.Wehavecreatedaclimatechangescenariothatalthoughnotthemostlikely,isplausible,andwouldchallengeUnitedStatesnationalsecurityinwaysthatshouldbeconsideredimmediately.ExecutiveSummaryThereissubstantialevidencetoindicatethatsignificantglobalwarmingwilloccurduringthe21stcentury.Becausechangeshavebeengradualsofar,andareprojectedtobesimilarlygradualinthefuture,theeffectsofglobalwarminghavethepotentialtobemanageableformostnations.Recentresearch,however,suggeststhatthereisapossibilitythatthisgradualglobalwarmingcouldleadtoarelativelyabruptslowingoftheocean’sthermohalineconveyor,whichcouldleadtoharsherwinterweatherconditions,sharplyreducedsoilmoisture,andmoreintensewindsincertainregionsthatcurrentlyprovideasignificantfractionoftheworld’sfoodproduction.Withinadequatepreparation,theresultcouldbeasignificantdropinthehumancarryingcapacityoftheEarth’senvironment.Theresearchsuggeststhatoncetemperaturerisesabovesomethreshold,adverseweatherconditionscoulddeveloprelativelyabruptly,withpersistentchangesintheatmosphericcirculationcausingdropsinsomeregionsof5-10degreesFahrenheitinasingledecade.Paleoclimaticevidencesuggeststhatalteredclimaticpatternscouldlastforasmuchasacentury,astheydidwhentheoceanconveyorcollapsed8,200yearsago,or,attheextreme,couldlastaslongas1,000yearsastheydidduringtheYoungerDryas,whichbeganabout12,700yearsago.AbruptClimateChange2Inthisreport,asanalternativetothescenariosofgradualclimaticwarmingthataresocommon,weoutlineanabruptclimatechangescenariopatternedafterthe100-yeareventthatoccurredabout8,200yearsago.Thisabruptchangescenarioischaracterizedbythefollowingconditions:•Annualaveragetemperaturesdropbyupto5degreesFahrenheitoverAsiaandNorthAmericaand6degreesFahrenheitinnorthernEurope•Annualaveragetemperaturesincreasebyupto4degreesFahrenheitinkeyareasthroughoutAustralia,SouthAmerica,andsouthernAfrica.•DroughtpersistsformostofthedecadeincriticalagriculturalregionsandinthewaterresourceregionsformajorpopulationcentersinEuropeandeasternNorthAmerica.•Winterstormsandwindsintensify,amplifyingtheimpactsofthechanges.WesternEuropeandtheNorthPacificexperienceenhancedwinds.Thereportexploreshowsuchanabruptclimatechangescenariocouldpotentiallyde-stabilizethegeo-politicalenvironment,leadingtoskirmishes,battles,andevenwarduetoresourceconstraintssuchas:1)Foodshortagesduetodecreasesinnetglobalagriculturalproduction2)Decreasedavailabilityandqualityoffreshwaterinkeyregionsduetoshiftedprecipitationpatters,causingmorefrequentfloodsanddroughts3)DisruptedaccesstoenergysuppliesduetoextensiveseaiceandstorminessAsglobalandlocalcarryingcapacitiesarereduced,tensionscouldmountaroundtheworld,leadingtotwofundamentalstrategies:defensiveandoffensive.Nationswiththeresourcestodosomaybuildvirtualfortressesaroundtheircountries,preservingresourcesforthemselves.Lessfortunatenationsespeciallythosewithancientenmitieswiththeirneighbors,mayinitiateinstrugglesforaccesstofood,cleanwater,orenergy.Unlikelyalliancescouldbeformedasdefenseprioritiesshiftandthegoalisresourcesforsurvivalratherthanreligion,ideology,ornationalhonor.ThisscenarioposesnewchallengesfortheUnitedStates,andsuggestsseveralstepstobetaken:•Improvepredictiveclimatemodelstoallowinvestigationofawiderrangeofscenariosandtoanticipatehowandwherechangescouldoccur•Assemblecomprehensivepredictivemodelsofthepotentialimpactsofabruptclimatechangetoimproveprojectionsofhowclimatecouldinfluencefood,water,andenergy•Createvulnerabilitymetricstoanticipatewhichcountriesaremostvulnerabletoclimatechangeandtherefore,couldcontributemateriallytoanincreasinglydisorderlyandpotentiallyviolentworld.AbruptClimateChange3•Identifyno-regretsstrategiessuchasenhancingcapabilitiesforwatermanagement•Rehearseadaptiveresponses•Explorelocalimplications•Exploregeo-engineeringoptionsthatcontroltheclimate.Therearesomeindicationstodaythatglobalwarminghasreachedthethresholdwherethethermohalinecirculationcouldstarttobesignificantlyimpacted.TheseindicationsincludeobservationsdocumentingthattheNorthAtlanticisincreasinglybeingfreshenedbymeltingglaciers,increasedprecipitation,andfreshwaterrunoffmakingitsubstantiallylesssaltyoverthepast40years.Thisreportsuggeststhat,becauseofthepotentiallydireconsequences,theriskofabruptclimatechange,althoughuncertainandquitepossiblysmall,shouldbeelevatedbeyondascientificdebatetoaU.S.nationalsecurityconcern.ClimateChange