#(!04%2 /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS ,INDA!*OYCE53$!&OREST3ERVICE2OCKY-OUNTAIN2ESEARCH3TATION 2ICHARD"IRDSEY53$!&OREST3ERVICE.ORTHEASTERN2ESEARCH3TATION )NTRODUCTION 4HEINCREASINGCONCENTRATIONOFATMOSPHERICCARBONDIOX IDEHASRAISEDCONCERNSABOUTTHEVULNERABILITYOFFORESTSTO POTENTIALCHANGESINCLIMATEANDCLIMATEVARIABILITY4HESE CONCERNSHAVEPROMPTEDGOVERNMENTSAROUNDTHEWORLDTO COMMISSIONTECHNICALASSESSMENTSONTHEIMPACTOFCLIMATE CHANGEONTHEENVIRONMENTANDTHEECONOMY"ASEDONTHE CURRENTSCIENTIlCINFORMATIONWITHINTHESEASSESSMENTSGOV ERNMENTS HAVE INITIATED NEGOTIATIONS ON POLICY ACTIONS TO REDUCEGREENHOUSEGASEMISSIONSANDTOADDRESSTHEVULNER ABILITIES OF THE ECOLOGICAL ECONOMIC AND SOCIAL SYSTEMS TO CLIMATECHANGE#RITICALTOPOLICYFORMULATIONISAPERIODIC SYNTHESISOFTHEEVEREXPANDINGKNOWLEDGEONFORESTECOL OGY THE IMPACT OF CLIMATE ON FORESTS AND OF FORESTS ON CLI MATEFORESTMANAGEMENTTHESOCIOECONOMICVALUEOFTREES ANDFORESTSANDTHEROLEOFFORESTSINTHEGLOBALCARBONCYCLE 4HE &OREST 3ERVICE CONDUCTS PERIODIC ASSESSMENTS OF THE CONDITION OF FOREST AND RANGELAND RESOURCES UNDER THE AUTHORITY OF THE 2ENEWABLE 2ESOURCES 0LANNING!CT 20!4HESTRUCTUREOFTHESEPERIODICASSESSMENTSALLOWS FORTHESYNTHESISANDINTEGRATIONOFTHECURRENTSTATEOFSCI ENTIlCKNOWLEDGE53$EPARTMENTOF!GRICULTURE&OREST 3ERVICE!SPARTOFTHE20!PROCESSTHISREPORT IS A SYNTHESIS OF CURRENT INFORMATION THAT ASSESSES THE IMPACT OF CLIMATE CHANGE ON 53 FORESTS 0OLICY QUES TIONS CRITICAL TO UNDERSTANDING THE IMPACT OF GLOBAL CLI MATE CHANGE ON CURRENT AND FUTURE TRENDS *OYCE ET AL FORM THE BASIS FOR THE SUBSEQUENT CHAPTERS IN THIS REPORT 4HIS CHAPTER DESCRIBES THE SYNTHESIS OF SCIENTIlC INFORMATIONANDASSESSMENTOFTHEIMPACTSOFCLIMATEON FORESTSCURRENTUNDERSTANDINGOFTHEGLOBALCLIMATEAND THEPOLICYQUESTIONSADDRESSEDINTHISASSESSMENT 4HE3YNTHESISOF3CIENTIlC )NFORMATION )NTERNATIONAL3YNTHESES -ANDATESTOSYNTHESIZESCIENTIlCINFORMATIONFORPOLICY FORMULATION HAVE DEVELOPED FROM INTERNATIONAL ORGANI ZATIONSINTERNATIONALAGREEMENTSBETWEENCOUNTRIESAND LAWSWITHINCOUNTRIESlG)NTERNATIONALLYCOUNTRIES 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n HAVEWORKEDTOGETHERTOORGANIZETHESCIENTIlCCOMMU NITYTOSTUDYTHEIMPACTOFCLIMATECHANGEONTHECLIMATE SYSTEMGLOBALECOSYSTEMSANDSOCIALANDECONOMICSYS TEMS7ITHINTHE5NITED3TATESASERIESOFLAWSHAVEMAN DATED THESE ASSESSMENTS WHICH IN TURN HAVE SUPPLIED INFORMATION TO INTERNATIONAL EFFORTS 4O PROVIDE CONTEXT WEINTRODUCETHISCHAPTERBYDESCRIBINGTHEDEVELOPMENT OFINTERNATIONALAND53ASSESSMENTSONCLIMATECHANGE 4HE5NITED.ATIONS%NVIRONMENTAL0ROGRAMMEANDTHE 7ORLD -ETEOROLOGICAL /RGANIZATION ESTABLISHED THE )NTER GOVERNMENTAL0ANELON#LIMATE#HANGE)0##ININ ORDERTOASSESSAVAILABLESCIENTIlCINFORMATIONONCLIMATE CHANGE ASSESS THE ENVIRONMENTAL AND SOCIOECONOMIC IMPACTSOFCLIMATECHANGEANDFORMULATERESPONSESTRAT EGIES4HElRSTASSESSMENTREPORTSWERECOMPLETEDIN (OUGHTONETAL)0##THESECONDREPORTSWERE COMPLETEDIN"RUCEETAL(OUGHTONETAL 7ATSON ET AL AND THE THIRD REPORT IS BEING WRITTEN 4HESERECENT)0##ASSESSMENTSHAVEIDENTIlEDTHEIMPOR TANCE OF INTEGRATING THE ECOLOGICAL AND THE ECONOMIC AND SOCIALANALYSES(OUGHTONETAL"RUCEETALTO DEVELOP POLICY DIRECTION FOR MITIGATION AND ADAPTATION TO ANINCREASINGLYCHANGINGCLIMATE4HETHIRDASSESSMENTWILL RELYONCOUNTRYASSESSMENTSSUCHASTHE53ASSESSMENTS WHERETHEANALYSISCANFOCUSMORECLOSELYONTHEIMPACTOF CLIMATECHANGEONINDIVIDUALCOUNTRIES )N THE 5NITED 3TATES AND OVER OTHER NATIONS SIGNED THE &RAMEWORK #ONVENTION ON #LIMATE #HANGE &###ANINTERNATIONALAGREEMENTWITHNOBINDINGOBLI GATIONS4HEPOLICYOBJECTIVEIDENTIlEDINTHE&###WAS TO ACHIEVE hSTABILIZATION OF GREENHOUSE GAS CONCENTRA TIONS IN THE ATMOSPHERE AT A LEVEL THAT WOULD PREVENT DANGEROUS ANTHROPOGENIC INTERFERENCE WITH THE CLIMATE SYSTEMv)NADDITIONTHESECOUNTRIESAGREEDTHAThSUCHA LEVEL SHOULD BE ACHIEVED WITHIN A TIMEFRAME SUFlCIENT TOALLOWECOSYSTEMSTOADAPTNATURALLYTOCLIMATECHANGE TO ENSURE THAT FOOD PRODUCTION IS NOT THREATENED AND TO ENABLEECONOMICDEVELOPMENTTOPROCEEDINASUSTAINABLE MANNERv4HESIGNINGOFTHISAGREEMENTINITIATEDASERIES OFINTERNATIONALMEETINGSSOCALLED#ONFERENCEOFTHE0AR TIES #/0 AT WHICH NEGOTIATORS DETERMINE THE MECHA NISMSBYWHICHGREENHOUSEGASCONCENTRATIONSCOULDBE STABILIZEDGLOBALLYlG !FTERSIGNINGTHE&###THE5NITED3TATESDEVELOPED POLICYANDPREFERREDACTIONSTOSTABILIZE53EMISSIONSBY THEYEARATTHELEVELS#LINTONAND'ORE 53$EPTOF%NERGY3TRATEGIESWITHINTHE#LIMATE #HANGE !CTION 0LAN INCLUDED EMISSIONREDUCING ACTIVI TIESWITHINTHETRANSPORTATIONANDMANUFACTURINGSECTORS OFTHEECONOMYANDCARBONSTORAGEACTIVITIESINTHEFOREST *OYCEAND"IRDSEY 53 ,AWS /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS 2ESOURCE0LANNING!CT 'LOBAL#HANGE2ESEARCH!CT &OOD0ROTECTION!CTAMENDS20! 20!!SSESSMENT 20!5PDATE 20!!SSESSMENT 20!!SSESSMENT 53 !SSESSMENTS 20!!SSESSMENT &IRST!SSESSMENTOF)0## 3ECOND!SSESSMENTOF)0## )NTERNATIONAL !SSESSMENTS &RAMEWORKFOR#LIMATE #HANGE#ONVENTION )NTERNATIONAL !GREEMENTS -ANDATES 4HIRD!SSESSMENTOF)0## &IRST#/0 3ECOND#/0 4HIRD#/0 &UTURE#/0S )NFORMATION&LOW &IGURE,AWSAND)NTERNATIONAL!GREEMENTSMANDATINGCLIMATECHANGEASSESSMENTSINTHE5NITED3TATESANDINTERNATIONALLY SECTOR4HEFORESTSECTORCURRENTLYSEQUESTERSMORECARBON THAN IT EMITS AND THERE ARE OPPORTUNITIES TO INCREASE THIS OFFSET OF FOSSIL FUEL EMISSIONS IN THE NEARTERM 4HE PROPOSED ACTIVITIES INCLUDED ACCELERATING TREE PLANTING AND ENCOURAGING FOREST MANAGEMENT EVALUATION IN NON INDUSTRIALPRIVATEFORESTS4HESECARBONSTORAGEACTIVITIES WOULD ALLOW TIME TO DEVELOP WAYS TO REDUCE FOSSIL FUEL EMISSIONS ! DISCUSSION ON THE IMPORTANCE OF GREENHOUSE GAS STABILIZATION LED COUNTRIES AT THE 4HIRD #ONFERENCE OF THE 0ARTIES HELD IN +YOTO *APAN IN $ECEMBER TO PRODUCEANAGREEMENTTHATINCLUDEDBINDINGTARGETSFOR REDUCING EMISSIONS AND mEXIBLE IMPLEMENTATION WHERE TARGETSWOULDVARYBYCOUNTRYANDGROUPSOFCOUNTRIES 5NDERTHETERMSOFTHEAGREEMENTWHICHHASNOTYETBEEN RATIlED BY THE 53 3ENATE THE 53 IS BOUND TO REDUCE EMISSIONSBELOWLEVELSBY4HISREDUC TION BY IS SUBSTANTIAL GIVEN THAT INCREASES IN POP ULATION AND ECONOMIC EXPANSION WOULD INCREASE FUTURE EMISSIONSINTHEABSENCEOFCONTROLS/NLYREDUCTIONACTIV ITIESINITIATEDINORLATERMAYBECOUNTEDSINCETHISIS THEREFERENCEPOINTAGAINSTWHICHALLFUTURECHANGESWILL BEMEASURED4HESEDISCUSSIONSINCLUDEDTHEROLEOFFOR ESTRY AND LAND USE CHANGE IN STABILIZING AND MITIGATING CARBONEMISSIONS.EGOTIATORSCONSIDEREDTHEPOTENTIALLY IMPORTANTROLEOFFORESTMANAGEMENTINTHEABILITYOFTHE 5NITED 3TATES TO MEET ITS BINDING TARGETS OF GREENHOUSE GASEMISSIONSYETITISSTILLNOTCLEARWHETHERFORESTMAN AGEMENTWILLBEINCLUDED 4HE IMPORTANCE OF FORESTS IN MAINTAINING THE GLOBAL CARBONCYCLEWASRECOGNIZEDFORMALLYFORTEMPERATEAND BOREAL FORESTS IN THE 3ANTIAGO $ECLARATION A STATEMENT SIGNEDINBYTHEGOVERNMENTSOF!USTRALIA#ANADA #HILE#HINA*APANTHE2EPUBLICOF+OREA-EXICO.EW :EALANDTHE2USSIAN&EDERATIONANDTHE5NITED3TATES 4HISSTATEMENTIDENTIlESACOMPREHENSIVESETOFCRITERIA AND INDICATORS FOR FOREST CONSERVATION AND SUSTAINABLE MANAGEMENTFORUSEBYGOVERNMENTPOLICYMAKERS!CRI TERIONISACATEGORYOFCONDITIONSORPROCESSESBYWHICH SUSTAINABLEFORESTMANAGEMENTMAYBEASSESSEDANDITIS CHARACTERIZEDBYASETOFRELATEDINDICATORSTHATAREMON ITORED PERIODICALLY TO ASSESS CHANGE 4HE 5NITED 3TATES IS IMPLEMENTING MANY OF THESE CRITERIA AND INDICATORS WITHINFORESTINVENTORYANDMONITORINGPROGRAMSNATION ALLY#RITERIONISTHEMAINTENANCEOFFORESTCONTRIBUTION TOGLOBALCARBONCYCLES 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS 53,AWSANDTHE&OREST3ERVICE2ESOURCE !SSESSMENTS 4HE&ORESTAND2ANGELAND2ENEWABLE2ESOURCES0LAN NING!CTOFDIRECTEDTHE3ECRETARYOF!GRICULTURETO PREPAREA2ENEWABLE2ESOURCES!SSESSMENTINAND A DECADAL UPDATE STARTING IN 4HE ASSESSMENT WAS TO INCLUDE hAN ANALYSIS OF PRESENT AND ANTICIPATED USES DEMANDFORANDSUPPLYOFTHERENEWABLERESOURCESWITH CONSIDERATIONOFTHEINTERNATIONALRESOURCESITUATIONAND ANEMPHASISOFPERTINENTSUPPLYDEMANDANDPRICERELA TIONSHIPSTRENDSv3INCETHEREHAVEBEENNATIONAL ASSESSMENTS AND TWO UPDATES WHICH HAVE REVIEWED THE CURRENT AND LIKELY FUTURE CONDITION OF FOREST AND RANGE RESOURCES INCLUDING WILDLIFE WATER TIMBER RECREATION RANGEFORAGEANDMINERALS!SSESSMENTSTYPICALLYINCLUDE DESCRIPTION OF THE CURRENT STATUS OF THE RESOURCE A PROJECTIONOFSUPPLYOFANDDEMANDFORRESOURCEOUTPUTS SOCIAL ECONOMIC AND ENVIRONMENTAL IMPLICATIONS OF THEPROJECTIONSMANAGEMENTOPPORTUNITIESTOIMPROVE THERESOURCESITUATIONANDADESCRIPTIONOF&OREST3ER VICEPROGRAMSANDRESPONSIBILITIES4HERESULTSOFTHE20! ASSESSMENTAREUSEDASTHEFACTUALBASISFORFORMULATING FUTURE RENEWABLE RESOURCE MANAGEMENT PROGRAMS 4HE STRUCTUREOFTHESEONGOINGASSESSMENTSPROVIDESAMECH ANISMBYWHICHCURRENTSCIENTIlCINFORMATIONCANALSOBE SYNTHESIZEDPERIODICALLYTOADDRESSPOLICYQUESTIONS 3UBSEQUENT LAWS WITHIN THE 5NITED 3TATES MANDATED ASSESSMENTSOFTHEIMPACTOFCLIMATECHANGEONTHE53 ENVIRONMENTANDECONOMYlG4HE'LOBAL#HANGE 2ESEARCH!CT OF REQUIRES THE .ATIONAL 3CIENCE AND 4ECHNOLOGY#OUNCILTOASSESSCURRENTHUMANINDUCED ANDNATURALTRENDSINGLOBALCHANGEANALYZEEFFECTSOF GLOBAL CHANGE ON THE NATURAL ENVIRONMENT AGRICULTURE ENERGY PRODUCTION AND USE LAND AND WATER RESOURCES TRANSPORTATIONHUMANHEALTHANDWELFAREHUMANSOCIAL SYSTEMS AND BIOLOGICAL DIVERSITY AND PROJECT MAJOR TRENDSFORTHESUBSEQUENTTOYEARS4HE&OOD 0ROTECTION!CTAMENDSTHE2ESOURCES0LANNING!CT ANDREQUIRESTHE&OREST3ERVICETOASSESSTHEIMPACTOF CLIMATE CHANGE ON THE CONDITION OF RENEWABLE RESOURCES ONFORESTSANDRANGELANDSANDIDENTIFYTHERURALAND URBAN FORESTRY OPPORTUNITIES TO MITIGATE THE BUILDUP OF ATMOSPHERICCARBONDIOXIDE 3INCETHE!MENDMENTOFTHE20!THE20!ASSESSMENTS HAVEINCLUDEDANANALYSISONTHEVULNERABILITYOF53ECO SYSTEMS TO CHANGES IN CLIMATE AND THE POTENTIAL IMPACT ONTHESOCIALANDECONOMICSYSTEMSFROMCHANGESINCLI MATE4HEASSESSMENTINCLUDEDAREVIEWOFTHECUR RENT SCIENTIlC UNDERSTANDING OF THE POTENTIAL EFFECTS OF GLOBAL CLIMATE CHANGE ON FORESTS *OYCE ET AL 4HE NEXTASSESSMENTUPDATEINUSEDANINTEGRATEDMODEL ING FRAMEWORK TO ANALYZE THE IMPACT OF CLIMATE CHANGE ON ECOSYSTEM PRODUCTIVITY TIMBER SUPPLY AND DEMAND ANDCARBONSTORAGE*OYCE*OYCEETAL7EUSE 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n *OYCEAND"IRDSEY THISMODELINGFRAMEWORKTOSTRUCTUREOURCURRENTSYNTHE SISOFTHEIMPACTOFCLIMATECHANGEON53FORESTSlG 4HEFOLLOWINGCHAPTERSREVIEWOURABILITYTOQUANTIFYTHE IMPACTS OF A CHANGING CLIMATE ON CHANGES IN VEGETATION COMMUNITIES#HAPTERFORESTPRODUCTIVITY#HAPTER FOREST ECONOMY LAND AREA TIMBER INVENTORY #HAPTERS AND AND CARBON STORED IN FORESTS IN WOOD PRODUCTS ANDINLANDlLLSANDDUMPS#HAPTERSAND 3IXPOLICYQUESTIONSRELATEDTOTHEIMPACTOFGLOBALCLI MATECHANGEONFORESTS*OYCEETALFORMTHEBASIS FOR THE SUBSEQUENT CHAPTERS IN THIS REPORT 4HIS CHAPTER DESCRIBESMANDATESANDSTRUCTURESOFSYNTHESIZINGSCIEN TIlCINFORMATIONANDASSESSINGTHEIMPACTSOFCLIMATEON THEFORESTSECTORCURRENTUNDERSTANDINGSOFTHEGLOBALCLI MATEANDPOLICYQUESTIONSADDRESSEDINTHISASSESSMENT 5NDERSTANDINGTHE$YNAMICS OF#LIMATE #LIMATE$YNAMICS'REENHOUSE'ASES AND'LOBAL#ARBON#YCLE )DENTIFYINGTHEVULNERABILITIESOFECOSYSTEMSANDECON OMIES TO CLIMATE VARIABILITY AND CHANGE DEPENDS ON AN UNDERSTANDING OF THE SENSITIVITY OF THOSE SYSTEMS TO CLI MATE!NALYZINGTHEEFFECTIVENESSOFPOLICYINSTRUMENTSIN STABILIZINGGREENHOUSEGASESSUCHASSEQUESTERINGCARBON IN FORESTS DEPENDS ON AN UNDERSTANDING OF SEVERAL FAC TORS CLIMATE PROCESSES THE PHYSICAL CHANGES IN CLIMATE ARISINGFROMALLGREENHOUSEGASESANDAEROSOLSBIOSPHERIC AND OCEANIC INTERACTIONS AND THE INmUENCE OF HUMANS ONCLIMATEPROCESSESANDFORESTBIOGEOCHEMISTRYTHROUGH ACTIVITIESSUCHASFORESTMANAGEMENTANDLANDUSECHANGE 7E BRIEmY REVIEW CURRENT OBSERVATIONS ON CHANGES IN ATMOSPHERIC CHEMISTRY CHANGES IN GLOBAL AND 53 CLI MATESANDTHEINmUENCEOFHUMANSONTHEEARTHSCLIMATE SYSTEM #ERTAINATMOSPHERICGASESHAVETHEPOTENTIALTOWARM THEATMOSPHEREANDARECOLLECTIVELYKNOWNASGREENHOUSE GASESCARBONDIOXIDEMETHANENITROUSOXIDESCHLOROmU OROCARBONSANDWATERVAPOR(OUGHTONETAL4HE AMOUNT OF WARMING IS A FUNCTION OF THE ABILITY OF THESE GASES TO ABSORB SOLAR RADIATION RADIATIVE PROPERTIES OF THE GASES AND THE ATMOSPHERIC CONCENTRATION OF EACH GAS 4HE RADIATIVE PROPERTY OF A GAS IS CONSTANT BUT THE ATMOSPHERICCONCENTRATIONSOFTHESEGASESAREALTEREDBY NATURAL PROCESSES AND HUMAN ACTIVITIES )T IS THE RISE IN ATMOSPHERIC CONCENTRATION OF THESE GASES THAT IS OF CON CERNGLOBALLY 4HE ATMOSPHERIC CONCENTRATION OF CARBON DIOXIDE METHANENITROUSOXIDESANDTHECHLOROmUOROCARBONSHAS *OYCEAND"IRDSEY /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS #LIMATE$ATA -ACRO %CONOMIC $ATA &OREST)NVENTORY $ATA &OREST3ECTOR #HAPTERS '#-S !REA -ODELS #LIMATE #HANGE #LIMATE #HAPTERS 4%.!7%&ORESTPRODUCTIVITY .!0!0 PULPANDPAPER &UELWOOD DEMAND 0RICES 4!-4IMBER !SSESSMENT -ARKET-ODEL 4IMBERLAND !REA )NVENTORY GROWTHPARAMETERS )NVENTORY 'ROWTH !4,!3 'ROWTH 2EMOVALS !4,!3# 2EMOVALS !CRESINVENTORY GROWTHREMOVALS #ARBON !CCOUNTING &/2#!2" #HAPTERS !LLHARVEST (!26#!2" &IGURE#OMPONENTSOFTHE)NTEGRATED-ODELINGSYSTEMUSEDINTHE&OREST3ERVICE20!!SSESSMENT5PDATE INCREASEDSINCEPREINDUSTRIALTIMESTABLE)NCREASES RANGE FROM PERCENT FOR NITROUS OXIDES TO PERCENT FOR METHANE -OREOVER THE ATMOSPHERE DID NOT CONTAIN CHLOROmUOROCARBONSINPREINDUSTRIALTIMES)NCREASESIN CARBON DIOXIDE ARE MAINLY THE RESULT OF FOSSIL FUEL EMIS SIONSFROMINDUSTRIALANDDOMESTICACTIVITIESANDLANDUSE CONVERSIONS -ETHANE INCREASES RESULT FROM THE PRODUC TIONANDUSEOFFOSSILFUELANDFROMANTHROPOGENICACTIVI TIESSUCHASRICECULTIVATIONANDLIVESTOCKPRODUCTION4HE SOURCESOFNITROUSOXIDESARESMALLANDHARDTOQUANTIFY BUTINCLUDEAGRICULTUREANDINDUSTRIALPROCESSES4HERATES OFCONCENTRATIONCHANGESTABLEAREPOSITIVEEXCEPTFOR #&#WHICHISBEINGCONTROLLEDASARESULTOFTHE-ON TREAL0ROTOCOL4HEPOSITIVERATESOFCHANGEDEMONSTRATE THATATMOSPHERICCONCENTRATIONSWILLCONTINUETOINCREASE FORTHESEGREENHOUSEGASESUNLESSTHEACTIVITIESINmUENC INGTHESECONCENTRATIONSAREMODIlED 7HILECONCENTRATIONSOFGREENHOUSEGASESARESOURCES OF ATMOSPHERIC WARMING OTHER PROCESSES HAVE RECENTLY BEEN IDENTIlED THAT ALSO INmUENCE THE EARTHS ENERGY !EROSOLS TINY PARTICLES OF LIQUID OR SOLID MATTER SUS PENDED IN THE ATMOSPHERE CAN BE DERIVED FROM MANY DIFFERENT MATERIALS INCLUDING SEA SALT SOIL SMOKE AND SULFURICACID3CHIMELETAL4HEYINCREASETHESCAT TER OF INCOMING SOLAR RADIATION SENDING SOME RADIATION AWAYFROMEARTH4HEYAREALSOAPARTOFTHECLOUDFORM INGPROCESS)NBOTHOFTHESEWAYSAEROSOLSCANINmUENCE THEEARTHSTEMPERATURE4HELENGTHOFTIMETHATAEROSOLS REMAININTHEATMOSPHEREISMUCHLESSAFEWWEEKSTHAN THERESIDENCETIMEOFCARBONDIOXIDEAPPROXIMATELY YEARS)NADDITIONHUMANPRODUCEDAEROSOLSDONOTMIX THROUGHOUTTHEGLOBELIKECARBONDIOXIDE#HARLSONETAL 4HEY TEND TO REMAIN NEAR THE AREA OF GENERATION ANDTHEREBYHAVEANIMPACTONTHEREGIONALCLIMATE ,ANDMANAGEMENTACTIVITIESINmUENCETHEUPTAKEAND RELEASEOFGREENHOUSEGASES4HEPROCESSESTHATINmUENCE THESECARBONmUXESOPERATEATDIFFERENTSPATIALSCALESAND TIMEFRAMES#URRENTLYTHEMAINSOURCESOFCARBONDIOX IDEINCLUDEFOSSILFUELCONSUMPTIONANDLANDUSECHANGE PARTICULARLY DEFORESTATION IN THE TROPICS 4HE MAIN RES 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS *OYCEAND"IRDSEY &IGURE/BSERVEDCONCENTRATIONOFATMOSPHERICCARBONDIOXIDEINPARTSPERMILLIONAT-AUNA,OA(AWAIIFROMTO 3OURCE#$+EELING3CRIPPS)NSTITUTIONOF/CEANOGRAPHY 4ABLE!SAMPLEOFGREENHOUSEGASESAFFECTEDBYHUMANACTIVITIES(OUGHTONETAL 0REINDUSTRIALCONCENTRATION #ONCENTRATIONIN 2ATEOFCONCENTRATIONCHANGE !TMOSPHERICLIFETIMEYEARS #/ #( ./ #2# ^PPMV PPMV PPMVYR YR n ^PPBV PPBV PPBVYR YR ^PPBV PPBV PPBVYR YR ZERO PPTV PPTVYR YR (#&# #( !#&#SUBSTITUTE !PERmUOROCARBON ZERO PPTV PPTVYR YR ZERO PPTV PPTVYR YR %STIMATEDFROMnDATA PPTVPARTPERTRILLIONMILLIONMILLIONBYVOLUME 4HEGROWTHRATESOF#/#(AND./AREAVERAGEDOVERTHEDECADEBEGINNINGHALOCARBONGROWTHRATESAREBASEDONRECENTYEARSS .OSINGLELIFETIMEFOR#/CANBEDElNEDBECAUSEOFTHEDIFFERENTRATESOFUPTAKEBYDIFFERENTSINKPROCESSES 4HISHASBEENDElNEDASANADJUSTMENTTIMEWHICHTAKESINTOACCOUNTTHEINDIRECTEFFECTOFMETHANEONITSOWNLIFETIME ERVOIRS FOR CARBON STORAGE INCLUDE THE ATMOSPHERE THE OCEAN AND THE VEGETATION )NCORPORATION OF CARBON INTO VEGETATIONISTHEFASTESTPROCESSANDATMOSPHERICCONCEN TRATIONSTHROUGHOUTTHEYEARREmECTTHESEASONALGROWTH OFVEGETATIONlG4RANSFERSTOSOILSANDOCEANDEPTHS OPERATEONTHEDECADETOCENTURYTIMESCALE 4RANSFERS OF CARBON DIOXIDE BETWEEN THE ATMOSPHERE OCEANANDLANDATTHEGLOBALSCALEHAVEBEENEXAMINED USINGABUDGETINGAPPROACH(OUGHTONETAL4HE AMOUNTOFCARBONDIOXIDETHATREMAINSINTHEATMOSPHERE 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n ISUSEDTOPROJECTLIKELYFUTURECHANGESINTHEGLOBALCLI MATE%MISSIONSFROMFOSSILFUELCOMBUSTIONANDCEMENT PRODUCTION ARE THE LARGER SHARE OF THE CARBON SOURCES IDENTIlED TABLE !TMOSPHERIC SAMPLING AND FOREST INVENTORIESINDICATETHATTHECARBONSOURCEOFLANDCLEAR INGINTHETROPICSISAPPROXIMATELYBALANCEDBYTHECARBON RESERVOIROFFORESTREGROWTHINTHE.ORTHERN(EMISPHERE %XPERIMENTALRESEARCHSUGGESTSTHATTHEUPTAKEOFCARBON INVEGETATIONMAYBESTIMULATEDBYINCREASEDATMOSPHERIC CARBONDIOXIDEANDNITROGENFERTILIZATIONFROMTHEDEPO *OYCEAND"IRDSEY /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS SITIONOFNITROGENINTHEATMOSPHERE+AUPPIETAL !BERETAL-AGILLETAL4HEFUTUREROLEOFVEG ETATIONINTHEGLOBALBUDGETISHIGHLYUNCERTAINBECAUSEOF OURLACKOFUNDERSTANDINGABOUTPROCESSESSUCHASFERTIL IZATIONFROMATMOSPHERICCARBONDIOXIDEANDOURINABIL ITY TO PREDICT FUTURE RATES OF DEFORESTATION IN THE TROPICS ANDREGROWTHINTHEMIDLATITUDES(OUGHTONETAL 7ATSONETAL5NDERSTANDINGTHEUPTAKEANDRELEASE OFCARBONINFORESTEDECOSYSTEMSESPECIALLYASAFFECTEDBY MANAGEMENT ACTIVITIES WILL BE IMPORTANT IN ADDRESSING THEROLEOFFORESTRYNOTONLYINMITIGATINGGREENHOUSEGAS EMISSIONSBUTALSOINTHEPROCESSESINmUENCINGTHEGLOBAL CARBONBUDGET3CHIMELETAL !NALYSESINTHERECENT20!5PDATEFOCUSEDONTHEROLE OF FORESTRY IN RELEASING CARBON THROUGH HARVEST AND IN STORING CARBON THROUGH GROWTH AND LAND CONVERSION TO FORESTSONTHE53MAINLAND4HENETEFFECTOFTHESEACTIV ITIES IN THE 5NITED 3TATES COMPRISE AN ESTIMATED CARBON SINK OF APPROXIMATELY 'T#YR "IRDSEY AND (EATH A SUBSTANTIAL PORTION OF THE TOTAL UPTAKE BY THE .ORTHERN(EMISPHERE4HESEANALYSESARESETINTHECON TEXTOFTHEGLOBALBUDGETOFCARBONINORDERTODETERMINE WHAT ROLE 53 FORESTS MIGHT PLAY IN MITIGATING CARBON 4ABLE !NNUAL AVERAGE ANTHROPOGENIC CARBON BUDGET FOR TO #/ SOURCES SINKS AND STORAGE IN THE ATMOS PHEREAREEXPRESSEDIN'T#YRWHERE'T#ISGIGATONSOFCARBON (OUGHTONETAL #/SOURCES %MISSIONSFROMFOSSILFUELCOMBUSTION ANDCEMENTPRODUCTION .ETEMISSIONSFROMCHANGESINTROPICAL LANDUSE 4OTALANTHROPOGENICEMISSIONS 0ARTITIONINGAMONGSTRESERVOIRS 3TORAGEINTHEATMOSPHERE /CEANUPTAKE 5PTAKEBY.ORTHERN(EMISPHEREFOREST REGROWTH )NFERREDSINK &ORCOMPARISONEMISSIONSINWERE'T#YR #ONSISTENTWITH#HAPTEROF)0##7ORKING'ROUP))7ATSONETAL 4HISNUMBERISCONSISTENTWITHTHEINDEPENDENTESTIMATEGIVENIN)0## 7ORKING'ROUP))7ATSONETALOF'T#YRFORTHEMID LANDHIGHLATITUDEFORESTSINK 4HIS INFERRED SINK IS CONSISTENT WITH INDEPENDENT ESTIMATES GIVEN IN #HAPTEROF)0##7ORKING'ROUP)(OUGHTONETALOFCARBON UPTAKEDUETONITROGENFERTILIZATION'T#YRPLUSTHERANGEOF OTHERUPTAKES'T#YRDUETO#/FERTILIZATIONANDCLIMATICEFFECTS EMISSIONSANDTHEREBYTOHELPSTABILIZETHECONCENTRATIONS OFCARBONDIOXIDEINTHEATMOSPHERE /BSERVED4RENDSIN#LIMATEATTHE 'LOBAL3CALE !T THE GLOBAL SCALE INCREASES IN AIR TEMPERATURE AND IN PRECIPITATION HAVE BEEN DOCUMENTED IN THE HISTORICAL RECORD OF OBSERVATION (OUGHTON ET AL "OTH SEA SURFACEANDLANDSURFACETEMPERATURESINDICATEAWARM INGPATTERN7HILEOBSERVEDCHANGESRELATEDTOTEMPERA TURE GENERALLY HAVE A HIGHER CONlDENCE THAN OBSERVED CHANGESINTHEHYDROLOGICALCYCLEPRECIPITATIONHASALSO INCREASEDGLOBALLY 3INCETHELATETHCENTURYNEARSURFACEAIRTEMPERATURES HAVERISENFROMTO #PARALLELINGSIMILARINCREASES SEEN IN NEARSURFACE OCEAN TEMPERATURES 4HE MOST RELI ABLE PERIOD OF OBSERVATION THE LAST YEARS INDICATES A WARMING OF TO # FOR THE GLOBAL AVERAGE SURFACE TEMPERATURE (OUGHTON ET AL 7HILE TEMPERATURES HAVE INCREASED OVER TIME IN URBAN CENTERS THE INCREASES INURBANTEMPERATURESANDTHEEXPANSIONOFURBANAREAS CONTRIBUTESMINIMALLYTOGLOBALSURFACEWARMING%ASTER LINGETAL5RBANIZATIONMAYBEIMPORTANTINSOME REGIONSHOWEVER3IMILARLYDESERTIlCATIONHASINmUENCED LOCALCLIMATESBUTHASANEGLIGIBLEEFFECTONGLOBALTEMPER ATURECHANGES(OUGHTONETAL 4HEDIFFERENCEBETWEENTHESURFACEMAXIMUMANDMIN IMUMDAILYTEMPERATURESHASDECREASEDSINCETHEMIDDLE OF THE TH CENTURY BASED ON AN ANALYSIS OF OVER PER CENTOFTHEGLOBALLANDAREA%ASTERLINGETAL4HIS NARROWINGOFTHEDAILYMAXIMUMANDMINIMUMTEMPER ATURES IS THE RESULT OF WARMER NIGHTTIME TEMPERATURES WHICHMAYREmECTNOTONLYTHEINCREASEOFCARBONDIOXIDE BUTALSOINCREASEDCLOUDCOVER$AYTIMECLOUDSOBSTRUCT THEDAYTIMESUNSHINEWHILENIGHTTIMECLOUDSREDUCETHE AMOUNTOFTERRESTRIALRADIATIONESCAPINGATNIGHT !NUMBEROFINDIRECTINDICATORSSUPPORTTHESEOBSERVED INCREASESINTEMPERATUREGLOBALLY4HETHCENTURYRETREAT OFMOUNTAINGLACIERSANDTHEUNDERGROUNDTEMPERATURES IN BOREHOLES ARE SEEN AS INDIRECT INDICATORS SUPPORTING THESEWARMINGESTIMATES(OUGHTONETALREPORTED MASSBALANCEDECLINESFORTHESIXGLACIERSFORWHICHLONG OBSERVATIONALDATAAREAVAILABLE3OUTH#ASCADEIN!LASKA SHOWED THE LARGEST LOSS IN MASS BALANCE 5NDERGROUND TEMPERATURESINBOREHOLESHAVEBEENOBSERVEDTOWARMIN .EW%NGLAND#ANADA!LASKA&RANCEANDTHEICESHEETIN THE!RCTICREGIONSBUTOTHERAREASHAVESHOWNNOCHANGES !NANALYSISOFALLTHE.ORTH!MERICANSTUDIESCONCLUDED THATUNDERGROUNDTEMPERATURESWARMEDBETWEENAND #SINCETHETHCENTURY$EMING4HEINCREAS ING TRENDS IN PRECIPITATION HAVE ALSO BEEN CORROBORATED REGIONALLY WITH INDIRECT INDICATORS SUCH AS STREAMmOW LAKELEVELSANDWHEREAVAILABLESOILMOISTURE 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS *OYCEAND"IRDSEY 4RENDSYEARS # # # &IGURE4EMPERATURETRENDSCONVERTEDTOMEANTEMPERATUREIN #PERYEARSCENTEREDWITHINSTATECLIMATICDIVISIONS AREREmECTEDBYTHEDIAMETEROFTHECIRCLECENTEREDWITHINEACHCLIMATICDIVISION3OLIDCIRCLESREPRESENTINCREASESANDOPENCIRCLES DECREASESFROM+ARLETAL 4HEVARIABILITYOFCLIMATEISCALCULATEDFROMTHEHISTOR ICAL RECORDS 'LOBALLY THE DATA ARE INADEQUATE TO ASSESS WHETHER CLIMATE VARIABILITY HAS CHANGED IN RESPONSE TO ELEVATED GREENHOUSE GASES (OUGHTON ET AL .O GLOBALSCALEPATTERNSINDROUGHTFREQUENCYORINTENSITYOR VARIATIONINRAINFALLEVENTSOREXTREMESHASEMERGEDFROM THE ANALYSIS OF THE AVAILABLE DATA 3UFlCIENT DATA HAVE BEENAVAILABLETOEXAMINETHESETRENDSFORSOMEREGIONS SUCHASDESCRIBEDBELOWFORTHE5NITED3TATES )NDICATORSOF#HANGEINTHE53#LIMATE !NANALYSISOFTHENEARSURFACEAIRTEMPERATUREREVEALS THATTEMPERATURESHAVEWARMEDOVERMUCHOFTHE5NITED 3TATES IN THE LAST YEARS lG +ARL ET AL 4EMPERATURE TRENDS AT THE NATIONAL SCALE IF REPRESENTED WITHALINEARTRENDINDICATEARISEOFABOUT #OVER YEARS4HISRISEOCCURSMAINLYINTHElRSTSIXMONTHSOFTHE YEAR2EGIONALRECORDSSHOWTHE3OUTHWITHASLIGHTCOOL ING #YEARSANDTHENORTHEASTNORTHCENTRALAND WESTERNPARTSOFTHE5NITED3TATESWITHAWARMINGTREND OFTO #!TTHECONTINENTALSCALE7ATSONETAL REPORTEDTHEHIGHESTINCREASESINWARMINGOCCURREDALONG 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n ANAREAEXTENDINGFROMNORTHWESTERN#ANADAACROSSTHE SOUTHERN #ANADANORTHERN 53 REGION TO SOUTHEASTERN #ANADAANDTHENORTHEASTERN5NITED3TATES4HETEMPORAL PATTERNOFTHESEINCREASESINDICATESANINCREASEINWARM INGFROMTHESTOTHESANDAGAINFROMTHES TOTHES 7ITHINTHE5NITED3TATESPRECIPITATIONWASSHOWNTO HAVE INCREASED SINCE ABOUT MAINLY THE RESULT OFINCREASESINPRECIPITATIONINTHELASTSIXMONTHSOFTHE YEARANDPRIMARILYINAUTUMN+ARLETAL4HELARG EST INCREASES UP TO WERE SEEN IN THE 'ULF #OAST STATES THE LOWER NORTHEASTERN PART OF THE 5NITED 3TATES ANDTHEMIDWESTERNSTATESlG(OWEVERSTATESSUCH AS#ALIFORNIA-ONTANA7YOMING.ORTH$AKOTAPARTSOF #OLORADOAND.EBRASKAHAVEACTUALLYHADADECREASEIN ANNUALPRECIPITATIONOFSIMILARMAGNITUDE +ARL ET AL PRESENT A FRAMEWORK FOR EXAMINING POTENTIAL CHANGES IN THE 53 CLIMATE 4HEY DEVELOPED TWOINDICESTHATREmECTTHEBEHAVIOROFINDIVIDUALCLIMATE METRICS THAT WOULD LIKELY REmECT CHANGES IN THE CLIMATE AS A RESULT OF INCREASING CONCENTRATIONS OF GREENHOUSE GASES4HEIR#LIMATE%XTREMES)NDEXSUPPORTSTHENOTION THAT THE CLIMATE OF THE 5NITED 3TATES HAS BECOME MORE EXTREMEINRECENTDECADES4HEIR53'REENHOUSE#LIMATE *OYCEAND"IRDSEY /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS 4RENDSYEARS &IGURE0RECIPITATIONTRENDSCONVERTEDTOPERCENTPERCENTURYCENTEREDWITHINSTATECLIMATICDIVISIONSAREREmECTEDBY THEDIAMETEROFTHECIRCLECENTEREDWITHINEACHCLIMATICDIVISION3OLIDCIRCLESREPRESENTINCREASESANDOPENCIRCLESDECREASESFROM +ARLETAL 2ESPONSE )NDEX IS CONSISTENT WITH AN ENHANCED GREEN HOUSEEFFECT(OWEVERNEITHERRESPONSEISLARGEENOUGH TOCONCLUDETHATTHEINCREASEINEXTREMESREmECTSANON STATIONARYCLIMATEORTHATTHEINCREASEINTHE'REENHOUSE #LIMATE2ESPONSE)NDEXMAYBETHERESULTOFOTHERFACTORS INCLUDINGNATURALCLIMATEVARIABILITY 4HE INCREASE IN EXTREMES IS INmUENCED MARKEDLY BY THREEPRECIPITATIONINDICATORSTHEFREQUENCYOFLONGTERM DROUGHT SEVERITY AND MOISTURE EXCESS THE FREQUENCY OF EXTREME DAY PRECIPITATION EVENTS AND A MUCH GREATER THAN NORMAL NUMBER OF DAYS WITH PRECIPITATION 7HEN +ARL ET AL ANALYZED THE EXTREMES ASSOCIATED WITH DROUGHT SEVERITY AND MOISTURE EXCESS THEY DETERMINED THATTHEREWASCONSIDERABLEDECADALVARIABILITYINDROUGHT SEVERITY AND IN MOISTURE SURPLUS 4HE LIKELIHOOD THAT THESE OCCURRENCES AROSE FROM A QUASISTATIONARY CLIMATE WAS)NTHELASTSEVERALDECADESHOWEVERTHEYNOTED ATENDENCYFORMOREOFTHEAREAINTHE5NITED3TATESTOBE EITHER IN A DROUGHT OR TO HAVE SEVERE EXCESS MOISTURE +ARL ET AL DETERMINED THAT THE PROPORTION OF THE COUNTRYTHATHASHADAMUCHGREATERTHANNORMALAMOUNT OF PRECIPITATION DERIVED FROM EXTREMELY HEAVY GREATER THAN MM OR IN DAY PRECIPITATION EVENTS COULD BE RELIABLY COMPUTED FROM CLIMATE DATA AVAILABLE SINCE lG4HEYCONCLUDEDTHATTHESTEADYINCREASEIN AREA OF THE 5NITED 3TATES AFFECTED BY EXTREME PRECIPITA TIONEVENTSWOULDBEHIGHLYUNLIKELYLESSTHANCHANCE IN IN A QUASISTATIONARY CLIMATE 4HE PERCENTAGE OF THE CONTERMINOUS 53 AREA WITH THE NUMBER OF WET DAYSMUCHABOVENORMALALSOINCREASEDBEYONDWHATONE WOULDEXPECTFORASTATIONARYCLIMATE4HISINCREASEINTHE NUMBEROFWETDAYSPARALLELSTHEINCREASEINPRECIPITATION ATTHENATIONALSCALE4HEPROPORTIONOFAREAINTHE5NITED 3TATES WITH A MUCH GREATER THAN NORMAL NUMBER OF DRY DAYSDIDNOTCHANGEOVERTHECENTURY+ARLETAL !NINCREASEBUTOFMORERECENTNATUREWASSEENINTHE PERCENTAGE OF THE CONTERMINOUS 53 AREA WITH A MUCH ABOVE NORMAL COLD SEASON /CTOBER THROUGH!PRIL PRE CIPITATION lG (ERE THE INCREASE IS MOST NOTICEABLE SINCE!NOTHERINDICATOROFPOTENTIALSHIFTSWASTHE DECREASE IN AREA AFFECTED BY MUCH BELOW NORMAL MAXI MUMTEMPERATURESNOTSHOWNHERE 2ECENT WORK HAS SYNTHESIZED MANY CLIMATE METRICS INCLUDING BIOLOGICALLY MEANINGFUL INDICATORS TO SHOW A RAPIDLYWARMINGCLIMATEIN!LASKA#HAPMANAND7ALSH DOCUMENTED A SIGNIlCANT WARMING TREND IN THE TEMPERATURE RECORDS OVER THE LAST FEW DECADES FOR MOST OF!LASKAWITHWINTERTEMPERATURESWARMINGMORETHAN 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS *OYCEAND"IRDSEY &IGURE 0ERCENTAGE OF THE CONTERMINOUS 53 AREA WITH A MUCHABOVENORMALPROPORTIONOFTOTALANNUALPRECIPITATIONFROM DAY EXTREME MORE THAN INCHES EVENTS FROM +ARL ET AL &IGURE 0ERCENTAGE OF THE CONTERMINOUS 53 AREA WITH MUCHABOVENORMALCOLDSEASON/CTOBERTHROUGH!PRILPRECIPI TATIONFROM+ARLETAL SUMMERTEMPERATURES*ACOBYETALCONlRMEDTHIS RECENTTRENDBYANALYZINGTREERINGS4HEYALSOCONCLUDED THAT TEMPERATURES ARE NEAR THE HIGHEST LEVEL OF THE PAST CENTURIESANOBSERVATIONALSOMADEBY,ACHENBRUCHET ALFROMDATADERIVEDFROMARCTICBOREHOLES-OST RECENTLY-YNENIETALEXAMINEDATMOSPHERIC#/ TRENDS AND CHANGES IN THE NORMALIZED DIFFERENCE VEGE TATION INDEX .$6) AN INDEX OF GREENNESS 4HEY CON CLUDED THAT THE ACTIVE GROWING SEASON LENGTHENED BY ABOUT DAYS AND THAT WINTER TEMPERATURE INCREASED BY # BETWEEN AND AT LATITUDES ABOVE . "EFORE THIS RECENT CLIMATE RESEARCH /ECHEL ET AL REPORTEDCHANGESINTHECARBONDIOXIDEmUXFROM!RCTIC TUNDRAECOSYSTEMSSHIFTINGTHECARBONBALANCEFROMANET CARBONDIOXIDESINKTOASOURCEOFCARBON4HISINCREASE WASPRESUMEDTOBETHERESULTOFINCREASINGSOILTEMPERA TURESSOILAERATIONANDDEPTHOFSOILTHAW/ECHELETAL COAST ARE INmUENCED BY PROXIMITY TO THE OCEAN AND THE 'ULFOF-EXICOANDTHEEPISODICEXTREMEEVENTSSUCHAS HURRICANES %VEN CLIMATES IN THE INTERIOR OF THE 5NITED 3TATESAREINmUENCEDBYLARGEBODIESOFWATERSUCHASTHE .ORTHCENTRAL COMMUNITIES SURROUNDING THE 'REAT ,AKES ANDTHECOMMUNITIESONTHEEASTERNSIDEOFTHE'REAT3ALT ,AKE IN 5TAH &OR A LARGE PART OF THE .ORTH !MERICAN CONTINENTDISTURBANCESINTHEUPPERLEVELWESTERLYWINDS PLAYANIMPORTANTROLEINTHETEMPERATUREANDMOISTURE REGIMES4HE0OLAR&RONTREFERSTOTHESURFACEBOUNDARY BETWEEN THE COLDER DRIER !RCTIC AIR AND THE WARMER MOISTERAIRINTHESOUTH$ISTURBANCESINTHEUPPERLEVEL WESTERLY WINDS SHIFT THE POSITION OF THE UPPER LEVEL JET STREAMANDHENCETHE0OLAR&RONTBACKANDFORTHACROSS THE .ORTH !MERICAN CONTINENT )N THE COLDER MONTHS OF THEYEARTHISFRONTMOVESSLOWLYBACKANDFORTHACROSSTHE 5NITED3TATESBRINGINGCOLDER!RCTICAIRTOTHENORTHERN ANDPARTSOFTHESOUTHERN5NITED3TATES3PRINGANDFALL SEE SHORTER WEAKER SYSTEMS MOVING QUICKLY ACROSS THE CONTINENT)NTHESUMMERTHE0OLAR&RONTRETREATSFARINTO NORTHERN#ANADA"ECAUSEOFTHESECLIMATEINmUENCESTHE CURRENT TEMPERATURE AND PRECIPITATION GRADIENTS IN THE EASTERN HALF OF THE 5NITED 3TATES ARE STRONG IN BOTH THE NORTHTOSOUTHANDEASTTOWESTDIRECTIONS &ORESTSDOMINATETHE%ASTANDPARTSOFTHE7EST-AJOR TIMBERPRODUCINGREGIONSINCLUDETHEMOIST0ACIlC.ORTH WESTCOASTTHEWARMANDMOIST3OUTHEASTANDTHEMOIST BUT COOLER .ORTHCENTRAL REGION !NNUAL PRECIPITATION IS HIGHEST ALONG THE 0ACIlC .ORTHWEST COAST AND IN THE 3OUTHEAST CENTERED MAINLY ALONG THE 'ULF #OAST STATES 7ATSONETAL(IGHPRECIPITATIONRATESLOWEVAPO RATIVEDEMANDSANDMODERATETEMPERATURESCHARACTERIZE THE 0ACIlC .ORTHWEST CLIMATE ,ASSOIE ET AL 4HE FORESTSINTHE%ASTRESPONDTOCLIMATESINmUENCEDBYPROX IMITYTOTHEOCEANANDSHIFTSINTHECONTINENTALAIRMASSES (ICK AND #HABOT &ORESTS ON THE EAST COAST PERI ODICALLYEXPERIENCEMAJORTROPICALSTORMSANDHURRICANES 0REDICTING&UTURE#LIMATESAND THE6EGETATION2ESPONSE !TMOSPHERIC"IOSPHERIC2ELATIONSHIPS &ORESTS AND CLIMATE ARE INTIMATELY CONNECTED IN THE 5NITED3TATES4HE.ORTH!MERICANCLIMATEISINmUENCEDBY THEREGIONSSIZETOPOGRAPHYANDTHEWIDELYVARYINGTEM PERATURESOFTHESURROUNDINGOCEANS4HECURRENTDISTRIBU TIONOFFORESTSISSTRONGLYTIEDTOTHESECLIMATEPATTERNS )NTHE0ACIlC.ORTHWESTOFTHE5NITED3TATESLOCALCLI MATESAREINmUENCEDBYELEVATIONPROXIMITYTOTHE0ACIlC /CEAN PREVAILING WINDS AND THE NORTHSOUTHORIENTED MOUNTAINRANGES3IMILARLYLOCALCLIMATESONTHEEASTERN 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n *OYCEAND"IRDSEY !NY CHANGE IN CLIMATE AND CLIMATE VARIABILITY HAS THE POTENTIALTOALTERTHESTRUCTUREFUNCTIONANDGEOGRAPHIC DISTRIBUTIONOFFORESTS )N THE 20!5PDATE CLIMATE SCENARIOS FROM FOUR 'ENERAL #IRCULATION -ODELS '#- WERE USED TO EXAM INE THE IMPACT OF CLIMATE CHANGE ON FOREST PRODUCTIVITY *OYCEETAL4HESEGLOBALMODELSPROVIDEDEQUILIB RIUMCLIMATESUNDERELEVATEDATMOSPHERICCARBONDIOXIDE CONCENTRATIONS AT A COARSE SPATIAL RESOLUTION 7E REVIEW BELOWTHEIMPROVEDUNDERSTANDINGOFCLIMATEDYNAMICS SINCETHISANALYSIS!NOTHERAREAWHERETHEUNDERSTAND INGOFCLIMATEDYNAMICSHASIMPROVEDBUTTHEREREMAINS MUCHUNCERTAINTYISTHEINTERACTIONBETWEENTHELANDUSE ANDATMOSPHERICDYNAMICS7EALSOREVIEWBELOWRECENT RESEARCHIDENTIFYINGTHECONTRIBUTIONSTHATLANDUSEMAKES TOLOCALCLIMATECONDITIONS )MPROVEMENTSIN#LIMATE3CENARIOS 3INCETHEDEVELOPMENTOFTHESEEARLY'#-SIMPROVE MENTS HAVE RESULTED IN BETTER DEPICTION OF LARGE SCALE FEATURESOFTHECLIMATESYSTEMSUCHASTHESEASONALGEO GRAPHICALANDVERTICALVARIATIONSINCLIMATE(OUGHTONET AL /UR ABILITY TO DETECT CLIMATE CHANGE IS CLOSELY LINKEDWITHOURABILITYTOPREDICTTHETEMPORALANDSPATIAL VARIABILITY OF CLIMATE 7ITHIN THE '#-S THE VARIABILITY INRESULTSISBROADLYCOMPARABLETOTHEOBSERVEDVARIABIL ITY IN TIME AND SPACE (OUGHTON ET AL )MPROVED '#-SCAPTURETHERELATIVELYSMALLERVARIABILITYOVERTHE OCEANS AND THE LARGER VARIABILITY OVER CONTINENTAL INTE RIORS (OWEVER ONLY RECENTLY HAS THE INTERANNUAL VARI ABILITY ASSOCIATED WITH THE %L .INO3OUTHERN /SCILLATION PHENOMENON BEEN CAPTURED BY A COUPLED ATMOSPHERIC ANDOCEANMODELTHE(ADLEY'#-4ETTETAL4HE (ADLEYMODELANDSEVERALOTHER'#-MODELSREPRESENT A SIGNIlCANT IMPROVEMENT IN THE PROJECTION OF CLIMATE CHANGETHROUGHTHETHREEDIMENSIONALREPRESENTATIONAND INTERACTION OF ATMOSPHERIC PROCESSES OCEANIC PROCESSES ANDTHELANDSURFACEPROPERTIESONATIMEDEPENDENTBASIS (OUGHTON ET AL 4HESE SCENARIOS ARE REFERRED TO AS TRANSIENT SCENARIOS IN CONTRAST TO THE EARLIER EQUILIB RIUMSCENARIOS4HESECOMPUTATIONALLYINTENSIVESIMULA TIONSALLOWANEXAMINATIONOFTHEBEHAVIOROFCLIMATEAS HUMANINDUCEDEMISSIONSINCREASEOVERTIME 7HILE CLIMATE SCENARIOS IN THE 3ECOND )0##!SSESS MENT INCLUDED THE NATURE OF CHANGE OVER TIME (OUGH TONETALTHE)0##ANALYSISOFTHEIMPACTOFCLIMATE CHANGE ON ECOSYSTEMS INCLUDING FORESTS WAS BASED ON THE EARLIER EQUILIBRIUM CLIMATE SCENARIOS /NLY NOW IS RESEARCH BEING REPORTED THAT HAS USED THE TRANSIENT SCE NARIOS TO EXAMINE THE IMPACT OF CLIMATE CHANGE ON FOR ESTS.EILSON(OWEVERTHELANDSURFACEPROPERTIES OFTHESEIMPROVEDATMOSPHERICOCEANCOUPLEDMODELSIS STATIC THAT IS THE LAND SURFACE PROPERTIES SUCH AS VEG /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS ETATION DO NOT CHANGE OVER TIME IN RESPONSE TO CLIMATE CHANGES OR HUMAN ACTIVITIES 2ECENT WORK HAS SHOWN THEIMPACTOFLANDSURFACEPROPERTIESONCLIMATEMODEL ING 0ITMAN ET AL 4HE DEVELOPMENT OF FEEDBACKS BETWEEN LAND SURFACE PROPERTIES AND THE ATMOSPHERE OCEANPROCESSESISANOTHERAREAOFNEEDEDRESEARCH 4HE ADDITION OF AEROSOLS TO THE '#-S HAS RESULTED INCLOSERAGREEMENTBETWEENMODELSIMULATIONSANDTHE OBSERVED GLOBAL MEAN SURFACE TEMPERATURE 4HE RELEASE OF STRATOSPHERIC AEROSOLS FROM THE -OUNT 0INATUBO ERUPTIONWASUSEDTOEXERCISEACLIMATEMODELTHEMODEL RESULTS OF A SHIFT IN THE GLOBAL TEMPERATURE VARIATION AGREEDCLOSELYWITHTHEOBSERVATIONS!NALYSESWITHTHE (ADLEY'#-INDICATETHATTHEINmUENCEOFAEROSOLSVARIES BY SEASON AND REGION OF THE GLOBE -ITCHELL AND *OHNS )NTHEWINTERAEROSOLSCOOLTHEWARMINGINmUENCE OFCARBONDIOXIDEINTHESUMMERTHEINmUENCEOFCARBON DIOXIDEONTHEHYDROLOGICALCYCLEISDISRUPTED2EGIONAL CLIMATES IN %UROPE AND 3OUTHEAST!SIA ARE SIGNIlCANTLY IMPACTEDBYTHEINCLUSIONOFAEROSOLSINTHEMODEL 4HESEIMPROVEMENTSIN'#-SHAVEBEENOUTPACEDBY ANEQUALLYIMPORTANTINCREASEINOURUNDERSTANDINGOFTHE COMPLEXITYOFTHECLIMATESYSTEMANDTHEIDENTIlCATIONOF ADDITIONALPROCESSESTHATNEEDTOBEINCLUDEDINTHECLI MATEMODELS4HERANGEOFTEMPERATUREINCREASES # TO #GIVENIN(OUGHTONETALAND(OUGHTON ETALINRESPONSETOADOUBLINGOFCARBONDIOXIDE CONCENTRATIONRESULTSFROMMODELUNCERTAINTYASSOCIATED WITH INTERNAL FEEDBACKS SUCH AS WATER VAPOR FEEDBACK CLOUDRADIATIVEFEEDBACKICEANDSNOWALBEDOFEEDBACK ANDUNCERTAINTIESINTHEREPRESENTATIONOFOCEANCIRCULA TIONANDLANDSURFACEATMOSPHEREINTERACTIONS #LOUDSINmUENCETHEGLOBALTEMPERATUREBOTHASACOOL INGAGENTANDASAWARMINGAGENT4HEFORMATIONOFCLOUDS IS DEPENDENT UPON THE INTERACTIONS OF ATMOSPHERIC WATER AND AEROSOLS 4HE UNCERTAINTY OF THE TEMPERATURE RISE IS PRIMARILYTHERESULTOFOURLACKOFUNDERSTANDINGOFCLOUD PROCESSES3EAICECOVERAGEVARIESBETWEEN'#-SANDFUR THER RElNEMENT OF THIS ASPECT WILL INCREASE THEIR ACCURACY (OUGHTONETAL#HANGESINTHECLIMATEFROMANTHRO POGENICEMISSIONSWILLINmUENCEENVIRONMENTALFACTORSSUCH ASSOILMOISTUREALBEDOANDVEGETATION#HANGESINTHESE SURFACEPROPERTIESWILLINTURNAFFECTTHELOCALCLIMATE '#-STYPICALLYOPERATEATACOARSERESOLUTION4HECOM PLEXTOPOGRAPHYOFLANDSCAPESSUCHASTHEWESTERN5NITED 3TATES IS NOT REPRESENTED IN DETAIL IN THESE '#-S !T REGIONALSCALESTHEINTERACTIONSBETWEENTHEATMOSPHERE AND THE SURFACE TOPOGRAPHY VEGETATION ARE IMPORTANT 4HEREGIONALINmUENCEOFHUMANGENERATEDAEROSOLSWILL LIKELY BE SIGNIlCANT AS THESE AEROSOLS DO NOT DISPERSE WIDELY FROM THEIR SOURCES OF GENERATION &URTHER MOST '#-SDONOTINCLUDECHANGESINLANDUSEANDTHESEHAVE BEEN SHOWN TO HAVE SIGNIlCANT IMPACT ON TEMPERATURE AND PRECIPITATION CHANGES ESPECIALLY IN THE TROPICS AND SUBTROPICS(OUGHTONETAL 53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n /VERVIEW!SSESSINGTHE)MPACTSOF#LIMATE#HANGEON53&ORESTS 7ATSONETALCONCLUDEDTHATLIMITEDCONlDENCE CANBEPLACEDINREGIONALCLIMATEPROJECTIONSBECAUSETHESE PROJECTIONS ARE UNABLE TO CAPTURE PRESENTDAY CLIMATES ANDINTERMODELVARIABILITYISQUITELARGE!LTHOUGHSTATIS TICALDOWNSCALINGTECHNIQUESANDNESTEDREGIONALMODELS HAVEBEENUSEDTORElNEREGIONALCLIMATEPROJECTIONSTHE CURRENT'#-SDONOTCAPTURETHECOMPLEXTOPOGRAPHICAL FEATURESLARGELAKESYSTEMSANDNARROWLANDMASSESTHAT SIGNIlCANTLY AFFECT REGIONAL AND LOCAL CHANGE SCENARIOS (OUGHTONETAL4HISDEGREEOFUNCERTAINTYCOMPLI CATESTHEASSESSMENTOFTHEIMPACTOFCLIMATEANDCLIMATE VARIABILITYONFORESTRESOURCESATTHELOCALSCALE(OUGH TONETALIDENTIlEDTHEFOLLOWINGURGENTSCIENTIlC PROBLEMS REQUIRING ATTENTION IMPROVED UNDERSTANDING OFREGIONALPATTERNSOFCLIMATECHANGEINCLUDINGLANDSUR FACE PROCESSES AND THEIR LINK TO ATMOSPHERIC PROCESSES COUPLING OF SCALE BETWEEN 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