ultra elitist environmental group forced to admit doubts on global warming science

8/8/2019 Ultra Elitist Environmental Group Forced to Admit Doubts on Global Warming Science

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Climate change:a summary of the scienceSeptember 2010


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GlossaryWm-2 (watts per metre squared)

The amount of energy that falls on a square metre in one second.

Sometimes known as a flux.

Carbon cycle

The term used to describe the flow of carbon, in its various forms,

between the atmosphere, oceans, plants, soils and rocks. In the

atmosphere, carbon mostly exists as carbon dioxide, but it exists in

different forms in other components, such as organic carbon in the soil.

Climate forcing (also known as radiative forcing)

The imbalance in the Earths energy budget resulting from, for example,

changes in the energy received from the Sun, changes in the amounts or

characteristics of greenhouse gases and particles, or changes in the nature

of the Earths surface. Hence climate forcing can result from both human

activity and natural causes. It is given in units of Wm-2.

Climate sensitivity

This is the amount of climate change (as measured by the change in

globally-averaged surface temperature) for a given amount of climate

forcing. It is often quoted (as will be the case here) as the temperature

change that eventually results from a doubling in CO2 concentrations,which is calculated to cause a climate forcing of about 3.6 Wm-2.

Internal climate variability:

Climate change that occurs in the absence of natural or human-induced

climate forcing as a result of interactions within and between the various

components of the climate system (such as the atmosphere, the oceans

and the frozen world).


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Introduction1 Changesinclimatehavesignicantimplicationsforpresentlives,forfuturegenerations

andforecosystemsonwhichhumanitydepends.Consequently,climatechangehas

beenandcontinuestobethesubjectofintensivescienticresearchandpublicdebate.

2 ThereisstrongevidencethatthewarmingoftheEarthoverthelasthalf-centuryhas

beencausedlargelybyhumanactivity,suchastheburningoffossilfuelsandchanges

inlanduse,includingagricultureanddeforestation.Thesizeoffuturetemperature

increasesandotheraspectsofclimatechange,especiallyattheregionalscale,arestill

subjecttouncertainty.Nevertheless,therisksassociatedwithsomeofthesechanges

aresubstantial.Itisimportantthatdecisionmakershaveaccesstoclimatescienceof

thehighestquality,andcantakeaccountofitsndingsinformulatingappropriate

responses.

3 Inviewoftheongoingpublicandpoliticaldebatesaboutclimatechange,theaimofthis

documentistosummarisethecurrentscienticevidenceonclimatechangeandits

drivers.Itlaysoutclearlywherethescienceiswellestablished,wherethereiswide

consensusbutcontinuingdebate,andwherethereremainssubstantialuncertainty.The

impactsofclimatechange,asdistinctfromthecauses,arenotconsideredhere.This

documentdrawsuponrecentevidenceandbuildsontheFourthAssessmentReportof

WorkingGroupIoftheIntergovernmentalPanelonClimateChange(IPCC),publishedin

2007,whichisthemostcomprehensivesourceofclimatescienceanditsuncertainties.

Climate change: a summary of the science ISeptember 2010 I1The Royal Society


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The greenhouse effect

4

TheSunistheprimarysourceofenergyfortheEarthsclimate.Satelliteobservationsshowthatabout30%oftheSunsenergythatreachestheEarthisreectedbackto

spacebyclouds,gasesandsmallparticlesintheatmosphere,andbytheEarths

surface.Theremainder,about240Wattspersquaremetre(Wm-2)whenaveragedover

theplanet,isabsorbedbytheatmosphereandthesurface.

5 Tobalancetheabsorptionof240Wm-2fromtheSun,theEarthssurfaceand

atmospheremustemitthesameamountofenergyintospace;theydosoasinfrared

radiation.Onaveragethesurfaceemitssignicantlymorethan240Wm-2,butthenet

effectofabsorptionandemissionofinfraredradiationbyatmosphericgasesandclouds

istoreducetheamountreachingspaceuntilitapproximatelybalancestheincoming

energyfromtheSun.Thesurfaceisthuskeptwarmerthanitotherwisewouldbe

because,inadditiontotheenergyitreceivesfromtheSun,italsoreceivesinfrared

energyemittedbytheatmosphere.Thewarmingthatresultsfromthisinfraredenergyis

knownasthegreenhouseeffect.

6 Measurementsfromthesurface,researchaircraftandsatellites,togetherwith

laboratoryobservationsandcalculations,showthat,inadditiontoclouds,thetwo

gasesmakingthelargestcontributiontothegreenhouseeffectarewatervapour

followedbycarbondioxide(CO2).Therearesmallercontributionsfrommanyother

gasesincludingozone,methane,nitrousoxideandhuman-madegasessuchasCFCs

(chlorouorocarbons).

Climate change

7 Climatechangeonaglobalscale,whethernaturalorduetohumanactivity,canbe

initiatedbyprocessesthatmodifyeithertheamountofenergyabsorbedfromtheSun,

ortheamountofinfraredenergyemittedtospace.

8 Climatechangecanthereforebeinitiatedbychangesintheenergyreceivedfromthe

Sun,changesintheamountsorcharacteristicsofgreenhousegases,particlesand

clouds,orchangesinthereectivityoftheEarthssurface.Theimbalancebetweenthe

absorbedandemittedradiationthatresultsfromthesechangeswillbereferredtohere

asclimateforcing(sometimesknownasradiativeforcing)andgiveninunitsof

Wm-2.Apositiveclimateforcingwilltendtocauseawarming,andanegativeforcinga

cooling.Climatechangesacttorestorethebalancebetweentheenergyabsorbedfrom

theSunandtheinfraredenergyemittedintospace.

9 Inprinciple,changesinclimateonawiderangeoftimescalescanalsoarisefrom

variationswithintheclimatesystemdueto,forexample,interactionsbetweenthe

oceansandtheatmosphere;inthisdocument,thisisreferredtoasinternalclimate

Climate and climate change:some background science



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variability.Suchinternalvariabilitycanoccurbecausetheclimateisanexampleofa

chaoticsystem:onethatcanexhibitcomplexunpredictableinternalvariationsevenin

theabsenceoftheclimateforcingsdiscussedinthepreviousparagraph.

10 Thereisverystrongevidencetoindicatethatclimatechangehasoccurredonawide

rangeofdifferenttimescalesfromdecadestomanymillionsofyears;humanactivityis

arelativelyrecentadditiontothelistofpotentialcausesofclimatechange.

11 Theshiftsbetweenglacialandinterglacialperiodsoverthepastfewmillionyearsare

thoughttohavebeenaresponsetochangesinthecharacteristicsoftheEarthsorbit

aroundtheSun.Whiletheseledtoonlysmallchangesinthetotalenergyreceivedfrom

theSun,theyledtosignicantchangesinitsgeographicalandseasonaldistribution.Thelargechangesinclimate,inmovinginandoutofglacialperiods,provideevidence

ofthesensitivityofclimatetochangesintheEarthsenergybalance,whether

attributabletonaturalcausesortohumanactivity.

Mechanisms of global climate change

12 Onceaclimateforcingmechanismhasinitiatedaclimateresponse,thisclimatechange

canleadtofurtherchanges;forexample,inresponsetoawarming,theamountof

watervapourisexpectedtoincrease,theextentofsnowandiceisexpectedto

decrease,andtheamountandpropertiesofcloudscouldalsochange.Suchchanges

canfurthermodifytheamountofenergyabsorbedfromtheSun,ortheamountof

energyemittedbytheEarthanditsatmosphere,andleadtoeitherareductionor

amplicationofclimatechange.

13 Theoveralleffectofthechangesresultingfromclimateforcingdetermineakey

characteristicoftheclimatesystem,knownastheclimatesensitivitythisisthe

amountofclimatechange(asmeasuredbytheequilibriumchangeinglobally-averaged

surfacetemperature)causedbyagivenamountofclimateforcing.Itisoftenquoted(as

willbethecasehere)asthetemperaturechangethateventuallyresultsfromadoublinginCO2concentrationssincepre-industrialtimes,andiscalculatedtocauseaclimate

forcingofabout3.6Wm-2.

14 Thenatureoftheclimatesystemisdeterminedbyinteractionsbetweenthemoving

atmosphereandoceans,thelandsurface,thelivingworldandthefrozenworld.The

rateatwhichheatismovedfromthesurfacetotheoceandepthsisanimportantfactor

indeterminingthespeedatwhichclimatecanchangeinresponsetoclimateforcing.

15Sincevariationsinclimatecanresultfrombothclimateforcingandinternalclimatevariability,thedetectionofforcedclimatechangeinobservationsisnotalways

straightforward.Furthermore,thedetectionofclimatechangeinobservations,beyond

theexpectedinternalclimatevariability,isnotthesameastheattributionofthatchange



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toaparticularcauseorcauses.Attributionrequiresadditionalevidencetoprovidea

quantitativelinkbetweentheproposedcauseandtheobservedclimatechange.

Modelling the climate system

16 Currentunderstandingofthephysics(andincreasinglythechemistryandbiology)of

theclimatesystemisrepresentedinamathematicalforminclimatemodels,whichare

usedtosimulatepastclimateandprovideprojectionsofpossiblefutureclimatechange.

Climatemodelsarealsousedtoprovidequantitativeestimatestoassisttheattribution

ofobservedclimatechangetoaparticularcauseorcauses.

17Climatemodelsvaryconsiderablyincomplexity.Thesimplestcanbedescribedbyafew

equations,andmayrepresenttheclimatebyglobal-averagesurfacetemperaturealone.

Themostcomplicatedandcomputer-intensivemodelsrepresentmanydetailsofthe

interactionsbetweencomponentsoftheclimatesystem.Thesemorecomplexmodels

representvariationsinparameterssuchastemperature,windandhumiditywith

latitude,longitudeandaltitudeintheatmosphere,andalsorepresentsimilarvariations

intheocean.Incomplexclimatemodelsclimatesensitivityemergesasanoutput;inthe

simplercalculationsitisspeciedeitherasaninputoritemergesasaconsequenceof

simplied(butplausible)assumptions.

18Byapplyingestablishedlawsofuiddynamicsandthermodynamics,themorecomplex

climatemodelssimulatemanyimportantweatherphenomenathatdeterminethe

climate.However,limitationsofcomputerpowermeanthatthesemodelscannot

directlyrepresentphenomenaoccurringatsmallscales.Forexample,individualclouds

arerepresentedbymoreapproximatemethods.Sincetherearevariouswaystomake

theseapproximations,therepresentationcanvaryinclimatemodelsdevelopedat

differentclimateinstitutes.Theuseofthesedifferentapproximationsleadstoarangeof

estimatesofclimatesensitivity,especiallybecauseofdifferencesbetweenmodelsinthe

responseofcloudstoclimatechange.Thereareintensiveeffortstocomparethemodelswithobservationsandwitheachother.Thespreadofresultsfromthesemodels

givesusefulinformationonthedegreeofcondenceinthereliabilityofprojectionsof

climatechange.

19Unlikeweather-forecastmodels,climatemodelsdonotseektopredicttheactual

weatheronaparticulardayataparticularlocation.Themorecomplexmodelsdo

howeversimulateindividualweatherphenomena,suchasmid-latitudedepressionsand

anticyclones,andaimtogivesimulationsofpossibleweathersequencesmuchfarther

intothefuturethanweatherforecastmodels.Fromsuchsimulations,onecanderive

thecharacteristicsofclimatelikelytooccurinfuturedecades,includingmean

temperatureandtemperatureextremes.



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Changes in global-average surface temperature

20

Measurementssuitableforshowinghowsurfacetemperaturehaschangedwithtimeacrosstheworldbecameavailablearound1850.Analysesofthesedata,inanumberof

institutes,trytotakeintoaccountchangingdistributionsofmeasurements,changing

observationtechniques,andchangingsurroundingsofobservingstations(e.g.some

stationsbecomemoreurbanwithtime,whichcanmakemeasurementsfromthemless

representativeofwiderareas).

21Measurementsshowthataveragedovertheglobe,thesurfacehaswarmedbyabout

0.8oC(withanuncertaintyofabout0.2oC)since1850.Thiswarminghasnotbeen

gradual,buthasbeenlargelyconcentratedintwoperiods,fromaround1910toaround

1940andfromaround1975toaround2000.Thewarmingperiodsarefoundinthree

independenttemperaturerecordsoverland,overseaandinoceansurfacewater.Even

withinthesewarmingperiodstherehasbeenconsiderableyear-to-yearvariability.The

warminghasalsonotbeengeographicallyuniformsomeregions,mostmarkedlythe

high-latitudenortherncontinents,haveexperiencedgreaterwarming;afewregions

haveexperiencedlittlewarming,orevenaslightcooling.

22Whenthesesurfacetemperaturesareaveragedoverperiodsofadecade,toremove

someoftheyear-to-yearvariability,eachdecadesincethe1970shasbeenclearly

warmer(givenknownuncertainties)thantheoneimmediatelyprecedingit.Thedecade

2000-2009was,globally,around0.15oCwarmerthanthedecade1990-1999.

23Localtemperaturesaregenerallyapoorguidetoglobalconditions.Forexample,a

colder-than-averagewinterintheUKdoesnotmeanthatcolder-than-average

conditionsareexperiencedglobally.Similarly,observedvariationsinglobaltemperature

overaperiodofjustafewyearscouldbeamisleadingguidetounderlyinglonger-term

trendsinglobaltemperature.

Other changes in climate24Notallaspectsoftheclimatesystemhavebeenobservedoveraslongaperiodas

surfacetemperaturesforexample,thosebasedonsatelliteobservationsdateback,at

best,tothe1970s.Norarethemeasurementsofotheraspectsoftheclimatesystem

alwaysofthesamequality.Collectively,however,theyprovidemuchevidenceof

climatechangeconsistentwiththesurfacetemperaturechanges.Thisincludes

increasesintheaveragetemperatureofboththeupper700moftheoceanandthe

troposphere(theatmosphereupto10-18km),widespread(thoughnotuniversal)

decreasesinthelengthofmountainglaciersandincreasesinaveragesealevel.Therehasbeenanoveralldeclineintheareacoveredbysea-iceoatingontheArcticOcean

overthepast30years(althoughtherehasbeenasmallincreaseintheareacoveredby

sea-icearoundAntarctica).

Aspects of climate change onwhich there is wide agreement



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Changes in atmospheric composition

25

Global-averageCO2concentrationshavebeenobservedtoincreasefromlevelsofaround280partspermillion(ppm)inthemid-19thcenturytoaround388ppmbythe

endof2009.CO2concentrationscanbemeasuredinancientairtrappedinbubblesin

ice,deepbelowthesurfaceinAntarcticaandGreenland;theseshowthatpresent-day

concentrationsarehigherthananythathavebeenobservedinthepast800,000years,

whenCO2variedbetweenabout180and300ppm.Variouslinesofevidencepoint

stronglytohumanactivitybeingthemainreasonfortherecentincrease,mainlydueto

theburningoffossilfuels(coal,oil,gas)withsmallercontributionsfromland-use

changesandcementmanufacture.Theevidenceincludestheconsistencybetween

calculationsoftheemittedCO2andthatexpectedtohaveaccumulatedintheatmosphere,theanalysisoftheproportionsofdifferentCO2isotopes,andtheamount

ofoxygenintheair.

26TheseobservationsshowthatabouthalfoftheCO2emittedbyhumanactivitysincethe

industrialrevolutionhasremainedintheatmosphere.Theremainderhasbeentakenup

bytheoceans,soilsandplantsalthoughtheexactamountgoingtoeachofthese

individuallyislesswellknown.

27Concentrationsofmanyothergreenhousegaseshaveincreased.Theconcentrationof

methanehasmorethandoubledinthepast150years;thisrecentandrapidincreaseis

unprecedentedinthe800,000yearrecordandevidencestronglysuggeststhatitarises

mainlyasaresultofhumanactivity.

Climate forcing by greenhouse gas changes

28Changesinatmosphericcompositionresultingfromhumanactivityhaveenhancedthe

naturalgreenhouseeffect,causingapositiveclimateforcing.Calculations,whichare

supportedbylaboratoryandatmosphericmeasurements,indicatethattheseadditional

gaseshavecausedaclimateforcingduringtheindustrialeraofaround2.9Wm-2

,withanuncertaintyofabout0.2Wm-2.Otherclimatechangemechanismsresultingfrom

humanactivityaremoreuncertain(seelater);calculationsthattakeintoaccountthese

otherpositiveandnegativeforcings(includingtheroleofatmosphericparticles)indicate

thattheneteffectofallhumanactivityhascausedapositiveclimateforcingofaround

1.6Wm-2withanestimateduncertaintyofabout0.8Wm-2.

29Applicationofestablishedphysicalprinciplesshowsthat,evenintheabsenceof

processesthatamplifyorreduceclimatechange(seeparagraphs12&13),theclimate

sensitivitywouldbearound1o

C,foradoublingofCO2concentrations.Aclimateforcingof1.6Wm-2(seepreviousparagraph)would,inthishypotheticalcase,leadtoaglobally-

averagedsurfacewarmingofabout0.4oC.However,aswillbediscussedinparagraph



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36,itisexpectedthattheactualchange,afteraccountingfortheadditionalprocesses,

willbegreaterthanthis.

Carbon dioxide and climate

30EvidencefromicecoresindicatesanactiveroleforCO2intheclimatesystem.Thisis

becausetheamountofcarbonheldinoceans,soilsandplantsdependsontemperature

andotherconditions.Inotherwords,changesinCO2 can lead to climate change and

climatechangecanalsoaltertheconcentrationsofCO2.



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Aspects of climate change wherethere is a wide consensus butcontinuing debate and discussionThe carbon cycle and climate

31 OnceatmosphericCO2concentrationsareincreased,carboncyclemodels(which

simulatetheexchangeofcarbonbetweentheatmosphere,oceans,soilsandplants)

indicatethatitwouldtakeaverylongtimeforthatincreasedCO2todisappear;thisis

mainlyduetowell-knownchemicalreactionsintheocean.Currentunderstanding

indicatesthateveniftherewasacompletecessationofemissionsofCO2todayfrom

humanactivity,itwouldtakeseveralmillenniaforCO2concentrationstoreturntopre-

industrialconcentrations.

Other drivers of global climate change

32Inadditiontochangesingreenhousegasconcentrations,therearealargenumberof

lesswellcharacterisedcontributionstoclimateforcing,bothnaturalandhuman-

induced.

33Volcaniceruptionsareexamplesofanaturalclimateforcingmechanism.Anindividual

volcaniceruptionhasitslargesteffectsontheclimateforonlyafewyearsafterthe

eruption;theseeffectsaredependentonthelocation,sizeandtypeoftheeruption.

34NaturalforcingduetosustainedvariationsintheenergyemittedbytheSunoverthe

past150yearsisestimatedtobesmall(about0.12Wm-2);however,directobservations

oftheenergyemittedbytheSunonlybecameavailableinthe1970sandestimatesover

longerperiodsrelyonobservationsofchangesinothercharacteristicsoftheSun.A

numberofmechanismshavebeenproposedthatcouldreduceoramplifytheeffectof

solarvariations;theseremainareasofactiveresearch.

35Humanactivityresultsinemissionsofmanyshort-livedgases(suchascarbon

monoxideandsulphurdioxide)andparticlesintotheatmosphere.Theseaffecttheatmosphericconcentrationsofotherclimate-importantgasessuchasozone,andother

particleswhichleadtoaclimateforcing.Calculations,coupledtoavarietyof

atmosphericobservations,indicatethatparticleshavecausedanegativeclimateforcing

ofaround0.5Wm-2withanuncertaintyof0.2Wm-2.Theparticlesalsodirectly

inuencecloudproperties;thismoreuncertaineffectisdiscussedinparagraph47.

Climate sensitivity

36Themorecomplexclimatemodels,supportedbyobservations,allowclimatesensitivity

tobecalculatedinthepresenceofprocessesthatamplifyorreducethesizeofthe

climateresponse.Increasesinwatervapouralone,inresponsetowarming,are

estimatedtoapproximatelydoubletheclimatesensitivityfromitsvalueintheabsence



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ofamplifyingprocesses.Thereneverthelessremainuncertaintiesinhowmuchwater

vapouramountswillchange,andhowthesechangeswillbedistributedinthe

atmosphere,inresponsetoawarming.Climatemodelsindicatethattheoverallclimate

sensitivity(forahypotheticaldoublingofCO2intheatmosphere)islikelytolieinthe

range2oCto4.5oC;thisrangeismainlyduetothedifcultiesinsimulatingtheoverall

effectoftheresponseofcloudstoclimatechangementionedearlier.

Attribution of climate change

37Thesizeandsustainednatureoftheobservedglobal-averagesurfacewarmingon

decadalandlongertimescalesgreatlyexceedstheinternalclimatevariabilitysimulated

bythecomplexclimatemodels.Unlessthisvariabilityhasbeengrosslyunderestimated,theobservedclimatechangemustresultfromnaturaland/orhuman-inducedclimate

forcing.

38Whenonlynaturalclimateforcingsareputintoclimatemodels,themodelsare

incapableofreproducingthesizeoftheobservedincreaseinglobal-averagesurface

temperaturesoverthepast50years.However,whenthemodelsincludeestimatesof

forcingsresultingfromhumanactivity,theycanreproducetheincrease.Thesame

resultisfound,albeitwithagreaterspreadbetweendifferentmodels,forthesimulation

ofobservedsurfacetemperaturechangesforeachofthehabitablecontinentsseparately.

39Whenknownuncertaintiesinbothobservedtrendsandclimatemodelsaretakeninto

account,theobservedverticalandlatitudinalvariationsoftemperaturechangearealso

broadlyconsistentwiththoseexpectedfromadominantroleforhumanactivity.There

isanongoingcontroversyconcerningwhetherornottheincreasedwarmingwith

heightinthetropicalregionsgivenbyclimatemodelsissupportedbysatellite

measurements.

Future climate change

40Aswithalmostanyattemptstoforecastfutureconditions,projectionsoffutureclimate

changedependonanumberoffactors.Futureemissionsduetohumanactivitywill

dependonsocial,technologicalandpopulationchangeswhichcannotbeknownwith

condence.Theunderlyinguncertaintiesinclimatescienceandtheinabilitytopredict

preciselythesizeoffuturenaturalclimateforcingmechanismsmeanthatprojections

mustbemadewhichtakeintoaccounttherangeofuncertaintiesacrossthesedifferent

areas.

41The2007assessmentbytheIntergovernmentalPanelonClimateChange(IPCC)made

projectionsoffuturechangesusinganumberofpossiblescenariosoffutureemissions,



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basedonadiverserangeofassumptions.TheIPCCsbestestimatewasthatglobally-

averagedsurfacetemperatureswouldbebetween2.5-4.7oChigherby2100compared

topre-industriallevels.Thefullrangeofprojectedtemperatureincreasesby2100was

foundtobe1.8-7.1oCbasedonthevariousscenariosanduncertaintiesinclimate

sensitivity.

42Evenintheextremelyunlikelyeventthatthereisnofurtherincreaseinclimateforcing,a

furtherwarmingwouldbeexpectedtooccurastheoceansslowlyrespondtothe

existingclimateforcing,amountingtoafurtherfewtenthsofadegreecentigradeby

theyear2100.

43Theuncertaintyinthepredictedwarmingasaresultofhumanactivityoverthenexttwodecadesissmaller,therangebeing0.2to0.4oCperdecade.Ontheseshortertime-

scales,theactualchangecouldhoweverbereducedorenlargedsignicantlybyinternal

climatevariabilityandnaturalclimateforcings.

44 Increasesintemperaturearepredictedtobelargeronland,particularlyonthenorthern

continentsinwinter.Lesswarmingispredicted,forexample,overtheNorthAtlantic

Ocean.Climatemodelstendtopredictthatprecipitationwillgenerallyincreaseinareas

withalreadyhighamountsofprecipitationandgenerallydecreaseinareaswithlow

amountsofprecipitation.45Becauseofthethermalexpansionoftheocean,itisverylikelythatformanycenturies

therateofglobalsea-levelrisewillbeatleastaslargeastherateof20cmpercentury

thathasbeenobservedoverthepastcentury.Paragraph49discussestheadditional,

butmoreuncertain,contributiontosea-levelrisefromthemeltingoflandice.



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46 Observationsarenotyetgoodenoughtoquantify,withcondence,someaspectsof

theevolutionofeitherclimateforcingorclimatechange,orforhelpingtoplacetight

boundsontheclimatesensitivity.Observationsofsurfacetemperaturechangebefore

1850arealsoscarce.

47 Asnotedabove,projectionsofclimatechangearesensitivetothedetailsofthe

representationofcloudsinmodels.Particlesoriginatingfrombothhumanactivitiesand

naturalsourceshavethepotentialtostronglyinuencethepropertiesofclouds,with

consequencesforestimatesofclimateforcing.Currentscienticunderstandingofthis

effectispoor.

48Additionalmechanismsthatinuenceclimatesensitivityhavebeenidentied,includingtheresponseofthecarboncycletoclimatechange,forexamplethelossoforganic

carboncurrentlystoredinsoils.Theneteffectofchangesinthecarboncycleinall

currentmodelsistoincreasewarming,byanamountthatvariesconsiderablyfrom

modeltomodelbecauseofuncertaintiesinhowtorepresenttherelevantprocesses.

ThefuturestrengthoftheuptakeofCO2bythelandandoceans(whichtogetherare

currentlyresponsiblefortakingupabouthalfoftheemissionsfromhumanactivity

seeparagraph26)isverypoorlyunderstood,particularlybecauseofgapsinour

understandingoftheresponseofbiologicalprocessestochangesinbothCO2

concentrationsandclimate.

49Thereiscurrentlyinsufcientunderstandingoftheenhancedmeltingandretreatofthe

icesheetsonGreenlandandWestAntarcticatopredictexactlyhowmuchtherateof

sealevelrisewillincreaseabovethatobservedinthepastcentury(seeparagraph45)

foragiventemperatureincrease.Similarly,thepossibilityoflargechangesinthe

circulationoftheNorthAtlanticOceancannotbeassessedwithcondence.Thelatter

limitstheabilitytopredictwithcondencewhatchangesinclimatewilloccurin

WesternEurope.

50Theabilityofthecurrentgenerationofmodelstosimulatesomeaspectsofregional

climatechangeislimited,judgingfromthespreadofresultsfromdifferentmodels;

thereislittlecondenceinspecicprojectionsoffutureregionalclimatechange,except

atcontinentalscales.

Aspects that are not wellunderstood



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Developments in climate science51Climatechangesciencehasadvancedmarkedlyoverthepast20years,asaresultof

manyfactors.Theseincludeimprovedmethodsforhandlinglong-termclimatedata

sets,theever-lengtheningrecordofclimateobservations,improvedmeasurement

techniques,includingthosefromsatellites,betterunderstandingoftheclimatesystem,

improvedmethodsforsimulatingtheclimatesystem,andincreasedcomputerpower.

52Oneindicationoftheseadvancesistheincreasingdegreeofcondenceinthe

attributionofclimatechangetohumanactivity,asexpressedinthekeyconclusionsof

IPCCWorkingGroup1(WG1)initsassessments.

53Initsrstassessmentpublishedin1990,IPCCWG1concludedthatthesizeof[the

observedsurface]warmingisbroadlyconsistentwithpredictionsofclimatemodels[whichsimulatetheimpactofhumanactivity],butitisalsoofthesamemagnitudeas

naturalclimatevariability.Itssecondassessment,publishedin1995,concludedthat

thebalanceofevidencesuggeststhatthereisadiscerniblehumaninuenceon

climatechange.Itsfourth,andmostrecent,assessment,publishedin2007,concluded

thatmostoftheobservedincreaseingloballyaverage[surface]temperaturessincethe

mid-20thcenturyisverylikelyduetotheobservedincreaseinanthropogenic

greenhousegasconcentrations.

54

Remaininguncertaintiesarethesubjectofongoingresearchworldwide.Someuncertaintiesareunlikelyevertobesignicantlyreduced,becauseof,forexample,the

lackofobservationsofpastchangesrelevanttosomeaspectsofbothclimateforcing

andclimatechange.

55 Otheruncertaintiesmaystarttoberesolved.Forexample,satellitesnowincorporate

improvedtechniquestomeasurecloudcharacteristicsacrosstheglobe.Usingclimate

modelsforday-to-dayweatherpredictionwillenable,forexample,identicationof

errorsintherepresentationofcloudsinmodels;anysucherrorswillleadtoerrorsin

forecastsofmaximumandminimumtemperatures(whichareeasilyobserved).New

high-performancecomputerswillallowclimatemodelstorepresentsomesmaller-scale

phenomena(includingcloudsystemsanddetailsoftropicalstorms)directly,andare

expectedtoimprovecondenceinregionalpredictions.

56 Thereremainsthepossibilitythathithertounknownaspectsoftheclimateandclimate

changecouldemergeandleadtosignicantmodicationsinourunderstanding.



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57Thereisstrongevidencethatchangesingreenhousegasconcentrationsduetohuman

activityarethedominantcauseoftheglobalwarmingthathastakenplaceoverthelast

halfcentury.Thiswarmingtrendisexpectedtocontinueasarechangesinprecipitation

overthelongterminmanyregions.Furtherandmorerapidincreasesinsealevelare

likelywhichwillhaveprofoundimplicationsforcoastalcommunitiesandecosystems.

58ItisnotpossibletodetermineexactlyhowmuchtheEarthwillwarmorexactlyhowthe

climatewillchangeinthefuture,butcarefulestimatesofpotentialchangesand

associateduncertaintieshavebeenmade.Scientistscontinuetoworktonarrowthese

areasofuncertainty.Uncertaintycanworkbothways,sincethechangesandtheir

impactsmaybeeithersmallerorlargerthanthoseprojected.

59Likemanyimportantdecisions,policychoicesaboutclimatechangehavetobemadein

theabsenceofperfectknowledge.Eveniftheremaininguncertaintieswere

substantiallyresolved,thewidevarietyofinterests,culturesandbeliefsinsocietywould

makeconsensusaboutsuchchoicesdifculttoachieve.However,thepotentialimpacts

ofclimatechangearesufcientlyseriousthatimportantdecisionswillneedtobemade.

Climatescienceincludingthesubstantialbodyofknowledgethatisalreadywell

established,andtheresultsoffutureresearchistheessentialbasisforfutureclimate

projectionsandplanning,andmustbeavitalcomponentofpublicreasoninginthis

complexandchallengingarea.

Concluding remarks



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Background readingExtensivebackgroundreferencestothescienticliterature,andsummariesthereof,canbe

foundinthefollowingtwodocuments.

ContributionofWorkingGroupItotheFourthAssessmentReportofthe

IntergovernmentalPanelonClimateChange,2007,Solomon,S.,D.Qin,M.Manning,

Z.Chen,M.Marquis,K.B.Averyt,M.TignorandH.L.Miller(eds.),CambridgeUniversity

Press,Cambridge,UnitedKingdomandNewYork,NY,USA.

ipcc.ch/publications_and_data/ar4/wg1/en/contents.html

AdvancingtheScienceofClimateChange,NationalResearchCouncil,2010.

americasclimatechoices.org/panelscience.shtml



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Acknowledgements

Professor John Pethica FRS (Chair)

PhysicalSecretaryofRoyalSociety

Ms Fiona Fox

Director,ScienceMediaCentre,UK

Sir Brian Hoskins FRS

DirectorGranthamInstituteforClimate

Change,ImperialCollege,UKProfessor Michael Kelly FRS

ProfessorofTechnology,Universityof

Cambridge,UK

Professor John Mitchell FRS

DirectorofClimateScience,MetOfce,UK

Professor Susan Owens

ProfessorofEnvironmentandPolicy,

UniversityofCambridge,UK

Professor Tim Palmer FRS

RoyalSocietyResearchProfessor,

UniversityofOxford,UK

Professor John Shepherd FRS

ProfessorialResearchFellowinEarth

SystemScience,University

ofSouthampton,UK

Professor Keith Shine FRS

ProfessorofPhysicalMeteorology,

UniversityofReading,UK

Professor David Spiegelhalter FRS

ProfessorofthePublicUnderstandingof

Risk,UniversityofCambridge,UK

Royal Society Science Policy Centre

Rachel Garthwaite

SeniorPolicyAdviser

Stuart Leckie

PolicyAdviser

Tony McBride

HeadofStrategy

Working Group

TheRoyalSocietywouldliketoacknowledgethemembersoftheworkinggroupthatproducedthisdocument:



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Dame Jean Thomas FRS (Chair)

BiologicalSecretaryoftheRoyalSociety

Professor Alastair Fitter FRS

Pro-Vice-ChancellorforResearch,

UniversityofYork,UK

Dame Louise Johnson FRSSeniorFellowatDiamondLightSources,UK

Professor Brian Launder FRS

ResearchProfessor,Universityof

Manchester,UK

Professor John Pyle FRS

CoDirector,CentreforAtmospheric

Science,UniversityofCambridge,UK

Professor Chris Rapley

Director,ScienceMuseum,UK

Sir Alan Wilson FRSProfessorofUrbanandRegionalSystems,

UniversityCollegeLondon,UK

Professor David Fowler FRS

CentreforEcologyandHydrology,

Edinburgh,UK

Professor Joanna Haigh

ProfessorofAtmosphericPhysics,Imperial

College,London,UK

Professor Cyril Hilsum FRS

CorporateResearchAdvisor/Visiting

ProfessorofPhysics,UniversityCollege

London,UK

Professor Anthony Kelly FRS

DistinguishedResearchFellowinthe

DepartmentofMaterialsScienceand

Metallurgy,UniversityofCambridge,UK

Professor John McWhirter FRS

DistinguishedResearchProfessorattheSchoolofEngineering,CardiffUniversity,UK

Sir John Pendry FRS

TheBlackettLaboratory,ImperialCollege,

London,UK

Sir Alan Rudge FRS

Chairman,ERAFoundationLimited,UK

Sir William Stewart FRS

FormerChiefScienticAdvisor(UK

Government)

Professor Andrew Watson FRS

RoyalSociety2010AnniversaryResearch

Professor,UniversityofEastAnglia,UK

Sir Arnold Wolfendale FRS

EmeritusProfessorofPhysics,Universityof

Durham,UK

Professor Carl Wunsch ForMemRS

CecilandIdaGreenProfessorofPhysical

Oceanography,MassachusettsInstituteof

Technology,USA

Review Panel

TheRoyalSocietygratefullyacknowledgesthecontributionoftheindependentpanelofreviewers.Thereviewpanelmemberswerenotaskedtoendorsethenaldocuments

conclusions.

Contributors

TheRoyalSocietygratefullyacknowledgesthecontributionofindividualswhohave

commentedonthedocumentatearlierstagesofitspreparation.Theseindividualswere

notaskedtoendorsethedocument.



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