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1、CLIMATEANDTHECHANGINGSUNJOHNA.EDDYCenterforAstrophysics,HarvardCollegeObservatoryandSmithsonianAstrophysicalObservatory,Cambridge,Mass.02138,U.S.A.Abstract.Long-termchangesinthelevelofsolaractivityarefoundinhistoricalrecordsandinfossilradiocarbonintree-rings.Typicalofthesechanges
2、aretheMaunderMinimum(A.D.1645-1715),theSpSrerMinimum(A.D.1400-1510),andaMedievalMaximum(c.A.D.1120-1280).Eighteensuchfeaturesareidentifiedinthetree-ringradiocarbonrecordofthepast7500yearsandcomparedwitharecordofworldclimate.Ineverycasewhenlong-termsolaractivityfalls,mid-latitudeg
3、laciersadvanceandclimatecools;attimesofhighsolaractivityglaciersrecedeandclimatewarms.Weproposethatchangesinthelevelofsolaractivityandinclimatemayhaveacommoncause:slowchangesinthesolarconstant,ofabout1%amplitude.I.TheSunandClimateIsclimateaffectedbychangesonthesun?Sinceitissolare
4、nergythatdrivestheatmosphereofearth-creatingcloudsandwindsandrainsandoceancurrents-theanswerwouldseemobvious.Yetthisquestionhasbeenthesubjectofcontinuingcontroversyinscienceformorethanacentury.Indoubtisnotwhetherthesunisapotentialsourceofweatherandclimatechange(itis),orwhetherthe
5、sunanditsmeasurableoutputsvary(theydo),butwhetherthereisanyclear-cutevidencethatthesunchangesenoughandinwayssufficientlyenergetictoproducedetectablechangesinourloweratmosphere.Knownchangesinsolaroutputaretodaylimitedtoenergetically-insignificantpartsofthesun'stotalenergyoutput:ch
6、angesinthesectorstructureandphysicalpropertiesofthesolarwind,thatcarrieslessthanabillionthpartoftheflowofenergyfromthesunandreachesonlytheuppermostatmosphere;significant,activity-relatedchangesinx-raysandultravioletwavelengthsthatcannotpenetratethestratosphere;andorder-of-magnitu
7、deincreasesinradioemissionsthatreachthesurfaceoftheearthwithnoapparentmeteorologicaleffect.Thebulkradiationfromthesun,whichthroughradiativeheatingistherealatmosphericdriver,isinthenearultraviolet,visible,andnearinfrared,andthisdominantcomponentisknown,ormoretruthfully,suspected,t
8、obeconstantwithinourpresentabilitytomeas
