There’sadimmerswitchinsidethesunthatcausesitsbrightnesstoriseandfallontimescalesofaround100，000years-exactlythesameperiodasbetweeniceagesonEarth.Sosaysaphysicistwhohascreatedacomputermodelofourstar’score.
RobertEhrlichofGeorgeMasonUniversityinFairfax，Virginia，modelledtheeffectoftemperaturefluctuationsinthesun’sinterior.Accordingtothestandardview，thetemperatureofthesun’scoreisheldconstantbytheopposingpressuresofgravityandnuclearfusion.However，Ehrlichbelievedthatslightvariationsshouldbepossible.
HetookashisstartingpointtheworkofAttilaGrandpierreoftheKonkolyObservatoryoftheHungarianAcademyofSciences.In2005，Grandpierreandacollaborator，Gáborágoston，calculatedthatmagneticfieldsinthesun’scorecouldproducesmallinstabilitiesinthesolarplasma.Theseinstabilitieswouldinducelocalisedoscillationsintemperature.
Ehrlich’smodelshowsthatwhilstmostoftheseoscillationscanceleachotherout，somereinforceoneanotherandbecomelong-livedtemperaturevariations.Thefavouredfrequenciesallowthesun’scoretemperaturetooscillatearounditsaveragetemperatureof13.6millionkelvinincycleslastingeither100，000or41，000years.Ehrlichsaysthatrandominteractionswithinthesun’smagneticfieldcouldflipthefluctuationsfromonecyclelengthtotheother.
ThesetwotimescalesareinstantlyrecognisabletoanyonefamiliarwithEarth’siceages：forthepastmillionyears，iceageshaveoccurredroughlyevery100，000years.Beforethat，theyoccurredroughlyevery41，000years.
MostscientistsbelievethattheiceagesaretheresultofsubtlechangesinEarth’sorbit，knownastheMilankovitchcycles.OnesuchcycledescribesthewayEarth’sorbitgraduallychangesshapefromacircletoaslightellipseandbackagainroughlyevery100，000years.ThetheorysaysthisalterstheamountofsolarradiationthatEarthreceives，triggeringtheiceages.However，apersistentproblemwiththistheoryhasbeenitsinabilitytoexplainwhytheiceageschangedfrequencyamillionyearsago.
"InMilankovitch，thereiscertainlynogoodideawhythefrequencyshouldchangefromonetoanother，"saysNeilEdwards，aclimatologistattheOpenUniversityinMiltonKeynes，UK.NoristhetransitionproblemtheonlyonetheMilankovitchtheoryfaces.EhrlichandothercriticsclaimthatthetemperaturevariationscausedbyMilankovitchcyclesaresimplynotbigenoughtodriveiceages.
However，EdwardsbelievesthesmallchangesinsolarheatingproducedbyMilankovitchcyclesarethenamplifiedbyfeedbackmechanismsonEarth.Forexample，ifseaicebeginstoformbecauseofaslightcooling，carbondioxidethatwouldotherwisehavefounditswayintotheatmosphereaspartofthecarboncycleislockedintotheice.ThatweakensthegreenhouseeffectandEarthgrowsevencolder.
AccordingtoEdwards，thereisnolackofsuchmechanisms."Ifyouaddtheireffectstogether，thereismorethanenoughfeedbacktomakeMilankovitchwork，"hesays."Theproblemnowisidentifyingwhichmechanismsareatwork."ThisiswhyscientistslikeEdwardsarenotyetreadytogiveuponthecurrenttheory."Milankovitchcyclesgiveusiceagesroughlywhenweobservethemtohappen.Wecancalculatewhereweareinthecycleandcompareitwithobservation，"hesays."Ican’tseeanywayoftesting[Ehrlich’s]ideatoseewhereweareinthetemperatureoscillation."
Ehrlichconcedesthis."Ifthereisawaytotestthistheoryonthesun，Ican’tthinkofonethatispractical，"hesays.That’sbecausevariationover41，000to100，000yearsistoogradualtobeobserved.However，theremaybeawaytotestitinotherstars：reddwarfs.Theircoresaremuchsmallerthanthatofthesun，andsoEhrlichbelievesthattheoscillationperiodscouldbeshortenoughtobeobserved.Hehasyettocalculatethepreciseperiodortheextentofvariationinbrightnesstobeexpected.
NigelWeiss，asolarphysicistattheUniversityofCambridge，isfarfromconvinced.HedescribesEhrlich’sclaimsas"utterlyimplausible".EhrlichcountersthatWeiss’sopinionisbasedonthestandardsolarmodel，whichfailstotakeintoaccountthemagneticinstabilitiesthatcausethetemperaturefluctuations.
Questions1-4
CompleteeachofthefollowingstatementswithOneorTwonamesofthescientistsfromtheboxbelow.
WritetheappropriatelettersA-Einboxes1-4onyouranswersheet.
A.AttilaGrandpierre
B.Gáborágoston
C.NeilEdwards
D.NigelWeiss
E.RobertEhrlich
Questions5-9
Dothefollowingstatementsagreewiththeinformationgiveninthereadingpassage
Inboxes5-9onyouranswersheetwrite
Tifthestatementistrueaccordingtothepassage
Fifthestatementisfalseaccordingtothepassage
NGiftheinformationisnotgiveninthepassage
Questions10-14
Completethenotesbelow.
ChooseonesuitablewordfromtheReadingPassageaboveforeachanswer.
Writeyouranswersinboxes10-14onyouranswersheet.
Thestandardviewassumesthattheopposingpressuresofgravityandnuclearfusionsholdthetemperature__10__inthesun’sinterior，buttheslightchangesintheearth’s__11__alterthetemperatureontheearthandcauseiceagesevery100，000years.ABritishscientist，however，challengesthisviewbyclaimingthattheinternalsolarmagnetic__12__caninducethetemperatureoscillationsinthesun’sinterior.Thesun’scoretemperatureoscillatesarounditsaveragetemperaturein__13__lastingeither100，000or41，000years.Andthe__14__interactionswithinthesun’smagneticfieldcouldflipthefluctuationsfromonecyclelengthtotheother，whichexplainswhytheiceageschangedfrequencyamillionyearsago.