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alreadydisappearing.Theevidenceavailablesuggeststhatawarminghastakenplace.Thisfitsthetheorythatcarbondioxidewarmstheearth.

However,mostofthefuelisburntinthenorthernhemisphere,wheretemperaturesseemtobefalling.Scientistsconclude,therefore,thatuptonownaturalinfluencesontheweatherhaveexceededthosecausedbyman.Thequestionis:Whichnaturalcausehasmosteffectontheweather?

Onepossibilityisthevariablebehaviorofthesun.Astronomersatoneresearchstationhavestudiedthehotspotsand“cold”spots(thatis,therelativelylesshotspots)onthesun.Asthesunrotates,every27.5days,itpresentshotteror“colder”facestotheearth,anddifferentaspectstodifferentpartsoftheearth.Thisseemstohaveaconsiderableeffectonthedistributionoftheearth’satmosphericpressure,andconsequentlyonwindcirculation.Thesunisalsovariableoveralongterm:itsheatoutputgoesupanddownincycles,thelatesttrendbeingdownward.

Scientistsarenowfindingmutualrelationsbetweenmodelsofsolar-weatherinteractionsandtheactualclimateovermanythousandsofyears,includingthelastIceAge.TheproblemisthatthemodelsarepredictingthattheworldshouldbeenteringanewIceAgeanditisnot.Onewayofsolvingthistheoreticaldifficultyistoassumeadelayofthousandsofyearswhilethesolareffectsovercometheinertia(惯性)oftheearth’sclimate.Ifthisisright,thewarming