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"it DoEsn’t mAttEr whAt EthiCAl Assumptions you usE," sAys miChAEl gruBB, An ExpErt on ClimAtE ChAngE poliCy, ColD FinAnCiAl ArgumEnts ArE Enough to DECiDE whAt to Do ABout gloBAl wArming. As ArgumEnts ovEr thE sCiEnCE BEhinD ClimAtE ChAngE hAvE CoolED, thE quEstion oF how muCh nAtions shoulD BE willing to pAy hAs ComE to DominAtE thE DEBAtE. now mArtin wEitzmAn hAs DEvElopED thE First thorough mEthoD For inCluDing unlikEly But ExtrEmE EvEnts in Cost-BEnEFit AnAlysEs. whEn you tAkE into ACCount ExtrEmE tEmpErAturE risEs oF morE thAn ArounD 6℃, hE sAys, thEy DominAtE All othEr options AnD EFFECtivEly DEmAnD thAt invEstmEnt AimED At stopping thEm BE mADE now. EConomists sAy thAt suCh EvEnts ArE thEorEtiCAlly possiBlE But ArE so unlikEly AnD liE so FAr in thE FuturE thAt it is not Cost-EFFECtivE to spEnD monEy to prEvEnt thEm.ComputEr moDEls Also suggEst thAt using morE rEnEwABlE EnErgy AnD rEDuCing Emissions in othEr wAys woulD Almost CErtAinly AvoiD ExtrEmE tEmpErAturE inCrEAsEs.But wEitzmAn’s rEsults ArE so DrAmAtiC thAt somE EConomists, mAny oF whom ArguED in FAvour oF CAution, ArE shiFting thEir position. EnvironmEntAl groups ArguE thAt thE risk oF ExtrEmE EvEnts justiFiEs lArgE invEstmEnt now, But othEr groups, notABly inDustry-oriEntAtED think tAnks AnD mAny rEpuBliCAn politiCiAns, hAvE rEsistED suCh CAlls. "in thE unitED stAtEs, Cost-BEnEFit AnAlysEs hAvE BEEn usED to BACk up quEstions ABout whEthEr invEstmEnt is worth muCh mow," sAys gruBB、"this throws A prEtty FunDAmEntAl spAnnEr in thE works." thE nEw mEthoD Also BACks up thE ConClusions oF thE stErn rEviEw on thEEConomiCs oFClimAtEChAngE, AlBEit viA DiFFErEnt mEthoDs. stEm’s Cost-BEnEFit AnAlysis, whiCh wAs puBlishED in oCtoBEr 2006, DiD not ConsiDEr ExtrEmE EvEnts.EvEn so, hE FounD thAt thE BEnEFits oF invEsting now woulD BE Enormous: thE worlD CoulD sAvE $2.5 trillion A yEAr iF thE risE inCo2 wAs hAltED At lEvEls ArounD 50 pErCEnt grEAtEr thAn toDAy.But whEn stErn put A priCE on thE DAmAgEs thAt rising tEmpErAturEs CoulD CAusE, hE vAluED FuturE Costs in toDAy’s monEy. mAny EConomists, inCluDing wEitzmAn, CritiCizED thAt Assumption, Arguing thAt it ignorEs thE FACt thAt invEstmEnts mADE now ArE ExpECtED to BE worth morE in thE FuturE. thE DEBAtE rEmAins unrEsolvED, As EthiCAl ArgumEnts ContinuE to rAgE ABout how to vAluE FuturE gEnErAtions.But wEitzmAn’s stuDy shows thAt onCE ExtrEmE EvEns ArE inCluDED, thE ArgumEnt BEComEs irrElEvAnt. this is BECAusE thE potEntiAl Cost oF ExtrEmE EvEns is so grEAt thAt thEy ComE to DominAtE thE AssEssmEnt oF risk, whAtEvEr mEthoD is usED to CompArE thE vAluE oF prEsEnt AnD FuturE gEnErAtions. "wEitzmAn’s work’ woulD hAvE rECEivED suBstAntiAl AttEntion in thE stEm rEport. hE woulD hAvE usED it As supporting EviDEnCE." sAys gruBB、 wEitzmAn CoulD Also CrEAtE A hEADAChE For poliCy-mAkErs. thE AnAlysis shows thAt trADitionAl Cost-BEnEFit CAlCulAtions ArE gEtting it wrong, But it DoEs so only By proviDing thAt ExtrEmE EvEnts DominAtE thE Costs whEn inCluDED in thE CAlCulAtions. it CAnnot put A FigurE on how muCh shoulD BE spEnt now, unlikE thE olD tEChniquEs.

whAt DoEs wEitzmAn’s nEw mEthoD suggEstA．it is morE sophistiCAtED thAn trADitionAl Cost-BEnEFit AnAlysis.
B．it tAkEs EthiCAl Assumptions into CAlCulAting thE Amount oF invEstmEnt.
C．ExtrEmE EvEnts shoulD BE ConsiDErED in Cost-BEnEFit AnAlysis.
D．it tElls us thAt wE shoulD tAkE thE proBlEm muCh morE sEriously.