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BULLEFIN OF THE ATOMIC SCIENTISTS Lip

A WARMING . THEORIES NEED WARNING LABEL BY aFCEDSINGER The debate over global warming has been more hype than solid fact. T he „,,nvt~ntinnnl tri: dont the: e du}: >eem~ to be x~ follotc>: increasing c:u'- hmm ~iimirle from bucninl* fossil fuel is rnhanc'ing the naturtd atmospheric •reenhou=e effect. BY the next centur.y. the resulting Fl.,bal tetu•ming• will present a clear :md present dange• to huntankind. We neecl to i'intl radical>olution., a; quicklc as possible to avert catssstrophes-inclucling N iolent weather. parched farmlands, rising sea levels, floocled continents, complete ecolog7cal collapse, and mil- lions of environmental refugees. I suppose that man,r readerr, uf the Brdleiur would agree. Fmthennore. ?onie of the more ardent propo- ?. ]• rrrl S, , '(i~r ix rliia.rdor nt Mr It~(r.<biny/iur- Iru",lSt'ir.„rnuJ li"r'ir.,urrnarfril Puliril Prn- irrt r SEF'1' . iunl proir,,nr nhr'u. ~irruru.wrtrrl sr'it'nrra reu2 Irrrrbl (II t/rr (", IY('I'.Cli'( ot 1 ii(lirrm iir r'bn(dorr." riilr, cuncetved that opiniun-makin,r und "publicatiuu hc pre=s releas,.., are be•ing used to intluence environmental pulic~. ACith montentum buil. lin_ tmt'xcd the "F..u'th aunimit"-the l'.\. Cmfez- ence on Emicomnent anti Dek'elopmerr CtiCEDI in Rio tie •Janeit'n this month-the issue of ctimate %r:u'ming has~ taken cetter ~tasl:e- :tianc scientists hare spoken uut. Philip Abei- son, in a lead editorial in the March au, 19bu. Sc'ierwr. ohaerN 'ed that "if Ilrlobal tearmingl i> anal}'zetl apphing the customat.c standards of scientific inquir}t one must conclude that there has been more h,% pe than solid fuct," Robert 1l. White, presirlent od'the Sationu, deademc of Eneineerin¢ and a cli<tinfnti,hv~l meteuraloc*ist.vrrote in tlteJulc 19911 ~rvr~mr.{o. rom ,r,.'GiN en thi-'crlv ~colf historuit is 1l-¢ wrpri,ing that manp mete7(ruloe'ists harbur ~ Ieep rrrer~a[ion± xUout takinp' cu~tl ~actiom r 1i , the basi,of predirtiott~ ol' a climate \cau'mini." And in late Decrmbe:.Julm Hotte'htun, chie['eui- tor of the C.A: ±pon~oreCl Inter,e'o% erntnentei Panel on Climate Chanee I IPCC I Repott, whic'it forms the ba>i~ for the global tcarmintT p~ ~rtinn of the CACED Earth 3ummit, announced a much reduced prediction of future climate warming based on nett~ntdies. As rellot'teI in the December 29. 1ySri Surrdr,u ul' L,ni- don, Hou¢hton. v hn alxo directs lhe Hriti=i~ MetewrologicalOffice,ca>tigatecle~ ronmennr, scaremun~'erins_. ac'tix i't, for ~ e l num r ~ e~ ~ r , ro n e a About global warming nent.~ of elobal Xcarmink theot'ie, seent t,l beliece that it is somehow inappropriate. if n~ d rlotcm:ght i:nmoral, for an.n scientist to eutphar size the theories' uncertaintied. Their argument ,rems to he that it is better for national g-oeerr ment± to do ~omething, honeter costlc lecen if it ttu'n< out that Ncttrmine theories are ~t'rong',. rather than risk waiting for ma~e certain an~l per<uasic e (lata. It is not smptisin~* that such views are ~tidel~~ heid. After all. the public ha; been exposed to a stead~~ diet ui' hrped news ,tories and TV ~pe- cial, and I~ropavamdized by environmental pres- sore erotn~~. Hu.cecer, these views are not Aharel h}' o-dLspecialists in atmospheric ph~~sic, on' climxtulok'}'-dcientist= ~cho acttudly- <ttul~ lhe>e problent,. There is no scientitic con>enstt, in suppm't ,,1a ereenhou,e %carmingthreat. h cnm • tci ~~ve U ~ P e t h ~1 ~ Um•ine the smnnter .. t' 1991, resr.u'cltec, at th< Science S Emironntental Polic'c Prnlec: i 5EP1' i, an inriepenQent. fotmdation-ftmQe~ l research kroup. sent -ur% e}' tiwm= to nwrr thau 120 C.S. atmoepheric ~cienti±t~. 11oat of thee • • 34 'I'lu1 hitll.aiuul'tLr~ Ai'.uuv ~vivnti-'

r. ~ ~cienti+t, hat' l i,,ntributed to or reciewed the summary clid nut reprement the report fairhIPCt' repurt. %0hich ha, heen nidelc d"cribed and cutild he misleadine to nom->cientist~. An h.rt-VCED>upil(Wt<•c<us~ presentinea"<cien- ocertchelminema,jorit~ofrespondentsdgreed titic con-rn>u~ ab lut the re:dit,V nnd datleer of that there Ncas nn clear ecidence in the climate enhanced ;.n-eenhou~~ waizninL. Colleaettes nho record nf the last 100 pears for enhanced green- %c()rke,l ()it the rep,rt had cumplained that it< house wmTning clue to human acticities. Nearly "PnlicN.makers ~ummtu;c" did not aectn•atelc all respondents espres<ed;kepticismabout the repredent the conclusinm in the repnrt it>elC. adequacc of the glohal climate modeLs (GC.lls i And jnurnalirtd amd bureaucrats presumabl%- u>ed to hredict future climate warming. read unl}dtrstintmurc, not tht• rtither technicd ()ther independent ~urtecl support these -tnu-paet. report. tindine>. For example. a Socember 1991 Gaflup The=unev results were remarkable. Of m-er poll of-4nu members of the .american Metenm, 30 scientists who re=ponded.'d'3 sip~•eed that the logical tiociet,v and the American Geophysicel lune 1992 > 35

Current models to not jibe with the climate history of the last 100 years. I"nion utcti% -elY invol~old in )rlobal climat,• reeearehi re, pon( la•, I t. ~ the , lue>tion: li„ }'" n think that ,elobal ucera¢e temperature" hace ittcrea' ed rhn•inc~ the pa, t luu }eae~ and, it,oi i, the c-urnline «'ithin the rtmee ut' natural, nuu- human-indueed t7uctuutiuu° The poll faund that nnl% Ill percent beliececl that human-Induced global warming has occurred. t;reenpeace International also sune}'ed : ci- entia, %\'ho worked on the I PCC report. A>ked whether bu,ine~s ~t:-u~ual-poticies might insti- gate a runa~caygreenhouse effect at some iunspeciiied i future time uulc 1:3 percent of the 113 respondents thought it "probable" and :iC'1 percent "po.aeible." But .}S percent said "proba- bl}- not"-far from a consensus. Jeremy Leg- gett. Director of Sciences in Greenpeace Inter- national's Atmosphere and Energ}' l ampaign. described this same ,tu•vey' as revealing "an as- ;: et poori}' expressed tear among a growing number of climate scientists that global ~carm- ing could lead not•iust to severe problems but complete ecological collap<e." These SurVeys all guaranteed respondents' anon}miq•. although >ome did ;ign their names. But this Febtuarc. SEPP «ent a step further and contacted some a00 atmospheric phcsicists and meteurulogist: tmost of them derving on technical committees of the American Meteoro- logical 5ociett•) and asked them to publicl}• endorse a strongh•-worded ~tatement (see the facing page) expressing concern that policy ini- tiatices being developed for the Earth Summit were being driven by "highlc uncertain scientif- ic theories." One of those «ho replied objected• [our wanted change:+, but more than 50 put their name; to the ~tatement. These surcey's all confirm that most climate scientists believe that some •lobal warming meic he uccurt•ing• but that eata±trophic prediction, are tmsupported by the scientific evidence, and that predictions of disaster are based on Yet-to- be % alidated climate mode<. But \chat do the ~url'e', 'I mean in terms of greenhouse «-atmina': Science is not democratic: truth is not at•t•iced ut ht• cote-The surcet•s tell un that there are still unans%cered questions that need to be settled by additional research before drastic and far-rettching policiee are undet•taken.And there i~ tinm fot• this re~earch. Model shortcomings Hu«' can we tell if' human activities are hacing a significant effect mt the gh,bal em'irontnent. eithm• good or had'.' There :ue reall}' onl}- t uo methods available: one is theorc-caicuiating the expected effect. baseii on some model of the earth's atnwsphere and at.<~oc•iated enciron- ments loceans• biosphere crcohphere or even litho: phere I. The other is entpit•ical-it t•equire: an eNamination or data based un actual obSer- % ationa of the anm,.pinere our =,,me utlter enri- rnmmental-parametern lilce >ea i<-rel ~ n. Ice "lke•r. If theoty antl ub<ercations the•n ue can he contident that the theurtt-; ali(l;mtl that it- ~ predictions are lilcelc Go he c~~rt'ect Ii tht• t%n~ metlmcls do not aerea. then trw th~rr\ tttiou- could he faultc, or the theot~incomptete, or both. This is the conclusiun that Iovic demant6 when lce are told that an e~rnt i~ ',~or=e than expected.•' After all. espectationn about the future ean onh' be based on theot~'. AV'hen ob,er- vations and theory cfi±avree• the theor•: cannot be uaed to forecast future ecent,. Any theory that attempt, a, explain the effectc of human intercention- and prelict future changea mult ine~itablv he hased un a model-a much sunpliiSed mathematical descrip- tion-uf the atmoaphere or other relecaurt enaironment. There is no ailte•natice. "llodeld are better than hancl-tcacing.•' ~avz, Stephen Schneider of the National C'enter ior dtm,l- spheria Rerearch. und an ardent proponent ~,[ globad-warming theories. But thuAc much better:' A good model uill incorporate tito'e teature"ot' the atmosphere that zu•e impurtaut, out lea~e uut those that are nut. Tlte model builder ha: tl~ decide what i= intportant arni \chat i> unimpor- tant-and therebc hane_ the tede. Ideally, one ~~rould like to ealctdate the charac- teri,tice of•the aanosphere at ell er}• point in space with the flne-t pod,ible re>olution. But computational limits prohibit thi~. Current cotn- ~ puters procide fairly cuarse reolution. Sam- p}ing points on the glube are t;.TicallYlIN i to ,5Oo kilometers apart, still nut cLu~e enough to dis- cern cloud s}stems, ur ecen such surtace t•ea- tures as the Florida pel A-ertical sampling of the atmo~pherr Grecmd unlc at a fe%L lecelz• n'pieall}' n tlozen. rmcing front thc earth's=urface to the: n•atu1l'ilen. ,. As computingput~er incrra>~>. finm• t,,,p a•aphie detail ~cill be ineorpoeated and cdimauc models will muce clu=er to rrtdit~..-1 rimilar argument appiies to time strp~: ~ampling at hourly intervals will giee Ln•eater precision than daily intetvals. Another difficult problem incohe, how much atmo~phetie phcsic, to pttt into the niodel-hrntto incorporate cloud=. ~matt-=cxle comectiun in the atmo.phere, transport "t' u'ater capor. effect_, oPaerosoL trum air pollut(un, and hoNc tu incot•porate and couple ucean circulatiun n'ith that of the atntoypiiere. Speciali,t~ ,u•~le etdle~sh' about the~e impor- tant yue<tion.v. It is clear thm uu:'rent mutlci, du notjibe with the climate hi,tol;t4 the pa,t lnn ceatx The challenge is tu imprl,ce the mudeL: o that thec t•epreSent the aunu~Unrrerucean cir- culattion sYstem more c•lo~elil llost models nlust he "tuned•'to c'iN 'e the richt mean tenr perattu•e and ;ea: unal temperattu-e % :nia[ion,• but thec often fall ~hort ot' accut•atelY repn1- 36 Tn, Bulletin ~4 lhe dtotnic <cienli~t

• • • ,iuc•mc manc ~,1 hr•r atnu,<nhrric t,,trametet=. A nla,i"r eomponent of thr rle'nate incu:e: in t he que<ttnn ,I t «ater t'aput' anrl "teerlback." It ;s tenerallv airecd tllat nto-t •Ii the nattlrailc „cctu'rinc 8rrenlhnu,-e efeCt i> ~iue to tcatrr ca:nrn ruther thtan o; caronn ,lireci,Oe, metharte• nnd <2nt-r Ut•eenhuu-r ea=e: :~r,me e-tintntes ;,?cn-ihr',I' per~•rnt „t'the ereenh~n~e et'feot to ntlilu,t,ncl'lc tCatel' in iL~ t'al'IUtb ti,1'mr. ENacth' „-hnt h.q,pens t- 1 +cate• tat,nt•-uhich i- not un.ler ilurntm cnna•ol-a? carhon dioxide incren-e=7 ('w'rent climate mndel> demon- strate In;sitiN 'o t«•e,Ibac•k-that ir, water t'apnr reinforc•es and amplites the effect r,i increasing em'hna dinxi,le.l:lir teit h hiyher t.emper:tture "Imld~°',t-ater t-«pnr h<=tter than crol air.t But leadine atmn?pheric <cienti;t=, ?uch as Htt.eh Ell~ae~=er ~,f Lnu-rence Licermm-e National LNhorao,rr and MIT rele,ureher Richard Lindzc,n, haco urcued to the cnntrar}'• that the I'eelbuclk i> smaller and c•nuhl eten he neEn- tic.--it couhl npl,nse aml diminish the green- }lnu<e ~ iiectd nf inere•a-erl carbr•n ~lioxide. .an rxaml-dr•,d'=uch ne•gatite feedback mieht necur itincrea~ed ocean temheratm-e~ lead to incrc•a}erl ecapuratinn and inereased cloud cncer. .althnuch clouds induce cnnlinc' bc retlect- ine ~nniight hack into space, the* y can also increa?e tcat'ming h}' keeping heat in. On bal- ance, hon'etec anri a= shown Mactual nbaerca- tion. Iotcclnuds pt'mmnte cooline, In contrast, a clear eNample •,t u positive feedback is ice cot-e'. As it -hrink- ti'nln trarmine, lt--, llmlight is retlected hticB nut to :~pxce mld m, ne L, abaorheQ to tcarm the eardi further. Global observations fn thr };re:rnce nf hoth po.eititr and negatfte ieedhacks ni hnmende cnmpluxie}t hot,ean a uon--peciali't judce the ndequae}' nf0ohmJ climate morieiy.' t Ine methnd i, to examine their ero~> charaetet•i~tie=-e,~mi-[ene,r-zmrl •: tdhiathm. t'r,ndi?tene' reter= to the extent tn taltich ,lifferent ntndeler:+ uc•ree. and differ- rnce+urv rather I.u-ee in ereenhou:e wm-m- inE mr,rlyd~. ll;lrmint In'ediction: ran¢e from neL:Iir_rihh• ;n' ~mali icomluu'ed to naturxllc rIccurrin<_• }<•ur-o~-c~•;u' all the tcatt,. csuurtt•;~Ilhic-6•om LS ti. 5.1) rie,rees cr•ntii:i•wle in resl,nn,e to u dh,ublinll of car- hon di,~Xi,lo in thc atmo~l,hrrc. Ecem more In7m;;unc,•rl ;a•e the iliffere,ce, heticeen prC- aictinn-odreeionld tenl};rraturr chaneer aml prucll,itNti-m pattern'• 1'onsi:tencCaknretelx tnuon.istency-acer timc•. .an anah,q}' fnonl the related field nl' ~,zone-Iirl,irtiun re>e;nch is illustratit-e. In 1!1-,°, them'ir- I,rrdict,•,1 tlerrea,e, in sn'atn- ~phr•t'ic r,znne <~i up tu Tu pereent asa result of the pl.mne l u=e nt hie'h-t1rinE ?ttper nnic air- vratt•,\hich wnuH I n'„r luce nit rn*en nside~, A, Dissent on warming [rr (nrr• li+q1. i!u• $<i<•,rrvS' Grnvrnuri+[vNal Prdic'r! Pruirri rjg'j'prerrcnlntrd tL~..slrrtr~r.rurto.~nurrJ,nrrltrnu.e/tbrrir•"-:- rntr..v_I in fbr Cbited Sthb-s. TL,rs tnr• niurc tholt J0,<cirnil,L: rrr n rrirlr' rrn,r/r nri,lstitcrlinr, . i i rrr_iru/iurl •lIIT. S7rlr. Itrmd.+ F(„/n „rrd tl,r I r+irartcitrl u71 %rrrirrinr hnr, .~iqrrr'rl ,1. As independent sciettist, reearchine atmo,pheric:md climat~ problems. we are concerned b}the a¢enda for L-NCED. the L-.~. Conference on Environment antt Development. bein¢ deceloped hc environmental activist 2roup~ and certain political leader?. This so-called Earth Summit is scheduled to concene in Brazil in iune 1992 and aims to impose a s}-=tem of global environmental re,eulations, including onerous tases on energc ftiela, on the pop- ulatiml of the United States and other indusnialized nations. Such policy initiaticea derice from highly uncertain scientific theorie>. Tktec are based on the unsupported assumption that cata~trophic global tcarmine• follntt: from the burning of fossil fuels and requires immediate action, We do not agree. A stu-vey-of C-S. atmospheric=cientists, conducted in the:<um- mer of 1991. conlitvtts that there is no con=ensus about the causr- ni the=li~,*ht «'al-min¢ obset't'ed during the pa<t centut^,: A trcent- Ic pubiished research pape'et'en stteeects that-ttnspot cariabilit,%', ratherthan tl lisein En'eenhouse gase<, is responsible i-or theglobai temperature incrett.=es and decrea>e, reeorder9 since about 18~iin. Fm'thermmre, the majority nf scientific patticipant= in the ?ur- ee}' agreed that the theoretical chmate model., used to predict a futtu'e warming cannot be relied upon and are not vafidated b~the existing climate record. Yet all predictions are based on such theoretical models. Finall}', apicultut•alists genertlh' agree that anY increase in car- bon dioxide levels from fossil fuel burning has beneticial effects on most crops antl nn trorld food suppl}-. We are disturbed that actic-ists, ansious to stop enerptyand ecn- namic grmcth-xre pushine ahead with drastic polieies without takne notice of recent chanees in t he unde'hvle =c ience. We feo-nthat the n1=h to impose elobul regulatinn> will have cataetrophic impacts on the anrld econom}t on iobs, <tandm-d= of licina, and healtlt care, ttith the most <eaere conserlut•nce, fallinoZ upnn rlecelaping coi and die poor. theori;t,i incor}loratecl more data. these predic- tions gradualh-climini~hed• Bc around 1977, them'ists suggested an increase in ozone. But after 1978, theorists predicted a modest ozone decrease. Current them-c, hotre~-er, holds dtat nitrogen nxirles ttnuld prntect ozone hc Cotm- teracting the ozone-de~n'nyinE* properties ,~t chlorof7uorocarbonr. The enncept of enhancecl!_-reenhoa e a'artnine has been unclergoing similar chwti,e- Aithoueh mndeler~' predictiun:; have necer c'haneerl from positive to nepxtiveh the maeni- turle ot'the predicted ch,me'e heetm to dro}1 a> gt'eenhotl+e tcatRnin,u: models itumimated nceau cu'culatinn. tile effects of sulfate pollutionI anti a better under~rmdin, ot' eloud formation. 1lost =taatlin- has been the <lotcnm'adine of the c'een- houde effect on sea let-el rise. tlnl}' a few cear~ an.>onle modelers ibrecu:t a So-tnot rise in>en Juoe LID? 37

levels: current IPCC estimates range from a three- to 11-inch rise, far short of'catastrophe. Levels of carbon dioxide have increased by 25 percent over the past 100 pears; and all green- Ambiguous conclusion The 1990 report qftke httergorerrunentaf Panel on Climate Change (LPCC) note.s that enhanced hunlan-induced global warminghas not yet been retiabtydetected: Because of the strong theoretical basis for enhanced greenhouse warming, there is considerable concern about the potential cli- matic effects that may result from increasing greenhouse gas con- centrations. Hoa-erer, because of the many significant uncertainties and inadequacies in the observational climate record, in our knowledge of the causes of natural climatic cariabil- itp and in current computer models, scientists working in this field cannot at this point in time make the definitive statement: "Yes, we have nowseen an enhanced greenhouse effect." It iz, accepted that global-mean temperatures have increased oeer the past 100 pems, and are now warmer than at an}'time in the period of instrumental record. This global warming is consis- tent ttith the results of;imple model predictions of greenhouse- gas-induced climate change. However, a number of other factors could hace contributed to this warming and it is impossible to prove a cause and effect relationship. Furthermore, when other details of the instrumental climate record are compared with model predictions, while there are some areas of agreement, there are man' v areas of disagreement. The main reasons for this are: 1. The inherent cariabilitc of'the climate system appears to be sufficient to obscure any enhanced greenhouse signal to date. Poor quantitative understanding of low-frequency climate cari- abilit}- (patticularly on the 10-100 pear time scale) leaves open the possibilitp that the observed warming is largely unrelated to the enhanced greenhouse effect. 2. The lack of'reliabilitY of models at the regional spatial scale means that the expected signal is not yet well defined. This pre- cludes an~fuTn conclusions being drawn from multivariate detec- tion .<tudie.<- :t The ideal model experiments required to define the signal have not yet been performed. What is requiretl at•e time-dependent sim- ulations using realistic time-dependent forcing carried out with fully coupled ocean-atmosphere GCMs [global climate models]. -1. Uncertainties in, and the shortness of available instrumental data records mean that the low-frequency characteristics of nat- ural cariabilitvare rirtuall ' ~ unknown for mam• climate elements. Thus. it is not possible at this time to attribute all, or even a large part. of the observed global-mean warming to the enhanced greenhouse effect on the basis of the observational clata cun•enth' available. Equally , however, tse have no observational evidence that conflicts nith the model-based estimates of climate sensitic- ity. Thus. because of model and other uncertainties we cannot preclude the possibilin• that the enhanced greenhouse effect has contributed substantially to past warming, nor even that the greenhouse-gas-induced warming has been greater than that obserred, but is partly offset by natural cariabilitY and, or other anthropogenic effects. .I. T HuuYhton, G.d. Jenltit, an~L7..I. Eptu mun . ed=. (7~~~~otr t'Oiurpe. Tfie (PC(' Sneitilir d.varn.=ruenL CamhiidQe: Cambddg Cnicetst.Y Pre~'.14ry p, :!A house gases tai<en together hace increa=ed car- bon-dioxide-equicalent levels bc anout.iu per- cent. In other i% rot•ds. " e have already gone I halN -aY towartis the greenhouse ga~ doubling ~chich is often taken as the benchmark for model ~ predictions. one would ha% e expected a warm- ing of at least U.76 degrees centigrade by now, and more likei}' a rise of 1.5 degrees centigrade, according to the predictions of manc models. The realitY is quite different. Since 1880. tem- perature has increased only 0.5 degrees centi- grade, and that primarily before 19-1C4-that is, before appreciable greenhouse gases «'ere added to the atmosphere. The global climate record during the last 50 peats sho%rs no appre- ciable temperature increase at all. In the United States. the warmest years were in the 1930s, not in the 1980s, based on the anal}•ses of the U.S. Climate Center in 1she~ille. North Carolina, which uses the U.S. observational network and also corrects for the "urban heat island" effect. Many climatologists identify the pre-1940 ts-atvnntgwith a recocet~v @nm an amomalous cool- ing of the precedingcentmiesg knoirn as the "Lit- tle Ice Age." Cetainl}'. the observed global cooling that inspired a fear of a coming ice age in the 1970s is not in accord ~cith greenhouse models. Adding to the problem. a\orember 1, 1991 S<d- etrce article bc Danish meteorologi~ts, E. Ftiis- Chtistensen and K. Lassen. shows that average tempet ature and solar actit-it' v ale closei}• cort•e- lated, as measured bY the length of the sunspot• c}~cle. If this is cotrect, then little or no ~carming can be ascribed to the greenhouse effect. The most appropriate data for validating cur- rent climate model: is the global temperature record from satellite microwave observations, which began in 197 9. This is the only nvl}-globai and continuous set of data acailable. with heat islands and other surface distortions of temper- atures eliminated. Contrary to an expected U: I degree centigrade rise per decade. based on cur- rent theorc, the satellite recortl shom s no sienif- icant temperature trend. Trend or fluctuation? Temperature observations geneal]r show large fluctuations from unknown causes. Some of the fluctuations maa be due to natural influences, such as volcanic acticitc. Other fluctuation., are a consequence of the chaotic behavior of the sys- tem itself, imoh-ing feedbacks. both positive and negative. on many different time scale~. These fluctuations make it difficult I ii not impos- sible) to identifY small long-term trends caused bv human ac*.icitie_. Interannual and longer- term fluctuations of global temperatnre exceed those predicted by many greenhouse model calculations. Disentangling natural changes from a green~ house effect enhanced by human activities will 38 The Hulletin nt':he Atumic icientirtr

• • • reyuit•e detailed examination and more refineci imiicatot•,, thtut ~impl}' acerave global tetn- perature. The climatoloaieal rec•urti may contain -pecitie "tingetlnint> ' t hat iu•e unique to ~pecitic mecham,snu otchanee. But• a~ pointetl out h' Hugh Elhae: ree neither the observed latitude. altitude. or hemi~pheric cariatiuns ni glohal ~.carmin~ in the I~ast centur}' are in cjet-eement ~cith U't-eenhou>e dtepr}. Ecen tite 19t>ti IF('C report on climate change affies on that is =ue. The report eaYs that the data are too ambigttous to fully atpport gt•een- house theor}'. \ecertheless,the data are not inconsistent tic-ith the greenhouee effect. See "~mbieuou? ~unclusion:' facing page.i l)ne re±ult ~,f detaiied climate studies was, the dkcove;t'that C.H. temperature records reflect a warmine trend mainlc for night-time temper- atm•es: that i~, there i:+ a dect•ease in the ilaY-t, .- nazht temperatw•c r:mL'e. Data )n the same effect.- in the hn'mer ~ociet Cnion and China ha% e nmc iieen puhli.heL If *reenhou<e ea, increa'e> n-e•e tht-cau,o ofthie increa~e in night n-mpet•aturNc<• dun't knottduu-then the ohtioua henetit, to am•iettlture tcotdd maln• thi~ climate chanee a plw rather than x ntinu>. This aitutunent is -tt•engthene.i bc the expecne tion that the pre•~ent interglac•ial itcauTni period• tt'hich stat2etl iu•ound 1] ,x N i}-etu^.+ ago, muat snnn cnme to an end. With n t•eneiceil ice a^e "on the hotizon: " t he po,sibilin- ot eneenhouee Wm-ming takes on a relaticel}' beneticial interpretation. What to do R"e can sum up pre1ent understanding of the enhancel inreenhouse effect as follmts: espe•t, Iseneralh' aeree that the expected doubling uf L-treenhwu~e vaye< in the nest centurc «-ill not cau<e a 1cere.,rextastrnl,hie ic:u-mine. Many <cienti,t-autd mo,t ac*ricultw'al experts «auld ut'eur that u hqttzcr tirntcin¢ ~ea=on and .1nhancul etu•hnn dioxlde let'el+ are. un the \cltole, beneficial to crnps, tchich require both warmth and carbon dioside to tiom•ish. It is also zgreed that it tcill take Yeat:l, maybe a decade ~n• more, hefure satellite data can e=tablish a definite climate treml and befm•e them•etical understandine ~~t the atmosphere is comprehen- rice enoueh t, ~ allow uccm•ate predictions. This uncertaint. rai~e= an important but cnntrucersial tlueetinn. Hotc long,hould goc- ernment= Vcait heDu'e taking drastic poliQ' action<-il'«'e cannot now identify a long-term climate n'end' And if a trend is e'entualh' iden- tified• hnttcan %ce he sure of its cause-nr tt-hether the cause is man-marle.' Answers to the:+e questions are cnmial if the pt•nposel polic.~ actiom hace :t negaice impact on nther human Nalue~-economie tcelfare, Itealth, and life expectanc}-. Em'irnnmental pre<stu•e gtroup- often~a}that "tce cannot afford to play Russian rualette with the planet's tuture." Put this 6an uppeal to emution, instead ofthe caretid mialy-.4i< that is called fur. Deaqine action i; not ml imitation to dintster. a, often claimed. C'ulculation, hY atnw-pheric >cienti<t Michael Schle<inger o[ the Cnirersit~~ o4' Illinois, a climate modeler, clearl}' dentmt- strate that po±tponing control:; on carbon clios- ide for eten a decade «-oultl have no noticeable impact ou the next centurc's temperature trends. Moreover even the most drastic limits on carbon dioxide emiesion, by indunttializecl cottn- a'ies «rould delac the doubling of green'nouse gases in the next century b}' onlr a few ~ears. A contributing factor to global warming i< thouKht to be popuLation growth and economic decelopment in Third li-ot•Id nations. tchich will ,oon determine the growth rate of greenhouSe ~tase. Carbon dioside will increase because ol fue[ burning and forest cieat•ing, and methane einittecl from rice padclier antl cattle rai%inll tcill increase. It is tcell t•ecngnizecl. but deldnnt+uidl that controlling tlte,e actititie< and titu- con- ilt-nmingLilllons tu continued p,eertn dtarc:r ti,,n anrl niieet'c-Or to dracnnian resn-ictinn~ nn population crmcth-c~rould rightly he regoudel uz immoral and as a form nt"'ero-imperiali~m." [t' greenhouse tcarming ahould bvcome a problem, two reports from the U.S. Satlonal Academy t,f Sciences during the past }ear han c- ~uggestecl that mitigation of the effect, Of cli- mate change. or atl•justment to the change, is quite pussible, and not prohibitivelp co~th-..a wide range ot technological options can be put'- sued. These include planting u•eea un e large ,cale tn replace Ing'ged or bmned fo1'ert>, and te-tilizing the ocean with trace mttrient= f,m plankton grotcth to Seluester and thu=reducaauno?pheric• carhon dioxide. Using satellites t~creen nut some incoming solar radiation al~- ha: been :uggeSted. Such schemea ma}' +otmci fm•fetchetl. but at one time so dicl manc other futuristic prr,iects that have since been realized. Drastic, precipitous, and eupeciallY unilateral :+tep, to roll back carbon dioxide emissions ;mm ply to delay an unlikelY greenhouae tcarming will imperil living etandards-and even poiitical Preedome-in the inclustrial tcorleL Yale economist 1Cilliam \rn•dhaus, who has been tr.N -- inz to deal quantitativel,c with the economfc> nf this issue, has pointed out that "those tchn ar2ve for ~trong measure> to slmc greenhou~e tcarttr in2 have reached their conclusimt nithout an.N cli?ce•nible analcsis of the costs and benetits." At this staee. there are ma,jor ttncertaintier about ereenhonse them-Nt about the effect~ oPa Itossihle tctu•mine, and about the economic and hoiitical impact ufha=t}-, ill-considered policie-. Does it make>ense to wa,te .~100 billion avear on tlhut i, still a phantom threat %chen there are so man}-pt•e<sing-and reatl-problem> in need ot're=owcec.  Drastic steps to roll back carbon dioxide emissions will imperil living standards. .R.m. t~.r~~ 39