Collection @0£¢-VowLeumana Review 2234 Box EetEcls of Wenfo ns Gw The Werth il i. 23 February 1955 ION US DOE cn GY 396 U.S. ATOMIMONE MEMORANDUM TO DR. JOHN VON NEUMANN O a4 BJECT: 108529 Effects of Large Yield Thermonuclear Weapons Upon the Climate of the World (U) 1, %In the fell of 1952 and 1953 the effects of large yield weapons upon e climate of the world were studied. (See inclosures 2 and 3). Since that me, however, additional information hes been obtained from atomic test oper akions, especially from the study of rediosctive fallout (see inclosure 4), which may throw some additional light upon this same subject. I have summari below for your ready reference my present thoughts on the effects of nuclear detonations upon the climate of the world: a, It is believed that if a total of 500 to 5000 megatons are conte. barst on dry land or underground, the solar radiation reaching the earth may | reduced by 10% (this refers to the 3000 to 7000 Angstrom region of the soler ws ectrum). The bombs must be in the yield range of from 10 to 200 megatons e: ry The use of 50 to 100 MT bombs would enhance this effect. If the yield of eac! "> bomb is very much less than 10 MT the majority of the particles would remain : & the troposphere or in the lower stratosphere thus producing a more transient effect. For yields from 50 to 100 MT, a substantiel portion of the cloud wil: be above 80,000 ft, and the maximum height may go above 150,000 to 200,000 ft. thus producing a more permanent effect. 2. The following calculations indicete one of the methods used to arrivi at the above-mentioned conclusion on the number of megatons required to produc an effect on the world climate: BEST AVAILABLE COPY a. The specific activity of the fallout from surface burst weapons1 found to be 0.1 to 0.5 curies per gram extrapolated to the reference time of « hour after bomb detonetion. At this same reference time, it is assumed that { totel residual activity yield, percent of th® residual - time (see inclosure 4). of the first shot of CASTLE Test Operation (14 MT tote was activity he bomb It is believed that 75 to 85 fell out within 24 hours after s} This means that the total weight of matter in the at< BY AU RiTY OF DOE CLASSIFIC ATION CANCELLED ye WITH DELE TIONS /OC cloud due to fission procupts, bomd material and crater material was in the re of from 6 x 1012 to 3 x 10 gm. This sppears reasonable since it is believec that the CASTLE Bravo crater represents a mass displecement of approximately 1 x 1015 gm, It is believed that the crater dimensions are accurate within a factor of 2, 30of the NY Operations 1 7 1 4 HH,Gaa NOIS Orrice adNO shows that approximete he totel activity of the IVI Mike or CASTLE Bravo shots coule be foundthroughout the world due to long te: fallout. loft. This means that It is therefore beffeved £ the totel activity of the bomb remains reasonable to assume here that at least 5% of the soil debris sucked into the cloud remsins aloft in the stratosphere, This means that 3 x 1011 to 1.5 x 1012 gm of finely divided soil debris remeins alc in the stratosphere from each 15 NT bomb surfece detonated on dry lend. Inci- dentelly, this represents spproximstely 0.0015 to 0.0003 of the total materia) displaced by the creter. There is some evidence that the distribution of particle radii at such heights (above 60,000 ft) is in the order of 0.5/(see page 2, Incl 2). bore, ai RatRIREEpRE SE C5-40959 |