MEHO TO DR, V c. NEUMANN (cont'd) a According to Tables I of inclosures 1 and 2, approximately 2x 10°) particles are required in the stratosphere with radii of 0.5<to reduce insoletion by 10% when the sun is at the zenith, This represents 3 x 1013 gm of finely divided dust and soil debris in the stratosphere, Our calculations in peragrapbh b above showed, however, that each 15 MT surface detonetion gtroduces more or less permanently into the stratosphere 3 x l tol.5x1 gn of finely Givided soil debris. This means thet 20 to 100 bombs of 15 KT each are required to reduce insolation by 10% for the cese when the sun is at the zenith. 4s indiceted on page 19 of inclosure 3, changes in the soler zenith distance reduce the insoletion excessively. Hence, for the average zenith distance of the sun in our latitudes, the insoletion may be reduced by 20% or greater for the above mentioned amounts of stratospheric dust. However, there is another effect which works in the opposite direction, and this is the scatter of soler radiation which may be predominantly in the forward direction, specielly for particles in the size range of the wave length of light. This ould require the presence of more dust aloft. For this reason we assume that he above-zentioned number of required bombs should be increased by a factor f 2. Hence, 40 to 200 bombs would now be required if the yield is 15liT, herefore, a total of 600 to 3000 MT would be required to reduce insolation by 0%. It should be noted that by "SUNSHINE" estimates at least 25,000 MT would e required in order for the world population to reach the Strontium 90 tolerance evel for the world populetion. Thus the climate effect may precede the carcinoenic effect. ad. It should be noted that if the bombs are exploded in the air, there ill be very little dust kicked aloft into the stratosphere. Therefore, the bove calculations apply only to surfece and subsurface shots on dry lané. It s not clear what type of effect shots over water or under water would have upon he climete of the world. My present discussion applies only to the effect prouced by soil particles. e. Finally one mey be permitted to conjecture that if there is the ppearance of a blue sun due to uniformly distributed, submicron stratospheric dust, the probebility may be high that an effect will be produced in the hemlspheric or world surfece temperatures, If the dust remains in the stratosphere essentielly unchanged in concentretion for a long period of time (1 to 10 yeers), it mey be worthwhile to look for the beginnings of a moderate ice age. 3. Thie memo classified SECRET-RD in accordance with peragréphs 23b and 56, AFR 205-1. an gen Wo Verein. NOR4IR M, LULEJIAN Lt Colonel, US4F Atomic Operations Division