A study of the possible effects of energy, debris, and radioactivity from nuclear detonations on weather and climate. The large quantities of debris injected into the troposphere and stratosphere seem to be the most likely agent of modification. This debris could act in several ways. It might provide an additional source of nonsoluble condensation nuclei and ice nuclei. As ice nuclei, it might increase the thin cirrus clouds, thus affecting the radiation balance, or it might increase the efficiency of the ice-crystal mechanism of precipitation formation in supercooled clouds. The very fine dust particles left behind in the atmosphere, if abundant, would interfere with the radiation entering and leaving the atmosphere. In addition to the effects of the debris, extensive fires ignited by nuclear detonations might change the surface characteristics of the area and modify local weather patterns. Despite the possibility of such changes, however, a more thorough knowledge of the atmosphere is necessary to determine their exact nature, extent, and magnitude.