Document Type


Journal/Book Title/Conference

International Geophysics Series




Anton L. Hales


Academic Press

Publication Date



It is an understatement to say that people are confused about cloud seeding. While it has been called "the crime of the century" and outlawed in Pennsylvania, the governments of the dry, western part of the United States continue to spend tax revenues on cloud seeding to increase water supplies. During the past five years, I have talked with officials responsible for decisions regarding cloud seeding programs in about 15 states of the U.S.A., in a dozen other countries, and in the World Meteorological Organization. Some of the officials involved are experts in atmospheric physics, but most are not. Members of the latter group have expressed a great need for reliable, concise information about how cloud seeding works and what it does to the weather. This book is addressed to them and to all students of the environmental sciences in general and of the atmospheric sciences in particular who need answers to those questions. The book should be useful to graduates of a university program in any of the physical sciences or engineering, and to upperclassmen in those subjects. A review of basic cloud physics is provided to make the presentation meaningful to persons with only minimal preparation in meteorology. The presentation of statistical methods used in the evaluation of cloud seeding projects presupposes no special knowledge of statistics on the part of the reader. The subject of weather modification has been studied by meteorologists, physicists, chemists, statisticians, lawyers, ecologists, economists, and sociologists, each from a different point of view. Disagreements among these groups sometimes obscure the larger issues. For example, the debate that followed the publication of the Final Report of the Advisory Committee on Weather Control in 1957 was dominated by statisticians. The real question of whether or not the Advisory Committee was correct in concluding that cloud seeding had increased precipitation in mountains of the western U.S.A. was obscured by debate over such details as the relative merits of square root and gamma transfonnations for nonnalizing rainfall statistics. This book attempts to present a general view of the subject but with the emphasis on physical rather than legal, economic, or sociological aspects. The current state of the art is described, and some,promising areas for additional research are pointed out. Underlying the entire book is the author's conviction that the evidence on the effects of cloud seeding can be sifted to yield a coherent picture that is consistent with the laws of atmospheric physics.


This work made publicly available electronically on May 21, 2012.