PROSPECTS FOR WEATHER MODIFICATION A. F. Butchbaker During the 1930’s and 1940’s, several import Can man willfully change the weather around ant concepts or theories were developed regarding him? This question has puzzled man for centuries. the precipitation process. In 1933, a Swedish mete If man could control the weather, he would be orologist, Tor Bergeron, advanced the theory that able to reduce some of the damages and conse rain in appreciable amounts could be released quent economic losses caused by hurricanes, light principally by the presence of ice crystals formed ning, hail, and fog and to benefit society by en in or transported through water clouds. Five years hancing precipitation at the right time and place. later, a German physicist, Walter Findeisen, re There is much evidence that man can intentionally confirmed this discovery. This theory formed the modify or possibly eliminate many types of weather basis of present day techniques of seeding super hazards or will have the capabilities to do so in the cooled clouds. near future. In 1946, two General Electric Company scien HISTORY OF WEATHER MODIFICATION tists, Vincent Schaefer and Irving Langmuir, dis The history of weather modification has gone covered that dry ice caused the formation of ice through several eras. First was the mystical era. In crystals in miniature super-cooled clouds and the beginning, man tried to influence rainfall by thereby triggered the precipitation process. Shortly hope and faith, magic and ritual. Many primitive afterward, Bernard Vonnegut, a co-worker, demon societies have practiced some type of religious or strated that smoke of silver iodide crystals would ritualistic rainmaking. The ceremonies and rituals accomplish the same results. have varied from dowsing holy men with water to The 1950’s brought on the rainmaker era. Dur burying children up to their necks in the ground ing this era there were many operations in the in hopes that God would be sympathetic and drop western United States, and a few in the Midwest tears from the heavens. Witch doctors and medi and East, which employed ground based silver cine men in some societies continue to perform iodide smoke generators for cloud seeding to mystical rites in hopes of increasing rainfall. attempt to increase precipitation. Unfortunately, In the 1800’s it was observed that the use of few programs were used to evaluate the effective explosives in some of the great battles, such as ness of the seeding operations. Meanwhile, the in the Civil War, caused significant rains. However, drouth in many areas of the country and the experiments in rainmaking based upon these theor claims of some of rainmakers and criticism with ies proved inconclusive. Another belief focused in the scientific community prompted Congress to around the possibility of increasing rainfall from create a special committee to study weather con convective currents caused by forest fires. An trol. In 1957, this committee reported on the state American meteorologist, James Espy, recommend of the art at that time. It found that precipitation ed that farmers burn brush and timber in dry was probably increased 10 to 15 per cent by seed weather to stimulate rainfall. Other early scientists ing storms during the winter and spring months suggested the use of extremely cold substances, in the mountainous areas, and supercooled stratus- such as liquid carbon dioxide or liquid air, which type clouds (low hanging clouds) could sometimes upon release into the atmosphere would result be dissipated by seeding with aircraft. There was in condensation and precipitation. These early at some theoretical basis at that time, but little exper tempts were on a hit-or-miss basis with virtually imental proof that lightning or hail could be sur- no knowledge of the physical principles of pre pressed. cipitation. In the 1960’s, the scientific community became Dr. Butchbaker was associate professor, Department interested in the possibilities of weather modifica of Agricultural Engineering. tion. This was prompted partially by seeing the 13 dramatic effects of artificially modifying clouds. Fog Dissipation. Also, two reports were released in 1966 which in There are two types of fog: cold fog, where dicated increased scientific and governmental in the water droplets are below 32 degrees Fahren terest in weather modification, one by the National heit; and warm fog, where the water droplets are Science Foundation (12), and the other by the above 32 degrees Fahrenheit. Cold fog dispersal National Academy of Science (21). These two re operations are based on the physical principles ports were optimistic about future weather modi that super-cooled water droplets cannot remain fication. liquid, but must be turned to solid crystals below During the past decade, significant changes -40 degrees Fahrenheit. Thus, dropping dry ice occurred which created an attitude making possi from an airplane or injecting liquid propane from ble a more rational and systematic exploration of a ground unit makes the cold fog precipitate out the potential for weather modification! These into fine crystals. changes were derived primarily from (1) formula Another cold fog dispersal method employs tion of more complete theories of the atmospheric helicopters to fly slowly across the top surface of processes, (2) the use of high speed digital comput a cloud or fog deck using the downward action of ers to solve, the complex mathematical formulas the rotors to force clear (normally drier) air from of the atmospheric processes, (3) the ability to mea above the cloud top down into the cloud deck. The sure and observe the atmosphere with radar tech air, upon descending, entrains and mixes with the niques, meteorological satellites, and airplanes, cloudy air and causes evaporation in the cloud. plus many other advances in instrumentation, and This method has been used to create clear trails in (4) significant advances and statistical procedures stratus clouds and fog over Thule Air Base, Green for resolving questions of cause and effect relations land (11). and field experimentation. Warm fog dispersal techniques have eluded researchers for many years. Only recently has PRESENT STATUS OF warm fog dispersal become a reality, Warm fog WEATHER MODIFICATION dispersal is based on the principle that when small To look at the present state of the art of water droplets are combined into bigger droplets, weather modification, different scales ranging the number of droplets per unit volume of air be from small-scale to large-scale weather phenomena come less and visibility correspondingly improves. might be considered. Moreover, when the water droplets grow to a size Micro-climate Alteration. where they cannot remain suspended in the air When one looks at the climate near the they will fall out in a fine drizzle—again improv ground surrounding plants and animals, one is ing visibility. Hygroscopic materials, such as salt concerned mainly with preventing frost, suppress (sodium chloride), are generally used as a seeding ing evaporation, or reducing the effects of wind agent for warm fog. The material has been seeded or temperature. The most important methods of by airplane and also dispensed through ground- influencing soil micro-climates are irrigation, based fog machines. A California airport has drainage, mulching, soil tillage, and windbreaks. found about 70 per cent success for this method Frost protection of plants can be performed (10). by using several different methods. A popular Precipitation Increase. method of frost protection is using a sprinkler In 1966, the views of the Panel on Weather irrigation system. Heat is released when ice forms and Climate Modification of the National Academy around the leaves. The released heat reduces the of Sciences (21) on the prospects of modifying possibility of the temperature becoming cool clouds and storm systems to stimulate precipitation enough to freeze the leaf. Other methods of frost were summarized: protection include the use of heaters or wind “There is increasing but still somewhat machines. ambiguous statistical evidence that pre There are many ways to control snow move cipitation from some types of clouds in ment due to wind. Vegetative cover, dead or alive, storm systems can be moderately increas is one of the most effective and most economical ed or redistributed by seeding techni controls of soil and snow movement. Windbreaks ques.” provide a formidable barrier to the wind. Other Results in South Dakota (16) have established barriers are crops in narrow rows, snow fences, beyond any reasonable doubt the ability to modify solid wood or stone fences, and earthen banks (20). individual cumulus clouds or portions of continu- 14 ous cloud decks. In many cases, modification treat ually dispensed into updraft regions from airplanes ments of the clouds were,followed by precipitation by burning the silver iodide-in-acetone solution or from the base of the cloud to the ground. The re by burning flares containing silver iodide. In Rus sults of this project indicated that cloud seeding sia, artillery shells containing silver iodide are produced significant increases in rainfall, especial fired directly into the hail formation zone of the ly when cloud systems moved from the southwest. storm. Reviewing projects over the past 10 years (5, 7, 16), seems to indicate an average increase of 10 to 15 per cent in the amount of rain reaching the ground. Note that this figure applies only to an in crease in rainfall from clouds which are already raining or late rainfall from air masses which do not contain a natural reservoir of water vapor or from clouds which are too shallow to contain the necessary liquid water content. Rainfall patterns and drouth cycles are pro duced by variations in the global circulation of large scale air masses. Cloud seeding is ineffective if the upper level air masses are dry. The answer to drouth problems will not come from cloud seeding, but will require means for influencing the large-scale motions of moisture- bearing air aloft. Also, it may be possible that in creased urbanization and the accompanying air pollution may be affecting large scale weather patterns, especially in the northeastern United States.
HAIL SUPPRESSION 3 Annual losses due to hail in the United The buildup of a high cloud formation that results in a S6Vt rfuhai st,ornV Research *s searching for ways to pre States have been estimated to exceed $100 mil- vent the costly devastation of a hail storm. hon (15). The most serious hail damage occurs in - the Great Plains area. A hailstorm is a severe storm containing vio lent updrafts which sustain large super-cooled liq uid water contents in suspension at temperatures below freezing. Ice crystals formed at lower levels of the storm are driven violently upwards into the super-cooled liquid water accumulation zone where they grow by successive collisions with super cooled water droplets. When the ice particles grow ■large enough to overcome the updraft forces or are turbulently tossed out of the updraft, a hail- fail resuits. The exact mechanism of hail formation is still not well understood, although through radar and airborne sensing devices scientists have gained considerable knowledge of hailstorms. Hail modification attempts in the United Sta tes, Russia, Switzerland, Argentina, and Kenya have utilized silver iodide as a seeding agent. It is hypothesized that silver iodide serves to freeze the liquid water in the accumulation zone of the storm and no longer make it available for ac cretion on other ice particles passing through the Farmers are all too familiar with the aftermath of a severe zone. In the United States, the silver iodide is us shower of hail, and the damage that can be the result of nan on a field of ripening grain. 15 Many tornadoes possess a high amount of Evidence to date indicates that cloud seeding electrical activity, as evidenced by nocturnal tor for hail suppression does have an effect on hail- nadoes having luminous characteristics and by fall (14). Hailfall may increase under light seeding sudden electric and magnetic field changes near rates (under 1,000 gms. per hour per storm) and be tornadoes. It has been hypothesized that the con reduced by heavier seeding rates (over 2,000 gms. trol of the electrical heating mechanism of a tor per hour per storm). There also is evidence for nado requires primarily the shorting of the elec rainfall augmentation from cloud seeding for hail trical energy to the ground by another less harmful suppression; no evidence is known that indicates path (3). Some possible control methods might rainfall decreases due to the seeding activity for include: (1) distribute a fine wire chaff in the seeding rates greater than -2,000 gms. per hour per cloud, shorting the charge to the ground, or (2) add storm. an electronegative gas such as Freon 12, as well In Russia, a hail suppression program report as smoke particles, to change the electrical con edly reduced crop damage by 80 per cent compared ductivity of the air. with nearby control areas and with previous re The approach to tornado modification has cords (18). Similar results were found for a hail sup been mainly confined to laboratory simulation and pression program in southwestern North Dakota theoretical computer modeling. There is hope that where cloud seeding reduced hail intensity by 30 severe storms which spawn the tornado may be to 60 per cent in the seeded area compared with amenable to treatment rather than the tornado south and west unseeded areas (1). No significant itself. A more feasible approach would be to pre changes in precipitation were found for the seeded vent the storm from reaching the proportions of or unseeded areas in the North Dakota hail sup tornado generation. pression program. In Kenya, hail damage to tea Hurricane leaves has been reduced by 40 per cent for seeded Under Project Stormfury, a joint ESSA - Navy cases compared with unseeded cases (8). program involving large-scale hurricane and cumu Lightning Suppression. lus cloud modification research, experiments are being performed to test models and mechanisms Lightning is the greatest single cause of forest of hurricane modification. The intent is to pro fires in the western United States, causing severe duce warming in the outer zone of the hurricane losses of timber, wildlife, watershed, and recrea eye wall by releasing latent heat of fusion from tional resources (17). Massive seeding of lightning the seeding and thus alter pressure and wind dis storms with silver iodide by the U. S. Forest Serv tributions. Research is being conducted to discover ice has indicated a significant reduction in cloud- the mechanisms of hurricane development and to to-ground lightning strokes. Over a three-year per find a critical ingredient for possible modification iod a reduction of 32 per cent in cloud-to-ground while the hurricane is in its formative stages (22). lightning was found for seeded storms compared Inadvertent Weather and Climate Modification with unseeded storms (22). The U.S. Army has ex Unintentional alteration of the atmosphere by perimented with the release of millions of tiny man is a serious problem. Man has been using the metallic needles from an aircraft into a thunder atmosphere as a dump without understanding the storm and observed a significant reduction in elec possible consequences. For instance, the amount trical field gradient in the vicinity of the charged of carbon dioxide in the atmosphere has increased cloud. The practicable reduction of lightning by 10 to 15 per cent in this century, primarily from strokes from clouds appears to be possible through increased burning of fossil fuels. The increased modification techniques in the reasonably near concentration of carbon dioxide has possibly creat future. ed a “greenhouse effect” and is thought to have Tornado caused an increase in surface temperatures of about Tornadoes are the most violent storms known 0.2°C since 1900. Other inadvertent changes in to man. Their time on earth is short, and their weather may arise from condensation trails of jet paths are small but devastating. Nothing known aircraft, pollutants arising from automobile and to man can presently control tornadoes. However, industry sources, urbanization effects from heat progress is being made toward a better under sources, and agricultural activities from wind ero standing of the phenomena associated with torna sion of soil, burning of residues, and deforestation does. Hopefully, scientists will find some possible or denuding the land (23). mechanisms that they can alter to modify the de Climatological studies of several large mid structive power of tornadoes. west and eastern cities have indicated urban- produced weather changes (2). Substantially great instance, an increase in precipitation may benefit er increases in annual precipitation (5 to 16 per a wheat farmer, but may ruin the crop of a fruit cent), thunderstorm days (7 to 20 per cent), and farmer in the same area. Benefit-cost analysis hailfalls (31 to 246 per cent) have been observed needs to be performed to determine economic in an area downwind from a major steel mill benefits to an area (6). complex. Social Problem Air pollution from automobile exhausts also The impact of weather modification may might account for high concentrations of ice crys reach deeply into social relationships and into tals downwind of larger cities (13). Laboratory aesthetic and spiritual values. The effects on some studies have shown that particles of lead com societies may be much more profound than on pounds can be found in auto exhaust. When these others. Some have wondered whether man really lead particles contact iodine vapors, they form lead should aim to control his environment and its re iodide which is a nucleating agent just like silver sources, for it would deny him the sense of excite iodide. Apparently, wood smoke and other organic ment and the spiritual enrichment that comes from sources, and the ocean, supply iodine vapors to trying to cope with sudden, and sometimes violent, the atmosphere. changes in the weather. Air pollution is also a threat to the environ mental health of man, animals and crop produc Legal Aspects tion. Air pollution causes losses to agriculture Weather and climate modification poses legal alone in excess of an estimated $325 million annu questions as to the existence of “property” inter ally (9). Damage to structural materials is estimated ests in weather and the responsibilities of weather to be $11 billion annually (23). Although difficult modifiers for damage to others, as well as problems to determine precisely, there does appear to be a of regulation. Many states have laws regulating correlation between certain lung, diseases and air weather modification. However, many of the legal pollution or smoking. aspects are still in the developmental stage. More comprehensive regulation in the public interest PROBLEMS may be required. Weather modification may not benefit every International Relations one. Some of the serious questions about weather By its very nature weather transcends national modification center around the biological, econom boundaries. It is anticipated that weather modifica ic, social, legal and international consequences (12). tion may require international cooperation (e. g. hurricane modification). There is also a remote pos Biological Problems sibility that one country could use weather modifi Great uncertainty has been encountered re cation to alter storm paths or weather patterns to garding the biological consequences of weather and inflict damage on the economy and civil popula climate modifications particularly precipitation tion of another country. changes. If properly controlled, weather modifica tion may furnish a means to overcome some of SUMMARY the world’s major problems, such as providing food Our knowledge of weather modification has for a growing population. However, there is an progressed greatly in the past 20 years since the accompanying possibility that imbalances may arise discovery that rainfall could be stimulated artifi in biological communities. Ecological changes from cially. There now appears to be a scientific con weather modification may result in moderate shifts sensus that weather modification is a subject of in rates of reproduction, growth and mortality of prime importance and one for legitimate scientific weather-sensitive species of plants and animals (4). inquiry and engineering development. There is evidence that small scale weather systems can be Economic Problems modified for man’s benefit. However, as the com Natural weather occurrences (hail, drouth, plexity of the weather systems increase, greater frost, floods) lead to serious economic losses. This uncertainty exists for their control. Thus, a greater has motivated many to pursue a means for modify chance for success is evident for modification of ing the weather. Weather patterns directly affect precipitation, hail, and lightning than for large many industries, ranging from recreation to trans storm systems such as tornadoes, hurricanes, and portation and manufacturing. large-scale or global weather systems. However, weather modification may not serve The present state of the art of weather modifi the interests of everyone at the same time. For cation appears to be as follows. 17 research will be needed to find the “trigger 1. Microscale weather changes can be affected by windbreaks, irrigation and local heating mechanisms.” to alter the environment near ground level. 8. The modification of tornadoes appears un likely with current technology. Intensive re 2. Cold fog can be dispersed around airports by seeding stratus clouds with silver iodide. search efforts are being made to gain a bet ter understanding of the characteristics of 3. Warm fog (water droplets above 32 degrees F.) has been dispersed around some airports tornadoes and the mechanisms that form by salt seeding; however, modification efforts them in hopes of finding methods to diminish are still in the developmental stage. their destructive power. 9. Large-scale weather patterns cannot be modi 4. Precipitation increases' of 10 to 20 per cent for both mountainous and plains regions have fied in a deliberate or predictable manner yet. been observed depending upon atmospheric 10. Inadvertent changes in climate may be occur conditions and when properly seeded. ring as a consequence of human activity (e. g., urbanization, air pollution, increased carbon 5. Hail suppression appears to be feasible with reductions in hail intensity of 30 to 80 per dioxide levels, wind erosion). cent following seeding reported in the U.S., In conclusion, weather modification appears Kenya, and Russia. More intensive research is to be a reality for small-scale weather systems but needed to understand the exact mechanisms more uncertainty exists for economical modifica of hail formation in storm systems. tion of weather systems as they become more com plex. Some of. the major problems appear to be 6. Lightning suppression attempts indicate promise that operational techniques will be the inadvertent modification of weather due to available in the near future. man’s activities and the social, economic, biological, legal and international consequences of weather 7. The suppression of severe storms, such as hur ricanes, appears promising but much more modification.
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