From the early days of civilization, we have been concerned with either too much or too little rain. The lack of rain posed the worst scenarios.  Too little rain and the crops would die, or drinking water became scarce. Too little rain could wipe out a population a few hundred years ago. To avoid problems of draught, we humans sought ways to make it rain.

     To our ancestors, the unreachable sky was divine territory, the place of the gods. Gods were rarely neutral, they were moody and could easily be provoked into causing draughts, floods, fires etc. When there was no rain, it was assumed the gods were angry and something must be done to appease them.

     The Aztecs took this sort of stuff real serious, not for them a few prayers and incense. They went right to the heart of the matter, human sacrifice. The Aztecs would sacrifice children to the sky gods. They would adorn the child in  fancy dress and carry it on a litter to the place of sacrifice. The more the child cried, the happier the Aztecs were, since they associated rain with tears and thought that more tears would mean more rain.

     Among the Native Americans, the rain dance is among the most sacred of rituals. Any holy man thought to have the "medicine" to make rain was held in the highest esteem. Various rituals and dances were performed to coax water from the sky. It is quite likely that these native rainmakers had no more than a natural inclination to understand weather by linking cloud formation that they had observed with the weather that followed.

     Today's rainmakers are neither shamans nor do they produce rain out of nothing. Rather, they take a truly scientific approach which has replaced the spiritual. Rattles and dances have been replaced by cloud seeding.

     Cloud seeding began in the 1940's and involves injecting particles into a cloud, which act as freezing nuclei. Cloud droplets adhere to the injected particles and fall to the ground as rain or snow. The presence of clouds, therefore is a prerequisite and they must be tall enough so that their upper portions extend into regions where temperatures are below freezing. The reason for this is that the particles must be super cooled, meaning they exist in the liquid state at temperatures below freezing.

     The earliest attempts at cloud seeding involved dropping crushed dry ice (carbon dioxide) pellets into the top of a cloud from an airplane. Dry ice is extremely cold (-108 F) and it cools the air around it which produces more condensation. The dry ice pellets also then act as the nuclei. The very first experiment was performed in 1946 by Vincent Schaefer.  Schaefer dropped three pounds of ground dry ice into a cloud. Five minutes later, snow began falling from that cloud.  The following year, Schaefer's colleague Bernard Vonnegut discovered that silver iodide makes an even better cloud seeding agent than dry ice.

     The 1950's saw a boom of rainmaking operations in drought areas around the world. It produced limited success and even greater criticism. Many people feared the broader implication of humans manipulating the atmosphere. They were concerned that entire weather patterns might be permanently changed. Despite the limited success and criticism, the US federal government launched a research program to study rainmaking.

     In 1972, cloud seeding became a major controversy when it was blamed for a flash flood in Rapid City, South Dakota which claimed over 200 lives. While a direct link was never established between the two events, no further cloud seeding was done in that area.

     Additional controversy occurred during the Vietnam war then cloud seeding was used to flood the Ho Chi Minh Trail. Again, it was not proven that cloud seeding actually produced the results, but many people felt it was questionable practice by the US Military to have tried at all. Eventually this led to a Senate investigation.

     Does cloud seeding really work? Nearly sixty years have passed since experiments first begun, and the results are still hotly debated. Some studies have suggested that under the right circumstances, cloud seeding can increase precipitation by five to twenty percent. It comes with risks however, because overseeding a cloud can reduce precipitation.

     Cloud seeding continues today and will likely continue. Our expectations now however, are more realistic. Seeding is used to increase both rain and snow. Overseeding clouds is also utilized around airports to help reduce fog. It is quite likely that we will perfect methods in the future, and with it will come the debate about changing our world around us.