In its most common form, specially formulated aerosols or very cold materials are dispersed in targeted locations within clouds to achieve precipitation enhancement, hail damage mitigation, fog clearing, and other intentional effects. Cloud seeding techniques have been developed over nearly 70 years through experimentation and trials.
Unintended consequences of cloud seeding, such as changes in precipitation or other environmental impacts downwind of a target area have not been clearly demonstrated, but neither can they be ruled out. In addition, cloud seeding materials may not be always successfully targeted and may cause their intended effects in an area different than the desired target area. This brings us to the ethical concern that activities conducted for the benefit of some may have an undesirable impact on others. At times unintended effects may cross political boundaries. Weather modification programs should be designed to minimize negative impacts. International cooperation may be needed in some regions.