Weather Modification

Weather modification is any change in the weather caused by humans. For centuries, the idea of "controlling" the weather has been an intriguing idea. Efforts have been made made to increase rainfall, reduce the size and duration of hailstorms, dissipate fog, reduce the intensity of lightning, and calm the winds of hurricanes. However, rain enhancement and hail suppression have shown the most promises.

There are some large-scale efforts to weather modification that aim to reduce extreme weather conditions. Here are some examples:

• Cloud seeding: This is the most common and widely used technique of weather modification, which involves spraying small particles (such as silver iodide or dry ice) into clouds to stimulate precipitation or reduce hail formation . Cloud seeding has been used for various purposes, such as enhancing snowfall in ski resorts, increasing water supply in drought-prone areas, and mitigating floods and landslides . However, the effectiveness and environmental impacts of cloud seeding are still debated and uncertain .
• Solar radiation management: This is a proposed method of geoengineering, which aims to reflect some of the incoming sunlight back to space to reduce global warming and its effects . Some of the possible techniques include injecting aerosols into the stratosphere, brightening clouds, or placing mirrors in orbit . Solar radiation management could potentially reduce the frequency and intensity of heat waves, droughts, and storms, but it also poses significant risks and uncertainties, such as disrupting the water cycle, altering regional climates, and affecting ecosystems .
• Hurricane modification: This is a hypothetical method of weather modification, which attempts to weaken or divert hurricanes by altering their structure or environment . Some of the proposed techniques include seeding clouds with ice nuclei, cooling the ocean surface with cryogenic material, creating sonic booms with aircraft, or detonating nuclear bombs . Hurricane modification is highly controversial and speculative, as it faces many technical, ethical, and legal challenges, such as unintended consequences, lack of scientific evidence, and international conflicts .

One of the first U.S. weather modification programs began in the 1890s. Investigators noted that in the major battles of the Civil War of the 1860s, rainfall seemed to occur after artillery had been fired. The U.S. Congress appropriated $9000 for the U.S. Department of Agriculture to conduct tests near Washington D.C., and west Texas. Cannons were fired into the sky, dynamite was detonated, and hydrogen-filled balloons were released into the atmosphere, but the results were inconclusive.

The first scientific breakthrough in weather modification occurred in 1946 when V. J. Schaeffer, a scientist with the General Electric Company (GE) in Schenectady, New York, accidentally discovered adding dry ice (frozen carbon dioxide) into a deep freeze full of super-cooled fog caused the moisture to quickly freeze and drop as snow particles. Schaeffer later found that silver iodide produced a similar effect. Before long, airplanes were dropping silver iodide into super-cooled clouds above New England to increase the growth of the ice crystals.

This process of introducing nucleating agents such as silver iodide (AgI), ammonium iodide (NH4I) or dry ice into clouds to enhance precipitation is called cloud seeding. Cloud seeding causes water vapor in a cloud to freeze, converting it from gaseous to a solid state. Other moisture is then induced around this nucleus until these water droplets become heavy enough to fall as precipitation. Ground-based generators or specially equipped aircraft deliver the nucleating agents into clouds.

Silver iodide is often introduced to a cloud by burning silver iodide flares. The smoke particles furnish the nuclei for ice crystal formation. A cloud temperature of -12 degree Centigrade is ideal, although a range of -4 to -30 degree Centigrade is acceptable. Cloud temperatures warmer than -4 degree Centigrade are not sufficiently super-cooled while temperatures below -30 degree Centigrade already contain ice crystals, since spontaneous nucleation occurs at -40 degree Centigrade.

Although cloud-seeding efforts have been conducted for over a century, many people adamantly oppose the concept because cloud seeding, they believe, increases the likelihood of damaging hailstorms. Reductions in precipitation downwind of seeded storm have also been attributed, opponents argue, to enhanced rainfall upwind. Some scientists and water resources managers are skeptical of the benefits of cloud seeding, since many scientific studies are inconclusive.

Some objectors argue that cloud seeding is unethical because it interferes with natural hydrologic processes. Supporters argue that cloud cloud seeding works and that effort should continue regardless of political boundaries. In 1972, the United Nations Conference on the Human Environment held in Stockholm, Sweden, urged establishments of an advisory committee to consider the international concerns of weather modification.

Concerns have been expressed over the environmental effects of using ammonium or silver iodide if large quantities accumulate on the ground after seeding efforts. Measurements have been made of the change of concentrations of silver iodide found in farm ponds, rivers, and other areas where cloud seeding is practiced. Only minor concentrations have been found, but widespread use of silver iodide could result in elevated local concentrations in precipitation and runoff.

It is very difficult to evaluate the effectiveness of precipitation enhancement projects. Since the atmosphere does not generate identical clouds, a complex statistical dilemma is created in determining the value of such cloud-seeding programs. One method is to compare the amount and extent of rainfall in a seeded area with a region outside the area, using several different cases. This type of analysis has shown an increase in precipitation of 10 to 20 percent.