Cloud-seeding safe, experts explain

10:07, February 17, 2011      

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With efforts to manipulate the weather and induce precipitation intensifying because of the drought that has hit much of China, atmospheric experts have been reassuring the public that the release of chemicals into the sky will not hurt the environment.

"The impact of weather manipulation can be ignored because the dose of the catalyst is too small to cause a problem," said Lei Hengchi, a professor specializing in weather intervention at the Institute of Atmospheric Physics under the Chinese Academy of Sciences.

While silver iodide - the most common catalyst used to encourage clouds to discharge their water - is considered a hazardous substance and a toxic pollutant, the quantities used are not large enough to have any effect on the environment, he explained.

China has discharged silver iodide, dry ice and liquefied nitrogen into clouds from aircraft or from stations on the ground to enhance precipitation in dry regions since the 1950s.

Dry ice and liquefied nitrogen have absolutely no effect on the environment, People's Daily quoted Wang Guanghe, deputy director of the artificial weather intervention center under the China Meteorological Administration, as saying on Wednesday.

Wang said they turn into carbon dioxide and nitrogen, elements that are ordinarily found in the air. Wang agreed that the quantities of silver iodide being used are too small to have an impact, even thought he said the substance is considered toxic.

Lei added that experiments failed to find any silver iodide in Huairou Reservoir, on the outskirts of Beijing, after silver iodide was dispersed into clouds upstream of it.

Beijing burned more than 2,000 silver iodide rods at weather manipulation stations to enhance recent snowfalls on the city. About 6.5 kilograms of silver iodide in total was involved.

The silver iodide was dispersed in a 10,000-square-kilometer area, meaning about 1.3 grams was used for every square kilometer, Beijing Times quoted Zhang Qiang, head of the capital's artificial weather intervention office, as saying on Wednesday.

"Such a small dose cannot make an impact on the environment," Zhang said.

In order to relieve the drought that has continued since October, China had carried out nearly 2,200 weather control measures as of Monday aimed at encouraging precipitation, according to the latest statistics from

By Wang Qian, China Daily

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