E&E Exchange

Over the past month there has been a growing concern over the extreme drought in the Midwest U.S. It has already had a dramatic impact on cattle ranchers and will likely hurt expected crop yields in the weeks and months to come. All this dependence on rain and nature begs the question: can we use science and engineering to influence (or control) the weather?

The prospect of weather engineering is an interesting one. Wouldn't it be nice to always have snow for Christmas, or on those ski slopes that you love to visit? Wouldn't it be helpful to force a rain on the crops during a drought? Wouldn't it be convenient to be able to guarantee a nice, sunny day for a holiday celebration?

(<--Credit: The Daily Green)

This prospect has been used and adopted by many different countries around the world in the form of cloud seeding, a means to influence the development and precipitation of rain clouds. The process involves putting loads of particles such as silver iodide, cement powder, and salt - or coolants such as dry ice (carbon dioxide in solid form), liquid propane, or liquid nitrogen - into the atmosphere and into clouds. This can be done via ground dispersants, planes, or even rockets. When particles are used, they provide freezing nucleation points for raindrops in clouds that already contain supercooled liquid water. Cooler substances like dry ice or liquid propane essentially cool the cloud enough to cause the spontaneous nucleation of ice crystals. The formation of ice crystals encourages an early release of rain or snow from clouds, or precipitation from clouds that might otherwise produce none.

It is interesting to note that the historical credit for weather-engineering science goes to employees at General Electric in 1946 in the nearby town of Schenectady, NY; a close neighbor to GlobalSpec. Most notable was a scientist named Bernard Vonnegut, who defined silver iodide's potential to provide crystals around which cloud moisture would condense.

Unfortunately, the science of cloud seeding is still bathed in controversy. Some say the use of dispersants could be harmful to the environment, while others are fearful of the unpredictable (and perhaps dangerous) results of forced climate modifications. And even though studies and experiments have been going on for more than half a century, the results do not provide many sound, reproducible conclusions of its success. As the Nation Research Council stated in an issued report on cloud seeding: "…it is the absence of adequate understanding of critical atmospheric processes that, in turn, lead to a failure in reproducing predictable, detectable and verifiable results."

Nonetheless, there have been many sound claims of seeding success. Certain regions with favorable conditions have seen seasonal increases in rainfall or snowfall as the result of cloud seeding trials. Seeding has also been seen to reduce the size of damaging hail storms. Russia and China have been using cloud seeding during special events and holidays to prevent rain in certain locations. Most notably was China's use of rockets to reduce air pollution and prevent it from raining during the opening and closing ceremonies of the 2008 Olympic Games.

There also have been some notable "incidents" related to cloud seeding. In February 2009, China blasted iodide sticks over Beijing to cause snowfall after months of drought. The a monster snowfall was over three days was the result, leading to the closure of 12 main roads around the city. Russia also experienced an 'oops' when a block of cement failed to break apart into powder. The result was a chunk of solid mass crashing through roof of a suburban home in Moscow.

(Credit: Universe Today -->)

In the end, any attempts at cloud seeding success are still dependent on the right conditions set by nature. Weather patterns like those in London can't be helped by artificial efforts due to the fast pace and abundance of low pressure fronts moving in from the Atlantic. The cost of seeding (based on the amount required) would far outweigh any possible benefits, so don't bet the farm on a clear sky when the games begin this Friday.