Monday, February 16, 2009

Is Cloud-Seeding a Viable Source of Fresh Water?

Given that its feasibility in creating rain was thoroughly evaluated in post-World War II America, does the practice of cloud-seeding represent a long-term solution for our freshwater needs?

By: Vanessa Uy

Believe it or not, the amount of fresh water suspended in the Earth’s atmosphere as water vapor is six times more plentiful in comparison to all of the fresh water flowing in all of the Earth’s rivers. Even though the relatively recent technology of cloud-seeding allows us to “almost literally” make water out of thin air, is the method really environmentally friendly given that it involves flying fossil-fueled manned aircraft?

When the Bergeron-Findeisen Theory of Rain – also known as the ice-crystal theory of rain – led to the successful field test of cloud-seeing or the artificial seeding of rain clouds to induce it to rain, had led many to ask whether if this is a viable way to meet with our increasing freshwater needs. The “miracle of science” of creating water out of thin air – even though it works with varying degrees of reliability – has been hailed as a triumph of mankind over the vagaries of our planet’s weather.

The practicality of cloud-seeding was first proved in 1946 when General Electric’s Vincent J. Schaefer and Irving Langmuir tried a newfangled method of rainmaking magnitudes more reliable than primitive man’s ancient rain dance. The principle behind how it works seems to be a model of logic and simplicity. By introducing into an existing cloud formation of super-cooled droplets an agent that promotes the formation of ice crystals in which it can serve as a catalyst to make suspended water droplets to fall back to the ground as precipitation or rain.

Two substances proved to be promising. One was silver iodide, whose crystalline structure is similar to that of naturally formed ice crystals and therefore provides hospitable nuclei on which ice crystals can readily form. The other one is solid carbon dioxide – or dry ice – which is so cold that it causes atmospheric water vapor to solidify into enormous numbers of tiny ice crystals. In both cases, precipitation should follow in accordance to the Bergeron-Findeisen Theory of Rain.

Ultra-fine pellets of dry ice are usually sown or dispensed into a cloud from airplanes. While silver iodide is released as smoke, sometimes from an airplane via dedicated cloud-seeding pyrotechnic flares, sometimes from the ground. Both methods only work if the dispensed agents reach the super-cooled rain clouds that occur at 18,000 feet - or higher.

Given that since the start of cloud-seeding programs the local area intended to receive the man-made rain resulted in an increase of rainfall by 8 to 12%, there had been plans to use cloud-seeding to replace the snows of receding glaciers affected by global warming. But the problem with cloud-seeding is that it involve the use of aircraft that have a significant carbon footprint that resulted in significant carbon dioxide emissions which is primarily what started the global warming / greenhouse effect problem in the first place.

While China has been lately using anti-aircraft artillery and surface-to-air missiles to deliver cloud-seeding agents to the desired altitudes to create rain for the drought-stricken farmers, whether this method is truly environmentally friendly – i.e. low carbon footprint source of fresh water - remains to be seen. Unless carbon neutral / zero-emission aircraft and other delivery systems are used in cloud-seeding, this method of obtaining potable fresh water is strictly for emergency purposes only.