– J. Stewart, San Diego

ANSWER: The first hurricane-modification mission, Project Cirrus in 1947, resulted in outraged citizens and threats of legal action. The targeted hurricane, which was heading away from Florida before intervention, turned around and pummeled Georgia and South Carolina. From what we know now, it is unlikely that the turn had anything to do with the intervention, but the inauspicious beginning cast a pall over hurricane modification efforts.

A couple of bad hurricane years led to the launch of Project Stormfury in the early 1960s. Stormfury's goals were to study hurricane formation and dynamics to improve forecasts and to find ways to modify hurricanes. Stormfury continued for 21 years, but modification attempts were made on only four hurricanes, in part because the region in which hurricanes could be targeted was restricted.

Cirrus and Stormfury employed low-tech “seeding.” Dumping dry ice or silver iodide into clouds can make it rain or snow because the particles provide a surface on which cloud-borne moisture can freeze. Heat is released during freezing, and the working hypothesis was that the heat produced by seeding a hurricane would disrupt airflow and weaken winds.

Results consistent with the hypothesis occurred in three of the four hurricanes seeded. Unfortunately, as the researchers studied more hurricanes, they found that the weakening observed in seeded hurricanes also occurred in unseeded hurricanes. Worse, the basis of their hypothesis turned out to be flawed. Seeding only works if there are not enough natural ice crystals to act as seeds, but there are plenty of natural ice crystals in hurricane updrafts and downdrafts.

Computer models show it is theoretically possible to weaken or reroute hurricanes. One suggested method is an array of solar power stations in orbit that would produce microwave beams to heat sections of a storm and perturb it. Another idea is to cool the ocean surface or cover it with a biodegradable film to reduce evaporation, starving the storm of the energy that fuels it.

The scale and power of hurricanes make any method a challenge, and although scientific understanding has advanced since project Cirrus, hurricanes remain unpredictable. Political problems are a risk if the intervention accidentally sends the hurricane toward another country.

Sherry Seethaler is a UCSD science writer and educator. Send scientific questions to her at Quest, The San Diego Union-Tribune, P.O. Box 120191, San Diego, CA 92112-0191. Or e-mail sseethaler@ucsd.edu. Please include your name, city of residence and phone number.