People have always wanted to change the weather – be it for better crops, prevention of damage, or just because they don’t like rain. Agencies for weather modification can be found in several countries. Has this become reality?
Hail cannons at an international congress on hail shooting held in 1901. Photo: Public Domain/Plumandon
Weather modification means manipulating the weather. The most common form of manipulation is cloud seeding, which conjures local rain by seeding the cloud with particles that mimic cloud condensation nuclei.
A tradition of pseudo-science
Hail cannons are an early example of weather modification in human history that is still used – even though there is no evidence that it works! Hail cannons are widely used by farmers, especially in the wine-growing industry, for the fear of losing an entire crop because of hail. They generate strong shock waves generally believed among farmers to prevent hail formation in the atmosphere. The shock waves themselves cause a strong noise, which disturbs animals and humans alike, but their traditional use is now all too common. If a hailstorm happens to occur you cannot say that you didn’t try, right? This is, of course, pseudo-scientific advice, and no practical reason for hail cannon use remains today.
Imagine a situation where you could create precipitation from clouds that wouldn’t normally precipitate – i.e., form rain. This could certainly solve some global problems of water supply, or at least so one would think. Cloud seeding requires clouds available to seed, so in the driest part of earth where there are no clouds, it is impossible. The most common form of weather modification, it causes precipitation by the – you guessed it – seeding of cloud condensation nuclei (CCN) or ice nuclei (IN) near water vapour, e.g. clouds, which then condensates on the CCN/IN. Silver iodide has similar chemical qualities to ice, which is why injecting silver iodide particles increases the number of particles available for water condensation in the sky. Ice crystals produced on these go on to fall down as snowflakes, or melt on the way producing rain drops. There are two schools of cloud seeding methodology; static seeding, done from ground, and dynamical seeding done in the air.
Cloud seeding. Photo: Public Domain/DooFi
A less-than-shiny solution
Statistic cloud seeding is done from the ground by releasing some particles to the atmosphere, so that the vertical motion will drive them to the clouds. Dynamic cloud seeding, on the other hand, is done above the clouds by airplanes spraying the substance on the cloud.
But does it really works? Cloud seeding was thought to be and efficient cure to precipitation problems, but, just like hail cannons, was later realized to not be the magic fix sought after. The window for cloud seeding to be effective is quite narrow because of the complexity of the atmospheric behaviour.
The window of opportunity for cloud seeding from the ground is limited, having three conditions: First, the seeded clouds should be relatively cold and continental. Second, temperature on the top of the cloud should be -10 to -25 degree Celsius. Third, the time scale during which the seeding has to be done is limited by natural processes taking place in the atmosphere. In addition to all of these requirements, the success of cloud seeding requires cloud forecasting skills that are far greater than what is currently used. So in the light of science, these kinds of cloud seeding don’t seem likely to be the one-fit-all solution they were once hoped to be.
There is, however, some statistical evidence supporting the use of one type static cloud seeding: orographic cloud seeding. Orographic clouds are clouds that are forced to rise upwards because of a mountain. And if the seeding is done while the cloud rises up, it is possible for successful condensation to happen
Donald Duck rain comic. Photo: Walt Disney
Dynamical cloud seeding from airplanes enhanced the dynamics of a cloud by stimulating bouncy and upward motions of air. Scientifically, dynamic seeding is plausible, and offers opportunity to increase rainfall, but it has problems of its own: being much more complex and requiring a really good understanding of cumulus cloud behaviour, it’s not an easy fit to achieve. For now we need to wait that cloud observation tools improve and multidimensional cloud models become available.
The atmosphere is a really complex system, and no experiments involving weather system can be done using the most basic aspect of the scientific method – a control. Another complication making meteorology a not so exact science is the fact that experiments in the atmosphere cannot be repeated. We cannot recreate the conditions present when the original experiment occurred. That’s why it is hard to predict what would have happened regardless, and what happened because of the tested weather modification.
Don’t blind me with science
The World Meteorological Organisation (WMO) states that the energies involved in the atmosphere to create weather systems are so huge that it is impossible to change the weather. Therefore, modification methods’ claims to effectiveness are not backed up by scientific evidence and should be treated with suspicion. This is despite of the seeding of the orograpical clouds having some evidence supporting its use.
Regardless of the absence of scientific proof, there have been many national projects aiming at modifying the weather around the world. Of the most famous of them is Project Cirrus from 1947. Cirrus was the first known US governmental effort doing weather modification. The project was a success, but sparked a lot of controversy. In the end the project was terminated after five years mostly because of the opposition. The hardest blow to its image occurred while modifying a hurricane: attempting to effect it over the sea, the hurricane suddenly changed direction and started to travel back towards the east coast of the US, ending up causing a lot of damage.
In any case, changing the weather involves both technical and ethical difficulties. If we can change the weather, who decides how it will be changed? What if we change the direction of a hurricane and it then causes damage somewhere? Who takes the responsibility?
Changing the weather sounds improbable for now, but who knows about the future. Maybe one day we can change the weather!
WMO Documents on Weather Modification
Abrams Hap (April 2nd, 2013), Project Cirrus: 1940′s Weather Modification, Opsec News