By Emilio Godoy
As half of Mexico endures one of the most severe droughts in its history, cloud seeding appears to be a promising way to bring desperately needed rain, although it remains a source of controversy.
While some promote the benefits of cloud seeding, others insist that there is no solid evidence of its effectiveness, in addition to the fact that the potential effects on the air, water and soil of the chemicals used have not been sufficiently studied.
“The methodology is not proven; the investment made has not yielded any results that demonstrate that cloud seeding leads to more precipitation,” Graciela Binimelis of the Atmospheric Sciences Center at the public National Autonomous University of Mexico told Tierramérica.
Binimelis, who holds a PhD in atmospheric sciences from the University of Washington, has studied the physics of clouds for more than two decades.
Cloud seeding involves the spraying of selected clouds with chemicals, usually silver iodide, either from aircraft or from the ground through the use of generators or rockets. This leads to the formation of ice crystals, which grow in size until they reach the necessary weight to fall in the form of rain at lesser altitudes.
Silver iodide can cause possible residual injury to humans and mammals with intense or continued but not chronic exposure.
Cloud seeding is practiced along the border between the southern United States and northern Mexico, as well as in Argentina, Chile, Spain and China, the country that uses it most.
“If it is carried out uninterruptedly, with the necessary logistical support, trained personnel and specially adapted aircraft before the rainy season, the results will be positive,” pilot Gustavo Dietz, who has flown aircraft used in cloud seeding operations in the northern states of Mexico, assured Tierramérica.
For his part, Gary Walker of Just Clouds, a company based in the southern U.S. state of Texas dedicated to cloud seeding operations and atmospheric research, told Tierramérica, “Properly seeded clouds will make clouds last longer and produce more aerial coverage.”
Cloud seeding is not considered to fall under the category of geoengineering, also known as climate engineering, a concept that refers to any large-scale, human-made effort to manipulate the planet to adapt to climate change.
As a result, it is not subject to the moratorium imposed by the United Nations in 2010 on geoengineering experiments, due to the potential hazard they pose to biodiversity.
There are two main areas of geoengineering research: solar radiation management and the removal of carbon dioxide from the atmosphere, to reduce the concentration of this common greenhouse gas.
“There are at least 25 reasons why geoengineering may be a bad idea,” according to Alan Robock, a professor of climatology in the Department of Environmental Sciences at Rutgers University in the United States.
These include, for example, “disruption of the Asian and African summer monsoons, reducing precipitation to the food supply for billions of people, ozone depletion, reduction of solar power, and rapid global warming,” he explained to Tierramérica.
Robock fears that “the prospect of geoengineering working may reduce the current drive toward reducing greenhouse gas emissions.” In addition, he said, “there are concerns about commercial or military control” of these technologies.
Mexico, where there are at least nine companies that provide cloud seeding services, particularly in the north of the country, is currently suffering its worst drought in seven decades. Half of the country’s territory is affected by the lack of rain, which is threatening food production and employment in the agriculture sector.
Between 1996 and 1999, a prolonged drought in the northeastern state of Coahuila gave rise to the Program for the Augmentation of Rainfall in Coahuila, sponsored by the state government, Altos Hornos de México (a steel company) and the U.S. National Center for Atmospheric Reserach (NCAR).
Over the course of two years, data were collected on 94 cases, 51 of natural clouds and 43 of clouds seeded with a mixture of sodium, magnesium and calcium chloride, which attract moisture from the surrounding area, growing into raindrops.
“Preliminary analyses suggest that cloud seeding had a positive effect on the amount of rain produced by thunderstorms,” stated the study “Statistical evaluation of a cloud seeding experiment in Coahuila, Mexico”.
The study, published in 2001 in the Bulletin of the U.S. American Meteorological Society, was headed up by three NCAR scientists and managed by the University Corporation for Atmospheric Research, a nonprofit consortium of over 65 universities.
The rainfall from seeded clouds covered a larger area, lasted longer, and was more abundant – sometimes, double the amount – than rain from clouds not seeded with chemicals, the study revealed.
When the drought ended, the program was cancelled.
In 2003, an article by U.S. consultant Bernard Silverman, also published in the Bulletin of the American Meteorological Society, concluded that experiments conducted in Mexico, India, Thailand and South Africa “have not yet provided either the statistical or physical evidence required to establish that hygroscopic seeding of convective clouds to increase precipitation is scientifically proven.”
None of the studies addressed the effects of rain from seeded clouds on soil. Experiments need to be carried out over the course of at least five years to produce valid results, according to experts.
“The positive or negative impacts on the environment are unknown. What has been seen over the course of decades is that there is a change in the way it rains, towards more intense and shorter-lasting rainstorms, but the amount of rain that falls has not changed much,” stressed Binimelis.