By David Pinto
There’s growing international interest in cloud seeding due to drought. (Credit: David Pinto)
Over the mountains of central China, a small plane releases chemicals into clouds. This causes ice crystals to form, water droplets to freeze, and rain to fall. The water flows downhill into farmland. Slowly, a cloud seeding program is turning this arid landscape greener.
A recent study published in the journal Atmosphere found that rainfall and vegetation cover in the Shiyang River basin increased considerably since cloud seeding began some 15 years ago. China invested $2 billion in this weather modification strategy between 2014 and 2021, making it the largest such program in the world, according to the U.S. Government Accountability Office (GAO).
“The Shiyang River basin is one of the regions most severely affected by ecological degradation in China,” said Wei Wang, associate researcher at the College of Aviation Meteorology in Guanghan. Local governments across China are now cloud seeding to fight water scarcity, according to Wang.
The study comes at a time of growing international interest in cloud seeding due to drought, as well as renewed global scientific debate over its efficacy and risks, including possible harmful effects on some pollinators.
“It’s definitely something people are revisiting,” said Kara Lamb, an associate research scientist at Columbia University’s Department of Earth and Environmental Engineering. “We’re seeing regions that are getting drier think more about climate adaptation.”
Wang and his team, funded by an arm of the China Meteorological Administration, used 25 years of satellite imagery to evaluate vegetation cover before and after the cloud seeding program, as compared to a control area. They found that rainfall increased more than 20% and that a clear reversal in vegetation trends followed the start of cloud seeding in 2010. Low and moderately low coverage areas shrank, while moderate to high coverage expanded. Between 2010 and 2024, the share of land with moderate to high vegetation cover grew from about 37% to 54%.
“The 20.8% rainfall increase is attributed to the use of aircraft, which have higher payload capacities and can deliver seeding agents directly to the most favorable locations in cloud systems,” said Wang.
Nonetheless, measuring the effectiveness of cloud seeding remains a problem—whether it is done via planes, the most common approach, or from the ground.
“It is very challenging to attribute an increase in rainfall to cloud seeding, due to the inherent complexity of predicting rainfall,” said Karen Howard, director of science and technology assessment at GAO, a congressional watchdog agency. The Israel Water Authority cancelled a 38-year cloud seeding program in 2021, for example, after concluding that the effects were too small to justify the costs. Other programs in the U.S. and Australia were scaled back after similar assessments.
In addition, few studies have looked at the downstream impacts of cloud seeding. Silver iodide, the most commonly used chemical, can have adverse effects on some animals at high concentrations, like insects and guppies. One recent study showed that it can impair learning and foraging behavior in honeybees. As a keystone species, honeybees have an outsized impact on both natural and agricultural ecosystems.
“Would you want to live on property that cannot support honey bees or earthworms—or, as Charles Darwin called the latter, ‘the intestines of the earth?’” asked Charles Abramson, professor of psychology at Oklahoma State University.
For their study published in Insects, Abramson and six colleagues fed honeybees 10 times and 100 times the “safe dose” of silver iodide—a level established by previous studies on other animals. Then they tested the bees’ ability to avoid electric shocks, respond to smell, and distinguish between flower colors. The chemical had negative impacts in all three tests. The amounts they tested have not been observed in the field, though Abramson noted that material comes down unevenly in cloud seeding areas.
“The current levels of exposure appear to be low enough to not be of significant concern for most cases,” said Howard from GAO. “However, if cloud seeding were drastically increased in scale, additional study could be warranted.”
Cloud seeding has a long and checkered past. During the Vietnam War, the U.S. Air Force launched Operation Popeye, a top-secret weather modification program designed to extend the monsoon season and to turn the enemy’s supply roads into muddy bogs. It remains unclear whether this really worked.
In 1972 Congress passed the Weather Modification Reporting Act, requiring that anyone involved in cloud seeding report their activities to the National Oceanic and Atmospheric Administration. And in 1977, the United Nations banned cloud seeding for military use. Private cloud seeding continued in the Western U.S. to increase snowpack and precipitation, but enthusiasm largely faded.
Now, cloud seeding appears to be making a comeback due to climate change. Last year, California-based cloud seeding startup Rainmaker raised $25 million. The global cloud seeding market is projected to grow 80% in the next eight years, with uses ranging from suppressing fog to reducing air pollution, according to Fortune Business Insights.
Kara Lamb is conducting one of the first comprehensive studies of historical cloud seeding in the U.S. Activity rose to a high of 48 projects in 2003 and then largely declined until the pandemic, when it fell off, though Lamb notes that it is unclear whether that drop was real or due to a lack of reporting. Since 2021, activity appears to be back up, with a high of 34 projects in 2024.
Cloud seeding can alter weather systems across national borders, yet there is currently no international oversight framework. While a 1977 international treaty prohibits cloud seeding for military uses, it says nothing about civilian programs. International disputes have already arisen over cloud seeding; in 2018, an Iranian general even accused Israel of “making clouds barren” before they reached Iran.
“Weather is increasingly becoming a policy issue owing to climate change,” said Harry Lambright, director of the Science and Technology Policy Program of the Center for Environmental Policy and Administration. “The more effective the technology is perceived to be, the more controversial it will become and eventually take on a geopolitical dimension.”
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Previously Published on columbianewsservice with Creative Commons License
Photo credit: There’s growing international interest in cloud seeding due to drought. (Credit: David Pinto)
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