A sign on a Los Angeles freeway reminds drivers to use caution while driving in severe weather conditions on February 6, 2024, as parts of Southern California experience record rainfall ( AFP / Frederic J. BROWN)

Weather manipulation claims flood social media after California storms

As torrential rains pounded California in February 2024, social media posts claimed "cloud seeding" triggered the storms and constituted an "environmental hazard." This is false; while the process has modestly increased precipitation in some regions of the western United States, experts told AFP it cannot create large-scale weather events.

"California, check this out, this may be the reason why the weather has been off lately," a narrator says in a February 17, 2024 TikTok video with more than two million views.

The clip shares footage (archived here) of a February 6 San Diego County Board of Supervisors meeting in which a resident blames geoengineering for the floods in California.

"You guys seeded us on purpose," the resident says. "You destroyed these people's homes. They didn't have flood insurance, but you all knew that."

In a video posted February 27 on Instagram, another person says: "They infuse silver iodide mixed with acetone particles into the clouds during a storm."

Screenshot of a TikTok video taken March 1, 2024
Screenshot of an Instagram post taken March 1, 2024

The posts rocketed across social media platforms as powerful storms drenched California due to a phenomenon known as a "pineapple express," a weather system that brings tropical moisture from the ocean near Hawaii (archived here).

Similar claims of weather manipulation circulated after a rare hurricane hit the state in 2023.

Like those allegations, the latest social media posts are baseless, scientists told AFP.

Cloud seeding introduces compounds into existing clouds to form supercool water droplets and boost the potential for rain or snow (archived here). Several western US states prone to drought, including California, have related programs (archived here).

The technique, usually administered via aircraft, is a physical reaction -- not a chemical one.

"Cloud seeding cannot create weather -- it can only enhance weather that is existing, exactly when it is occurring," said Kala Golden, a cloud seeding program manager for the state of Idaho, on March 1.

"Precipitation in the natural environment forms when supercooled water droplets collide with aerosols or dust particles in the air; the droplets freeze on contact with the particles and form ice that grows until it becomes heavy enough to fall from the sky."

There is no evidence the process can create drastic weather events.

"Current cloud seeding methods are highly localized and can only coax marginally more precipitation out of existing clouds," Di Yang, an assistant professor in the Wyoming Geographic Information Science Center at the University of Wyoming, told AFP on March 1. "The amounts are tiny compared to these recent powerful storm systems."

Atmospheric scientist Troy Zaremba agreed, saying in a February 29 email that cloud seeding "is not capable of creating major weather systems that impact the coast of California like atmospheric rivers or altering large-scale weather patterns."

Explainer of the atmospheric rivers weather phenomenon, which is closely tied to water supply and flood risks, in particular in the western part of the United States (AFP / Paz PIZARRO, Nalini LEPETIT-CHELLA)

Decades of research

Cloud seeding has been documented and studied for decades (archived here and here). The first experiment was conducted in 1946 (archived here). 

Cloud seeding usually involves silver iodide -- a compound that, in large amounts, can constitute an environmental hazard, according to the National Institutes of Health (archived here). 

But Yang said "extensive research has shown no definitive large-scale or long-term impacts from cloud seeding."

Documentation for a pilot program in California's Santa Ana River Watershed, for example, indicates the concentration of silver iodide in water or snow from a seeded cloud "is nearly 1,000 times less than the Environmental Protection Agency standards" (archived here).

"When done properly, it appears safe for the environment based on current evidence," Yang said.

In her comments shared on social media, the San Diego County resident also says cloud seeding experiments "fell out of favor" in the 1980s because they were hazardous, referencing an article by a Northeastern University assistant professor (archived here).

But Jeffrey French, a professor of atmospheric science at the University of Wyoming, said research stopped in the 1980s "not because of worries of environmental hazards or ethics, but rather because 35-40 years of research had failed to provide any compelling evidence that cloud seeding was effective."

French told AFP on February 29 that more recent studies with better technology and weather modeling have shown that, "at least in a very limited set of environmental conditions, it is possible to marginally increase precipitation through cloud seeding over a reasonably large area (the size of a mountain range)."

Still, Yang said that "doesn't mean we should leap into wholesale weather modification without caution."

"Like any human technology interacting with complex natural systems, we cannot forecast all unintended consequences," she said. "That is why governance, risk assessments, transparent monitoring and maintaining public trust are so important for these types of projects."

AFP has debunked other claims about the climate here.

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