What do you do when you urgently need to improve a city’s air quality ahead of a major event? If you’re the Chinese government, the answer is launching a military-style strike on the sky.
That’s according to a scientific paper out Tsinghua University first seen by the South China Morning Post, which details the Chinese government’s attempt to rapidly lower pollution levels ahead of the centenary celebration of the Communist Party’s founding in July. Though factories and other industrial activities were ordered to slow down production ahead of the event to temporarily reduce air pollutants, an unusual stagnant weather pattern kept the particles lingering in the air. So, hours before the event, scientists reportedly shot rockets filled with silver iodide at the sky.
Silver iodide is commonly used in cloud seeding, a questionable technique to coax precipitation from the sky for various reasons, including knocking down pollution. Particles like silver iodine essentially act as nuclei for raindrops to form, allowing water droplets to coalesce until they become so heavy that they fall from the sky as rain or snow. Dry ice, table salt, and liquid propane have also been used to entice the clouds into producing rain in the past. In theory, the practice can both speed up rain and snowfall while also inhibiting hail and fog. The track record is spotty, but in this case, it seems like it may have worked.
According to the researchers, the simulated rain may have helped reduce the amount of PM2.5 air pollutants by more than two-thirds, enough to increase air quality standards from “moderate” to “good” on the World Health Organisation’s rating system. One nearby resident claimed to have seen the silver iodine-filled rockets in action and described the launch to the South China Morning Post.
“It was very loud, like thunder — and it went on for a very, very long time…it was like a war zone,” the resident said. “Then the rain came down, it was quite heavy.” The researchers claim the cloud seeding operation lasted for about two hours the night before the event.
China’s apparent success at the centenary celebration would mark a meaningful inflection point in the country’s cloud seeding pursuits. Officials claim the country has spent $US1.3 (A$1.81) billion on experimental weather technology between 2012 and 2017 and that the tech was responsible for inducing 233.5 cubic kilometres of additional rainfall, according to state-run outlet Xinhua. (That volume of rain would fill Tahoe one-and-a-half times over.) State officials also claim the firing off of silver iodine-packed shells and using other weather modification techniques were able to reduce 70% of hail damage in the Xinjiang region in 2019.
The country has much larger ambitions for the technology around the corner. Last year the government reportedly announced a plan to expand its already extensive weather modification program to an area of 5.5 million square kilometres. It then plans to grow that area by an additional 100,000 square kilometres each year. All told, Chinese officials reportedly believe these programs could increase rainfall in Beijing alone by 15%.
Around 50 other countries are also currently exploring cloud-seeding in some capacity. Most recently, Dubai made waves with plans to seed clouds using drones. The U.S. is also no stranger to cloud seeding; at least eight states have used the technique to try and boost precipitation amid historic droughts and as a means to potentially increase snowfall. State agencies across Colorado, Wyoming, and Utah have reportedly combined to spend around $US1.5 (A$2.09) million on cloud seeding operations in the Upper Colorado River Basin, according to Scientific American.
The problem, though, is that it’s historically been frustratingly difficult to prove whether or not cloud seeding itself was the driving factor for increases in precipitation. Recent advances in radar and computer modelling are providing researchers with better ways to observe the effects of cloud seeding, and the recent findings could help refine the approach.