China ?modified? the weather to create clear skies for political celebration ? study

Chinese weather authorities successfully controlled the weather ahead of a major political celebration earlier this year, according to a Beijing university study.

On 1 July the Chinese Communist party marked its centenary with major celebrations including tens of thousands of people at a ceremony in Tiananmen Square, and a research paper from Tsinghua University has said an extensive cloud-seeding operation in the hours prior ensured clear skies and low air pollution.

The Chinese government has been an enthusiastic proponent of cloud-seeding technology, spending billions of dollars on efforts to manipulate the weather to protect agricultural regions or improve significant events since at least the 2008 Olympics.

Cloud-seeding is a weather modification technique, which sees the adding of chemicals like small particles of silver iodide, to clouds, causing water droplets to cluster around them and increasing the chance of precipitation.

On Monday the South China Morning Post reported a recent research paper which found definitive signs that a cloud-seeding operation on the eve of the centenary had produced a marked drop in air pollution.

The centenary celebration faced what the paper reportedly termed unprecedented challenges, including an unexpected increase in air pollutants and an overcast sky during one of the wettest summers on record. Factories and other polluting activities had been halted in the days ahead of the event but low airflow meant the pollution hadn't dissipated, it said.

The paper, published in the peer-reviewed Environmental Science journal and led by environmental science professor, Wang Can, said a two-hour cloud-seeding operation was launched on the eve of the ceremony, and residents in nearby mountain regions reported seeing rockets shot into the sky on 30 June. The paper said the rockets were carrying silver iodine into the sky to stimulate rainfall.

The researchers said the resulting artificial rain reduced the level of PM2.5 air pollutants by more than two-thirds, and shifted the air quality index reading, based on World Health Organization standards, from "moderate" to "good".

The team said the artificial rain "was the only disruptive event in this period", so it was unlikely the drop in pollution had a natural cause.

Last year Beijing announced plans to expand its experimental weather modification program to an area 1.5 times the size of India - 5.5 million square kilometres - covered by artificial rain or snow. The State Council has said it aims to have a developed weather modification system by 2025, including another half a million square kilometres hosting hail suppression technologies.

There is a growing body of scientific evidence around the success of the technology, but also debate about whether manipulating the weather in one area could disrupt weather systems elsewhere.

In the five years to 2017 state media claimed China had spent more than US$1.3bn on the technology and induced about 233.5bn cubic meters of additional rain. In 2019 officials said weather modification practices, usually the firing of iodine-packed shells to disrupt unfavourable weather fronts, had helped to reduce 70% of hail damage annually in agricultural regions of Xinjiang.

However it has also been used for political and other significant events, including the 2008 Olympics, the 2014 APEC summit, as well as National Day parades and annual Two Sessions meetings.

The weather manipulation activities, also known as "blueskying", are usually implemented in conjunction with social changes in the lead up to events, including the shutdown of factories, construction and other polluting industries, and encouraging people to stay off the streets or leave the region, said Dr Shiuh-Shen Chien, of National Taiwan University's department of geography, in a 2019 essay for Society+Space.

Dr Chien said China's weather authorities had "institutionalised" climate controls for decades, with technological attempts dating back to the 1980s, but was unique in using it not just for commercial or agricultural reasons but also for "propaganda purposes".