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Airplanes loaded with cloud-seeding chemicals swept across southwest China early last month in a bid to bring rain to the drought-parched region. Tens of thousands of rockets and battalions of cannons stood poised to ambush stray clouds that might pass unwittingly into view.

By mid March a light, sporadic drizzle over Yunnan province brought welcome relief to farmers and residents struggling into a fourth consecutive year of severe drought. Local newspapers heralded the rains as the province’s first successful large scale cloud-seeding operations of the year.

This was the latest episode in China’s attempts to control the weather.

The water-starved country already has the world’s largest weather engineering programmes, and these look set to grow. In February, China’s top economic planner, the National Development and Reform Commission, announced plans to step up cloud-seeding and other weather modification techniques to tackle drought and boost agriculture.

Cloud-seeding is the oldest and most common weather modification technology, and often a resort during drought. It involves injecting clouds with frozen carbon dioxide (dry ice) or silver iodide, using military aircraft, cannons or rockets, to speed up the production of rain.

China’s bid to use cloud-seeding to guarantee blue skies during the 2008 Beijing Olympics caught global attention. But the country’s history of “rainmaking” stretches back into the distant past. Marco Polo reportedly returned to Europe from Cathay with an “explosive yellow powder” – and tales of how the Chinese used it to trigger rain, historian James R Fleming points out in his book .

Today, China spends US$100 million a year on operations to make rain, prevent hailstorms, contribute to fire fighting and counteract dust storms in almost every province.

It’s a figure expected to grow. “Weather modification technology is crucial to China,” Zheng Guoguang, head of the China Meteorological Administration, told China Daily in 2012. During China’s 12th Five-Year plan period “our goal is to reduce losses caused by weather disasters from 3% of GDP last year to 1% by the end of the period.”

Doubts about effectiveness

China is not the only country looking for technological fixes to water scarcity. The popularity of cloud-seeding has rocketed over the past decade, as governments, companies and scientists turn to large-scale interventions in our climate systems – known as geoengineering – as a potential fix for water shortages and global warming.

In the US, cloud-seeding is used to boost rainfall during spring planting, suppress hail, increase snowpack in the Rocky Mountains and divert and weaken hurricanes. Scientists working for the Abu Dhabi government claimed to have created more than 50 rainstorms in Al Ain in July and August of 2010, the peak of summer. Indonesia recently said it had used cloud-seeding to prevent further flooding in its inundated capital Jakarta.Iraq, Yemen, India and Mexico all have their own programmes.

“Worldwide more than 40 or 50 countries are doing cloud-seeding,” says Roelof Bruintjes one of the world’s leading experts on weather modification at the US National Center for Atmospheric Research who has helped many countries design and improve weather modification programmes, including China.

“With so many countries doing this, getting the science right is important.”

China’s false hopes on geoengineering

Though a prominent advocate of weather modification, Bruintjes is critical of China’s methods. Despite the wishful thinking of policymakers, cloud-seeding is “not a drought busting tool”, he says, pointing out that drought tends to mean less cloud – and without cloud, you can’t cloud-seed. Such techniques should be used as a long-term water management tool rather than a quick fix, he says.

Paul Sayers, a water expert at the University of Oxford who is advising the Chinese government on drought planning, also dismisses cloud-seeding as a solution to drought, arguing the authorities need to get a better balance between supply and demand management. “Drought plans can’t just be about infrastructure – desalination, cloud-seeding – China needs to think about drought in a more strategic way.” A start would be to find a way of prioritising water allocations during drought to avoid irreversible environmental damage, he says.

Experts are in fact sharply divided on the efficacy of cloud-seeding. TheChina Meteorological Administration claims its weather manipulations helped to release 490 billion tonnes of rain – about 12 times the water storage of the Three Gorges Project – between 2002 and 2012. But many are sceptical about such lofty claims, as well as China’s recent noises about more ambitious programmes.

“My first impression is that it’s very much more of a public relations effort than it might be a technically sound proposition,” says Fleming, who is professor of science, technology and society at Colby University in Maine. Being seen to do something about China’s worsening drought at least demonstrates an attempt to fix the problem, even if it achieves little.

As the world invests more in geoengineering, China is also likely to want to stay at the front of the pack, he says: “If China is becoming a world leader economically and in some ways militarily, they’re going to have to position themselves as a player in this field, even if from my point of view it’s a slight fantasy.”

Does it work?

The danger, Fleming argues, is that a focus on weather manipulation distracts from the lifestyle changes that can really make a difference to our environment. The biggest impact on the Beijing Olympics came not from the much-hyped “cocktail of artillery shell ordinance” used to bust up clouds, he says, but lower-key measures to slow down traffic into the city, which reduced hydrocarbons and helped clear the air, compounded by a “fortuitous weather pattern”.

This gets to the heart of the problem with evaluating cloud-seeding, namely the difficulty proving cause and effect. Weather is complex, shifting and difficult to understand – crediting shell fire for subsequent rain is easy enough in political rhetoric, but harder to stand up scientifically.

Some of the research that has been done strikes a sceptical tone. In 2003, the US National Research Council published a study that questioned the effectiveness of cloud-seeding and the extent of impacts outside of local areas. The report called for greater research into practices for understanding and improving cloud-seeding impacts.

To complicate things further, rising levels of pollution in the atmosphere could reduce the effectiveness of cloud-seeding, says Bruintjes. His research on inadvertent weather modification, including the effects of smoke and pollution on clouds and rainfall, suggests that what works in an unpolluted region may not in a highly polluted one.

He says more research is urgently needed in China, where the approach has been chaotic and unscientific:“They have made some claims but there is no evaluation available that can substantiate their claims,” he says. China has started to invest more in upgrading technology and evaluation methods, adds Bruintjes, but results will be slow to show.

Research is costly, admits Bruintjes, but if you can get 10-15% of water out of cloud, it’s cost-effective – “five to 15 times cheaper” than any water-saving alternative, such as building reservoirs, desalination plants or water-transfer programmes.

Fears of local and regional conflict

Concerns stretch beyond efficacy and cost, however. Fleming points out that commerce is playing a driving role in weather modification. His studies of dry areas of the US show funding for rainfall enhancement is coming not from the government, but from water companies, irrigation companies and hydropower companies.

Officials in China have also talked about providing cloud-seeding as a service to the private sector. The prospect of companies paying for rain to fall in one area – potentially meaning it won’t fall somewhere else – will inevitably raise knotty questions about water rights and public access to resources.

Some commentators are also fearful that growing use of weather modification could lead to conflict both within and between states.

Its development is already closely linked with military espionage. During the Cold War, US scientists debated weather modification as one way to destroy Soviet agricultural harvests and incite internal dissent. The US military used cloud-seeding in the Vietnam War to disrupt transport of military supplies along the Ho Chi Minh, a move it’s claimed triggered catastrophic flooding and widespread starvation.

James Lee, professor at the American University, Washington and author ofClimate Change and Armed Conflict, has even suggested the US military is investing in cloud-seeding as an excuse for developing drones. Almost inevitably, Lee fears the widespread use of weather modification could trigger resource conflicts: “There are so many countries involved in this that I think at some time, one country is going to say to the other ‘hey, you’re stealing our rain’.”