Here's the plan: pick a cloud. Shoot a laser at it. Make it rain. Sound crazy? Maybe, but a group of scientists have some concrete evidence that it could be possible. Good thing, too, as lasers are a lot more environmentally friendly than the other methods being tried.
We can sort of make it rain already. The current method, called cloud seeding, involves using planes and rockets to deliver silver iodide into a cloud formation. Dozens of nations around the world experimented with cloud seeding all through the 1900s, and many still employ the tactic. It's most famously used in China, where the country used aircraft and artillery launching silver iodide to try and control the weather before the 2008 Olympics. China has even claimed to have used cloud seeding to make it snow in Beijing. Cloud seeding is something that goes on a lot in America, too.
Problem is, silver iodide is toxic. Whether or not using silver iodide in cloud seeding is harmful — or indeed, if cloud seeding even works at all — is a topic of debate. A topic, it seems, that may be made moot if researchers at the University of Geneva in Switzerland can continue to gain ground in using lasers for weather modification and control.
Right now, the results are literally up in the air: firing out of a mobile laser lab, the team has managed to create nitric acid particles, which form the bud of condensation. Get enough condensation coming together, and you can create water droplets heavy enough to fall as rain. The mobile lab being used is called the Teramobile, billed as the "first mobile terawatt laser in the world." It pretty much just looks like a trailer.
Rain droplets typically weigh in at around a tenth of a millimeter. The nitric acid particles that the Geneva crew has been able to create are only a few micrometers in size. (There are 1,000 micrometers in every millimeter.)
Still, it's a promising development, and one that means that work on the project will continue.
Up above you can see a test shot from last year, when the Geneva team managed to create a droplet using lasers that was around 50 micrometers in diameter in a controlled setting. That this method is now showing promise in the open air is another big milestone for the project.