The theory behind so-called marine cloud brightening is that adding particles, in this case sea salt, to the sky over the ocean would form large, long-lived clouds. Clouds appear when water forms around particles. Since there is a limited amount of water in the air, adding more particles creates more, but smaller, droplets.
“It turns out that a greater number of smaller drops has a greater surface area, so it means the clouds reflect a greater amount of light back into space,” Wood says. That creates a cooling effect on Earth.
Marine cloud brightening is part of a broader concept known as geoengineering which encompasses efforts to use technology to manipulate the environment. Brightening, like other geoengineering proposals, is controversial for its ethical and political ramifications and the uncertainty around its impact. But those aren’t reasons not to study it, Wood says.
“I would rather that responsible scientists test the idea than groups that might have a vested interest in proving its success,” he says. The danger with private organizations experimenting with geoengineering is that “there is an assumption that it’s got to work,” he says.
Wood and his colleagues propose trying a small-scale experiment to test feasibility and begin to study effects. The test should start by deploying sprayers on a ship or barge to ensure that they can inject enough particles of the targeted size to the appropriate elevation, Wood and a colleague wrote in the report. An airplane equipped with sensors would study the physical and chemical characteristics of the particles and how they disperse.
The next step would be to use additional airplanes to study how the cloud develops and how long it remains. The final phase of the experiment would send out five to 10 ships spread out across a 100 kilometer, or 62 mile, stretch. The resulting clouds would be large enough so that scientists could use satellites to examine them and their ability to reflect light.
This sounds infinitely preferable to similar schemes that propose to use sulfur.