Team urges test of cloud brightening

Posted by Emma Woollacott

Scientists are proposing a test of cloud brightening as a possible way of countering global warming.

They want to use special ships to shoot salt water high into the sky over the oceans, creating clouds that would reflect sunlight away from the Earth.

"What we're trying to do is make the case that this is a beneficial experiment to do," says University of Washington atmospheric physicist Rob Wood.

Clouds appear when water forms around particles, and the theory behing cloud brightening is that adding sea salt to the sky over the ocean would form large, long-lived clouds. 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," says Wood.

Wood wants to carry out a small-scale experiment to test the feasibility of the idea and look at its effects. The test, he says, should start by deploying sprayers on a ship or barge to ensure that they can inject enough particles of the right size to the appropriate elevation.

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 more planes to study how the cloud develops and how long it remains. Finally, his team would send out five to 10 ships spread across a 100 kilometer stretch. The resulting clouds would be large enough so that scientists could use satellites to examine them and their ability to reflect light.

There will, naturally, be strong opposition to such an experiment. But Woods says there's very little chance of long-term effects.

"I would rather that responsible scientists test the idea than groups that might have a vested interest in proving its success," he says.