Zapping clouds with lasers could alter Earth’s climate

Laser blasts might one day help scientists tweak Earth’s temperature. To do that, the lasers would be aimed at thin, wispy cirrus clouds. By shattering the ice crystals in them, those laser zaps might help cool the ground-level climate.

It’s a clever idea, although not ready for prime time. It also has its critics.

In the new study, researchers zapped tiny ice particles in the lab. This formed new, smaller bits of ice, they reported May 20 in Science Advances. Clouds with more — and smaller — ice particles reflect more light. So if used on clouds, this laser therapy might cause them to reflect more sunlight back into space. And that, the scientists propose, might offer one way to help combat global warming.

The scientists work at the University of Geneva in Switzerland and the Karlsruhe Institute of Technology in Germany. They injected water droplets into a chilled chamber. Its frigid conditions mimic those high in Earth’s atmosphere, where cirrus clouds live. The water froze into spherical ice particles. The scientists then walloped these spheres with short, intense bursts of laser light.

As each was hit, ultrahot plasma formed in the center of the ice particle. That produced a shock wave that split apart the particle. It also vaporized much of the ice. The excess water vapor left in the aftermath then condensed and froze into new, smaller ice particles.

Applying this technique to clouds is “a long, long, long way in the future,” says Mary Matthews. She is a physicist at the University of Geneva and an author of the study. Current laser technology is not up to the task of cloud zapping — yet. “What we are hoping for is that the advances in laser technology, which are moving faster and faster all the time, will enable high-powered, mobile lasers,” she says.

But tinkering with cirrus clouds could backfire if scientists aren’t careful, warns Trude Storelvmo. She is an atmospheric scientist at Yale University in New Haven, Conn. Clouds trap heat, through the greenhouse effect. So breaking up a cloud’s ice particles — which makes more of them — might actually warm Earth. The cooling tactic “could potentially work, but only if you target certain types of cirrus clouds,” she argues. It might be better to target very thick clouds only.

There also could be warming if fossil fuels are burned to power the laser, points out David Mitchell. He is an atmospheric scientist at the Desert Research Institute in Reno, Nev. When fossil fuels are burned, they produce greenhouse gases. Those gases are responsible for global warming. “I think it’s really interesting research,” he says of the new study. Still, he says, “I’m just not seeing how it’s going to make the world a cooler place.”