Mitigating climate change takes several forms, yet more are needed to ensure we’re covering all the bases, according to Lynn Russell, a climate scientist at Scripps Institution of Oceanography at UC San Diego.

Russell is part of a group of 31 atmospheric scientists who recently published a paper in the journal Science Advances about the potential of marine cloud brightening.

What is marine cloud brightening?

Marine cloud brightening is a process through which clouds reflect more sunlight back into space, reducing the amount of heat absorbed by the water below.

All clouds can warm or cool the planet, Russell said; “the ones that cool the most are the ones that cover the most area for the most time and are relatively low in the atmosphere.”

The clouds cool by reflecting sunlight back into space, she said. Marine cloud brightening, then, might work by creating smaller droplets in clouds “to make them reflect more, because brighter things reflect more sunlight.”

Is marine cloud brightening a viable option?

Russell and her colleagues have observed the process working with pollution. Using satellite imaging, “we can actually see … the tracks of certain pollution sources, especially over the ocean, like cargo ships, … the cloud actually gets brighter that follows where that ship went and emitted a bunch of particles.”

Russell was also the lead investigator on a local, year-long study completed in February at the Scripps Pier and Mount Soledad in La Jolla, during which the effects of pollution on clouds were shown to have brightened the clouds.

Marine cloud brightening, then, would be a viable way to create droplets without the added harm of pollution, “which isn’t very healthy,” Russell said, adding there are no specific studies yet on marine cloud brightening, only its potential.

Brightening the clouds would involve adding sea salt to clouds, she said. The salt would be sprayed into the air, becoming particles “small enough to be suspended” in the atmosphere and lifted into the clouds.

Cloud brightening vs. cloud seeding

To those who might align marine cloud brightening with cloud seeding, during which solutions are added to clouds to encourage more precipitation, Russell noted that the processes are different. 

Marine cloud brightening, she said, “can tend to make the clouds rain less [and is] targeted at clouds that generally don’t rain much at all,” like those that gather persistently in San Diego in the spring, earning the names “May Gray” and “June Gloom.”

Cloud seeding has not yet been tried in San Diego.

Potential in climate intervention 

To those who would decry marine cloud brightening as needlessly manipulating Mother Nature, Russell usually responds that “marine cloud brightening is a stupid idea, but it may not be as stupid as doing nothing or continuing to warm the climate with fossil fuel emissions.”

If we weren’t burning fossil fuels, she said, “who would do marine cloud brightening?”

Should marine cloud brightening experiments begin, one of the places with “the best type of cloud” is right here off the coast of San Diego, Russell said.  

“Our Eastern Pacific stratocumulus clouds are pretty world famous, not just for May Gray and June Gloom, but for being a big contributor to some of the planet’s cooling from clouds,” she said.

“The idea is to target offshore, where the clouds persist for days and days,” Russell added.

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