Controversial trial of technology that could be used to brighten clouds gets voted down in California

The City Council of Alameda, California, voted early Wednesday to deny scientists permission to continue a controversial trial of technology that could one day be used to brighten clouds. 

The project, among the first of its kind, involved spraying saltwater on the deck of a former aircraft carrier moored at a city pier. The scientists behind it planned to test devices that can create and measure plumes of aerosols. 

Long-term, the research could have served as a step toward a type of climate intervention known as marine cloud brightening. The concept, still mostly theoretical, is to make clouds more reflective of sunlight, which would send more heat back into space and help mitigate global warming. 

No such efforts are underway yet — rather, scientists are designing experiments to investigate how the technology might work. The trial in Alameda would have been part of those efforts, but the City Council voted unanimously against it. 

The episode has put Alameda officials at the center of a public debate that extends far beyond the city, over the promises and perils of geoengineering and whether tests of this kind of technology should be pursued at all. The council’s decision follows similar actions in other areas, including a state-level ban on geoengineering implemented in Tennessee and the abandonment of a geoengineering project that Harvard scientists sought to deploy in Sweden.

However, the council’s vote was not a repudiation of the science or the idea of geoengineering, but rather of the researchers’ approach. The members complained that the project’s leaders hadn’t been transparent, hadn’t provided sufficient review from medical professionals about its safety, and had put the wrong foot forward by beginning to spray saltwater first then asking for permission afterward.

The University of Washington scientists behind the trial had indeed already started their work — and had not widely publicized the details in advance — when Alameda city leaders learned more about it from reports in The New York Times and other news outlets. The researchers had been spraying saltwater along the deck of the USS Hornet, which is now used as a museum on the Alameda waterfront. Their plan called for spraying three times per day on four days of the week for 20 weeks. 

But after city leaders learned about the project, they quickly shut it down to investigate its safety and hold a vote on its fate.

The idea of cloud brightening is to increase the number of water droplets within clouds to boost how reflective they are. Sending more sunlight back to space in that way could reduce the overall warming of the Earth but would not help with other climate problems like ocean acidification. 

Geoengineering research remains a tough public sell despite worsening climate change effects, and the events in Alameda demonstrate the stiff skepticism scientists face over even the most basic experiments.

Much of the City Council members’ deliberation avoided the project’s larger implications, focusing instead on potential local health risks — including the proximity of spray to school soccer fields and neighborhoods — and whether project leaders had taken the proper regulatory steps.

Sarah Doherty, a University of Washington professor who manages the cloud brightening research program, faced sharp questioning. 

“I actually want you to tell us exactly what you did to us,” Councilmember Trish Herrera Spencer said. “I think it’s unfortunate. I think you should all be able to tell us what you sprayed when you sprayed, so we all know what we were exposed to.” 

Doherty told the council that the sprays contained extremely low concentrations of salt and would have little impact on the environment.

“We are not brightening any clouds. We’re not changing the weather. We’re not changing the climate,” Doherty said. 

A city-hired consultant similarly told the council that the project was safe and “not expected to present an unacceptable risk to the surrounding community.”

Other council members bemoaned learning of the project from news reports.

“I don’t like hearing things or getting things from The New York Times. I’d prefer to actually have an opportunity to review them,” Councilmember Malia Vella said. 

The project’s organizers, including Doherty, said in a statement that they were disappointed with the city’s decision and had begun exploring “alternative sites.” The group added that they had sought to be “fully open and transparent.”

“All of the experts engaged affirmed the safety of the sea-salt spray involved in the studies,” the scientists wrote. “These supported our own evaluation that this is a safe, publicly accessible way to further research on aerosols in the atmosphere, to support environmental goals and to promote education and equity in science.”

Alameda Mayor Marilyn Ezzy Ashcraft said the city didn’t need to be on the cutting edge of such research. 

“There are so many competing considerations we need to take into effect and I don’t think you made your case,” Ashcraft told Doherty at the council meeting.  

Some outside environmental organizations, meanwhile, expressed opposition to the project based on more global concerns. 

More than 70 environmental groups released a statement last month urging Alameda to nix the project. The opponents were concerned that someday, wide use of geoengineering technology could shift weather with unintended consequences or reduce the ambition of global efforts to stop using fossil fuels. 

“Our real concern with this is that it opens the Pandora’s box,” said Mary Church, the geoengineering campaign manager at the Center for International Environmental Law.

Church, speaking before the vote, said her organization was not worried about immediate impacts in Alameda, but rather that the project would lay the groundwork for widespread manipulation of the climate.  

“It does nothing to attack the root causes of the crisis,” she said.