This ‘cloud brightening’ study wasn’t a health risk—but a California city’s officials blocked it anyway

A California city blocked a study related to cloud brightening —a form of geoengineering that could one day be used to cool the Earth— despite findings that the experiment wasn’t a risk to the local environment or community.



In April, University of Washington researchers began an experiment on how particles move through the atmosphere, using a machine that would spray plumes of saltwater mist into the air. That study was part of the Coastal Atmospheric Aerosol Research and Engagement (CAARE) Facility on the USS Hornet , docked in Alameda, California.



But in early May, Alameda officials halted the study due to health and safety concerns. Officials called the research a “cloud brightening study,” though researchers involved said it wasn’t actually testing cloud brightening—which involves spraying saltwater into clouds above the ocean, spurring condensation that makes clouds appear fuller and brighter. Brighter clouds then reflect more sun away from the Earth’s surface, offering a cooling effect. 



Instead, researchers were looking to understand how particles move through the atmosphere . This could later inform scientific models of cloud brightening, but is also important for understanding the effects of pollution. Pollution particles in the air create a cooling effect, and researchers were hoping to understand how cleaning up that pollution may accelerate global warming. 



City officials halted the study in order to complete an assessment of the safety risk of spraying sea-salt particles into the air. That report, released at the end of May, concluded that the experiment would not generate “a measurable health risk to the surrounding community.” 



After those findings came out, the City Council planned to review the report and decide whether the experiment could resume. At that June 4 meeting, all five members of the Alameda City Council voted to reject the continuation of the University of Washington’s experiment.



The machinery in question, a piece of equipment called a “cloud aerosol research instrument,” or CARI, is a small-scale, 2-foot-wide “modified snowblower,” explained a resource manager for the City of Alameda at that meeting. Researchers would measure the effects of that spray between 10 and 200 meters from the nozzle.



“We’re not out to prove marine cloud brightening would work, but to provide data,” Sarah J. Doherty, program director for the Marine Cloud Brightening Program at the University of Washington, said at the meeting. The activities of the experiment, she added, are at a very small scale. “They are not done at a scale that could alter clouds, weather, or the climate,” Doherty said. Still, the city voted to cancel the experiment, citing continued concerns about its impacts.



“We are disappointed by the decision from the City of Alameda,” the researchers said in a statement. Given the impact that cleaning up air pollution may have on global warming, “controlled studies designed to improve models of these aerosol effects are increasingly critical to improving tools for planning and responding to climate change.”



Those involved in the experiment—including from the University of Washington and SilverLining, a nonprofit working with the university—said they’re “already exploring alternative sites” for the research, but also that they “urge the City of Alameda to reconsider.”