Support local news in Alameda. Give Now!

City Halts Climate Experiment

University of Washington cloud brightening experiment on hold while Alameda investigates impact

The City of Alameda has instructed the University of Washington (UW) to halt the cloud brightening experiment that it was conducting in partnership with the USS Hornet Sea, Air, & Space Museum.

Alameda Post - the USS Hornet
The USS Hornet at Alameda Point’s Pier 3 on Veterans Day, 2023. Photo Brock de Lappe.

Led by an interdisciplinary team of scientists, experts, and researchers, UW’s Marine Cloud Brightening (MCB) Program investigates how aerosol particles created from natural and human activities interact with and impact the brightness and reflectivity of clouds. The Program aims to shed insight on the feasibility of mitigating global warming by increasing the reflection of sunlight from marine clouds, achieved by spraying sea salt particles into the air from ships on the ocean.

Alameda Post - a science graphic that says "basic principle behind marine cloud brightening". One one half of the page, a cloud with "fewer larger drops" says "Lower reflectivity." On the other side of the page, a cloud of "more smaller drops" says "higher reflectivity."
“Changes to the size and number of droplets in clouds can change how much sunlight those clouds reflect back into space.” Graphic University of Washington.

To help facilitate its research, the Program team established the Coastal Atmospheric Aerosol and Research and Engagement (CAARE) Facility at the USS Hornet to conduct smaller-scale field studies in a localized environment.

According to MCB Program Director Sarah Doherty and UW atmospheric scientist Robert Wood, the team identified the USS Hornet as an ideal testing ground due to its museum status and ample facilities to support research operations, as well as Alameda’s atmospheric conditions, which are similar to the ocean environment the team is interested in simulating.

At the experiment’s core is the Cloud Aerosol Research Instrument , or CARI, a machine resembling a snowmaker that shoots a plume of water and salt droplets—an imitation of ocean water—across the Hornet’s flight deck. Researchers take measurements to determine the scalability of the process to the open ocean and its effects on the atmosphere.

Alameda Post - a detailed scientific illustration labeled "Single Plume Cloud Perturbation Experiment." With photos indicating the positioning of a ship, a UAV deployed from the ship, and two research aircrafts measuring the experiment. The experiment is measuring a sea salt plume on clouds
Proposed aerosol-cloud interaction studies to be conducted on the ocean. Photo Robert Wood/University of Washington.
Alameda Post - on the deck of the USS Hornet, an American flag waves while people use a very large fan apparatus to spray salt and water across the deck
CARI, the testing apparatus that generates the plume of water and salt droplets, is located on the flight deck of the USS Hornet. The cloud brightening experiments have since been paused. Photo USS Hornet.

But on Saturday, May 4, the City released a public notice saying that it had stopped the experiment on the grounds that it was in violation with the City’s lease with the USS Hornet.

“We believed that our existing permits and lease covered these activities when we started,” Laura Fies, Executive Director of the USS Hornet, told the Alameda Post. “We are committed to working with the City to meet all of their needs.”

The City also announced that it is working with a team of independent consultants to evaluate the health and environmental safety impacts of the spray testing, but noted that there is “no indication that the spray from the previous experiments presented a threat to human health or the environment.”

An expert assessment published by UW prior to the experiment reached a similar conclusion: particles released during the spray testing fall below thresholds that would require additional approval or permits from state and local environmental regulatory agencies.

“This review was not unexpected given that this is something new,” Doherty and Wood said. “The facility is designed to help regulators, community members and others review things closely, and we consider the current interactions with the city to be an integral part of that process and we are really happy to support this.”

Findings from the City’s evaluation will be shared with City Council and the public for consideration in June.

Although the experiment’s progress is now on hold, Fies’ vision for future testing could position the USS Hornet as a key player in highlighting and celebrating the ample STEM-driven innovation happening in Alameda Point.

“I would be interested in exploring running the studies during the Museum’s open hours to allow guests the option to engage with the project,” Fies said, “in the hope that we all might benefit from the opportunity to support and engage with this important climate research effort.”

Ken Der is a contributing writer for the Alameda Post. Contact him via [email protected]. His writing is collected at

KQED Curated Content

Support our mission to provide trustworthy news and information for Alameda every day.

Thanks for reading the

Nonprofit news isn’t free.

Will you take a moment to support Alameda’s only local news source?