Cloud experiment isn’t dangerous, California town officials decide

A technology that could one day cool the planet cleared a key hurdle Thursday.

At the beginning of April, scientists from the University of Washington began testing a device that sprays tiny sea-salt particles into the air. The initial tests, held on the deck of a decommissioned aircraft carrier in Alameda, California, were simply to see if the machine propelled a mist of suitable size. But, in the future, versions of that device could eventually be used to spray particles into clouds, causing them to reflect more sunlight back into space and to temporarily ease global warming.

Two weeks later, Alameda officials ordered the researchers to stop their experiment, citing possible health and environmental risks. The city said it would commission its own assessment to determine if the experiment posed threats.

On May 23, Alameda released its findings: The experiment does not generate “a measurable health risk to the surrounding community” or pose a risk to wildlife, the city said.

“The chemical components of the saltwater solution [which is similar to seawater] being sprayed are naturally occurring in the environment,” the report said. It also noted that seawater “is one of the largest sources of natural aerosols in the atmosphere.”

The Alameda City Council plans to meet June 4 to consider the report and to decide whether to allow the experiment to resume. Researchers had hoped to test the device in different weather conditions over several months or more.

The report, presented by

Alameda’s city manager, recommends that City Council “consider granting” that permission, with additional safeguards in place. The recommended safeguards include setting up air quality monitors at the test site and limiting the hours during which the device can be used.

Brightening clouds is one of several ideas to push energy from the sun back into space, a concept sometimes called solar radiation modification, solar geoengineering or climate intervention.

The idea is built on a scientific concept called the Twomey effect: Large numbers of small droplets reflect more sunlight than small numbers of large droplets do. So, spraying vast quantities of minuscule aerosols into the sky, forming many small droplets, could change the reflective properties of clouds.