Peace Magazine: Shall We Whiten Clouds?

Peace Magazine

Shall We Whiten Clouds?

• published Jul 06, 2024 • last edit Jul 11, 2024

Early in June, Project Save the World hosted a forum in which three experts explored the intriguing field of Marine Cloud Brightening. Here’s part of what they said.

Marine Cloud Brightening (MCB) is a proposed method to combat global warming by enhancing the reflective properties of clouds. It involves spraying salt water into clouds to increase their albedo, or reflective power.

By enhancing the whiteness of the clouds, this can reflect more sunlight back into space, thus reducing the amount of solar energy reaching our planet’s surface and potentially cooling the planet. Here is our expert panel:

Hugh Hunt, who holds the distinction of being the “keeper of the clock” at the University of Cambridge, where he also holds another high post, teaching and researching mechanical engineering. At the university’s Centre for Climate Repair, he focuses on various innovations that may cool the planet.

Daniel Rosenfeld, an emeritus professor from the Hebrew University of Jerusalem, shares his recent practical experience aboard a vessel near Australia, where experimental salt water spraying into clouds was conducted.

Steven Rogak is a professor of mechanical engineering at the University of British Columbia. His expertise is in aerosols, which are crucial in cloud formation, for each droplet must form around an aerosol nucleus.

We were joined by Adele Buckley, a physicist and retired engineer in Toronto — who asks difficult questions that are beyond my expertise.


The panelists began by sharing news about a recent experiment in San Francisco that attracted significant attention but was temporarily halted because many in the Bay Area worried that the sea water might be a health hazard.

Fortunately, the investigation found that the experimental spray is just like the natural spray that is continuously present in the region’s environment, so the experiment was allowed to proceed.

It was an early test of the spray mechanisms and their environmental impacts, as the researchers had not yet tried to modify clouds. They were not surprised that there had been public opposition to the experiment, as many people have worries about potential health effects. Therefore, experiments must be robustly designed and carried out with extreme care, so as to allay public misgivings about the safety of such technological solutions.

The main challenge is to create salt particles of the right size to achieve the cloud brightening effects. It is important for the aerosols to be of the right size to form nucleuses in clouds of the desired brightness and potentially larger size.


The experts discussed the practical and ethical challenges surrounding Marine Cloud Brightening:

Rogak emphasized the importance of MCB’s energy efficiency. Unlike carbon dioxide removal, which requires much energy, he said that Marine Cloud Brightening operates on a much smaller scale, making it less energy-intensive than other approaches – particularly another proposed method of climate repair, Direct Air Capture.

Rosenfeld shared his experiences from field tests in Australia, highlighting the difficulty of visibly impacting clouds even with substantial effort.

The technology’s current limitations in scalability and efficiency were discussed, pointing to the need for more advanced engineering solutions, particularly in the development of effective salt water spray nozzles.

We discussed the public’s attitudes and concerns about the potential health impacts of increased particulate matter from salt sprays.

Predictably, the conversation touched on the widespread demand for any geoengineering efforts to be authorized by an explicit global consensus before any significant intervention is undertaken — a valid prerequisite for authorizing experimentation that might affect the whole globe or even one hemisphere.

However, Rosenfeld suggested that experiments which would have only local or regional effects should require the permission only of any local neighbors who might be affected. For instance, the MCB that would be used to cool the Great Barrier Reef can have only local regional effects, so Australia would not need the consent of other countries.

Rosenfeld emphasized the importance of preparing these innovative technologies soon, for use later in emergency climate situations. And of course, the urgency of preparing climate repair technologies now must not distract the public’s attention from the primary global challenge: reducing greenhouse gas emissions.

Hunt gave an apt analogy – the similarity of our situation today with the crisis that arose on Apollo 13’s mission to the moon.

When the technical problem arose on the rocket, the only possible solution was with procedures that had not been tested. If these procedures had not been used, the astronauts would surely have died. But fortunately, they did work and Apollo’s crew returned safely to earth.

Today, we may have too little time to test the potential solutions before we have to use them. But Hunt says that we can “learn by doing” these innovations. The other panelists agreed, with Rogak adding this caveat: if we start deploying some of the new innovations and “learn by doing them,” at least we should start with small-scale pilot projects, to allow for adjustments and improvements as the initial projects gradually become larger scale.

Hunt noted the significance of engaging with local communities, particularly Indigenous populations, to ensure that geoengineering efforts are conducted responsibly and with respect.

The experts mentioned the Great Barrier Reef as an example where local support is crucial to the success of environmental interventions. The local Aboriginal populations are enthusiastic in supporting the MCB project, though Hunt does not know whether all Indigenous groups in Australia share a common opinion.


The panel concluded with thoughts on the future of Marine Cloud Brightening, stressing the crucial necessity of expanding research and development. However, the experts underscored the potential benefits of this technology in reflecting solar radiation and its relatively low energy requirements compared with other geoengineering techniques.
We encourage you to watch the whole video and share your ideas on this page of our website:

Published in Peace Magazine Vol.40, No.3 Jul-Sep 2024
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