An engineering experiment to cool the earth
In Alameda, scientists are embarking on a novel attempt to cool the Earth — by spraying salt into clouds.
The work, known as marine cloud brightening, is controversial and is just one method of geoengineering — which describes interventions meant to slow Earth’s warming. But proponents say the technology may be needed to mitigate climate change.
To brighten clouds, researchers spray microscopic sea salt into the air over the ocean to boost clouds’ reflectivity. This means less sunlight is absorbed, leading to a planetary cooling effect.
On Tuesday, scientists from the Marine Cloud Brightening Program scaled up their research from the laboratory to the flight deck of the decommissioned aircraft carrier Hornet in Alameda, kicking off a field campaign that will continue until autumn.
The scientists from the University of Washington are experimenting with the size and concentration of sea salt particles emitted from a spray machine. Cloud brightening has been simulated by computer models, but the field work is the first of its kind in North America and only the second of its kind in the world. The foggy climate of the Bay Area, the researchers say, is ideal for these experiments.
The group hopes to refine their formula for artificial sea salt and determine whether their recipe could brighten clouds and cool the planet in a significant way.
How marine cloud brightening works
In order for clouds to form, water vapor droplets need a surface on which to stick. Over land, dust, pollen and ash serve as seeds for cloud droplets, while marine clouds are mainly composed of sea salt particles.
Scientists hypothesize that by manually increasing the number of particles in the atmosphere, clouds will reflect more sunlight back to space, causing Earth to cool.
When clouds reflect more sunlight, they look brighter and whiter to the human eye.
“A white car in a parking lot on a sunny day is going to be cooler than a black car … same idea,” said Lynn Russell, an atmospheric chemist at UC San Diego’s Scripps Institution of Oceanography, who is not involved in the project.
But scientists are just beginning to test cloud brightening in the real world, and they aren’t yet sure whether it will actually work. Simulations project that if 15% of Earth’s marine clouds were brightened, the globe would cool by roughly a degree, said Rob Wood, the lead scientist for the project and a professor at the University of Washington.
“If you increase the number of cloud droplets by increasing the number of sea salt particles, it’s like increasing the number of mirrors to reflect sunlight back to space,” Wood said.
In fact, particles from human pollution, such as wood burning and vehicular exhaust, provide a cooling, a slight offset to the greenhouse warming effect. Bad air quality is linked to health problems like asthma, so over the last decades, officials have ratcheted up regulations, and global air quality has generally improved. But recent studies find clouds are becoming less reflective as pollution declines, accelerating Earth’s warming trend.
“How much extra warming we get now from aerosol reductions is kind of telling us how much cooling we could have if those aerosols were somehow returned into the system,” Wood said.
One way to do that: Seed clouds with salt.
From a large machine resembling a giant snow maker, the group at the Hornet sprays salt water into the air. As the salty plume moves downwind, the water evaporates, leaving behind tiny salt particles nearly a thousand times smaller than the width of a human hair. In the coming months, the scientists will document what happens in the atmosphere.
“We take those measurements and the (weather) conditions on the flight deck … and we’ll see how the model simulations of the plume compares to what we measure,” said Sarah Doherty, the director of the program and an atmospheric scientist at the University of Washington.
Scientists aim to replicate the natural size and concentration of sea salt particles found in marine clouds. If particles are too big in size or number, clouds become too heavy, produce rain and dissipate. Too few particles, and the brightening effect is negligible.
The experiments are brief and small scale. Residents will not see changes to clouds in Alameda in this first phase of the work, according to the scientists.
The next step of research, potentially in the coming years, would attempt to brighten clouds off the California coast. Airplanes, equipped with the same measurement tools, would fly through clouds and test the particle effects.
Interested residents can explore the research equipment and information posters aboard the Hornet’s Sea, Air and Space Museum as early as Friday. Occasionally, visitors will also be able to watch the studies in action aboard the flight deck.
Alameda’s perfect weather
California is a cloud-forming machine in spring and summer. During these seasons, cool, humid winds blow from the Pacific Ocean into San Francisco Bay, making Alameda the ideal climate for marine cloud brightening research.
“When you look at satellite images, there’s often this low layer of clouds that’s relatively thin and near the surface,” Russell said. “And those are the best for brightening because, well, they last a long time.”
The summertime clouds and fog that Bay Area residents are accustomed to blow straight out of the west, over San Francisco and toward Alameda. With the Hornet aligned in a west-to-east orientation, the salt spray can be released at the west end of the flight deck and measured on the east end.
A controversial science
Scientists say the implementation of large-scale marine cloud brightening projects and other geoengineering technologies is still years or decades away, if it is feasible at all.
Geoengineering is a complicated science in its early days. And climate interventions raise serious social, political and economic questions. But global warming is accelerating — 2023 was Earth’s hottest year on record. And geoengineering alone won’t solve climate change.
Scientists like Russell say that before more drastic solutions are deployed, the focus should be on reining in greenhouse gas emissions and making further investments in solar and wind power.
“Emitting particles to offset global warming is not the smartest idea … but it may be better than doing nothing,” Russell said. “Given the point we’re at with warming and climate change, we feel it’s important to know what our options are.”
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