Shortly before 9 a.m. Tuesday, an engineer named Matthew Gallelli crouched on the deck of a decommissioned aircraft carrier in San Francisco Bay, put on a pair of hearing protectors, and flipped a switch.
A few seconds later, a snow-machine-like device began to rumble, then produced a large, deafening hiss. A fine mist of tiny aerosol particles shot out of its mouth and traveled hundreds of meters through the air.
It was the first outdoor test in the United States of a technology designed to illuminate clouds and bounce some of the sun’s rays back into space, a mechanism to temporarily cool a planet that is now dangerously overheating. Scientists wanted to see if the machine that took years to create might consistently spray appropriately sized salt aerosols outdoors, outside of a laboratory.
If it works, the next stage would be to try to change the composition of clouds over Earth’s oceans.
As humans continue to burn fossil fuels and pump increasing amounts of carbon dioxide into the atmosphere, the goal of keeping global warming at a relatively safe level is slipping away. This has forced the idea of purposely intervening in climate systems that are closer to reality.
Universities, foundations, private investors and the federal government have begun funding various initiatives, from sucking carbon dioxide out of the atmosphere to adding iron to the ocean in an effort to store carbon dioxide on the seafloor.
“Every year that we have new records for climate change and temperatures and heat waves occur, the field is forced to look for more alternatives,” said Robert Wood, the lead scientist on the University of Washington team leading the bleaching project. of the sea clouds.
Cloud bleaching is one of several ideas to return solar energy to space, sometimes called solar radiation modification, solar geoengineering, or climate intervention. Compared to other options, such as injecting aerosols into the stratosphere, bleaching marine clouds would be localized and use relatively benign sea salt aerosols rather than other chemicals.
And yet, the idea of interfering with nature is so controversial that the organizers of Tuesday’s test were very discreet regarding the details, worried that their detractors would try to stop them. Although President Joe Biden’s administration funds research into various climate interventions, the White House distanced itself from the California study, sending a statement to The New York Times that read: “The United States government is not involved in the experiment.” of Solar Radiation Modification (SRM) taking place in Alameda, California, or anywhere else.”
In 1990, a British physicist named John Latham published a letter in the journal Nature, under the title “Control of global warming?”, in which he presented the idea that injecting tiny particles into clouds might counteract rising temperatures. .
Latham had a proposal that might seem strange: create a fleet of 1,000 unmanned ships that would propel sails to traverse the world’s oceans and continuously spray tiny droplets of seawater into the air to divert solar heat from the Earth. .
The idea is based on a scientific concept called the Twomey effect: large numbers of small droplets reflect more sunlight than a small number of large droplets. Injecting large amounts of tiny aerosols, which in turn form many small droplets, might change the composition of clouds.
“If we can increase the reflectivity by three percent, the cooling will balance the global warming caused by the increase in C02 in the atmosphere,” Latham, who died in 2021, told the BBC. “Our scheme offers the possibility of buying time” .
Whitening clouds is not an easy task. To be successful, the size of the aerosols needs to be just right: particles that are too small would have no effect, explained Jessica Medrado, a research scientist on the project. If they are too large, they might be counterproductive and cause clouds to be less reflective than before. The ideal size is submicron particles, almost 1/700 the thickness of a human hair, Medrado mentioned.
Then, you have to be able to expel many of those correctly sized aerosols into the air: a quadrillion particles, more or less, every second. “There is no standard solution,” Medrado said.
The answer to that problem came from some of the most prominent figures in the US technology industry.
In 2006, Microsoft founder Bill Gates was briefed by David Keith, one of the leading researchers in solar geoengineering, which is the idea of trying to reflect more of the sun’s rays. Gates began funding Keith and Ken Caldeira, another climatologist and former software developer, to advance their research.
The pair considered the idea of marine cloud bleaching, but questioned whether it was feasible.
So they turned to Armand Neukermans, a Silicon Valley engineer with 74 patents. One of his first jobs was at Xerox, where he devised a system to produce and spray ink particles for photocopiers. Caldeira asked him if he might develop a nozzle that would not eject ink, but rather sea salt aerosols.
Intrigued, Neukermans, now 83, brought some of his former colleagues out of retirement and began research in a laboratory borrowed in 2009, with $300,000 from Gates. They called themselves Old Salts.
The work was moved to a larger laboratory. Medrado became the project’s chief engineer two years ago. Late last year, the sprayer was already assembled and waiting in a warehouse near San Francisco.
The machine was ready. The team needed a place to test it.
The Hornet’s flight deck rises 50 feet above the Alameda shoreline, on the east side of San Francisco Bay. On Tuesday, she had a series of precisely calibrated sensors sitting atop a row of scissor lifts rising into the air.
Beneath an American flag, at the far end of the flight deck, was the sprayer: bright blue, regarding the shape and size of a projector, with a ring of tiny steel nozzles around its mouth. one meter wide. Researchers call it CARI (Cloud Aerosol Research Instrument).
On one side of the sprayer was a container-sized box that housed a pair of compressors, which supplied high-pressure air to the sprayer through a hose. On the other side was a water tank. A series of switches, turned in a careful sequence, introduced water and air to the device, which shot a fine mist toward the sensors.
The goal was to determine whether aerosols coming out of the sprayer, which had been carefully manipulated to reach a specific size, maintained that size when shot through the air under different wind and humidity conditions. It will take months to analyze the results. However, according to Wood, the answers might determine whether and how marine cloud bleaching will work.
Kelly Wanser, a former technology executive, helped establish the marine cloud bleaching project at the University of Washington. In 2018, Wanser created SilverLining, a nonprofit organization to advance research into what she calls “short-term climate interventions,” such as cloud bleaching. Wanser’s group is contributing some of the funding for the research that includes the study aboard the Hornet.
Wanser said he hoped the tests, which might continue for months or longer, would demystify the concept of climate intervention technologies.
Wanser is already thinking regarding the next phase of that research. “The next step is to go out into the ocean, point the spray a little higher and touch the clouds,” he said.
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