A company at the forefront of solar geoengineering — the notion that blocking radiation from the sun could cool a warming planet — has disclosed details of the materials it wants to sprinkle in the atmosphere.
Stardust Solutions, led by former members of Israel’s nuclear energy program, is publishing research on Thursday that reveals the chemical properties of its particles, how they would affect the atmosphere and how high-flying aircraft would disperse the material.
The privately held company, founded in 2023, is farthest ahead in the contest to take an idea that was once the stuff of science fiction and move it into the mainstream. It has attracted $75 million from investors, has applied for a patent and is submitting its research to scientific journals for peer review.
Its chief executive, Yanai Yedvab, said Stardust Solutions had only tested its materials in its laboratory and had no plans to conduct outdoor tests. Outdoor trials would only be done in collaboration with a government that would set ground rules and guardrails, he said in an interview.
As humans continue to burn fossil fuels and greenhouse gas emissions reach record levels, Dr. Yedvab and others say that managing solar radiation deserves serious consideration.
“This is a very powerful tool that will be ready for testing very soon, and we want policymakers to start thinking seriously, ‘What will it take in practice?’” he said.
But the idea of manipulating the atmosphere to turn down the temperature of the Earth remains contentious, and more than 600 scientists and academics have called for an international ban.
Prakash Kashwan, a professor of environmental studies at Brandeis University, is among them. He said solar geoengineering could tamper with weather patterns, damaging food production and local economies.
It’s especially worrisome for residents of South Asia and parts of East Africa and Latin America who rely on yearly monsoon rainfall to irrigate crops, Dr. Kashwan said.
“There’s this social risk for at least two billion people that is directly connected to the lack of scientific understanding about how interfering with the global temperature thermostat is going to interfere with the monsoon formation,” he said. “We don’t have a solution for those kinds of risks.”
Tennessee and Florida have banned geoengineering and, in February, Representative Greg Steube, a Florida Republican, introduced a bill in Congress that would do the same. In 2023, at the direction of Congress, the Biden administration issued a report on the need to study solar geoengineering. That research that has not been pursued by the Trump administration.
Dr. Yedvab said that Stardust officials were having preliminary conversations with policymakers in the United States and Europe about the company’s proposal but declined to identify them. Stardust Solutions spent $370,000 last year on federal lobbyists, according to OpenSecrets, which tracks lobbying spending.
The materials produced by Stardust are made from amorphous silica, which is used as a food additive and in some consumer products, and calcium carbonate, a compound found in eggshells and limestone. The company said its particles were biodegradable, were not harmful to people or animals, and would not accumulate in the oceans or soil. Released in the upper atmosphere, the particles could reflect a small amount of sunlight away from Earth, the company said.
Until Thursday, the company kept the ingredients under wraps, requiring anyone who wanted to see its data to sign a nondisclosure agreement.
Michael S. Diamond, a professor of meteorology at Florida State University, said he was surprised by the simplicity of the Stardust particle.
“It’s quite an elegant idea, and I like that it is using relatively well known particles,” said Dr. Diamond, who studies how aerosol particles affect the climate. “I’m a little bit surprised that they’ve kept this so secretive. I thought they were going to do something really out there, but amorphous silica itself is a very widely used product.”
David Keith, professor of geophysical sciences at the University of Chicago who has researched the idea of slowing climate change with reflective particles for more than two decades, said he needed more information.
“This is really good idea, it’s cool and it might be useful,” Dr. Keith said. “But the big question is, what is this environmental impact? The answer has to be, from anybody, is that we don’t know.”
Dr. Yedvab likened his company to a drug development lab that conducted its initial work behind closed doors before applying for approval from the Food and Drug Administration.
“Solar reflection technology is heavy lift,” Dr. Yedvab said during an interview. “You want to make sure that you’re doing it when you can say credibly. You don’t want to say, ‘Yeah, I overlooked something or something was missing and I need to go back and correct it.’ This was the responsible thing to do.”
In addition to concerns about unintended consequences, environmental groups have worried that geoengineering could reduce pressure on countries and industries to reduce the emissions that are driving climate change. But in the past several years, record global temperatures, increasing risk of drought and wildfire, and the increasing intensity of severe storms and floods, have pushed many researchers and some environmentalists to accept the notion that solar geoengineering must at least be studied.
Dozens of academic labs in the United States, Europe, and Asia are now modeling how spraying various amounts of reflective particles in different locations might cool the planet. A team from the University of Cambridge and Harvard University, with backing from the British government, plans to launch a high-altitude drone sometime next year to test reflective particles in a metal tray without releasing them into the atmosphere.
Most of these efforts have contemplated using sulfur dioxide, a compound released during volcanic eruptions that changes from a gas to sulfate, an aerosol particle that reflects sunlight. Because sulfate particles in some concentrations can damage the protective ozone layer, and because they might warm the stratosphere, Stardust officials said they chose something different.
Stardust Solutions is registered in Delaware as a U.S. company with an Israeli subsidiary called Stardust Labs. Its laboratory is in Ness Ziona, Israel, about 12 miles south of Tel Aviv, near the renowned Weizmann Institute of Science.
Dr. Yedvab, co-founder Amyad Spector and a team of 25 researchers have developed two kinds of particles. The first is made of amorphous silica and coated in a material to prevent it from interacting with atmospheric gases. The second particle is a shell of amorphous silica around an inner core of calcium carbonate.
The company said the amorphous silica would be used as in initial effort to reflect up to 1 percent of the coming sunlight, while the silica-carbonate particle could be used at higher concentrations to block more than 1 percent.
Using a chamber that mimics the subzero conditions of the stratosphere, Stardust researchers tested the silica particle with atmospheric trace gases to see how they would react.
The second silica-carbonate particle has similar surface chemistry to the first one but is still being tested, Dr. Yedvab said.
Stardust also tested a dispersion system to make sure the particles would spread out after being sprayed from an aircraft and would not react with water vapor to form ice crystals and drop toward the ground.
Stardust executives said that initial effort to begin atmospheric cooling would cost about $10 billion. That would cover the material, the aircraft that could disperse it at high altitudes and a monitoring system using a chemical tag to track the particles in the air and, later, on the ground.
By adding 10 million tons of the reflective particles to the atmosphere over the course of several years, the atmosphere could be cooled by 1.5 degrees Celsius, the company said. There are no known health effects from exposure to amorphous silica at the levels found in the environment or in commercial products, according to the Agency for Toxic Substances and Disease Registry, a branch of the Centers for Disease Control and Prevention. But some scientists said they wanted more information about how the particles might affect human respiratory health.
Dr. Yedvab noted that the Department of Homeland Security sprayed amorphous silica into the New York City subway system in 2016 as part of an experiment to test emergency preparedness against a potential bioterrorism attack. The silica was used as a nontoxic tracer to check how a potential pathogen might spread in the subway.
Still, the conflict between Stardust and some critics is not over the safety of its particles but whether a private company should be involved in geoengineering research at all and Stardust’s lack of transparency until now.
Daniele Visioni, professor of earth and atmospheric sciences at Cornell University, said Stardust should follow the traditional path of announcing scientific discoveries by presenting data at a conference and answering questions from scientists working in the same field.
“I keep seeing that all the moves they make are the wrong ones process-wise,” Dr. Visioni said.
The American Geophysical Union, the Natural Resources Defense Council and two other nonprofit groups have formed a coalition to write a code of ethics for research into cooling the planet.
Shuchi Talati, who founded the coalition, said she was troubled by the idea that a private for-profit company could own the rights to a something that could profoundly affect the planet.
“There’s no trust whatsoever,” Dr. Talati said. “Where has the scientific merit review and the transparent public review process been for the last two years for this alleged particle? This idea of intellectual property with solar radiation management is massively problematic.”
Dr. Yedvab said that research into geoengineering had been stalled and that Stardust was shaking things up. “We feel that our role is to disrupt this field to make sure that governments have options,” he said.
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