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Startups want to cool Earth by reflecting sunlight. There are few rules and big risks


Coming out of the hottest year on record, people are desperate for climate solutions. A few startup companies think the answer is a new and controversial technology that involves shooting particles into the stratosphere, as NPR's Julia Simon reports.

JULIA SIMON, BYLINE: A few years ago, Luke Iseman, an American entrepreneur, was living in Mexico.

LUKE ISEMAN: I guess semi-retired, and I figured I'd eventually get tired of spearfishing for 20 to 30 hours a week.

SIMON: One day, he turns on an audiobook, a science fiction novel by Neal Stephenson called "Termination Shock."

UNIDENTIFIED PERSON: Two elements, T.R. said, alike in dignity.

SIMON: In the novel, a Texas billionaire shoots sulfur into the stratosphere - that's about six to 30 miles above Earth's surface - to combat global warming. And this is real science. If you create certain particles in the stratosphere, they can reflect sunlight, which can cool the planet. Iseman finished the book and started Googling this technology, called solar geoengineering.

ISEMAN: When I started researching, I was like, what the hell am I missing here?

SIMON: Iseman is not a scientist, but he read scientific papers and decided this is the climate solution. In 2022, he made a solar geoengineering startup called Make Sunsets, and Iseman is not alone. He's part of a growing number of startups, research projects, and nonprofits getting this tech ready to possibly use it to cool Earth on a massive scale.


SIMON: Late last year, I went to a parking lot in Silicon Valley to meet Iseman. He had a mohawk hairstyle, an orange T-shirt that read, cool Earth. He showed me inside an RV with big metal tanks full of helium and sulfur dioxide gas. He opened the tanks, and the gases flowed through long tubes to a big white weather balloon.


SIMON: As Iseman and his business partner filled the balloon outside...

Ooh, jeez. Yup, you can smell that (coughing).

Sulfur dioxide began to leak out, which in high quantities is bad for human health.


When the balloon was about six feet wide, they tied it up.

ISEMAN: Do you want to let it go?

SIMON: I'll let you do it.

ISEMAN: Three, two, one.

SIMON: There she goes.

The balloon sailed into the stratosphere. They released two more, creating enough particles, the company says, to offset the heating of about 175 cars for a year. That's not a lot, but Make Sunsets is attracting investors - more than 1.2 million dollars from venture capital. A U.S.-Israeli startup also working on this tech has raised $15 million. Gernot Wagner at Columbia Business School says the idea of geoengineering the planet to avoid the worst impacts of climate change is capturing the imaginations of lots of people.

GERNOT WAGNER: Climate tech is sexy. Right? Because it's the lure of the techno fix. Look to D.C., and, you know, things are messy. Politics is messy. Wouldn't it be nice if we could cut through all of this with the ultimate techno fix that will solve this thing once and for all?

SIMON: But scientists say this type of solar geoengineering can pose lots of risks. It could affect global crops. It could weaken rain patterns that billions of people rely on. As for the particles, they only stay up for a year or two, and then they fall back to Earth. Depending on the material, they can have health and environmental risks, including acid rain. If you suddenly stop this type of solar geo engineering and you haven't been simultaneously reducing emissions, that can be a big problem, says Christopher Trisos, climate scientist at University of Cape Town.

CHRISTOPHER TRISOS: You get a whole rush of global warming and climate change in a very short period of time. And that would be very dangerous for ecosystems, for biodiversity, in many cases, very dangerous for crops and food supplies as well.

SIMON: The U.S.-Israeli company Stardust Solutions notes their focus is research. They see a future for getting government contracts for this work, and write in an email that governments should make decisions about deployments. Make Sunsets hopes to grow, but experts say they need significantly more material to have an impact, and that could be years away. Still, legal scholars see near-term risks, Tracy Hester at University of Houston Law Center says, as global warming gets worse.

TRACY HESTER: There's going to be a strong desire by someone somewhere to do something, and they're going to do it now, not after five or 10 years of research.

SIMON: There is little domestic and international regulation of this technology, he says. Alia Hassan, from the nonprofit the Alliance for Just Deliberation on Solar Geoengineering, worries regulations are following behind.

ALIA HASSAN: Do we want the governance process to be ahead of the deployment of these technologies or do we want to try and run after it once it's too late?

SIMON: Last month, Hester and other academics filed a petition with the National Oceanic and Atmospheric Administration asking them to consider requiring solar geoengineering companies like Make Sunsets to file more information about what they're doing. They haven't received a formal response yet. Iseman of Make Sunsets says he's open to more regulations, but he isn't waiting for the government's green light. He thinks the risks of global warming outweigh the risks of this tech.

ISEMAN: I have an obligation to do what I can to cool the planet, as does anyone else who actually reads the science.

SIMON: Still, Imran Khalid, a climate policy expert in Islamabad, says Make Sunsets needs to think more about people in places like Pakistan. Solar geoengineering's risks, like droughts and diseases, could potentially affect developing countries more. Khalid says there should be a global discussion before, not after, advancing this technology. What the world doesn't need, he says, is a climate cowboy.

IMRAN KHALID: A John Wayne out there to take things into his or her own hands and try and go alone - we need to avoid that.

SIMON: Just like climate change, solar geoengineering could affect much of the planet. Khalid says this time, people around the world need a seat at the decision-making table.

Julia Simon, NPR News, Silicon Valley.

RASCOE: You could learn more about solar geoengineering by listening to this week's The Sunday Story podcast and find photos of the balloons at Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Julia Simon
Julia Simon is the Climate Solutions reporter on NPR's Climate Desk. She covers the ways governments, businesses, scientists and everyday people are working to reduce greenhouse gas emissions. She also works to hold corporations, and others, accountable for greenwashing.