Marketplace - From "How We Survive": How to Dim the Sun

Episode Date: June 14, 2026

Today, we’re featuring an episode from the new season of “How We Survive.” Could dimming the sun be the key to cooling things down before the climate crisis worsens? Some scientists say yes, that we can cool the earth by launching tons of sulfur dioxide into the stratosphere. It’s a type of solar geoengineering that was once seen as preposterous, meant to exist only in the pages of a sci-fi novel. But now, it’s a reality. To find out for ourselves, we travel to Northern California where two entrepreneurs are launching sulfur-filled balloons from the top of stacked shipping containers. Later, we talk with scientists on both sides of this issue to find out if solar geoengineering could help prevent catastrophic tipping points or introduce a whole new slew of cascading consequences.

Hey, everybody, it's Kai. We know the climate crisis is escalating. The question is, what are we going to do about it? Today, we're sharing the first episode of the latest season of our climate solutions podcast, How We Survive. Amy and the team are exploring large-scale climate interventions, like dimming the sun. Really? It's actually a fascinating episode, only slightly terrifying. Enjoy it. So what are we going to do right now? We're going to launch some balloons and send them into the stratosphere, filled with sulfur dioxide and hydrogen gas to get it up there. So, in other words, just another Wednesday morning in Northern California. Exactly.

At an undisclosed location in the San Francisco Bay Area, I'm with Andrew Song and his business partner, Luke Eisman. We're in an industrial area near a deli and a bunch of warehouses. We'll heads up. This is, we'll have to be careful walking. It's actually the roof of a container at my friend's warehouse around the corner. Okay. Good thing I'm not wearing heels. Right.

My producer, Haley, and I are about to embark on an assignment that is not, not sketchy. To launch these special balloons, we first have to climb up some ladders to the top of two shipping containers stacked on top of each other. Be careful, Haley. You should be telling me to be careful. I know. I'm like, I'll catch you. Yeah. Let the middle-aged lady go first. We're about 21 feet off the ground with no guardrails. Don't stand on the edge.

We don't want anyone dangling. I am so nervous for you. No broken bones. And lying on the roof are several long cylindrical gas tanks. Hydrogen to lift the balloons up into the stratosphere. It's cheaper than helium. Hydrogen gets an unfairly bad rap. You have one Hindenburg and everyone gets all nervous.

To be fair, that was a big disaster. And also sulfur dioxide, a pungent toxic gas that's a byproduct of fossil fuel production. If you've ever lit a match, you know the smell. But it does have one thing going for it. When it's released into the upper atmosphere, it reacts with water vapor to form tiny, particles that reflect sunlight away from the Earth and cool the planet. That's the idea, anyway. Luke and Andrew are co-founders of Make Sunsets, a startup that sells what they call cooling credits. For as little as $1, you can pay them to release one gram

of sulfur dioxide into the stratosphere, which they say is roughly enough to offset the warming caused by a ton of carbon dioxide. This type of climate intervention, is known as geoengineering, or in other words, messing with the Earth's natural systems to undo some of the damage we've done by burning fossil fuels. Okay, so at this point,

if you guys want to put on some masks, I would invite you to do so. I'm going to do it myself. We put on some intense-looking PPE, goggles and respirators. All right, so we're all masked up, except for Luke. What, you don't wear a mask?

We, honestly, what do we wear? like half the time, would you say? Yeah. And Luke and Andrew get to work, carefully lifting up the tanks to start filling up a weather balloon. One of those big latex ones meteorologists used to take atmospheric measurements.

The stinging, like, sensation of my eyes, is that from cycle? My eyes are stinging, too. Okay, yeah, try and blink a little bit and should pass. Hopefully. Once the balloon has been filled, it's about six feet in diameter, floating above Andrew's head.

They attach a small black box to the string, which tracks the balloon's altitude. That's how they verify it gets high enough into the stratosphere before it bursts and releases the sulfur dioxide. You guys can launch it if you want to. Oh, yeah. I mean, could I get in trouble for launching it? No. We've had five-year-olds launch it before, so perplexed it fine.

It's not illegal in California. yet, though several states have banned or proposed banning solar geoengineering, I step over the gas tanks and stand precariously between Andrew and Luke as they hand me the balloon. You're going to let go and just pull your hand back so that this doesn't catch your hand. So I'm just going to let it go? Go for it. All right. One, two, three.

We watch as the balloon floats up into the clouds and disappears as a balloon. it makes its way some 60,000 feet into the stratosphere. Do that a couple more million times with bigger balloons. Orders of magnitude bigger balloons per year. Is that a goal for you guys personally to build your business to do meaningful cooling? I mean, the goal of makes sunsets is to cool Earth as quickly as we safely can. It sounds crazy and I'll be the first to agree that this should not be a private company doing this. but the only thing worse than a private company doing this is no one doing this at all.

I'm Amy Scott. Welcome to How We Survive, a podcast from Marketplace about the messy business of climate solutions. And this season is all about engineering nature. From injecting sulfur dioxide into the stratosphere to sucking carbon out of the air, manipulating clouds to make more rain and snow, even bringing back extinct sun. species, we're looking at the wild, unsettling, and potentially hopeful ways that we're tinkering with nature to save the planet. This is episode one, How to Dim the Sun. Back on the ground with the make sunsets guys, we head to Andrew's RV that's parked around the corner for a quiet place to talk. My kids' car seats are also in there, so I can clean up a little bit.

So how old are they? Six and seven. Andrew is a single dad with full custody of his kids. How much does that motivate what you do? I mean, it's everything. My kids didn't choose to use fossil fuels to power their lives. And I'd really hate myself if knowing that there was a way to cool down the planet effectively and safely. And you didn't do anything about it. Do either of you have a science background? We don't.

No. So why are you qualified to do this? I think I'm no more or less qualified to do geoengineering than anyone else who does geoengineering by getting onto a plane or turning on their gas-burning vehicle. We just don't call or scientists try not to call those things geoengineering because we're just used to them. Mother nature, it turns out, doesn't really care about our intentions at all. It's geoengineering, whether we're helping or hurting the planet, whether we're warming or coaling the planet, it's still geoengineering. Luke and Andrew met in 2015. while they were working for different startups.

Andrew was at Indiegogo, the crowdfunding site. Luke was at Y Combinator, the startup accelerator that helped launch Reddit, DoorDash, and OpenAI, among many others. Launching sulfur into the stratosphere is technically known as stratospheric aerosol injection, a type of solar geoengineering. Luke first learned about it from the sci-fi novel Termination Shock by Neil Steenberg. In it, a billionaire gas station owner in Texas appropriately builds the biggest gun in the world to shoot canisters that then turn into engines that burn sulfur in the stratosphere. And complications ensue, to put it mildly. The title, Termination Shock, refers to one of the serious potential risks of doing stratospheric aerosol injection.

If we regularly put large amounts of sulfur into the stratosphere and suddenly stop, the swift and intense war, forming that would results could be catastrophic. So isn't termination shock kind of a cautionary tale? Seems like you kind of took it the other way. Yeah, it is. We should do this. You're not wrong. But Luke says as he learned about the science behind stratospheric aerosol injection,

he saw a lot of potential. It's probably like a 20-syllable German word for this feeling. But as I'm listening to the audiobook of this, I'm realizing that I'm going to have to dig into this a lot more. The more I learned, the more I became convinced that there wasn't any good reason we weren't doing this. It was just that nobody had done it. So Luke decided to do it, on a small scale anyway. The company's name makes sunsets refers to the vivid colors created by aerosol pollution.

And to be clear, Luke and Andrew are quite a ways away from being able to meaningfully change the temperature or the color of the sky. To date, they've released over 250,000 grams of sulfur dioxide. Scientists say it would take millions of tons. Is your business sustaining your livelihoods? Like, are you making enough money that you can do this full-time, and that's it? We've raised enough venture capital that we can do this full-time. We're about halfway to break even in terms of revenue from cooling credits versus our costs.

So first goal is to get to where we're profitable so that we can continue doing. doing this forever and scale up? They founded Make Sunsets in 2022 and have raised almost $2 million in venture funding. Supplies are pretty cheap, and Luke is the only employee. Andrew recently stepped back into an advisor role. Every month, they send out financial updates to their customers and email subscribers. The majority of our customers is what I like to call climate dads. Usually there are people who, you know, like your typical soccer mom.

And so these guys are either in their early 30s to late 40s. They usually have young children at home. They probably have an EV in the driveway, some solar panels on the roof. They deeply care about their environment. They deeply care about the future of their children. They have STEM or finance backgrounds. And so they're very well-educated. And they understand, hey, I'm doing everything that I can, but makes sense that's helping me do more.

Andrew says they've had more than 1,000 customers so far. they run the gamut from billionaires to scientists and professors and even a few moms. Luke and Andrew have a casual vibe about them. Luke has a foe hawk and Andrew is rocking a man bun. They can sometimes come across like a couple of goofballs doing science experiments on rooftops. It's a dynamic, I think they play up a bit to court media attention. But they're quite sincere about why they're doing this. it sometimes feels like a plea for someone, anyone, to start taking meaningful action. There are no ideal options at the end of the day.

We didn't ask to be born into a world one sea warmer than it was before the Industrial Revolution. Like, we don't, I think it is irresponsible to act like we can just do nothing or only do feel-good measures like throw up a few solar panels and plant a couple trees because those demonstrably will not solve the problem. Solar geoengineering is still a bit theoretical, mostly done in the confines of computer climate modeling. There is a U.S.-Israeli company called Stardust Solutions that's raised $75 million in funding. Stardust recently revealed what it calls biodegradable particles that could be used to reflect sunlight, made out of calcium carbonate, a compound found in limestone, and amorphous silica.

an anti-caking agent used as a food additive, though so far the particles have only been tested indoors. And then there have been several academic field research projects, some of which never fully got off the ground. So from what we can tell, Luke and Andrew are the only ones actually attempting solar geoengineering in the real world, even if it's not taken seriously by everyone.

I see them as kind of a political fear. and I don't mean that in a bad way. David Keith is professor of geosciences at the University of Chicago. He's been working in this field since 1990, and what Luke and Andrew are trying to do with Make Sunsets is largely based on his research. From what I can tell talking to them, their goal is to spark conversation about this,

and they certainly don't go about it the way I do, and it's hard to know how effective it is. David is a polarizing figure in his own right. In 2021, while he was a professor at Harvard, he led a stratospheric aerosol injection project called Scopex, funded in part by Bill Gates. They had planned to release less than a few kilograms of sulfur into the stratosphere from Sweden until it got shut down by the Swedish government. And in 2023, David again made waves when he sold his carbon removal. company, carbon engineering, to an oil company for more than a billion dollars. After spending time with Andrew and Luke, I had a lot of questions about the science behind stratospheric aerosol injection, like what exactly are aerosols? And why shoot them into the stratosphere? So aerosols are just a fancy name for a particle that's so small it doesn't fall quickly. Aerosols are extraordinarily efficient at reflecting light, and that's why they're so important.

important for climate in general. The aerosol we understand the best is sulfuric acid. When sulfur dioxide is released into the atmosphere, it reacts with water vapor to become sulfuric acid. Which is both naturally put in the stratosphere and also put in the stratosphere by our pollution. So the way to do sunlight reflection that's most studied and best understood and most technically possible in the sense that we could start basically now is putting sulfuric acid droplets of aerosols into the stratosphere. And why the stratosphere? That's because a material stay in the stratosphere for about two years.

Whereas if you put aerosols in the lower atmosphere from, say, a pollution source, they just stay for about a week before they fall back to Earth. The stratosphere is the second layer of the atmosphere, starting between 31,000 and 58,000 feet above the Earth, depending on the location. For reference, commercial jets tend to fly at around 30 to 40,000 feet. Starting around 60,000 feet is where proponents suggest we put sulfur aerosols. What happens when they do eventually fall back to Earth? How dangerous is it?

So it is dangerous, but the good thing about it is we know a lot about what that danger is and we can quantify it. And the reason is that sulfate aerosols are perhaps humanity's worst environmental pollutant of all time, literally. So overall human history, something more than 100 million people have been killed by sulfate aerosol air pollution. And people have known that it's a toxic danger for a very long time. The first formal regulation of it was a proclamation that the King of London made to stop burning what were high sulfur sea coals in the year 900. So this is a very old thing. This isn't just theory. Even today, as we speak, pollution from industrial activities around the world is putting aerosols, largely sulfates, into the atmosphere.

And those are killing people today, more than a million people a year. From respiratory illnesses, cardiovascular disease, and cancer. But David says those aerosols are doing something else, too. They're reflecting sunlight. They're reflecting enough sunlight to cool the world by something like a third of a degree centigrade. One of the uncomfortable realities of climate change is that as we decarbonize, the Earth could get temporarily warmer as those pollutants quickly disperse, but the planet-warming carbon remains far longer. We actually saw this happen on a small scale in 2020, when new regulations in the shipping industry dramatically reduce the sulfur in the fuel and led to a slight warming event, One study called it an inadvertent geoengineering termination shock.

As we transition away from fossil fuels, stratospheric aerosol injection could be used to offset that temporary warming. David says one big benefit it has over straight up pollution, the sulfur is less harmful way up there away from people and our environment. It's also more effective at cooling the planet, so it takes much less of it to get the same cooling effects. So to give you some numbers, currently we're emitting about 30 million tons of sulfur into the lower atmosphere every year, which is being immensely destructive. If we wanted to cool the planet by something like half a degree centigrade late this century, we need to put something like a million tons a year of sulfur in the stratosphere. So that's one-th of what we're adding now. Still, putting sulfur in the stratosphere could damage the ozone layer, letting through more harmful radiation. And in stark terms, David says the sulfur required to cool the earth by half a degree Celsius

could cause 10,000 additional deaths a year from air pollution, but it could reduce half a million deaths from heat. So nobody is selling this as something that's magic. Any of these interventions is going to cause harms, but we have the CO2 in the air. The harm from climate change is real, and it might make sense to do this, understanding that the benefits would be pretty large and the risks appear to be pretty small.

And he says it's pretty cheap, cheap enough that one lone billionaire, let alone a wealthy government with access to a fleet of airplanes, could do this. One estimate I've seen says deploying stratospheric aerosol injection initially would cost just over $2 billion a year. The main cost comes from developing the airplanes needed to. to fly into the stratosphere. And we actually have some idea of how it might go. Three powerful explosions sent molten rock, mud, and ash more than 10,000 feet into the sky. From volcanoes. In 1991, Mount Pinatubo erupted in the Philippines and spewed millions of

tons of sulfur dioxide into the stratosphere, enough to drop global temperatures by about one degree Fahrenheit for over a year. To avoid sudden drastic effects, David thinks we should start small and slowly ramp up injection of sulfur to a million tons, which he says is about one-eighth of Pinatubo over, say, half a century. But there would still be uncertainties, uncertainties that some think are not worth the risk. I think we have to understand that if we do this, this is. is a decision that will affect all life on the planet.

A lot of the proponents of geoengineering, they really don't want scrutiny. Because if you look at it closely and you start to peel the onion, you find some really, really smelly, rotten sections underneath. That's after the break. On the San Francisco Bay in the city of Alameda, just a short drive from where we launched some sulfur into the stratosphere, Haley and I pull up to the USS Hort. it, an aircraft carrier built at the end of World War II. It's been turned into an aircraft and space museum that's open to the public. There's not much else around. It's a gray day and

feels a little eerie out here. This does really have the vibe of like a drug deal is going to go down out here or like something shady. You watch the wire too much. You meet at the docks. I know. It's a good thing it's not dark. Yeah. You like to I thought it might fit with the story. We're here to meet Gary Hughes, a longtime environmental activist. Gary is involved with geoengineering monitor, a group that opposes geoengineering in favor of solutions that address the root causes of climate change. Just a few years ago, this museum was at the center of a geoengineering dispute.

A controversial decision coming out of an Alameda City Council meeting earlier this week is now making national headlines. In early June, city officials in Alameda blocked the scientists from continuing basic research into an experimental approach that might one day help slow global warming. Scientists from the University of Washington chose the Hornet as the site for a study related to a type of solar geoengineering called marine cloud brightening. It involves spraying sea salt particles into the lower atmosphere, where the particles can attach to class, allowing them to reflect more sunlight away from the area. Unlike the global effects of stratospheric aerosol injection,

the impacts of marine cloud brightening are thought to be much more regional. The experiment was set up on the deck of the USS Hornet. They had a machine up there that was kind of a little bit like a snowblower at a ski area. The scientists wanted to test the way sea salt particles emitted through this blower, behaved under different atmospheric conditions. They weren't going to do any actual cloud brightening, but still, people got spooked when they heard about it. I mean, for me, a lot of it is really,

it's very science fictiony that it's come to this. Back in 2024, when the Alameda City Council held a meeting, Gary attended to learn more about the experiment. I'm just kind of an old-school forest and river defender from way back, and now this is what I'm working on. It can be kind of trippy. So I was in that city councilors meeting, and I was like, wow, this is really something else.

He says the community felt blindsided about what was happening in their own backyard. The city councilors were actually very clear that they're not like Luddites. They're not anti-technology. But they were very fiercely clear with the proponents that it was really offensive that they never asked for permission of the city beforehand.

So the city council shut it down. Gary sees what happened here as a symptom of a much larger issue with geoengineering. A lot of the proponents of geoengineering, they really don't want scrutiny. They don't want there to be a full assessment of what it is that they are suggesting that we need to be dedicating huge amounts of resources to. Because if you look at it closely and you start to peel the onion, you find some really, really smell. rotten sections underneath. Like what? Like the fact that number one is that these technologies are untestable.

So we won't really know what the impacts were to be until they do large-scale, even global deployment. And at that point, then all we are are guinea pigs in their laboratory. And Gary worries about the moral hazard, that investing in engineering solutions that mask the effects of carbon emissions takes the pressure off the worst climate offenders to change their ways. We have a whole new class of billionaires who, number one, kind of understand that climate is an issue, right?

But number two, what they don't want to do is to relinquish the power and the wealth that they've acquired. And they want to keep acquiring more. And that is why they are really intent. on trying to find an engineered solution to the climate problem because then ostensibly they could fix the climate thing, but they'd still be able to live, you know, with all this obscene amount of wealth that they've accumulated.

Fly in their private jets and buy mansions around the world. Exactly. We know that a huge percentage of emissions, for instance, from flying, just as one example, are attributable to the habits of the super rich. To be fair, David Keith and Luke and Andrew from Make Sunsets are not advocating that we continue on with business as usual. They say decarbonizing isn't enough, that even if we stopped burning fossil fuels today,

some further warming is baked in. And they see solar geoengineering as a necessary tool to be used in tandem with decarbonizing our lives. And frankly, I've been swayed at times by their optimism that this could work. I mean, in these times, I really don't want to stomp on anybody's optimism. I think we need as much as we can get. What I will say is that I am a lot more cautious. Kate Marvel is a climate scientist.

A few months ago, she made headlines when she left her job at NASA because of the continued attacks on the scientific community from the Trump administration, she's now at Project Drawdown. I am a lot more cautious, and this is coming both from my position as a scientist who has studied how the physical Earth system works, but also from my position as a human being who knows what I know and what I don't know. And it's actually all of the things that I don't know that scare me the most about geoengineering. And you wrote beautifully about those in an essay, a handful of dust, about the perils of geoengineering, and specifically solar geoengineering.

The takeaway I thought from your essay is this is a pretty bad idea. Do you still feel that way? What is it? Six years since you wrote that? I do. I feel very strongly that it's a bad idea. And I actually think that the vast majority of researchers would agree with me, all but the most zealous. geoengineering advocates would say, I would rather we not have to do this. What do you think of the way that the conversation around solar geoengineering has evolved since you wrote your essay? As you know, there's a couple of guys in California that are doing it, sort of. It's always the guys in California, isn't it? Seems that way. I mean, I think we have to understand that if we do this, this is a decision that will affect all life on the planet. I don't think it should be up to a couple guys in California.

So, you know, that scares me. What also scares me is this emerging narrative that it's inevitable and it's easy. I am an agnostic about geoengineering. I think it is a bad idea, but it may be that it turns out to be a less bad idea than some of the horrific consequences of a warming planet. I'm willing to keep an open mind on that. But what I am really disturbed by is the suggestion that it is somehow an easy thing, that all we have to do is turn down the sun, that we can cancel, out a century of greenhouse gas emissions and continued greenhouse gas emissions with, you know, one simple trick. I think that rhetoric is extremely dangerous. For one thing, just turning down the

thermostat won't cancel out some of the other effects of greenhouse gas emissions, like the ocean acidification that's killing off coral reefs and other marine life. But there's something even more basic than that, I think, which is that rainfall is very sensitive to the energy balance at the surface. So rainfall is something that is going to be very, very sensitive to the difference between heating up the planet by trapping outgoing heat and trying to cool down the planet by blocking sunlight. We have reason to expect that that will have consequences for rainfall that are not just an exact cancellation out of the consequences of greenhouse gases. But the thing for me that is the scariest, the thing that is really hard for me to wrap my mind around and makes me extremely reluctant to advocate geoengineering as a climate solution is the social implications of it.

Right now, I don't see that we have a world government that is capable of making a decision on behalf of everybody who lives on the public. planet. And I don't see that as something that is coming down the pike anytime soon. A lot of times we hear about volcanoes as an example of how this works. I mean, in a way, we have seen real world testing, right? Although I guess David Keith says he thinks the penitubo example is overblown. But what do you think about, what we know about how the climate responded after a couple of big eruptions and what that can teach us? You might regret having asked this because I love volcanoes. I will talk about volcanoes forever. I'm sure I won't regret it.

So volcanoes are a really interesting test case for geoengineering because they naturally spray a bunch of aerosols in the stratosphere. And you can see very, very clearly in the global temperature record that there are little spikes, little downward spikes in the global average temperature immediately after certain. kinds of volcanoes go off. What we don't really have a good handle on is the hydrological consequences of what happens when volcanoes go off. How do they affect regional precipitation patterns? How do they affect things like drought risk? And all of these things are really complex and all of these things are really unknown.

When you look at volcanoes throughout history, that's when you kind of. kind of smack into the biggest unknowns. And this is why I am completely obsessed with volcanoes. Because if you look through human history, there seems to be one constant, which is whenever a massive volcanic eruption happens, stuff gets real weird. So in 1789, there was a massive volcano in Iceland that went off called Lockhe. and following Locky, things happened, and we don't really understand the causes of those. So the temperatures dropped, but then in Europe the next summer, it was abnormally hot.

There were massive hailstorms that killed livestock. And as a result, harvests failed. There were food shortages. And I think we all know, especially in France, what those angry peasants and urban dwellers, ended up doing. So I'm not saying that, oh, a volcano caused the French Revolution. That's way too simplistic. That's way too deterministic. But when you look back through history, the really, really impactful things that happen when a volcano goes off are changes to human societies. We are meddling with forces that are completely outside the power of physics

to understand. I guess in a small way I have meddled with these forces. A couple hours after launching that balloon from the roof of the shipping container, we got an email from Luke. Our stratospheric aerosol injection was successful. Some 20 miles northeast, above a cemetery in Contra Costa County, our balloon reached about 74,000 feet before popping and releasing its sulfur payload into the I'm still grappling with how to feel about it. I mean, obviously, it seems like a terrible

idea to mess with the climate intentionally in ways that will have global effects. We can't begin to fully understand. But we do know that without meaningful intervention, life on this planet is going to keep getting hotter and harder, and many more people will die. This season on How We Survive, we're going to be a lot of. going to get into some hard questions. Like, who gets to decide if we dim the sun? My expectation is that nothing's ever going to happen unless it's a rogue nation kind of scenario.

Or a rogue billionaire, maybe? We'll look at a growing backlash against climate interventions happening across the country. How far do you go to say we need rain, but let's poison and do these certain technologies? Where's the line? For me, I feel like, let God do it. Plus, we'll look back to see how we've messed with nature before. He who controls the weather will control the world. And find out how a technology once used for war...

The Pentagon today, the United States, has been seeding clouds over North Vietnam. Could help prevent an environmental and economic catastrophe. Come on, hurry up, guys. You're not working fast enough. about that every day. I feel that big time. Stay tuned. Thanks for listening. And if you like what you hear, please rate, review, and share us with a friend. It really does help. Also, we want to hear your questions about geoengineering and other

climate interventions. You can send us a note or better yet a voice memo to survive at marketplace.org. We're going to answer some of your questions in an upcoming episode. I'm your host, Amy Scott. Haley Hirschman, produced this episode and is our senior producer, production support by our intern, Rachel Kahn. Caitlin Esch is deputy managing editor. She also edited this episode. Special thanks this week to Daniel Ackerman and Marissa Cabrera. Scoring, sound design, and mixing by Brian Allison.

Our theme music is by Wonderly. Bridget Bodner is director of podcasts. Kelly Silvera is news director. Joanne Griffith is Chief Content Officer, and Neil Scarborough is the Vice President and General Manager of Marketplace.