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

14 Jun 2026

Transcription

Transcript generated automatically by AI and may contain errors.

Chapter 1: What is the main topic discussed in this episode?

0.031 - 26.477 Kai Ryssdal

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.

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27.718 - 29.92 Amy Scott

So what are we going to do right now?

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30.659 - 37.446

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.

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37.967 - 41.271 Amy Scott

So in other words, just another Wednesday morning in Northern California.

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41.611 - 42.072

Exactly.

42.112 - 57.088 Amy Scott

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.

57.676 - 64.225 Andrew Song

Little 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.

64.525 - 66.809 Amy Scott

Okay. Good thing I'm not wearing heels.

67.009 - 67.309 Andrew Song

Right.

Chapter 2: How are sulfur-filled balloons launched for geoengineering?

98.419 - 102.786 Amy Scott

We're about 21 feet off the ground with no guardrails.

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102.901 - 107.106 Luke Eisman

Don't stand on the edge. We don't want anyone dangling.

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107.606 - 109.148 Amy Scott

I am so nervous for you.

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109.669 - 111.391 Luke Eisman

No broken bones yet.

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111.411 - 121.242 Amy Scott

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.

122.143 - 128.47 Luke Eisman

Hydrogen gets an unfairly bad rap. You have one Hindenburg and everyone gets all nervous.

129.26 - 156.97 Amy Scott

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.

157.852 - 179.318 Amy Scott

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.

179.979 - 192.351 Amy Scott

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.

Chapter 3: What is solar geoengineering and how does it work?

756.115 - 770.04 Amy Scott

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.

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770.425 - 775.813 David Keith

I see them as kind of a political theater, and I don't mean that in a bad way.

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775.833 - 790.493 Amy Scott

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.

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790.709 - 802.153 David Keith

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.

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802.64 - 826.133 Amy Scott

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.

826.619 - 851.327 Amy Scott

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?

853.737 - 868.083

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 for climate in general. The aerosol we understand the best is sulfuric acid.

868.544 - 875.998 Amy Scott

When sulfur dioxide is released into the atmosphere, it reacts with water vapor to become sulfuric acid.

876.232 - 894.817

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?

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