Good morning, John.

Last month, I had a big Twitter thread and then a vlogbrothers video about the temperature of the surface of the North Atlantic Ocean and how it seemed to have increased at least in part because we mandated low-sulfur fuel and cargo ships and the sulfur had been reflecting light and seeding clouds which decreased the sunlight hitting the ocean. And how, in effect, we had been, like, accidentally doing geoengineering and maybe accidentally doing it would be useful in figuring out how to intentionally and thoughtfully do it. And some people got pretty mad. Some of them for good reason. Mad enough that Radiolab called me and was like, "Hey, do you want to talk about how that day went for you as a way of exploring geoengineering?" and we did that and that episode is out and it's great and I'd love it if you listen to it. But look, I knew that people were gonna get mad, I just didn't know how mad they were gonna get. Some people, like, felt betrayed by me because the reality is geoengineering is the most controversial idea in climate science by far.

Some people think that it is criminal that we are not doing it right now. Some people think that we should ban even doing research on it. But I haven't been in that space professionally for a long time so I had some catching up to do. Luckily, a couple of climate scientists who have YouTube channels agreed to talk to me in a video on hankschannel that I have just uploaded. Adam of ClimateAdam and Miriam of zentouro talked me through a lot of the global warming conversation and you should definitely check that video out. And also, their channels are amazing and if you follow both of them, you will be among, like, the 99.9% most informed people on climate change, so you should definitely do that. It's low-lift, the content is super accessible and great. But I wanted to make a video here that's just sort of, like, quick and dirty intro to why geoengineering is interesting and also so controversial. And why I think the fact that most climate scientists are opposed to geoengineering is, in fact, very good news.

First, let's define the term. What is geoengineering? The definition is controversial. But broadly, it's anytime you take an action to intentionally change the systems of planet Earth. More specifically, these days when we talk about geoengineering, we're almost always talking about the amount of heat in the system. There is other geoengineering, like, if you wanted to restart

an ocean current, if you wanted to change ocean acidity, if you wanted to decrease the amount of storms. All those things would be geoengineering. Now, importantly, intent does matter because if it didn't, then the last 100 years of burning fossil fuels would all be geoengineering. We would have been engineering the planet to get warmer, but it wasn't engineered. It was accidental. We did it for other reasons and so it's not geoengineering, it's just an oopsy. It was initially an oopsy, it's not really an oopsy anymore. Now it's like a stop hitting yourself kind of situation.

So these days, we're mostly talking about intentional actions taken to decrease the amount of heat in the planet Earth system. And importantly, there are lots of different ways to do that. We talk about geoengineering as if it is one thing and it is not. Like, already we are doing some geoengineering. We paint roofs white and that has like a main benefit of decreasing the air conditioning bills for those buildings which also decreases energy consumption, but additionally it does reflect some amount of energy back to space. Not a measurable amount, but that's part of the reason why we do it. So painting roofs white is geoengineering. But heading up the ladder of complexity and impact and controversiality, here's an incomplete list of other geoengineering things.

High-albedo crops, like crop plants that are more reflective and lighter colors, could make the planet more reflective. Ocean mirrors could reflect sunlight back to space. Marine cloud brightening would seed clouds over the ocean reflecting more light up. High-altitude cloud thinning would thin the wispy cirrus clouds that actually do a better job of trapping heat in this system than reflecting it back to space. And finally, stratospheric sulfur injection would mean putting a ton of sulfur dioxide into the stratosphere because those sulfur particles are good at reflecting light and they'd stay up there for a long time.

Each one of these has advantages and disadvantages and as we went down that list, we got more impactful and scary. Like, high-albedo crops would have a small and mostly local and temporary reversible effect whereas stratospheric sulfur injection would have a large and global and long-term effect. Now the argument in favor of doing these things, and each one of them is a solar

radiation management technique, that's the term we use for managing the amount of the sun's energy that gets trapped in the system. The reason why we do that is because the heat is a big part of the problem. It's not the only part of the problem, like ocean acidification would not be helped by any of these things and that's also a big problem, but the amount of heat in the system already is making life harder on the planet and that's just gonna keep getting worse decade by decade for a while. And honestly, we don't know exactly how much worse it's gonna get. And, in fact, that is another vote in favor of doing geoengineering research. It could be that things get worse than we expect faster than we expect and it would be nice to have a tool in our back pocket just in case we need it, even if we don't wanna use it, even if we're not sure if it's gonna work or we don't understand all the harms it's gonna do.

The arguments against are many and they are varied and I have sort of different feelings about them personally. And I'm gonna give them to you as I understand them and this is gonna be biased.

First is: This is gonna be good for fossil fuel companies because they're gonna do a lot of this work, whether it's like moving carbon around, or it's doing all the chemistry that's necessary to do geoengineering. I don't care--I look--I wanna be on the record, I do not care who gets rich saving the planet. I would give the guy I hate the most in the world all of my money if I knew for sure he could fix this problem. I would hate it! I would hate to--I'm thinking of who it is, I would hate giving him all that money but I'd do it. I might even say nice things about him afterward. Maybe. That would be harder honestly.

But relatedly, number two: This would be good for fossil fuel companies because we'd just keep burning fossil fuels forever if we didn't have to worry about the heat. If we could manage the heat, then we'd just keep burning. This doesn't worry me that much 'cause I just think it's wrong. I recognize that there are people who are like this, who are like, "We should just spend the money to do the geoengineering and not change anything." But ultimately, renewables are just better. I would be more worried about this if the cost of solar and wind and batteries hadn't gone down by like a thousand times since I graduated from college, but they have and already in most ways, they are better better than fossil fuel 

infrastructure, and I think 10-20 years from now, they will be way better than fossil fuel infrastructure and we just won't use fossil fuels? Because they're worse.

Now on to the things I find more compelling. 

Number one: This is going to be, by definition, a trolley problem. What do I mean by that? I mean that if you're trying to do something that's going to help the whole planet, there will be areas of the planet that are harmed. The scientists I've talked to are quite uncomfortable with this. They understandably do not like the idea that they might be put into a position where they'll be asked to advise on whether we should take an action that will, like, save a million lives, but actually cause the deaths of thousands of people. And this is, like, not abstract. Now, for clarity, we already do this with accidental release of carbon dioxide all the time. Not accidental. Incidental. We make decisions here in America to produce carbon dioxide and that's gonna have a negative impact on the world and it will result in death and suffering. It's not a comfortable idea but it's a real idea. But we're not doing it on purpose, we're doing it so that we can go visit our family in Indiana. It matters when you're doing it on purpose and part of me thinks it shouldn't matter, but it does.

So say, like, low-level example, you just do some marine cloud brightening. You're just making it some low-level temporary clouds are over the oceans and that increases the amount of sunlight being reflected to space. But maybe the water that's forming clouds there now would have formed clouds over land and fallen as rain and you're creating a different rain pattern. And those people's crops fail, so they don't have the income they expected. They don't have the food that they expected and there's a famine. So yeah, trolley problem uncomfortable. Now, we do that nationally all the time. Like, when we say we're going to shut down a coal-fired power plant or we don't want as many coal-fired power plants, that has negative impacts on people. But we do it 'cause it has positive impacts on more people, but that's very different when that's one country making decisions for itself than if it's one country making decisions for another country, which leads me to the second thing that is a good thing to point out.

Actively doing geoengineering could cause war. So say one country is taking actions that's

making it better for the people in that country, but it's resulting in less rain falling or flowing into another country, and that country has instability because of that. They're not gonna like each other and that feels intentional and different in a way that having, like, the U.S. and China burn a bunch of coal and then having a global impact doesn't. And I'm trying to get comfortable with the idea that the way that it feels matters, uh, because the way that it feels matters.

Third: If we did it for a while and then suddenly stopped, that's very scary. So basically, if we're doing this radiation management, the amount of heat that would be in the system if we weren't is going up and up and up, but we're getting that heat out of the system through radiation management. If one day through an accident or a policy decision or the fact that like one country was doing it and the other countries were like, "You need to stop." If suddenly it all stopped after having done it for a while, climate models don't like that. That could result in, like, a very chaotic series of events for the planetary system. There's even a term for it. It's called termination shock. That's scary both practically and 'cause the term. That's just a scary term. That's a good one. Neal Stephenson.

Next on the list, Miriam really drove this point home to me and helped me understand it. This isn't a thing that should be done unilaterally but it is a thing that could be done unilaterally. It's inexpensive enough to do some pretty large scale geoengineering that a single country and not even a big one could start doing. Also, it's totally possible that the countries doing that would be the ones who created the problems and might be doing it without regard for local impacts that would happen, so you wanna do this in a way that involves ideally all of the countries kinda coming together and reaching some sort of agreement. And in a complicated system like the Earth and complicated idea like geoengineering, that sounds very hard, uh, and almost like it literally couldn't happen. But maybe it could, like, we've done diplomacy on big hard things before.

Next, and this is the second most compelling of all of these arguments to me; we actually don't understand

this stuff that well yet. Miriam was talking about how like of all the variables and climate models, the things that, like, increase the error bar the most is actually aerosols. So like, the effect of particles in the air reflecting light back to space. That's a lot of what we're talking about in geoengineering and we don't understand yet very well the mechanism of how that works and how it much it does what it does. And this isn't just about like energy out energy in. If it was just energy out energy in, then we'd understand it, but what it's also about is how it's going to affect the climate system as a whole.

If we do stratospheric sulfur dioxide injection and it decreases the temperature of the planet by a degree, that would be amazing. But what if it also dried up the monsoon season in Southeast Asia and then hundreds of millions of people are now food insecure when they were not before? If that's a thing that might happen, you don't wanna do that, which leads me to the last most important thing on the list of reasons to be very cautious about geoengineering which is: We just got one planet.

This is the only one. We're already messing with it and that's really scary. And to solve the messing with it problem by messing with it is understandably terrifying. And I'm like, "Okay, so we got to understand it better," and Adam makes a great point which is that in order to do an experiment that actually will tell you about the potential impacts of geoengineering, you kinda already have to be geoengineering. When I made that original video, what was so compelling to me about this marine cloud brightening that had been unintentionally happening, reflecting extra energy to space, cooling the North Atlantic, is that we'd been doing it and it wasn't controversial while we were doing it because we were doing it on accident. And so to me, like, keeping doing it doesn't seem that scary, but maybe it is because, like, we keep doing it in a different way. It might seem like blowing a bunch of sea water into the air so that salt crystals seed clouds would be a pretty benign way of doing things, but maybe it's not. Maybe it sucks water out of the air that would fall somewhere else. Maybe the salt that

seeded those clouds would be a significant amount of salt falling on crop lands and thus making that crop less productive over time as the salt content builds up. None of this is simple. The only thing more complicated than, like, the Earth's climate is the human brains it contains. And both of those things are very important things to consider when taking really big actions like trying to intentionally affect the systems of the planet.

But the most hopeful thing I got out of this was that for the most part, climate scientists don't think that we need to be doing geoengineering yet because we're not in that situation yet. And what I hear a lot on social media and from friends is that we are in the most dire of circumstances, but when you look at what's possible, it does still feel possible to solve this problem without resorting to geoengineering which might very well be a last resort. Which leads me to what I think is a fascinating question: Is taking carbon dioxide out of the air solar radiation management? 'Cause like, yes it is. It would have been solar radiation management to put it in there in the first place if we'd done it with that goal. There is a kind of geoengineering that everyone is in favor of, which is reducing the amount of methane and carbon dioxide that is released into the atmosphere and then reducing the amount that is currently in the atmosphere. And just like with geoengineering, there's a long list of ways to do that that range from controversial to non-controversial.

But if there is less carbon dioxide and methane in the atmosphere there will be less heat in the system. We know this and we are doing things as individuals and societies to act upon that knowledge. We are not doing it as fast as I would like. There will be tremendous negative consequences to not doing it faster. At least about this thing, everybody who knows what they're talking about on this topic agrees on that, and that's a nice thing to have. I've put the link to the conversation that I had with Miriam and Adam on hankschannel in the description, along with Adam's video that he made about my video which is very good. And also a link to to both of their channels because as I said, if you

follow both of them, you will be among the most educated people on climate science in the world. And their content is so good, it's not complicated, it's very accessible, and they know what they're talking about.

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John, I'll see you tomorrow.