Will We Solve the Climate Problem?

I have some disagreements with most climate scientists, not about the really big questions — we agree that climate change is happening, that it’s man-made, and that it’s likely to lead to big negative impacts on human welfare. Where we tend to disagree is on what to do about it. And that is definitely the case with my guest today, climate scientist Kate Marvel. But the good news is, she turns out to be a really fun person to disagree with. She’s got a new book, it’s called Human Nature: Nine Ways to Feel About Our Changing Planet. As the title suggests, it’s a book about feelings, but it’s deeply informed by facts.

MARVEL: We are tied to the planet. If we all move to another planet, first of all, that wouldn’t be fun because all of the other planets that we know about are garbage, but we would still be tied there to our environment by the laws of physics. We all have to obey those laws, whether we want to or not. And what I was trying to do is explore the feeling of being alive on this earth as it changes.

Welcome to People I (Mostly) Admire, with Steve Levitt.

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As I read the book, I was surprised that she spent so much time justifying the existence of human-driven climate change. I thought that by now just about everyone had come around to accepting that climate change is real. But after doing a quick Google search, I was stunned to discover that while over 99 percent of scientists working on the topic believe climate change is real and primarily driven by human activity, only about 60 percent of Americans think that’s true. I started our conversation by asking Kate how she feels about statistics like that.

MARVEL: Yeah, I got a lot of feelings about that. From my understanding, and I’m not a social scientist, but my understanding is that the polling reveals six Americas as the Yale Center on Climate Change puts it. Where people tend to fall into one of six different buckets, ranging from alarmed: people who believe climate change is real, know that it’s happening and are really freaked out about it. And then at the other end of the spectrum, the dismissives: the people who are hardcore climate deniers. And I think last time I checked it was about 7 percent. I think the vast majority of Americans sit somewhere in the fuzzy middle. There’s a lot of people who are alarmed. There’s a lot of people who are concerned. There’s a lot of people who just simply don’t know what to think.

LEVITT: So, 85 to 90 percent of Democrats think climate change is real compared to only 30 percent Republicans. I had no idea.

MARVEL: That’s people. I am a physicist and I became a physicist because I was afraid of people, you know? Social science is the hard stuff. You’re studying things that don’t behave themselves. We know F = ma. We know that if I shove a glass of water off the table, it’s going to fall. I don’t know what people are going to do when I shove them, so I just don’t shove them. But that kind of illustrates something that I really wanted to explore, which is, Yes, physical climate science can get us so far, it can tell us this is real. It can tell us some of the consequences of it. But the thing that really matters is what it does to us and how we react to it. And that’s your domain. That’s economists, that’s social scientists. I am happy to kick the can down the road and say, “It’s in your court now.”

LEVITT: Yeah, so being a social scientist, I couldn’t stop going and looking at these polling data. And what really surprised me is I went back, I found a Gallup poll from 1997, and at that time, 57 percent of Democrats said they worried either a fair amount or a great deal about global warming. Compared to, in 1997, 40 percent for Republicans. Now the numbers are 95 percent for Democrats and 26 percent for Republicans. So the political gap went from 17 percent in 1997 to 69 percentage points. I don’t have any answers. I agree with you, people are complicated. And mostly in my research, I try to point out how weird the world is, not necessarily try to solve why the world is so weird.

MARVEL:   I agree that it’s interesting. I’m just sort of aggressively trying to distance myself from the notion that I have anything to say whatsoever about that. Because that is human beings. That’s human behavior. But that is not something that the tools that I use can really tell us.

LEVITT: So I’d love to talk to you in some detail about climate models, ’cause people talk about climate models all the time in a very vague sense but I’ve never actually heard anyone describe the various pieces that go into a state-of-the-art climate model. So for instance, how many equations would you guess there would be in this model total?

MARVEL: The one that I work with is over a million lines of code. But, I mean, we can build a simple climate model right now, just using our imaginations. We know that the earth gets most of its energy from the sun. The earth warms up and it radiates that energy back into space. But because the earth is so much cooler than the sun, when it radiates out in this space, it radiates in the infrared, just like our bodies because we’re a similar temperature to the earth. And greenhouse gases, naturally occurring greenhouse gases in the atmosphere, trap that infrared radiation as it’s coming out from the earth; they absorb it; and then they spit it back out in all directions. And some of it gets directed back down to the earth’s surface. So that description of what’s going on is a very simple climate model. If you want to know, What is the average temperature of the earth?, then that model can tell you that. But it’s not going to tell you anything about the ocean because there’s no ocean in that climate model. It’s not going to tell you anything about the land. It’s not really going to tell you anything about the atmosphere and why it rains and how water moves through the atmosphere. So you need to add layers and layers to that very simple picture until you build up a more comprehensive picture of the earth. Now, that simple model, I can write down the equations that describe it and I can solve them by hand. But the more physical processes I am describing and how they’re interconnected, the more equations I need. And so that’s why we need to run climate models on supercomputers. The way that I think about a computer climate model is, it’s essentially a digital toy planet that we can play with. It’s like a very fancy, expensive version of the Sims. I shouldn’t say this, but that’s what I do all day. I essentially play the Sims.

LEVITT: You also play the Sims when you get home from work? Do you play the Sims in your spare time as well?

MARVEL: Does the Sims still exist anymore? Am I dating myself?

LEVITT: I don’t know if it does or not. I think it might.

MARVEL: People tend to think, Oh, well, a climate model is a crystal ball. It’s going to tell us exactly what the future looks like and what to do. And that’s not what they’re for. A climate model’s a research tool because if we want to do an experiment on the earth, if, for example, we want to understand, What would the planet look like without human influence?, we have two choices, right? We can tell everybody to move to another planet for 500 years while we observe this one, or we can do that experiment in the digital safety of a climate model. We write down the physics of everything we know about how everything on Earth works, and we solve those equations. And — actually, I want to hear from you about this because my understanding is that in economics you use models, but your models are very different from our models in climate science.

LEVITT: Yeah, it’s true. About 50 years ago, there was a big push to build the kinds of models that mirror modern climate models. So they were complicated, they had many equations. They tried to build up to some big equilibrium off of individual equations. And, the fact was, we gave up on them. We gave up on them a long time ago. It was before I was an economist. I think the reason was that they just didn’t work well. They couldn’t predict outcomes any better than the median guess of human economists. And I think in part that relates back to something you said earlier, which is physics is relatively easy compared to human behavior and macroeconomic models were trying to model human behavior and they didn’t have any luck. So, yeah, it’s interesting because I think you really tap into something. At least initially, I was, as an economist, I was highly skeptical of the idea that climate models could work because I can understand how each individual equation would do a good job of modeling whatever it was trying to do. But the real magic of a complicated model like this is its ability to pick up on non-linearities and on feedback effects and things that just seem hard to do really well. But judging from the way you write about these models in your book, you put a lot of faith in their accuracy.

MARVEL: Yeah, I mean, it is literally my job to complain about climate models. If our models were perfect, then I wouldn’t have to go to work every day. And I think they are better. And you can’t see me, I’m using air quotes here, but they’re better than economic models. And it’s not because climate scientists are superior to economists. It’s because we are trying to model things that behave themselves. Air parcels, water droplets, they are always going to do the same thing. And people are not always going to do the same thing. You’ve got these laws of economics that seem to work until they don’t, until somebody has a bad day or is cranky or is irrational. Water does not wake up hungover and decide to do something dumb. Water always behaves in exactly the same way. And so I have faith in climate models insofar as they are describing processes that exist in the real world and physics that we’ve understood for a really long time. Where climate models exhibit imperfections is, like you said, in the interconnectedness of everything — when we start solving these equations and we let them talk to each other. But also in the fact that stuff happens in the climate system on different scales. So, clouds are a really good example. We understand cloud formation. This is not a mystery to physics. We understand that when there’re certain atmospheric conditions and you’ve got little cloud condensation nuclei, so little specks of dust or sand or salt or whatever, then you can get cloud formations; you can get water droplets or ice crystals coagulating around that, and then you have a cloud. But in order to put that in a model of the entire globe, we do not have computers that are powerful enough and will ever be powerful enough to track every single dust grain and bit of sand and salt and soot and whatever in the atmosphere. As a result, there’s this real scale mismatch. And so we have to make approximations about how clouds form so that we can put those equations into a global climate model. Different climate modeling groups make different decisions about how to do that, how to represent clouds. As a result, we see a spread in what climate models are predicting for the future because basically how hot it’s going to get in the future in response to a given amount of carbon dioxide in the atmosphere, that boils down to, What are clouds going to do?

LEVITT: For me, one of the most interesting sections of your book was your discussion about these large differences in the predictions that are made by the leading climate models with respect to how big the impact on temperature will be if we double greenhouse gases. So, it’s in some sense the most fundamental predictions of the model. And I think you said the model estimates of the impact of doubling CO2 range roughly from 1.5 degrees Celsius increase in temperature to 4.5 degrees Celsius. So, first, it’s my sense that climate scientists generally don’t advertise this uncertainty. And I suspect the feeling is that if the general public knows that there’s such uncertainty magnitudes, it will lead people to say, incorrectly, “See these climate scientists? They don’t have any idea what’s going on.” So in light of that, were you nervous to talk about the uncertainty across models?

MARVEL: No, and I think it’s really important to say, We don’t know everything, but that doesn’t mean we know nothing. There’s certain stuff that we understand very, very well because it’s so basic. And I’m not super sympathetic to the notion that, Oh, if we talk about uncertainty, the fossil fuel industry will lie about that. They lie about everything, right? So you might as well just tell the truth and trust people to think about where those uncertainties come from. Yeah, I think if you’re just reporting, you know, This is going to happen and this is the confidence interval, people shut down, they don’t care. Or they say, “Well that sounds really fuzzy.” But if you actually engage with people and you say, “We know carbon dioxide’s a greenhouse gas, we know that it traps infrared radiation. We understand that when you put a bunch of carbon dioxide and methane and other greenhouse gases in the atmosphere, that’s going to warm up the earth.” There’s no disagreement on that because that is physics that we’ve understood for over a hundred years. We don’t know exactly how hot it’s going to get because we don’t know exactly what clouds are going to do. That is why it makes sense to study what clouds have done, what clouds are doing, what clouds might do. But that doesn’t mean that we know nothing. And actually we have made some progress, unfortunately, mostly in ruling out the lower end of that range.

LEVITT: And so this range of 1.5 to 4.5 degrees Celsius as the impact of doubling greenhouse gases, it sounds like you’re saying, It’s almost all driven by uncertainty about what clouds would do. Is that a fair statement? 

MARVEL: Yes. I think that’s a fair statement. We’ve even made progress in narrowing it down to uncertainty in what the actual type of clouds will do. So we think a lot of that is due to uncertainty in what we call the low-cloud feedback. So clouds have this dual effect on the climate. Clouds are pretty effective greenhouse agents they trap infrared, heat radiation coming out from the planet. But they also, block the sun, right? And we’ve been able to really make progress in narrowing down the uncertainties in what are those low clouds that are really good at blocking the sun, what are they going to do in the future?

LEVITT: So the real key is that there are some clouds, these low ones, which are really good for fighting climate change. And then the high ones are the opposite, they pushed in the other direction.

MARVEL: You can see this if you look up on a summer’s day, you see those little wispy cirrus clouds up high. Those have a greenhouse effect, but they are obviously really bad at blocking sunlight. Like you have wispy cirrus above and it’s still counted as a sunny day. You have more of those clouds and they are better at trapping the infrared radiation and they are worse at blocking the sun coming in.

LEVITT: It’s interesting that we hear all the time about CO2 and about methane more and more, but, in general conversations about climate change, I don’t hear clouds or water vapor mentioned hardly at all. It hasn’t pervaded the public dialogue yet.

MARVEL: There have been some attempts to talk about water vapor in bad faith. We get told a lot, Well, water vapor is the most prevalent greenhouse gas in the atmosphere. And yeah, that’s absolutely true. But there is a water cycle. Water vapor gets taken up from the surface of the earth, it gets rained out. And at any given time it has a pretty powerful greenhouse effect. It is a really potent, naturally occurring greenhouse gas. But there is more water vapor in the atmosphere as it warms up, and that is a feedback effect. So warm air — I’m going to say this, and this makes physicists really angry: Warm air holds more water vapor. The actual, physical way to say that is, The saturation vapor pressure increases exponentially with temperature. But then you say that and nobody listens to you. Basically what that boils down to is, there’s more water vapor in warm air. And so that is a destabilizing feedback effect where you get more water vapor in warmer air; water vapor is itself a greenhouse gas, and that makes the earth even warmer. But we see that manifest in consequences for us. So we’re seeing extreme rainfall get even more extreme, and that is leading to tragedies like the floods we saw in Kentucky, what we’ve seen in Texas. When there is more water vapor in warmer air, more of it can be dumped on us.

We’ll be right back with more of my conversation with climate scientist Kate Marvel after this short break.

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LEVITT: Now, the test ultimately of these climate models is whether they can predict things, and I think if you go back in time and you ask how the leading climate models have done in terms of predicting the rise in temperature, at least at the global level, they’ve done really, really well. But it also hasn’t been a very hard problem because I think a simple linear regression would’ve done pretty well also because temperatures have been rising pretty steadily for the last 50 years. But I’ve also heard maybe they haven’t done as well in predicting precipitation, especially in smaller areas. Is that again, all related to the uncertainty around clouds?

MARVEL: It is not just related to the uncertainty around clouds, it’s related to the fact that Why it rains differs in different regions. So in the tropics it rains mostly because it’s really hot there, and you’ve got this hot, moist air that’s ballooning up that’s rising from the surface. And when it rises up from the surface, it cools the vapor and the air condenses and it rains down on the tropics. Here in New York where I am in the mid-latitudes, we tend to get what’s called frontal precipitation. So basically, air masses smashing into each other and air being forced up, either sliding on top of an incoming mass or kind of being forced up. And those are, like clouds, processes that happen on fairly small scales and therefore are difficult to explicitly have in a climate model. So we have to make approximations there as well. Temperature is fairly straightforward. We tend to do a pretty good job of getting the temperature rise right. The precipitation is much more difficult, but we are getting the large scale precipitation patterns right. We are seeing things happening in the real world that were predicted by the models. Can I start a fight with you about linear regression?

LEVITT: Yes! Please do.

MARVEL: I actually don’t think that’s true, that a simple linear regression would do just as good a job. And that is because greenhouse gases are not the only things that humans do to the climate. Humans also emit what we call aerosols, what you might colloquially think of as pollution. Dust and dirt and soot that gets put in the atmosphere that blocks the sun. And so aerosols have a cooling effect, because they are directly blocking the sun and they’re also seeding clouds that block the sun, at the same time that greenhouse gases are having a warming effect. And so if you want to explain what was happening over the 20th century in the first bit of the 21st century, you really need both of those stories. You need the story of greenhouse gases and you need the story of aerosols. I guess I just want to stand up for physics as opposed to linear regression. You do need a more complex physical understanding to really capture what’s been going on.

LEVITT: Yeah. Fair enough. It’s too bad that aerosols are so disastrous for humans. My friend and colleague Michael Greenstone is an economist who’s shown — just it’s unbelievable how many people are dying because of air pollution. And because it’s mostly invisible, we really, I think, didn’t have a sense of that for a long time. But the flip side, as you’re saying, is as governments have done something, which is absolutely the right thing to do for human health and longevity, which is to dramatically reduce these particulates in the air, it’s fed into the rising temperatures because these particles have a cooling effect.

MARVEL: Absolutely, yeah.

LEVITT: Let me just talk about Michael Greenstone. I kept on thinking back to him as I read your book because he made a comment to me once where despite the fact that he is an environmental economist who believes fully in human-driven climate change and writes about aerosols and whatnot, he said to me that his sad belief was that humanity would burn every drop of fossil fuel we could get our hands on before we stopped. Reading your book, was the first time I ever bothered trying to figure out, back-of-the-envelope calculations, Well, how bad would that be? And as I worked through it, it looks like we have maybe 50 years of known reserves of oil and natural gas and much more coal. But let’s ignore coal now because I think we might not burn all the coal. And as I tried to just figure out the impact of burning everything we have left, so far, we’ve gone from a pre-industrial level of 280 CO2 parts-per-million up to something like 420. And by my very rough calculations, if we burn all the oil and gas we have left, it would put us up to 550 parts-per-million. Just from the direct effects. There might be some indirect effects as well. And honestly, you’re going to probably be extremely angry at me for saying it, but it actually made me a little bit optimistic. I had in my mind that if we just kept on burning forever, that carbon dioxide would go to infinity, but actually we’re limited by the fact that we don’t have that much to burn. How angry does it make you when I say things like that?

MARVEL: I’m not in general a very angry person, so, not super angry. I’m interested in why you said we wouldn’t burn all the coal and whatever is leading us to not burn all the coal, why that wouldn’t arguably apply to oil and gas as well?

LEVITT: So I don’t know anything, but I think the view was that coal is especially dirty and there’s been a lot of pressure to shut down coal plants and whatnot. And that same pressure doesn’t seem to be being felt for oil and natural gas. I was just thinking that by the time we were running out of oil and gas, we wouldn’t have been burning very much coal anyway and we would’ve moved on hopefully to something much better, whether it’s solar or wind power or hydroelectric or fusion or whatever it’s going to be. And so we just wouldn’t bother burning the coal. 

MARVEL: I mean, again, I’m not an economist. I don’t know how people work. My suspicion is that burning coal is a particularly stupid way of getting solar energy, because it’s much more efficient to just have a solar P.V. panel that captures sunlight directly than what fossil fuels do, which is you let the sunlight grow the plants and then you let the plants die and then you wait 400-million years or so and then you dig it up and you set it on fire. So it strikes me that directly using sunlight to move electrons around is a much more efficient and cost effective and cheap way than fossil fuels. But back to your point of, What would happen if we burned all of the fossil fuels in the earth right now?, we actually have an analog for when that happened before. Two-hundred-and-fifty-million years ago, there was natural tectonic activity; very, very violent volcanic eruptions, lots of giant pools of lava everywhere. And essentially what that did is burn most of the fossil fuels that were at the time available in the earth of 250 million years ago. That caused a very rapid spike in greenhouse gas concentrations in the atmosphere. And as a result, almost every living thing on Earth died. The end Permian mass extinction led to the wipe out of I think more than 90 percent of species on earth. And that was the event that kind of paved the way for the rise of the dinosaurs. So the Permian is followed directly by the Triassic, which is when we start seeing dinosaurs evolving on essentially a world that’s been cleared out for them. And so the earth has done this experiment before, and I would argue that didn’t end well for anybody.

LEVITT: But at least relative to my own flawed mental model, which is that CO2 in the atmosphere could essentially go to infinity and drive temperatures to infinity. It seems like the upper limit of the damage that humans can do will be to double the CO2 content, which then, hopefully, the upper limit of the damage would be something which, obviously a crazy high number, is something like four-and-a-half degrees Celsius increase, which I’m not saying is a good outcome in any way, but it’s lower than infinity, which is the model I had walked around with in my own head.

MARVEL: I feel very confident saying, Lower than infinity. What I don’t feel confident in saying is what the concentration of carbon dioxide will be in the future atmosphere. And that is because of another kind of feedback effect. So earlier we were talking about clouds as a feedback to a given concentration of carbon dioxide in the atmosphere. You arbitrarily double carbon dioxide, what do clouds do? That’s a feedback. But now we’re talking about, Well, what if you don’t double carbon dioxide? What if you just emit carbon dioxide? How much of that is going to stay in the atmosphere? And the reason that we expect feedback loops there is right now about half of the carbon dioxide that human beings emit is being taken up by photosynthesizing stuff on the earth’s surface, so plants, forests, phytoplankton. That’s what they do. When there’s carbon dioxide in the atmosphere, plants tend to like it. Plants tend to grow. Like people tell climate scientists all the time that, “Oh, carbon dioxide is plant food.” And, yeah, it is, plants like carbon dioxide, but it is really hard to take carbon dioxide out of the atmosphere when you’re on fire.

LEVITT: I probably shouldn’t laugh at that, but that was funny.

MARVEL: Well, it’s true. We expect that in the future there’s no reason that the terrestrial biosphere, stuff that’s growing on the planet, there’s no reason to expect it’s going to continue to remove half the carbon dioxide emissions from the atmosphere. So we have these two competing effects. We have the carbon dioxide fertilization effect, which is plants like carbon dioxide. It’s plant food. But that is going to be limited by water availability. It’s going to be limited by nitrogen availability, other nutrient availability. At the same time, we start seeing climate change effects on the earth. Places that used to have forests maybe cannot support forests anymore. The absolute nightmare scenario would be the Amazon rainforest becomes a savanna. And so we expect to see shifts in what grows where and how healthy stuff is. And as a result, we expect that as carbon dioxide emissions increase, we can no longer rely on the earth to remove a lot of those for us. We think that is going to be a destabilizing feedback as well.

LEVITT: So that was a flaw — in my simple thought experiment, I was only thinking about the direct effects of just When we burn the stuff that we can burn, how much will go into the air? And it left out all these feedback effects. So you have made me less hopeful about the scenario in which we wantingly burn everything we can over time.

MARVEL: Yeah, I think we shouldn’t do that.

LEVITT: Look, I think many people agree that we shouldn’t do that, but I also think realistically there’s a good chance that we will just by virtue of human nature and by virtue of the difficulty of agreeing on things. I mean, let me give you a great example. As I was doing research to talk to you, I kind of had a view that, No government is really going to be able to impose the costs on their citizens of really fighting climate change. And so there’ll be a lot of talk, but nobody will really do it. But the fact is, much to my surprise, the European governments have really committed to fighting climate change and they’ve done a good job. The last data I looked at, European emissions were down 37 percent relative to their 1990 levels, even though their economic output had grown by 70 percent over that same time period. That’s really a sign of a set of folks who are willing to pay the costs to try to fight this. Even the U.S. is down 20 percent from our peak commissions in 2007. And that’s a start, and that might actually make you feel kind of optimistic about things.

MARVEL: I would first quibble with the framing that addressing climate change is imposing costs on your citizenry because it might be expensive to transition your energy system, but it is even more expensive to deal with unmitigated climate change. We are not comparing the costs of mitigating climate change to the costs associated with a pre-industrial climate. We are comparing it to an earth that is three degrees, four degrees, five degrees Celsius, warmer.

LEVITT: The Europeans have done an amazing thing in reducing their emissions. But over the exact same period, 1990 to the present, Chinese emissions have gone from 2.5 billion tons to 12.5 billion tons. Now, that increase must be at least five-times greater than the magnitude of the reduction that’s happened in Europe. And so the totally natural thing for an economist to think is, Well, at some point the Europeans are going to say, “Wait a second, we’re paying money to do the right thing. And the Chinese just keep on going along business as usual.” And at some point they’re going to say, “Look, the climate doesn’t care where the carbon dioxide came from. It treats all dioxide the same. And it just stinks to keep on paying the costs of doing reductions while other people freeride on what you’re doing.”

MARVEL: Well, yes, and I think there’s another major factor at play here. And, again, this is not something that I’m qualified to talk about, but that has never stopped me before, which is geopolitics, which is the fact that Europe does not want to be buying a bunch of gas from Russia anymore. That doesn’t seem to be a sustainable pathway forward for reasons that aren’t necessarily purely economic reasons. In China, we actually are starting to see Chinese emissions flatline. Last month China installed a hundred solar panels a second. The amount of renewable capacity that China is installing is absolutely mind blowing. And part of that is just this stuff is cheap and it works. But part of it is that China is looking ahead to the future and saying, “We want to be an electro-state. We want to be in charge of the supply chains for these materials. We want to be the world’s leading manufacturer of solar panels. We want to really be leading in the research and development of this stuff.” And other countries are seeing that and they’re saying, “We want to be part of the 21st century. We want to be part of this energy transition because being stuck using fossil fuels is going to be like doubling down on using whale oil. That’s the technology of the past. We want to be leaders in the technology of the future.” So I think that there are other considerations that come into it besides purely an idealized market model.

LEVITT: So I hear what you’re saying, but I still, in my heart, have this really negative view of human nature. And I do think the data have not been inconsistent with that. We’ve been worried about emissions for a long time, but year-by-year global emissions have still been going up. and Let me use that pessimism to go back to thinking about when Stephen Dubner and I first wrote about climate change, and that was in our second book called SuperFreakonomics. We had the basic belief that humans weren’t going to do the right thing. And as a consequence, one of the ways humanity might have to try to work our way out of this dilemma was to try to intentionally alter the earth’s environment, to cool it down. A set of strategies that people call geoengineering. So let me ask you, were you aware of SuperFreakonomics when it came out? And, if so, I have no doubt it made you really angry.

MARVEL: Yeah, I think there were a lot of real cranky climate scientists after that came out.

LEVITT: You have not historically been much of a fan of this concept of geoengineering. That’s fair to say, right?

MARVEL: No. My view is that it’s like having your stomach pumped; you’re going to be glad that’s an option on the table if you really need it, but you should really stop eating poison in the first place. So, in my mental model of geoengineering, there’s two buckets. One is trying to cool down the planet by blocking the sun, and the other is trying to cool down the planet by hacking the carbon cycle, by taking carbon dioxide out of the atmosphere. And so in this particular context, which one of those, or both are you talking about?

LEVITT: I’m more taken with the solar radiation approaches to geoengineering. In the book we talked about sulfur dioxide and how you put that in the stratosphere, but my own personal favorite one was the ideas that John Latham had. Building a bunch of solar powered dinghies, which would putter around in the ocean and spray up salt water to seed the right kind of clouds.

MARVEL: So on a scientific level, we know that solar radiation management, whether spraying stuff in the stratosphere or seeding clouds that block the sun, that would probably work if your definition of work is to lower the global average temperature. But nobody cares about the global average temperature. People care about the consequences that come along with the change in a climate. Putting a bunch of carbon dioxide in the atmosphere warms the entire atmospheric column, whereas blocking the sun basically prevents sun from reaching the surface. Those are different things and they do not exactly cancel each other out. And so as a result, we know that we will see impacts on the global water cycle. We will see shifts in precipitation patterns. We will see droughts get worse in some places, rainfall increase in other places. So that’s something that we know will happen. And then there’s known unknowns. We don’t know exactly how that will play out. And then there’s unknown unknowns, the things that we haven’t even thought to think about. But the thing that really freaks me out about geoengineering is that science can inform this problem, but I don’t want to be involved in making these decisions. I don’t think scientists should be the ones making these decisions because this is an experiment on the entire planet, and I want to acknowledge that right now we are currently doing an uncontrolled experiment on the entire planet. But I don’t believe that — well, there definitely is not now and I do not believe there will ever be a global governance structure that is capable of making the decision to deploy or not to deploy.

LEVITT: Exactly what you said, it seems totally crazy that there’s no entity right now that is trying in a unified way to think about both the ethics of doing these things, but also, in a pragmatic way saying, “Look, as an insurance policy shouldn’t we be building our knowledge so that we have more options when we need them?”

MARVEL: Yeah, and I am strongly supportive of model-based geoengineering research. I think we should be doing these experiments in our climate models. I think we should understand what we know, what we don’t know, what we really need to focus more research on. For example, I, myself, am thinking lately about what would happen to the carbon cycle if we do this, if we spray particles in the stratosphere, if we block the sun. That’s going to give us less direct sunlight, but it’s going to give us more diffuse sunlight. And plants tend to like direct sunlight, but also like more diffuse sunlight. What’s that going to do? Are we going to be able to mitigate some of these temperature induced effects on plants? When it comes to deploying trials in the real world, I think those need to be approached with incredible care. And I feel incredibly out of my depth when it comes to who needs to be in the room, who needs to be making these decisions, should these decisions even be put forward? Should we even be asking these questions in the real world at all? That’s something that makes me feel completely unqualified to even have an opinion on.

LEVITT: You’re clearly not excited about geoengineering, but you do write in your book about one form of it that I think hasn’t been talked about very much, which is rock weathering. Could you explain how that works and why you think of the various options that have been offered about geoengineering, that might be one of the better ones?

MARVEL: This kind of falls under that second bucket of How do we take carbon dioxide out of the atmosphere? And there are a lot of methods that have been proposed to do this. So enhanced rock weathering is a way to try to speed up the slow carbon cycle. So there’s two carbon cycles: there’s a fast carbon cycle, which is carbons in the atmosphere. Plants take carbon out of the atmosphere through photosynthesis to make more of themselves. They die, they get eaten, things that eat them die, they rot, their carbon goes back into the atmosphere. So that is a carbon cycle that basically happens on the timescale of lives of living things in the biological world. And then there’s a very slow, millions or hundreds of million years carbon cycle where rocks get weathered by the small amount of natural carbonic acid that’s in rain. And then they go down, they get washed to the bottom of the ocean. The carbon is locked away there, and eventually it’s released back into the atmosphere by large-scale tectonic activity — volcanoes, basically.

LEVITT: So you’re saying the carbonic acid by eating away at the rock, it actually gets absorbed into the rock and then it falls to bottom of the ocean. Okay, gotcha.

MARVEL: Exactly. And this process is painfully slow. Just geological timescales. And so the thinking behind enhanced rock weathering is, Well, what if we tried to speed it up? And the simplest way to speed that up is just to grind up the rocks so that you have more surface area of rock that can get weathered, that can react with the carbonic acid in rain. And there have been some papers that are arguing that, this would have what we call co-benefits. If you spread rock dust, volcanic rock dust on a field in some regions, that could actually make the field more productive, that could raise agricultural yields. That sounds great. Amazing miracle cure, but there are no miracle cures here. There’s nothing that is going to be the one weird trick that’s going to solve climate change. Enhanced rock weathering might be a particularly useful tool in our incredibly large tool belt, and we’re going to need everything.

LEVITT: Economists are all in favor of a carbon tax.

MARVEL: You guys love that.

LEVITT: It just seems like such an obvious thing to do because the price of oil and gas and coal should reflect the damage it does via climate change. And we have some estimates of how big that damage is. And it’s actually pretty easy to implement because we only pull oil and gas and coal out of the ground at a very distinct set of places. And virtually every economist I know thinks it’s a good idea, politicians don’t seem to warm up to it, but it also seems like climate scientists aren’t very excited about the idea. If we can’t even convince you that it’s a good idea, we’re not doing a very good job as economists of making the case for why this is a good idea.

MARVEL: I think the reason that climate scientists are so suspicious of a carbon tax is that we know what we don’t know. We, physicists, are fairly aware of the fact that we don’t understand how people work. On paper, it sounds like a great solution: Just tax carbon, give a rebate back, or do something productive with all that money. Sounds great. But we know that climate change happens in the real world. It happens in the world that we make for it. So all of these rising temperatures and worse heat waves and more severe droughts, they are happening to a planet filled with humans and preexisting human structures. They’re happening on a planet that has a history. It has a geological history, but it also has a human history. It’s not a blank slate. If you try to implement a carbon tax on this incredibly messy, disorganized, ornery earth full of humans who don’t do what they’re told and don’t do what they’re supposed to, you know, I don’t necessarily understand the consequences of that. I don’t understand how you get it done. So my objection is not to a carbon tax in the abstract. My objection is to How do you actually get it done? And if you say, “This is the only policy solution that I will accept,” is that shutting you off to other ways that we might be able to make a dent?

You’re listening to People I (Mostly) Admire. I’m Steve Levitt, and after this short break, Kate Marvel and I will return to talk about why she’s probably finding this conversation frustrating.

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I spent most of this interview asking Kate about the aspects of climate change that are most interesting to me: public policy, carbon taxes, geoengineering. As she’s made clear several times, these things are actually mostly outside of her area of expertise, which is physics. But it’s become commonplace for climate scientists to be asked to fill roles that extend beyond science, acting as advocates for the environment, and more and more it seems, serving as therapists to people dealing with climate anxiety. Let me just say that as an economist, nobody asked me to be their therapist. I asked Kate if it was frustrating as a climate scientist to be expected to have opinions and thoughts on so many things outside of science.

MARVEL: It’s frustrating, it’s also just bizarre to me because obviously I would not be a good therapist. Obviously I do not know that much about public policy. And there are people who spend their lives studying these things. Something that I find very confusing and baffling and scary is people expect me to have the correct opinion on literally everything bad that’s going on in the world. Climate change really illustrates the interconnectivity of everything. How the ice and the atmosphere and the ocean and the land all talk to each other. But it also illustrates the interconnection of society. And so, on a very high level, yes, everything is interrelated, but it can be extremely overwhelming to ask a climate scientist to have strong opinions on every conflict, every tax policy, every unfairness in the world. They are all related and they all do matter, but I think we only make progress when we zero in on the things that we are actually good at. And I am fundamentally, deep in my core, a nerd. And I like doing science, I like doing physics, and I think that’s where my contribution can be.

LEVITT: So you are a physicist, but in your new book, Human Nature: Nine Ways to Feel About Our Changing Planet, you’re questioning what it means to be a scientist who feels things about the thing she’s studying. Could you talk about that?

MARVEL: I struggled with this for a while because scientists in general are supposed to be neutral and objective. But I study the earth and that means that I have a conflict of interest because everybody and everything that I care about lives here. So I can’t be neutral and emotionless. And I worried that if I say I feel things about this planet, is that going to make me less credible? And then I realized that, no, that makes me a liar. And I don’t want to be in the business of saying things that are not true. As scientists, we have tried for a really long time to talk about climate change through the prism of science, right? We’ve been like, Oh, just one more chart, and it will convince everybody. Like, Hey, look guys, we have another equation. Now does everybody believe us? And that hasn’t worked because that’s really not how people relate to information. We like stories. And stories make us feel things. I want to be really clear that I haven’t said anything productive or useful about emotions in this book. People ask me, “I have climate anxiety, what should I do?” I don’t know. Go talk to somebody who knows what they’re talking about. What I am saying is that it’s okay to feel things and it’s okay to tell stories about climate change and what it has meant in the past and what it means in the future. 

LEVITT: So each chapter of your book has the name of an emotion: wonder, fear, anger, guilt, grief, surprise, pride, hope, and love. But after reading your book, I think my own overriding emotion is resignation, which is probably not at all what you hoped for when you were writing the book.

MARVEL: That is not. I have failed utterly. Why do you feel that way?

LEVITT: When I think about climate change, actually sit down and think about it carefully and thoughtfully, like your book caused me to do, I’m always left with the feeling like we’re not going to crack it. And we’re just going to ride this thing out, and either we’re going to be kind of lucky or we’re not. I just don’t have enough faith in humanity to think we’re going to solve it in a good way. Interestingly, when we wrote SuperFreakonomics and everyone got so mad at us, I actually had hope. Because at that time I had a feeling that science, clever science, really smart people were going to be the answer to this problem. But I think more and more I have the sense that this might be a problem that scientists just can’t get us out of.

MARVEL: I actually am the opposite of you. I have gotten more optimistic as time has gone on because the problems are getting worse, but the solutions are getting better. And I agree that it is overwhelming to look at this on a global scale and say, “Are human beings good?” “Yes.” “No.” If you frame it that way, then you are always going to have a pessimistic outlook, because if it requires human beings to be uniformly selfless and good, then, yes, we will never get out of this. But I actually don’t think we need hope. People always ask me if I hope that we can solve climate change. And for me that’s asking, Do you hope you can clean the bathroom? I don’t know, just clean the bathroom, right? And we do have most of the tools that we need to solve this. And we have had incredible progress on people making solar panels better and cheaper. We have seen an absolutely stunning decrease in the cost of wind and solar. We are seeing a jaw-dropping decrease in the cost of batteries to the extent that I think the global energy transition is now inevitable. Will it be fast enough? Will it be fair enough? No, I don’t think that. But I think we are looking at a future that is powered very differently than our current world. I’m not a defeatist. I think there’s still so much to do and there’s still so much joy and purpose and meaning to be found in doing things and actually looking at, Where does my skillset fit in to helping solve some aspect of this problem? If you look at it from, What needs to be done and what can I do?, then you start, just like Mr. Rogers said, “You start looking for the helpers.” And they’re everywhere. And that actually does give me hope, even though I don’t need it.

It’s always interesting to me when two reasonable, thoughtful people like Kate Marvel and myself can look at the same set of data, agree on the facts, and still come to opposite conclusions. When I look at where we’re heading with the climate, I have the overriding sense that we’re on a bad path with little or no chance of getting off. Kate, on the other hand, is optimistic, feeling that the solutions are starting to fall into place. I’m curious, what’s your view about our future climate? Are you optimistic or pessimistic about the state of the earth’s climate 50 years from today? I’d love to hear your answer to that question. Send us an email. The address is PIMA@Freakonomics.com. And also, your age, and the country that you currently live in. Feel free to write as much as you want, but also feel free to write literally a three-word email that has either the word optimistic or the word pessimistic, your age, and your country. I’ll tally up the responses and report back on them in a future episode.

LEVITT: So this is the point in the show where I bring on my producer Morgan to pose a listener question.

LEVEY: Hi, Steve. So a listener named Jasper sent us an email with an idea, and he’s curious to know your opinion. Jasper proposes that the government should charge one penny for every email sent. The fee would be charged to the sender. Our inboxes fill up with a lot of clutter, and Jasper thinks this could disincentivize senders of spam and promotional emails. He also says that even if one penny per email doesn’t prompt anyone to change their behavior, it would be a lot of revenue for the government. So Steve, what do you think of this idea?

LEVITT: I love the idea. I love the way Jasper is thinking. Let me explain why, with the caveat that I’m sure there is scientific literature that studies optimal message sending. I’ve never read that literature. So this is just my own impressions. So all of my logic starts from a basic premise, Morgan, which is that I think the sender in general cares more about the message being delivered than the receiver cares about receiving it. And you can think of exceptions, but don’t you think that’s basically true?

LEVEY: Yeah, absolutely. Any business that’s sending out a promotional email is doing it for their own self-interest in the hopes that 5, 10 percent of recipients will open it.

LEVITT: Yeah, but even if you send me an email, usually it’s more important to you. And sometimes it’s important to me and sometimes it’s not.

LEVEY: When I send you an email, it’s always about this podcast, so it should always be important to you.

LEVITT: Okay, so let’s think about a world where it’s costless for the recipient to receive a message. So if you send me a message, I can just know what it says without having to spend any time or money doing it. Of course, that’s not true, right? It takes me time to sift through messages, even if I don’t read the actual message. Deleting it from my inbox takes a little bit of time. It’s no accident that snail mail — when you send letters through the post office, it’s the sender who pays the postage, not the recipient. And that’s in line with what Jasper’s talking about here. One other thing I want to bring up: I have long loathed voicemail. It takes as long for the listener to listen to the voicemail as it does for the sender to have recorded it. And that’s really inefficient because in general you want to have technologies where it’s relatively hard to send the message and relatively easy to receive the message. And so that’s good about email, right? It takes you a lot longer to compose the emails that you send to me than it does for me to read them. So, in general, I think email’s moving in the right direction already of putting the burden on the sender.

LEVEY: Well, this might be true in a one-to-one basis, but what about emails to thousands of people like spam?

LEVITT: Exactly. You totally nailed where I was going with that, which is you can pose a spam email once and then you send it to 10,000 people. And that’s incredibly inefficient because almost all of the effort goes to getting rid of the spam and very little to sending it. And that’s what we call in economics a negative externality. And how do you deal with negative externalities? Well, you want to tax them. And just like a carbon tax would tax the negative externality of climate change, Jasper’s idea would be to tax the negative externality of spam. So I think it’s a great idea.

LEVEY: So you think this should be enacted?

LEVITT: I think it’s a good idea, but I think it’s impossible to do for the reason that micro-payments have never been figured out. I don’t know why, but it’s turned out that nobody has found a good way to allow people to be charged 1 cent for doing something, and it would be a great application here if people could pay a half a cent or a cent for this, but an equally good application and one that I’ve been frustrated by for years is how you could use micropayments for podcasts. Because advertising on podcasts is an incredibly inefficient way of wasting everybody’s time listening to ads that most people don’t really want to hear. If instead you could charge someone a penny to download our podcast, that would be better for everyone, and that technology has just been elusive. So what we really need is some super smart listener to figure out how to create a world in which micropayments are possible. And once that happens, then Jasper, the first thing I’d do is I’d tell the government to apply it to emails, just like you said.

LEVEY: Jasper, thanks for writing and great idea. Listeners, if you have an idea for us or a problem that could use an economic solution, send us an email. Our email is PIMA@Freakonomics.com. That’s P-I-M-A@Freakonomics.com. Steve and I read every email that’s sent and we look forward to reading yours.

Next week we’ve got an encore presentation of a conversation I had with my good friend and former Secretary of Education, Arne Duncan. And in two weeks we’ve got a brand new episode featuring behavioral scientist Uri Simonsohn. He’s both an incredibly inventive and productive academic, and he’s been at the center of efforts to catch cheating academics. As always, thanks for listening and we’ll see you back soon.

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People I (Mostly) Admire is part of the Freakonomics Radio Network, which also includes Freakonomics Radio and The Economics of Everyday Things. All our shows are produced by Stitcher and Renbud Radio. This episode was produced by Morgan Levey, and mixed by Jasmin Klinger. We had research assistance from Daniel Moritz-Rabson. Our theme music was composed by Luis Guerra. We can be reached at pima@freakonomics.com, that’s P-I-M-A@freakonomics.com. Thanks for listening.

MARVEL: Oh, man. I mean, talk about the things that I am not an expert in. The psychology of weird, rich people is probably number one.