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David Keith (intro): So, if you're hotter when you are learning as a child, you learn less well, you do less well on tests and you are less economically productive 30 years later, there's actually a really beautiful study that shows that, so I'd say, in total, there's this very strong evidence that heat is a big driver of overall climate impacts. And it's clear that the impacts of heat are much worse for places that are already pretty hot. And in fact, there may be benefits for places that are cold, and most of the world's poor are living in places that are hot, not exclusively, of course. And so that's the central reason why climate is expected to be very regressive: that the impacts of climate change hurt the poor on average, more than they hurt the rich.

Ralph Ranalli (intro): Welcome to PolicyCast and the third and final installment of our Systems Failure Series. I’m your host, Ralph Ranalli. In recent episodes, we’ve examined both technology and the economy as examples of systems that play a huge role in determining how we live, but that also contribute to inequality and other society harms.

Today we turn to climate, which, since it holds the key to humanity’s future as a species, is arguably our most vital system of all . Right now, leaders from around the globe are meeting in Scotland for the COP26 summit, talking about ways to speed up efforts to fight global warming. Yet even the optimists in Scotland admit that the scientific consensus is that it’s already too late to cut emissions fast enough to avoid a dangerous rise in the earth’s temperature by 2 degrees Celsius, which is expected to lead to severe droughts, blistering heat waves, deadly flooding, and rising seas. 

Despite these dire predictions, there has been one potential weapon in humanity’s anti-warming arsenal that even in terms of practical research, has been a taboo subject. But Professor David Keith says it’s time for that to change. Keith is an award-winning physicist who holds professorships at both Harvard Kennedy School and Harvard’s School of Engineering and Applied Sciences. Working at the intersection of physics and policy, he is perhaps best known for his work in solar geoengineering, which is the science of making man-made changes to the atmosphere that would cool the planet by either preventing some of the sun’s energy from getting through, or making it easier for heat already in the atmosphere to escape.

Critics have had a tough time wrapping their heads around solar geoengineering, calling it the stuff of science fiction, saying it could be used as an excuse not to further cut emissions, and even that governments might use it as a weapon. But Keith says that it’s now time to explore four major strategies to fight warming, including cutting emissions, helping people and societies adapt to the effects already being felt, and solar geoengineering. Keith is also known for his work in the fourth strategy, carbon capture, and founded a company working on technology to pull carbon out of the air — although he says it is at best a long-term strategy that could take decades to have any beneficial effect.

So what does any of this have to do with inequality? Well, Keith says it is one of the primary arguments for starting serious research on solar geoengineering. After all, he says, planetary warming doesn’t play fair. It is mostly people the world’s poorest countries who will suffer the worst harm from a warming climate, yet they are the least responsible for it in terms of per capita emissions. And amid all the recent talk of climate adaptation, there is comparatively little mention that it is much easier for a rich country in a colder latitude to adapt than it is for a developing one in a hotter region. 

It’s a complicated subject, but an important one. Professor David Keith is here to help us sort it out.

Ralph Ranalli: David, welcome to PolicyCast.

David Keith: Thanks. Thanks for having me, good to be here.

Ralph Ranalli: With any scientific discussion, it's probably best to start with definitions. So, can you lay the foundation for us by talking a bit about what solar geoengineering is? And you're advocating for researching it, as a potential solution or palliative to climate change, broadly speaking. I think many people know that it's about making intentional man-made changes to the atmosphere to counteract global warming, but can you talk a little bit more about specifically what it is?

David Keith: The core idea is that humans could deliberately make the earth a little bit more reflective, so it absorbs a little bit less sunlight. And when you think about this, the central thing that's causing climate change is the buildup of greenhouse gases like carbon dioxide in the atmosphere, and that makes it harder for the Earth to radiate away heat, and at some level you can think of the climate as a balance between how easy or hard is to radiate away heat and how much heat, or energy the Earth absorbs from the sun. And so if you've warmed the planet up and changed the climate by adding carbon dioxide, you could at least reduce some of the changes by reducing the amount of sun that was absorbed a little bit. The best way to understand it, is to think about it, in relation to the other things we can do about climate.

And, in my view at the very top level, there are four fundamental things to do. One is to reduce emissions, the emissions that are causing the build up of greenhouse gases in the atmosphere by changing the industrial basis of our civilization. The second one is to remove carbon dioxide from the atmosphere, the third one is this Solar Geoengineering, or climate intervention, or whatever you want to call it, and the fourth one are local adaptive measures that reduce the amount of suffering or ecological damage for a given amount of climate change. So very broadly, I think you should see solar geoengineering as one of those four things that are potential ways to reduce. The only one of those that we clearly have to do is to cut emissions, the other ones are choices.

Ralph Ranalli: Obviously with COP26 going on we're talking a lot around the world about cutting emissions. But in terms of Solar Geoengineering, you’re advocating for seriously researching it as part of the overall effort against warming. Would you say that we're moving from a scientific conversation about geoengineering towards a more practical conversation about policy?

David Keith: Yeah, I wouldn't say that. So I would say this never was really a purely scientific conversation. Science is about understanding how nature works better, and Solar Geoengineering is not a question of science, it's a question of technology—ultimately of engineering. It's a question of applying scientific knowledge and engineering knowledge to do something. And from the very first discussions of these technologies in the 1960s, they were framed as potential things to do, to reduce the harms from climate change. So, that's not a scientific question, it's a question about the potential development of use of a technology, very different from science.

Ralph Ranalli: Can you walk us through some specifics about the technologies of Solar Geoengineering? I understand that different techniques try to affect different layers of the atmosphere.

David Keith: So, maybe from the top, literally the highest place to the lowest place, there's a big range of ways that humans might do this, humans might alter the Earth's energy balance. So, from the highest, it's at least conceptually possible to put huge reflective screens in space that would reflect some sunlight before it got to the earth. I think that's kind of laughable in the next decades, but this is a 150 year or so problem. And I think it's not crazy to imagine that humans could do that late this century. The second way, going down, is to add aerosols, fine particles that reflect sunlight into the upper atmosphere, the stratosphere, which is about, in the tropics, about twice as high as a conventional aircraft flies above our heads. And, the reason that people focus on the stratosphere is that materials stay there for about two years.

Ralph Ranalli: And that's, that one is basically creating a man-made version of the after-effects of a big volcanic eruption, right?

David Keith: Some volcanoes put sulfur dioxide in the stratosphere, which makes fine aerosols, which does cool the planet globally. So certainly part of it is based on that. Yes, so you can think of it as a deliberate analog to that natural phenomena. And then moving down, there's possibilities for reducing certain kinds of cirrus clouds, and then further down, it's possible to make some lower-level clouds whiter, or to make the surface brighter.

Ralph Ranalli: So the subtractive version of this—which is when you're talking about breaking up the cirrus clouds in the troposphere—what does that do for us?

David Keith: So that actually does something a little bit different, at least partly. It makes it easier for the infrared light to get out rather than reflecting more of the solar light. That, of course, it actually does a little bit of both, and so at least in principle, that could actually be better in compensating for the damage of carbon dioxide. But it's deeply uncertain whether it works at all, or what areas it would work in.

Ralph Ranalli: This podcast is part of a series that we're calling Systems Failure, and it's about the systems that affect how we live our lives and how they can contribute to inequality. Now climate is arguably the most important system that affects our lives, but you've said that inequality is also a fundamental issue here in regards to the climate crisis and that these strategies, including solar geoengineering, can address that inequality. Why do you say that?

David Keith: Yeah. I mean, let's start with inequality. I mean, one of the really amazing things that has come out of the literature on climate change in the last decade, or so is actually coming from applied econometrics is really a quantitative understanding of how heat impacts people. It shouldn't have been a surprise, but there's now really strong evidence that high temperatures obviously kill people in heat waves, but they also reduce intellectual and physical productivity. You can see that as reduced economic productivity. So on a hot year, the GDP grows less in India, say than on a cooler year. And, that's true in general, in most countries, that are not the coolest countries. So a warmer year in Sweden or Canada, that can actually make economic growth slightly larger. 

And, it's clear that some of this is a long term effect, as an economist we think about it maybe as an accumulation of intellectual capital, and heat can reduce that. So, if you're hotter when you are learning as a child, you learn less well, you do less well on tests and you are less economically productive 30 years later, there's actually a really beautiful study that shows that, so I'd say, in total, there's this very strong evidence that heat is a big driver of overall climate impacts. And it's clear that the impacts of heat are much worse for places that are already pretty hot. And in fact, it may benefit places that are cold, and most of the world's poor are living in places that are hot. Not exclusively, of course. And so that's the central reason why climate is expected to be very regressive: that the impacts of climate change hurt the poor on average, more than they hurt the rich.

Ralph Ranalli: I can remember 30 years ago, when we were talking about reducing carbon, we talked about having this comparatively long runway where we had a chance to reduce admissions and really affect climate change. And I’m struck now by the fact that now we’re talking so much about adapting to warming now rather than preventing it. And it seems like the same fundamental unfairness applies there too, since your ability to adapt is really a product of where you live. It's just a lot easier to adapt when you're in a rich country in a colder region.

David Keith: For sure. I do want to take issue with this sort of assumption that our opportunity or the benefit for cutting emissions was bigger then, and somehow we've lost our chance. I think obviously many of us feel we ought to have done much more decades ago, but it's still absolutely imperative to cut emissions. And it's still true that cutting emissions will reduce the growth of the underlying thing that causes climate damage and so will make the future better off.

Ralph Ranalli: Let's talk about some of the arguments against Solar Geoengineering, because there seemed to be a lot of them. The first one being that,