My Climate Journey

Ep 79: David Keith, Professor at Harvard School of Engineering and Applied Sciences and the Kennedy School, and Founder of Carbon Engineering

Episode Summary

Today’s guest is David Keith, Professor at Harvard School of Engineering and Applied Sciences and the Kennedy School, and Founder of Carbon Engineering. This is a deep dive episode into the important topic of solar geoengineering. Whether you are for it, against it, or just want to understand it better, this one is for you!

Episode Notes

Today’s guest is David Keith, Professor at Harvard School of Engineering and Applied Sciences and the Kennedy School, and Founder of Carbon Engineering.

David has worked near the interface between climate science, energy technology, and public policy for twenty-five years. He took first prize in Canada's national physics prize exam, won MIT's prize for excellence in experimental physics, and was one of TIME magazine's Heroes of the Environment. David is Professor of Applied Physics at the Harvard School of Engineering and Applied Sciences and Professor of Public Policy at the Harvard Kennedy School, and founder of Carbon Engineering, a company developing technology to capture CO2 from ambient air to make carbon-neutral hydrocarbon fuels. Best known for his work on the science, technology, and public policy of solar geoengineering, David led the development of Harvard’s Solar Geoengineering Research Program, a Harvard-wide interfaculty research initiative. His work has ranged from the climatic impacts of large-scale wind power to an early critique of the prospects for hydrogen fuel. David’s hardware engineering projects include the first interferometer for atoms, a high-accuracy infrared spectrometer for NASA's ER-2, and currently, the development of pilot plants for Carbon Engineering and the development of a stratospheric propelled balloon experiment for solar geoengineering. David teaches courses on Science and Technology Policy and on Energy and Environmental Systems where he has reached students worldwide with an online edX course. He has writing for the public with A Case for Climate Engineeringfrom MIT Press. Based in Cambridge, David spends about a third of his time in Canmore, Alberta.

In today’s episode, we cover:

Links to topics discussed in this episode:

Additional Reading:

David Keith, “Let’s Talk About Geoengineering,” Project Syndicate, March 21, 2019.

David Keith, “Toward a Responsible Solar Geoengineering Research Program,” Issues in Science and Technology, Spring 2017.

James Temple, “What is Geoengineering—And Why Should You Care?MIT Technology Review, August 9, 2019.

Lizzie Burns, David Keith, Peter Irvine, and Joshua Horton, “Belfer Technology Factsheet Series: Solar Geoengineering,” Harvard Kennedy School Belfer Center for Science and International Affairs, Technology and Public Purpose Project, June 2019.

Jon Gertner, “Is It O.K. to Tinker With the Environment to Fight Climate Change?,” The New York Times Magazine, April 18, 2017.

You can find me on twitter @jjacobs22 or @mcjpod and email at, where I encourage you to share your feedback on episodes and suggestions for future topics or guests.

Enjoy the show!

Episode Transcription

Jason Jacobs:                Hello everyone. This is Jason Jacobs and welcome to My Climate Journey. This show follows my journey to interview a wide range of guests to better understand and make sense of the formidable problem of climate change, and try to figure out how people like you and I can help. Today's guest is David Keith, a professor at the Harvard School of Engineering and Applied Sciences, and at the Harvard Kennedy School, and founder of Carbon Engineering, a Canadian company developing technology to capture CO2 from ambient air.

Jason Jacobs:                David's worked near the interface between climate science, energy technology and public policy for 25 years. He's best known for his work on the science, technology and public policy of solar geoengineering. He led the development of Harvard solar geoengineering research program. David also took first prize in Canada's national physics prize exam, won MIT's prize for excellence in experimental physics and was one of Time Magazine's heroes of the environment.

Jason Jacobs:                We have a long form discussion in this episode where we take a deep dive into solar geoengineering research, why it matters, some of the inherent risks, how they can be overcome, the state of that research today, where it needs to go. And, if you feel so inclined, how you might be able to help. David Keith, welcome to the show.

David Keith:                  Thanks a lot, great to be here.

Jason Jacobs:                I'm glad we're finally making this happen. Now, you were one of the first people I reached out to a year ago on My Climate Journey and you got right back to me when I emailed you cold and gave me some book recommendations, and that started… I guess at this point we've met three or four times, so… but never with the mics on.

David Keith:                  I want to know what the books were and how much I misled you. What books? Do you remember?

Jason Jacobs:                I want to say, because there were a few that I read on top [inaudible 00:01:57] but one of them I think was Planet Remade.

David Keith:                  Oh yes, yes. Oliver's book, which I think is just terrific.

Jason Jacobs:                Yes, and I feel like there was another one as well, but I'm blanking on the name. I'll have to [crosstalk 00:02:05]

David Keith:                  I'll give you a smeal book. I often give people smeal books that [inaudible 00:02:09] energy.

Jason Jacobs:                He didn't, but I did. I've got one sitting there that I've been meaning to read. That is a hard one to get. As a non-scientist, that's an intimidating one to crack open. It seems pretty thick.

David Keith:                  Yes, so there are thick and thin smeal books? I've been reading one just to get off on it, maybe a bit of a tangent. A lot of people think that technology is changing much faster now than it did and so I teach technology policy at The Kennedy School and I have to struggle with this, and I don't think it is or if it is, you got to really define what measures speed and why.

David Keith:                  And one of my absolutely favorite smeal books is about this age of synergy. This age of very rapid technological change from the late 1860 roughly till the first World War were just so many of the major technologies that shaped the last century were invented. And I've been actually rereading it [crosstalk 00:02:58] and get young students to realize that technological change is not as… not just about iPhones and not as new as they think and it's been really fun.

Jason Jacobs:                Maybe for some forced accountability, I'm not allowed to meet with you again until I've read that book, so-

David Keith:                  Read some smeal energy books anyway, but yes, all right.

Jason Jacobs:                I'm super excited to dig into the topic of solar geoengineering today. You are one of the most knowledgeable people out there on the topic and it's in a very important one, so maybe let's just jump right in. What is solar geoengineering?

David Keith:                  Solar geoengineering which goes by a bunch of other names, you'd call it climate geoinvention or solar radiation management or solar radiation modification. I'll go with solar geo, but I don't really care much. It's the idea that humans might deliberately alter the Earth's radiative forcing to offset some of the risks of accumulated greenhouse gases. Let me step back. Radiative forcing is just a technical word that people use in the climate science world for how much we're pushing on the climate.

David Keith:                  We start with one geeky term, which is watts per square meter, which is a measure of how much in total humans are pushing on the climate, so times CO2 is about four watts per square meter. That's the instantaneous amount that human actions, greenhouse gases and other things are putting the radiative balance of the earth out of balance and causing the climate change.

David Keith:                  That probably sounded pretty theoretical. Let me give you some examples about how it might be done. Most of the examples involve aerosols, so for example, it'd be possible to add to the aerosol burden in the stratosphere. What's an aerosol? It's just a small particle of a liquid or a solid, like a dust that is simply so small it doesn't fall down rapidly. A Cannonball, you could argue is an aerosol but it falls out of the atmosphere right away.

David Keith:                  Aerosols are suspended just because they gravitationally settle slowly and they are also very, very effective at scattering light. It turns out the optimal size of a thing to scatter light per unit of weight. The thing that that is, it'll scatter the most light per unit weight is something that has a size about the wavelength of light. Aerosols have ordered a micron or half a micron in size are the things that are most effective at scattering light.

David Keith:                  Aerosols in the upper atmosphere can scatter light back to space and that reduces the total amount of sunlight that the earth absorbs, and that is a negative radiative forcing that will offset some of the positive radiative forcing from greenhouse gases like carbon dioxide. Now to go to the all the different ways you might do solar geoengineering, there's aerosols in the stratosphere of different kinds.

David Keith:                  There's ideas of modifying high cirrus clouds. Cirrus clouds, it turns out are warming clouds because they have an infrared heat trapping effect that's bigger than their sunlight scattering effect, or generally do. And so there's ways that we might be able to reduce the density of those cirrus clouds in some locations, and that could be a quite effective way to lever for modifying the radio forcing.

David Keith:                  Then there's also ideas for increasing low-lying clouds, particularly marine stratus cloud which only occurs in parts of the world, but it might be possible that by adding more aerosols to those clouds, you could make them a little wider or live a little bit longer. That was starting the stratosphere and going down [inaudible 00:06:08], stratosphere and go up. The other possibilities, you could build big structures in space in principle.

David Keith:                  Build a structure at the L1 point in between the earth and the sun. That's a very quick run through of the technical methods by which solar geoengineering might be done. And to go a little further on technical methods, I would say the method in which there is the highest level of [inaudible 00:06:30] confidence that in some crude way, it is doable and doable with essentially commercial off-the-shelf technology and doable cheaply is to put sulfuric acid or sulfate aerosols into the stratosphere. That's a thing that I think there's a really enough knowledge that we can say with very high confidence that could be done to produce, say two watts per square meter of radio forcing offsetting half of CO2-driven warming effect.

David Keith:                  And that could be done quite easily in pure technical terms. That's not making any claims about how useful it is or how risky it is, but just the raw ability to do it. Whereas some of the others it's much less clear that they could actually be done at scale and produce significant radiative forcing, which is not a reason not to look much harder because some of them have advantages and disadvantages, but there are different things.

Jason Jacobs:                Got it. Is it basically blocking out the sun to mask some of the symptoms that come with increasing carbon in the atmosphere?

David Keith:                  Yes, I think that's a useful way to think about it. I certainly think that it's… if you want to get into analogies, think about it as a band aid or chemotherapy for cancer or so on are common analogies that we use. To go a little deeper technically now, the reason CO2 and other long lived gases, greenhouse gases heat the climate is they make it relatively harder for the climate to radiate away infrared light to space.

David Keith:                  And so the temperature is balanced or the Earth's climate is balanced by how much light it absorbs from the sun and all the energy absorbed from the sun, it has to radiate back to space in infrared. And that radiative natural balance will always stay roughly in balance. But if you make it harder to radiate away sunlight for a given temperature, then the temperature has to come up, to come back in equilibrium.

David Keith:                  If you add CO2 to the atmosphere, that means that at a given surface temperature, there's a little less what we call outgoing long wave radiation, a little less of this infrared radiation going up to space, and so then the earth needs to go to a higher temperature to bring itself back into energy balance. And the idea is that by reducing the sunlight input a little bit, you could bring the earth a little closer back to the original climate, [crosstalk 00:08:42] to its original radiative balance.

David Keith:                  And that actually gets at one of the basic limits to solar geoengineering, so the biggest thing to say is solar geoengineering is not anti CO2. There is nothing that you could do with solar geoengineering that completely undoes all the climate risks that come from carbon dioxide. Partly, that's because some of the climate risks that come from carbon dioxide aren't about climate, they're about the chemistry of carbon dioxide. Carbon dioxide is a weak acid, carbonic acid and it… as your listeners all know it acidifies the ocean and that direct effect of carbon dioxide basically depends on the amount of CO2 in the atmosphere, and it's more or less unaffected by what you do with the solar geoengineering.

David Keith:                  But even in the story I just told with carbon dioxide making it harder for infrared light to get out, that turns out to happen in the middle of the atmosphere, maybe five kilometers over our heads. It's where a lot of the infrared light gets out and then goes back to space. Whereas sunlight, it's basically mostly absorbed at the surface, so it's not only scattered by clouds, but the sunlight that actually is absorbed, that heats the earth, mostly it's absorbed at the surface.

David Keith:                  It's funny. Even though the sun is above us, when you teach a climate class, you teach people that it's actually quite useful to think about the earth system is being heated from below, because that's where the sun is absorbed. That means that if you warm up the climate with say, doubling CO2 and then you cooled it back down to the same original global average temperature by solar geoengineering which is turning physically possible, you do not get back to the same climate.

David Keith:                  And in particular, in that scenario, the precipitation, the total amount of hydrological cycle, the total amount of evaporation of water and precipitation water, which have to balance, those two have to go down. It turns out they go down more than the temperature goes down. If you bring temperatures back to their original equilibrium point, you have to have precep down. Actually, that's only true if you assume you have to reflect away sunlight in a spectrally broad way, reflecting about the same amount of sunlight to every spectral band.

David Keith:                  There's actually a mostly theoretical possibility, but it is true in principle that if you had scatters that were spectrally selective, and they reflected just in the near infrared, in some wavelengths that are actually absorbed in the atmosphere and don't make it to the surface, then that doesn't have that same problem. And then you can actually in principle, get both temperature and precipitation back closer to pre-industrial.

Jason Jacobs:                And so when solar geoengineering is deployed, how concentrated can it be versus… Do you deploy it once and it goes horizontally across the earth or is it in a very concentrated geography? How does that work?

David Keith:                  I think you really need to divide this up into two completely different things. One is about how we make the radiative forcing by one of those methods I said, and some of the choices about how dispersed it is. It is a human choice. It's not a fact of nature or it's a mixture of human choice and fact of nature. And then there's a question of what is the climate response to that radiative forcing.

David Keith:                  I would say the following. It is certainly theoretically possible and for some methods it's easier or harder to make radiative forcing in a limited area. For example with say the cirrus thinning idea, the aerosols that would alter the cirrus clouds if it works at all and it's only going to work in some particular cirrus clouds, but you could certainly limit that to a pretty confined geographical area, say a thousand kilometers circle.

David Keith:                  And likewise at these ideas of marine cloud brightening of these stratus clouds, if you're in the right area, you could do that in a way that was a quite limited occasion. And likewise in principle, there are space-based systems, low earth orbit space based systems I think that are not very practical that would allow you to do the radiative forcing only in one place, but, and there's a huge but.

David Keith:                  If you do radiative forcing in one place, that is theoretically possible, but it is impossible to only affect the climate in that place, because climate is all interconnected by flows of heat and momentum. I should say, if it was really possible for each region to just technologically change its own climate, then the politics would be easy because there wouldn't be any international conflict. Each country could just set its climate knob, but that is definitely not possible.

David Keith:                  It's deep in the climate that we only live on one planet and that the climate system is interconnected. While it is possible, not necessarily easy to… With some of these methods have the radiative forcing be more local, if you make it more local, there will definitely be non-local effects. We call these teleconnections in the climate world where if you make a change someplace, you'll get through the way weather systems work. You'll get some corresponding change somewhere else.

David Keith:                  Long story, but my view to jump a little bit to the politics of this is that if you're looking for solar geoengineering that has the best chance of providing the largest global benefits of reduced climate risks with the minimum harms, and the minimum extent to which any place is worse off. It's likely that you do not want to use one of these localized methods and you want to do something that provides a pretty uniform radiative forcing where you have about the same radiative forcing North to South and East to West over the whole world.

David Keith:                  And I think there's pretty strong reasons to believe that doing that has the best chance or is near the best chance of reducing climate change and in a way it's pretty uniform and doesn't or does the minimum to leave any region worse off.

Jason Jacobs:                How does one test solar geoengineering in terms of what are the steps to go from a concept to actually something that feels like it could be ready to deploy, and where are we with that research today?

David Keith:                  Yes, so that's getting the core of it. I'll try that in a couple of different ways. Maybe what I'll first do is tell you a little bit about what I think is known and not known today, and then say a little bit about where research is happening and how much research funding there is and why. And then we can go from there. This topic has been for reasons that we can do a taboo, where there has been very little research in total until maybe recently.

David Keith:                  While the idea isn't new, the idea appeared in the climate reports of the 1965 and ‘77 and the early ‘80s at [inaudible 00:14:56]. The topic was woven into all the early work about climate, and many of the things we work on aren't remotely new. It's not a new innovation. There's been very little systematic research about how it might be done and about how... what I call the efficacy would be.

David Keith:                  That is how much it accurately reduces climate risk we care about, and also very little understood about what the risks would be. Now, fast forward to now, while there has been a taboo, there's been more research. They're about a thousand papers published. Actually, roughly half of them, social science, roughly half climate science, a lot of them just taking generic line models and applying them.

David Keith:                  But here's some of what I think we know. I think that for aerosols in the stratosphere, I think that there is reason to believe, pretty strong reasons to believe that if you put aerosols, say sulfates or other aerosols in the stratosphere, you could adjust the amount that you put in with feedback. You'd observe how the aerosol distribution was and adjust where you were putting it in based on your observation of where it is.

David Keith:                  That if you do that, it wouldn't be too hard to produce a pretty uniform radiative forcing. The stratosphere naturally has this long slow two-year circulation, so any material that you put up there lasts for roughly two years, very round numbers. And mostly what you do is you inject in the tropics roughly between plus and minus 30 degrees, 30 degrees at North and South latitude.

David Keith:                  You actually only have to do that at one longitude, so you could do it in principle essentially from a single set of airfields near the tropics, and then the material spreads pretty evenly globally. You need to do a little bit of tuning, and I think the evidence that you could get something that was quite uniform, meaning that the differences in say a 10 degree zonal band might be no more than 10%.

David Keith:                  I think the evidence for that is pretty strong, that's doable in principle, and that you could do that… Let's just take a benchmark case. Let's say you want to do two watts per square meter. I'll come later and defend that benchmark, but let me for the next while assume that you want to do this two watts per square meter benchmark. If you want to do it with sulfur, that would take something of order a million and a half or 2 million tons a year of sulfur in the stratosphere.

David Keith:                  Does that say a little bit about how that could be done, physically, and what its risks would be? And then we'll talk about what the… what we know about what the benefits would be. That can be done with not existing aircraft or there's ways to do it not very effectively with [inaudible 00:17:13], but best done with new aircraft, but new aircraft that aren't particularly hard to build.

David Keith:                  There are new aircraft that are built with existing edging technologies and existing airframe building technologies and lots of different air frame makers can make these things. And maybe aircraft that would have roughly a 10 ton payload and fly to roughly 20 kilometers, 65,000 feet level, and I think the evidence that you could move that much material to the stratosphere in reasonable… well, reasonable is a value judgment, but the costs of order are a couple of dollars a kilogram.

David Keith:                  Then you're looking at total costs when you do the overall amortized cost. The program has a few billion dollars a year category to put that much material in the stratosphere. Let's assume it's sulfur for now, they're probably a lot better ideas we can get to, but just for sulfur, we are talking about putting a million and a half tons of sulfur as sulfuric acid in the stratosphere. Your obvious reaction should be, “What? That's crazy.” It's important to think a little bit about the risks, so here's some numbers to help give that some perspective. Moderate, big, but not by any means monstrous. Volcano like Pinatubo in ‘91 put 8 million tons in a single year, and we have lots of observations from that. And we know lots of it.

David Keith:                  Models got calibrated, models in stratosphere, in circulation and climate response. We're talking about something that's a lot less than that each year, maybe less than a quarter of that per year. Right now in the lower atmosphere, humans put about 50 million tons of sulfur into the atmosphere as pollution for fossil fuels, and that kills several million people a year globally or air pollution to [inaudible 00:18:44] do.

David Keith:                  For bad reasons, we know a huge amount about the science of sulfuric acid, aerosols in the atmosphere and we absolutely know that they're harmful, but we know that the good side is we know a lot about it and exactly how harmful they are. We and some others have now done some research to understand what the health impacts would be of putting a million and a half tons a year in the stratosphere.

David Keith:                  And of course, everything you put in the stratosphere has to come down, so it will eventually rain out. But it turns out that it mostly rains out, so most of that does not make it as aerosol into the lower atmosphere where we live to be breathed in and it's also evenly distributed whereas the current sulfur emissions mostly are, of course in industrial places where people live. This is a correlation between the sulfur emissions and humanity.

David Keith:                  Here's a maybe a useful thing to say. The ratio of the radiative forcing, the cooling benefit per ton of say sulfur in to the health impacts, you get about a thousand times more cooling per unit health impacts if you put material in the stratosphere than if you put it with a current distribution resources. Maybe what I didn't say is, well, solar geoengineering is the idea of people deliberately modifying the climate.

David Keith:                  People are modifying the climate. Most obviously they're putting CO2 in the atmosphere, but we are also modifying the climate by putting aerosols in form of pollution in the atmosphere and those are currently reflecting away some sunlight and cooling the planet by an amount that's actually quite uncertain. That has actually important consequences that might surprise some of you listeners.

David Keith:                  If you stopped all industrial activity tomorrow, most people's assumption is that it would get cooler in 10 years, because you stopped putting the CO2 in the atmosphere. Everybody knows that it lasts a long time, but that's in fact wrong because the industrial activity is doing two things. It's adding to these long-lived greenhouse gases like CO2 that basically produce this long cumulative warming, but there's this short term effect of cooling and that cooling effect only lasts for about two weeks.

David Keith:                  That is the aerosols last for about two weeks. If you shut off all natural activity, you'd be removing that mask, that veil that is blocking some of the warming. You'd be unmasking of the underlying warming from our CO2, and the world actually warms up if you stop everything. That was a long digression to say we are already modifying the climate through those methods.

David Keith:                  That's not a justification to say it's morally okay to do it deliberately because deliberate is different from as a side effect, but we are already doing that. And to give you this quantitative number that if you wanted to use sulfur aerosols to cool the climate in the stratosphere, you have about a thousand times less direct health impacts per unit cooling than from the current distribution of sulfur aerosols.

David Keith:                  That's a long story about what it might mean to do two watts per square meter of radiative forcing by sulfur aerosols. And the basic summary, I would say is that the cost is tiny, which doesn't say it's a good idea. It just means it's a fact. Some ways it's a bug because it allows unilateral action, so more a bug than a feature, perhaps. I think there's very high confidence that it could be done.

David Keith:                  Not that it's a good idea, but that it technically is doable with existing technologies. And I think there's not as high confidence but pretty high confidence, at least among the community of those of us who've looked at it, but maybe there's groupthink that you could get this pretty even radiative forcing by adjusting things. Then let's turn to the question on what that radiative forcing does to reduce climate changes. That makes sense?

Jason Jacobs:                Yes.

David Keith:                  This depends on climate models and it depends… Everything I'm about to say has uncertainties that are essentially very similar to the uncertainties in predicting the climate change from CO2, which are still deep. From a climate models perspective, the uncertainty in predicting response to radiative forcing from a pretty spatially uniform solar geoengineering, it's actually similar to the uncertainty in predicting response to CO2.

David Keith:                  Every single model that I'm aware of that has tried, and it's 12 or more climate models that has tried a scenario like I'm saying where you use solar geoengineering enough to divide the radiative forcing in half. And to be clear, I think that relevant policy thing is not actually dividing in half, it's stopping it rising, so the point is we've got rising radiative forcing for more and more CO2 in the atmosphere, and at least the way I think it would make sense to use solar geoengineering is to gradually, gradually ramp it up.

David Keith:                  Starting very slowly and ramp it up to say divide that rate of change in half as we gradually stop emissions, and then gradually bring things down by carbon removal. When I say divide in half, I really mean divide the change in half. I think it's unlikely you actually want to cool the world. I think you probably want to stop it warming, or cut that rate of warming in half. Thinking about that, but for now, thinking about just what we know about what happens if you cut the radiative forcing roughly in half using methods.

David Keith:                  I think we know that many of the key climate hazards including water availability, so that's precipitation minus evaporation, extreme storms, especially tropical cyclones, peak temperatures and obviously average temperatures and sea level rise, that for all those variables, those core climate hazards, there's evidence that doing this would tend to drive them closer to pre-industrial.

David Keith:                  If a more risky world is further from preindustrial, so for example, climate change, a classic thing we know is it tends to make the dry regions drier and the wet regions wetter. And it turns out that solar geoengineering looks like it neatly reverses that, so it tends to make the regions that were getting wetter get a little drier, which reduces the risk, is getting them back towards pre-industrial and vice versa. And to the extent that we've looked at this carefully, it looks like that's true without any big regions getting worse off.

David Keith:                  That may actually not be true in the real world, but from some state-of-the-art models, the best climate models we have, if you look at large regions, none of those large regions are made worse off by doing this. That may not be what actually happens, but if there's a single reason in my view to take this seriously, that's it. Because what it suggests is that these methods when used in combination with emissions cuts could actually reduce some of the core climate hazards by roughly a factor of two over the century, which is a giant human and ecological benefit.

Jason Jacobs:                How does one go about testing this in a way that can get you confidence that if it is rolled out globally like this that it will do what you think and then a follow-up to that is, if for some reason it didn't, how easy or possible is it to unwind?

David Keith:                  Those are two good questions. Let me try the second one first because it's the easiest. If you're talking about stratospheric aerosols, they last for about two years, and if you were doing it by wrapping them up slowly, you'd be starting very slowly. And so unwinding at the beginning is really easy because there isn't very much there. Obviously, if you do it over the whole century and there's some point in the middle where you have maybe two watts per square meter radiative forcing, unwinding that suddenly has more consequences we can talk about.

David Keith:                  That's often called the termination shock, but let me come back to research. I think the answer is that, as I said before, there are two different scientific questions with linked uncertainties. One is a question of, how we actually technically go about making these radiative forcing, and there are questions involving aerosol dynamics and stratospheric circulation or the dynamics of these clouds, cirrus clouds, whether they're homogeneously or heterogeneously nucleated.

David Keith:                  There's a whole bunch of technical questions that are about how you make the forcing and the specific risks that come from any specific way you make the forcing. And those questions all depend on it all but significantly dependent on things that are testable at small scale, because they're basically about, say the way individual clouds react to [inaudible 00:26:24], or the way aerosols in a pluminous stratosphere react.

David Keith:                  And that you could test by a whole series of experiments, some involving actually releasing materials, some just involving normal climate science without releasing materials. There's a whole network of tests you could do building on a century of climate and aerosol science that would improve our understanding of that. The second part of it is the uncertainty about what the large scale climate response is to the aerosol radiative forcing, and there's a sense in which that can never be tested.

David Keith:                  Because we only have one century we're going to live through, and there's going to be one actual radiative forcing trajectory for that century, that is a combination of long-lived greenhouse gases and whatever we do depending on when we bring emissions to zero, what we do to reduce, to do carbon removal afterwards and then whatever aerosol burden there is both the actual aerosols that we have from pollution plus any additional solar geoengineering, there's only one version of that that actually will happen.

David Keith:                  And the uncertainties in predicting how the climate might be different if we have different amounts of CO2 or different amounts of polluting aerosols or different amounts of solar geoengineering aerosols. Those uncertainties are pretty linked and they are correlated, if you like. And so I think there's nothing… there's no experiment you can do that will tell you anything new about that

Jason Jacobs:                And how much do you worry if we were to deploy it at scale that it would have some unintended consequences that haven't properly been factored in, predicted or accounted for?

David Keith:                  It's 100% certain that we'll have some unintended consequences that aren't intended or predicted for. That's true. Any big thing like this, anything the humans have ever done that's an intervention at scale has unintended consequences. If you're looking for a consequence-free world, this is not it. But I think that's a ridiculous question.

David Keith:                  Well, it's intuitively a right question because we should worry about consequences, but if the implicit idea is it should be… the right number of consequences should be zero, the answer is there's no consequence-free choices here for anything, including cutting CO2 emissions. Because we do have to cut emissions, but cutting emissions involves transitions to low carbon energy, which themselves have social and environmental impacts.

David Keith:                  That's not an argument that we shouldn't cut. We must cut emissions to zero. But the ways we do it have big social environmental tradeoffs and risks. Carbon removal, same. There's no risk-free outcome. This is a risk to risk decision. At least the way I think about it is that, let's say we have this magic day where we have global celebrations where net emissions come to zero.

David Keith:                  And I think I expect to see that day in my lifetime. I certainly don't expect to see it in 20 years, but I think seeing it soon after mid-century seems pretty realistic to me. Let's say we get to this point where that emissions are zero. That's more or less the point where carbon concentrations, the amount of carbon, in the atmosphere peaks and more or less is the point where climate risk peaks, not exactly.

David Keith:                  At that point, you can ask yourself, “Which world is more dangerous?” Let's say that at that point, you have a total of whatever the number is. Maybe it's 450 ppm, you name it, nobody knows, but some number like that are a little bit higher, and radiative forcing terms, let's say it's five watts per square meter, at the peak. The question is, which world is more dangerous?

David Keith:                  A world with that five watts per square meter given what we actually did to cut emissions and start carbon removal, or a world with five watts per square meter from the longer greenhouse gases and minus one or minus two from solar geoengineering. Both worlds have risks. Both worlds have risks we can't predict that well, because remember we do not know. Climate models are still quite uncertain about predicting the impacts of that high CO2 world, and they'll be uncertain about predicting the impacts of the high CO2 world with solar geoengineering.

David Keith:                  I think there are actually strong reasons to believe that overall the risks and the uncertainty in the risks mostly scale with the net grade of forcing, so that is a world with, let's say to be specific, five watts per square meter [inaudible 00:30:24] gases CO2, both as a more risky world and in some ways, a world where the uncertainty about the risks is bigger than a world with, say four watts per square meter. That is the five watts minus one. But both worlds were uncertain and for sure, there will be unexpected consequences.

Jason Jacobs:                Now, where are you in terms of your knowledge and conviction level as far as their solar geoengineering research and then their solar geo engineering deployment? Where are you in terms of what you believe is the right path and I have a follow up but I'm going to stop there.

David Keith:                  That's another really, really good question. I would be dead set against deployment now or I'd say anytime, and let's say the next decade. I think the actual technical evidence that these methods if used in certain special ways, and that's especially if you have tri spatially uniform and moderate that is not trying to offset all the doubled CO2 radiative forcing. I think there's actually very strong evidence that that could substantially reduce many of the key climate risks we care about.

David Keith:                  But I don't think that evidence is in any way strong enough to warrant deployment now and moreover, I think there's a real danger of groupthink. There's a very relatively small number of people who've looked at this, thousands, but still the core groups are not very many. And it might be that there's some way in which we're just wrong. And it's also true that even if we're correct, there's no reason that the larger world should trust us.

David Keith:                  My view is that from here to a place where you could make credible decisions about deployment, you need a much broader research effort. Broader in terms of having many more climate scientists involved, many more climate scientists involved around the world because part of this is representational. People from different parts of the world have legitimately different points of view and you need to hear those.

David Keith:                  They need to be involved in science and shaping what science has done, and it needs to be technically deeper. There's lots of communities like parts of the stratosphere and science community that are crucial for understanding geoengineering stratosphere that have hardly been engaged. My view is you'd want to have this embedded in the mainstream of climate and atmospheric science with total spending of order, several, let's say, 5% of total [inaudible 00:32:37] climate atmospheric science designed to understand this.

David Keith:                  And then also I think it's structurally important this not all be in one program. Not that it's going to be, but I think one program inevitably tries to produce one answer and there's all means of groupthink. My view is it's good to have some different groups around the world whose job it is to try and figure out in a sense what is a realistic pathway to safe deployment, and articulate exactly what will be done technically, and why and many more groups trying to think of what will go wrong and what the risks of that are.

David Keith:                  And only after there's a larger research effort like that, would it make sense to actually be in position to make deployment decisions? My view is that's at least a decade out, but it is imperative that we get that research going, because whatever my view is, I'm not the one making the decision and neither are you and neither are your listeners. And the reality is within the next couple decades, it's quite plausible that some country is going to feel enough climate risk that it's going to want to push this onto the international stage.

David Keith:                  Maybe by actually deploying or maybe by just taking steps that are close to deployment to drive it onto the international agenda. And then we're going to make decisions in a crisis, and I think it's far better if when that day comes, there's much more knowledge, both technical knowledge and also discussions about how-

Jason Jacobs:                How hard is it to deploy… Could some street gang get an airplane and go rogue and do this in a small country without a lot of regulation and also how noticeable would it be? Would we absolutely know if somebody was doing it or is it possible they could fly under the radar for some period of time?

David Keith:                  Those are both good questions. Street gangs, I'm not too worried about, but so there are different methods as I said, and some methods that may not be thought about yet maybe even easier. But if you talk about this stratospheric aerosols with either… We've talked about sulfur but there's ideas of calcium carbonator and other things, but talking about stratospheric aerosols where you need an aircraft that can reach this upper stratosphere, then I think the answer is… Let's talk about the aircraft.

David Keith:                  The correct aircraft, aircraft that are optimal, you'd need to develop fresh. They're a huge number of aircraft developers that could do that. We've now begun to really talk to some of them and I think we have a sense that it's not hard. In new standing aerospace or Embraer, or… there's a long…there's probably a list of 30 companies that could happily do this. If a government comes to them and says, “We want this, deliver us these aircraft.” work out a contract or we could haggle about the contract, but the fundamental ability to do it wouldn't be hard.

David Keith:                  For that matter, that's only to get aircraft to get to this optimal height where everything is the most optimal, but you don't need to get that high if you just want to get materials in the stratosphere to begin and demo mode to do this. You could do it with modified existing aircraft, for sure, because you could do it meaningfully at like 45,000 feet if you do it at the mid latitude more. And then there's a bunch of range in between, so you could start relatively easily.

David Keith:                  So the capital costs, so it depends on what start means. If you are starting a serious plan where the idea to ramp up global radio forcing in a way that I've sort of suppose would be to cut the rate of radio for the net rate you're forcing in half, if you wanted to do that, the capital cost of just building up the aircraft fleet, all the tooling and development costs, people have estimated it's a few billion dollars, and then the amortized cost would be billion a year after that. But on the other hand, you could probably do something, you were a country and you wanted to make a statement. You said that for whatever reason you believed it was really in your country's interest to begin this.

David Keith:                  Arguably, you could begin it quite a lot cheaper. Order more like a hundred million to just develop some... a smaller fleet of modified aircraft, maybe just a few aircraft that will at least allow you to make a claim about starting deployment even if you weren't doing anything that was that meaningful. So the answer is that's when the capability of not every government in the world, but a lot of them. I don't think street gangs are meaningfully an issue. I think this happens through governments and I think private organizations, be they international environmental groups.

David Keith:                  Because after all, we've got and it's a world where environmental offense is like it's on the satellite. And I think environmental groups... my view is I hope they're the ones that actually do substantially own this and help to set the international agenda for what happens. And I think international NGOs could be very profoundly important in shaping what happens. But I still think in the end, this probably actually gets done by a set of nations. And the question is what configuration, what set of nations do it?

David Keith:                  And we go a little further to politics, people I think often fixate on two polls and neither of them is likely. So one poll is the poll that's a full UN resolution through the safe framework convention on climate change, unanimous resolution. I think it's actually very important that we keep developing these international mechanisms. And I want to come back to the fact that some of this is happening now through a guy called Janich Pasture. But I think the chance of those mechanisms actually getting to some kind of near global consensus for some kind of step by step deployment is very low.

David Keith:                  The other poll is the idea that one nation just does it. I think that probably is actually also very low because this is an interconnected world and there are lots of checks and balances. And if you imagine yourself sitting in the corridors of power of that nation and let's say you've got like legitimate reasons that you want to do it, your scientists convinced you it really will reduce climate risks a lot and you've just had some huge flooding or heat wave, still you assume that you're self-interested, that is you just thinking about your nation but you're smart. Why would you just do it unilaterally? Because that's very likely that it'll produce blow back.

David Keith:                  What you're going to do is look for some like-minded nations and negotiate, and come up with a small group of nations to do it together. So I think that's actually a much more likely case.

Jason Jacobs:                I heard a talk you gave, maybe it was a year ago, where you said there was about $2 million in total funding going towards solar geoengineering research. And then before we started recording today, I think you told me that number is 10 million. So I guess where is that funding primarily coming from today? Where does it need to be coming from looking forward? And also you mentioned there's a lot more research we need to do. How do you quantify?

David Keith:                  So we have, and it's publicly available, you can provide a link to your readers. We've done a job, I mean not necessarily correctly, but we tried to ask the organizations that we knew about what their budgets were and provide data. So we have some data that they chose the answer and divide it up by time and region. We think that there's roughly 10 million a year of everything, and that's by the way, lots of that's not research. So a big chunk of that, for example, is this guy Janich Pastures, CTG, Carnegie governance initiative, climate governance initiative, which is really about governance of these technologies.

David Keith:                  But the total we think is about 10 million, and there are research efforts in China, India, a significant one in Australia, Germany, and here. I mean there are a few more of it, that's just some I rattled off. And actually now through a program called Decimals that Andy Parker's helped to drive out of environmental offense. There's funding for a bunch of developing country people. So Brazil, South Africa, Ghana, several others. So there's people in some of the most effective countries now doing research.

David Keith:                  So that's about the scale of it now. And that funding, it's pretty heterogeneous, if you look at it globally. I can roughly half government. Our program at Harvard is all, or almost all, if not quite all, philanthropic funding. Yanno [inaudible 00:39:48] is all, or almost all philanthropic, I think, but there are government programs like the Australian and Indian, and Chinese ones are government. So it's a mixture. So that's roughly the current state.

David Keith:                  And I think the answer is if you really wanted to get to a place where credible decisions could be made about deployment, if you wanted to do the kinds of work need to be done, which is not just running existing client models but making specific modifications that we now know about to address specific problems in those models, and making specific observations that we can now I think begin to have an idea what they look like. If you want to do all that and do it over a timescale of a decade, I think you need a funding that, as I said, is more like 5%-ish of overall climate science.

David Keith:                  And so in the U.S., the global change research budget is about $2.7 billion. That's including climate science of all different kinds and related sciences, and the NASA satellite programs, and so on. I think you need to be at some level that's of order of 5%-ish of that. So that's 100 million a year category or maybe a few times that globally.

Jason Jacobs:                I think what I've been hearing from you is that as the PPM, as you said, continues to grow and at some point we'll hit peak PPM and net zero, and then we'll start working our way in the other direction. And that that should hopefully occur in our lifetime, although not necessarily soon. What I'm hearing is, it sounds like this could be an important tool as a stop gap to minimize the symptoms while we're working through that transition. And then ultimately, would you see this phased out or is it something that once we start we would do in perpetuity?

David Keith:                  I think it's only ethical to even contemplate beginning doing this if you have some reasonably clear idea of how you stop. And at least the way I personally, as a voter, I'm not saying there's some objective right answer, I only think about it as a temporary thing. Yeah, to pull that out a little bit, I think stop gap includes just one right answer and I think that gets back like what is the root cause and if the root cause is CO2 emissions or capitalism, or a number of things.

David Keith:                  What I think you can say and what to me is more objective language is that first of all, if we don't stop emissions in the very long run, we truly are done. I mean, I don't think it's that useful to talk about climate being an existential threat in the near term, but if we really did emissions forever, for the thousands of years without stopping you, you are an existential threat territory.

Jason Jacobs:                Which is different than 12 years.

David Keith:                  Which is what you hear in the media, correct. But I think make no mistake, if we do not decarbonize the economy, none of this other stuff will save you. You must decarbonize the economy. You must bring that emissions down towards zero. And if I think about the larger... what are the tools for managing the climate problem, the climate crisis, I'd say the central tool is decarbonizing the economy. And there is no question whatsoever that we have abundant ways, solar power, nuclear power, what have you, way in which we could make deep cuts in emissions and what's missing is the political will to do it.

David Keith:                  So that's the central thing to do, but no problem is complex as climate change is solved by any single action. As you know, even if you eliminate emissions, you don't make the problem go away, you basically just stop it getting worse. Carbon removal can take CO2 out of the atmosphere, so it can reduce that, but carbon removal is inherently stokes. You actually have to deal with all the amount of carbon. It has its own, and in some cases, a pretty significant large scale environmental impacts.

David Keith:                  And I think of carbon removal as mostly something that will allow us to gradually pull down the amount of CO2 in the atmosphere after we're done with the decarbonization effort. Of course there's some handoff in the middle between the two. So if you think that with a combination of emissions cuts and carbon removal, there's some curve, some curve of CO2 concentration, which is more or less we're working on climate risk versus time. A curve that now is still going up and will peak, and then will gradually come back down.

David Keith:                  The way I think about solar geoengineering is it is used to flatten that curve. It's used to reduce climate risks at the peak. A consequence of that is you want to start it well before the peak. This is not something you use as an emergency measure. Suddenly, everything's going wrong and you hit the red button. In fact, I don't think it's very useful for that. I think it's something that you want to do well before the peak, building it up slowly so you could watch and learn as you go, and look for the unexpected, which will certainly occur, and adjust what you're doing because no plan is ever correct from the beginning.

David Keith:                  Do it as it's sort of a wedge that builds up to the peak and that the day of peak CO2 concentrations is also roughly should be the day of peak solar geoengineering and then it gradually ramps down. And the net effect then is it's a combination of emissions cuts, solar geoengineering carbon removal and of course, local adaptation, are the things that collectively manage climate risk.

Jason Jacobs:                So I know a lot of the timelines and depend on how quickly we hit net zero emissions. But if you had to ballpark, I guess, about how many years do you see geoengineering on the way up, and then I guess it would it be about that same amount of time on the way down.

David Keith:                  The answer is I'll be dead and you'll be that, and doesn't really matter much what we think. I don't think anyone's going to be back listening to this podcast. [crosstalk 00:45:00] That's the point, yeah. I think it's important to have some humility. But fundamentally, everybody likes to make these plans for a hundred or a thousand years. And I do think it's important to talk about it, but the thing that really matters is that people like you and me, and listeners, and many other humans around the world will shape what we do in the next decade or something, and then we'll learn and we'll rethink. And start what we did, we'll be wrong.

David Keith:                  I'm happy to answer that question, but I think the real issue here is do we have a serious research program? And just to make the strongest case I can make for that, the point is a variety of people including, I'm sure LSU listeners, will have a big range of views about whether solar geoengineering can ever be deployed in a politically stable way and about how risky it will end up being technically. And I've got my views too.

David Keith:                  The truth is the group of us probably listening, your listeners and me are not mostly the ones who are going to make this decision. This decision really gets made a generation later about deployment. And my view is that the decision we make now is basically do we have a serious research program or not? And if we decide not to have a research program, which is the current decision, we have tiny little bit, but there's no serious effort, then we're just giving our kids less information to make the decision.

David Keith:                  We can't take away their ability to do it because the underlying ability to actually do this is already here. You don't need any new research on solar geoengineering to deploy it, and that's the frightening thing. You could just go do it now. I think that I view research as providing information that gives people more chance to make less stupid decisions. That doesn't mean I think people will make some smart, optimal decision. People never do.

David Keith:                  That doesn't mean that I think everything will go in some way that it looks like in these beautiful models with smooth curves, but I think people do make better decisions in general if they have more information. So we may well find out that some of the methods we thought were good were a lot riskier than we thought and they'll get abandoned. That's already happened in lots of parts of geoengineering, and we may find out that the politics of doing this is easier than we thought or harder.

David Keith:                  But I think we'll make better decisions if we take it out of the closet. I think people make very bad decisions with their taboos we can't talk about, because the fact that's taboo doesn't mean it won't happen. So that's my case for having it out of the closet, having a serious open access international search effort, and that's what I'm primarily spending my time fighting for. That's a long way to an answer, the question that got this started was will the calm down on the other side of the peak be slower?

David Keith:                  Well, that depends on how expensive carbon removal is in 2075. And you know the honest truth? I can give you an opinion, but I don't think my opinion is worth anything because I've looked at how good… I mean, I've published papers on this at how good technology forecasters were for energy environmental technologies who were forecasting stuff in 1970 about the year 2000, and the answer is they were pretty lousy. There's just not much skill there.

David Keith:                  So I can tell you that I think that a calm down will be slower because I think carbon removal will be possible but relatively hard, and we won't drive it down really fast. But I don't think it really matters what I say and I don't have really any confidence in my judgment.

Jason Jacobs:                What do the big fossil fuel companies think about solar geoengineering?

David Keith:                  That's a good question, which in practice means what do a few senior people like the environmental VPs or whatever at those companies think. And I think the answer is most of them have at least had some conversations about it, my guess is they would love it if it was happening more because they could use it as a, at least rhetorical tool, to reduce the pressure of climate regulation. So to be clear, we need to do much more to regulate to dry fossil emissions down, and that means to regulate those companies out of existence.

David Keith:                  So of course, their viewpoint is that if they could use this as a way to say, “Hey, we've got this, get out of jail free,” they'd want to do that. I also think they're smart enough to mostly know that if they publicly are seen to be driving it or supporting it, that takes away the value they get out of jail free card. So my guess is the guess is that they're probably indirectly happy that some of this research is happening, but they're really not involved.

Jason Jacobs:                I think that's one concern that comes to mind and it's not a scientific concern. It's a human psychology concern or a self-interest of capitalism concern where if solar and geoengineering is meant to manage that peak emissions risk, right, that the timeline to peak emissions gets extended because people know that this is here and see it as a license to keep right on emitting.

David Keith:                  Of course. So that's the central concern that is often called the moral hazard. And I think it is the underlying reason why this has been a taboo and it's the reason that underlies most of the folks who say we shouldn't do this. So there are lots of people elite in the climate science and policy world who may say that there shouldn't work on this because it's very risky. But mostly, if you really talk with them, the underlying reason they think we shouldn't deal with this and they think no matter how well it works, that it will get misused and allow people just to keep emitting in the future.

David Keith:                  And so this is really a fear about addiction, and a fear about political misuse in the future, so a couple things. In some deep way I think it's legitimate, no question. I think I've been one of the people to raise that fear. I think first, I think I was the first one to actually use moral hazard in a formal article about this. And I believe it is a serious fear in my near term thing that I think we should do, is that the community working on this should do their very best to be allied with those who want to cut emissions, should not take money from the fossil fuel industry and should, as much as possible, divide itself clearly from that and be unequivocally clear that solar geoengineering cannot substitute for cutting emissions.

David Keith:                  That the very best thing you can say about it is that a combination of emissions gas and solar geoengineering might allow less climate risk than cutting emissions alone. That's the strongest statement you can make, but there's no question that even with solar geoengineering, long term risk is proportional to cumulative emissions. We have to stop thinking a little more pragmatically about the ethics of that. I think the leap for those who say we really… that this implies we shouldn't research solar geoengineering, I think for me anyway is hard to defend ethically.

David Keith:                  Because remember there are different people making decisions at different times, and so in argument that says we really should not allow this technology out of the closet because we're worried that it'll get misused. Sounds a lot like an argument by ultra-wise elite who thinks that they know the right answer and that lay people can't get access to it, and that's a pretty ugly thought. And also it sounds a little bit to me like people who argued that we shouldn't allow airbags in cars because it would encourage people to drive faster. The worst serious arguments and papers published and so on about that-

Jason Jacobs:                The ticket analogy, yes.

David Keith:                  -or arguments that we shouldn't allow that when the AIDS three-drug cocktail really became effective, there were people argued that inevitably, it would be misused and create a resistance in Africa and so we shouldn't allow those less competent people access to it. And [inaudible 00:52:15] extremely racist bizarre argument. I think there are a myriad ways in which we might wish people will act, but it's coming back for it. The idea that you would withhold a risk reducing technology because you are worried that people will make decisions to take on a little bit more risk is a worry that comes up a lot, but it's hard to defend actually withholding the risk reducing technology, because we are going to really hold that ethic. You got to think about what is the ethical argument and how does that argument roll.

Jason Jacobs:                I have two final questions for you. One is just, you talked about the need for an exponentially larger research budget, and so let's say-

David Keith:                  Exponential, now that's a Silicon Valley term. I actually did not use that word because that's just the Silicon Valley. It all has to be exponential and then there has to be a value proposition, and we only want businesses that are these exponential businesses that basically fuck people by creaming the crop. That is such the Silicon Valley word. That is absolutely not what I said or what I think.

Jason Jacobs:                Okay, so-

David Keith:                  Sorry, I know there's a bunch of Silicon Valley people probably listening to this, but wow.

Jason Jacobs:                Okay, so let's say bigger, 20X bigger, right? 20 X bigger, so all other sexy buzzwords I can put around that, but if that budget was here today, and you can wave your magic wand and have it allocated in a way that would be most impactful to accelerating solar geoengineering research in the ways that it needs to be, the proper ways, where do you put it? How do you allocate that funding?

David Keith:                  It's all buried in proper, but I can say I would allocate it to funding that seems most likely to produce the largest benefits for most people, especially produce benefits that come most to the poorest and the most risk to climate change, and to be least likely to be unequal, least likely to produce harms. In a sense a minimax principle. We should aim to develop methods of doing this that produce the least harm to those who are most impacted.

David Keith:                  And then separately, I think there's a principle that says we should develop technologies that are least amenable to political misuse. The point is geoengineering isn't a thing. This isn't science, this is technology development, and we have choices about how we develop that technology. I said that in very general terms, let me give you some specific examples of things I would and would not develop.

David Keith:                  I would not put zero effort into, but I would put significantly less effort into things that are inherently local and have fast time constraints. Cirrus cloud thinning and marine cloud brightening both have the underlying time cost and response is only hours, that is burn the aerosols and the effect last for hours.

David Keith:                  That has some profound consequences. It means that if you really did either of those at the scale to provide a substantial large scale climate benefit, so a scale of say a watt or two per square meter, it means that you've basically bought yourself significant weather control. Because it means you can manipulate those things in fast frequency and use feedforward in a climate model and do weather control.

David Keith:                  It also makes the termination shock problem much more unstable, because you can turn the thing off in a day. Whereas other methods turn off over years. And it inherently is patchy, so it has this winner and loser piece built into it. I wouldn't put zero effort into those things because I think first of all, there's big climate co-benefits and there's ways in which they certainly could in addition to other methods, be useful.

David Keith:                  And also we don't know, we might be wrong, but I do think that those have more capacity to look more like weapons or look more disruptive. And so I think there's more chance of political misuse and some evidence that they might have bigger environmental side effects. I would put most of my effort into stratospheric aerosols, looking for ones that could have less impact and looking for ways that you could have as much as possible transparency in who gets access to data and in the methods for getting access to data.

David Keith:                  And I would put a little bit of effort into these space-based systems, which I think are almost certainly irrelevant for the initial deployment in the first decade or two, but later in the century, are actually plausible things that humans could do and have some advantages.

Jason Jacobs:                My last question is just there's two different audiences I'd love for you to address with some advice. One audience is people that might be listening and saying, “I'm up the learning curve and I want this research to happen and what can I do with my time or my dollars that can be most impactful for that research?” And then the second audience is people that say, “Wow, I really didn't know too much about this, but it's intriguing, at least warrants me getting up to speed more.” And for those people it'd be great to talk about where those people should dig in to become more educated on the topic.

David Keith:                  For that first group, for people who have dollars and or political energy, I think the biggest thing we need is to broaden this conversation, which isn't about money, but it's about getting a larger suite of people to really engage with this topic. I think the big thing about the junior attorney debate is a lot of people come to it with some preconception and certainty about what it is and when they dig in, they find it's not quite what they thought.

David Keith:                  And I think if we want to make the decisions, we need to have the conversations. Your listeners can affect that. I do think there is room for philanthropic funding and very much room for government funding, so I think we need more serious government funding of this, and in the end a democracy thing is really important that a core of this be funded through government, because that gives some democratic control over what happens.

David Keith:                  I think people can influence that through the normal tools of political influence, some of which involve money to buy [inaudible 00:57:47], or to buy the beginning of social ventures to try to promote it. I think direct funding for philanthropic science funding I think is really important. There's a long history of philanthropic funding, of science, of some things that were thought to be socially questionable but ended up being really useful, birth control.

David Keith:                  And I think there are good arguments for doing it, but it has to be done the way that's open and whether its transparency and real checks balances. And I think there's a very large scope for both, for growing a serious government effort and for growing philanthropic efforts of different kinds. Our effort at Harvard, which you haven't asked about directly, but it's prototypical, has been almost entirely philanthropically funded.

David Keith:                  Our idea was to raise 20 million of funding to be spent over seven years and I think we'll get there where it's 16 and a half or so now, and my hope would there be 10 other programs like that. I don't actually think our program should get much bigger, because I think it's important to have these things be balanced, but I'd like to see similar programs at a bunch of universities around the world and not just in the rich world.

David Keith:                  Because there are people that IIT Delhi who have a great program for example, who could use more funding for it. Then for the second category people, well, for people who want to dig in, one thing I'm happy to do is just give you a whole bunch of links. I don't know if you post them on your podcast, but I can definitely do that. I think Oliver Morton's book, The Planet Remade, a couple of other books.

David Keith:                  I wrote a book which is much less good prose but at least it's short. It's called A Case for Climate Engineering. There's several other books, there are probably a total of five books that have been published. There's nice one recently by Jesse Reynolds on governance, so there's now quite a few different books. There's a book by Holly Buck, big range of them.

David Keith:                  There are lots of good reports. Reports from National Academy of the U.S, the UK Royal Society had an early report. If you want consensus science reports, there have been some very good things. There was a debate. I was part of an IQ2 debates that gives people a sense of a real pro and con, back and forth. What happens if you have a formal debate? There's been a lot of really thoughtful long-form press articles. I'm happy to point to you to some of those and in hot beds and so on, so-

Jason Jacobs:                That'd be great. Yes. Yes, maybe offline. If you want to send me some links, I'll put them in the episode [crosstalk 00:59:53] show notes.

David Keith:                  That's great, sure.

Jason Jacobs:                All right. Anything I didn't ask you that I should have or any parting words for [crosstalk 00:59:57] listeners?

David Keith:                  Yes, good question. Maybe… so yes, what do you think I might be missing?

Jason Jacobs:                Gosh, I think this was pretty comprehensive. We're not going to cover it all in one episode, but I think that just does a good job of getting people up the learning curve, making them think, giving some resources if they want learn more and giving them some places for action if they want to help.

David Keith:                  Let me try to give you an example of why just doing climate models isn't enough, and why some experiments are really crucial to allow us to understand better how these things could work and those experiments could happen at scales that are much too small to have any significant environmental… Almost for certain, if humans are actually going to do stratospheric aerosol solar geoengineering, it's going to be released from aircraft.

David Keith:                  And that's true whether you're putting diamond powder in the stratosphere or calcium carbonate or sulfuric acid or SO2 which turns into sulfuric acid. For all of those things, you got to do it from an aircraft and aircraft make these really long thin trails in the stratosphere, and the stratosphere is stratified. Things don't mix much. There's not that much diffusion Things move around like smoke in an old smoke filled room.

David Keith:                  For example, we know that Newman, for example on a ER-2 to mission and NASA, U-2, they intercept the [inaudible 01:01:10] rocket plume 12 days after that rocket plume, and it was still a coherent plume. We know these things stay coherent in narrow filaments in the stratosphere for a long time. Basically, all climate models, including all the published models of sulfur aerosols in the stratosphere use these huge grid boxes in which everything is perfectly mixed.

David Keith:                  We know those will not get the right answer for what happens in that first few weeks as that plume spreads out. I think climate models do a pretty decent job once things are well mixed, but the dynamics between the initial plume injection and that point where it's well mixed in a month, that dynamic has this profound impact through shaping the aerosol size distribution, which in turn is really important for how the whole thing works.

David Keith:                  No amount of conventional client modeling will get that right, because the models just don't see those plumes. That's an example where you need two things. You need new model development that builds a integrated plume model into the models. We're actually trying to do that. That's like a person year or two of working. We'll get it done. Eventually, it'll get into a climate model, a few more person years of work.

David Keith:                  But our plume model needs to get validated. We need actual evidence about how these aerosols actually work and to do that, you need to get an aircraft in the stratosphere. It needs to release a plume of those materials over say 30 or a hundred kilometers so you've got the long length, and they need to fly back and forth through that plume and observe it. That is completely doable with existing technologies.

David Keith:                  You could take the NASA ER-2 or WB-57, and if you had authority and the right size team, you could [inaudible 01:02:38] a year from now. Right now it's completely no near term possibility of doing that, but I would say doing that would release far too little sulfur to have any big impact. We're talking about doing that if it was sulfur with half a ton or something of material, but that would tell you a huge amount about how these things actually worked, and without doing those experiments you cannot trust the large scale models.

David Keith:                  That's a clear example of where specific doable science could greatly improve our knowledge. But the reality of those experiments is they take a lot of time, take a lot of planning, you've got to develop instruments and grad students and teams of people, and that can all happen at once. If you want to have that information 15 years from now, you need to… you should have started 10 years ago, but you need to start now.

David Keith:                  You need to start a bunch of those experiments really pretty soon, because some experiments, you'll get stuff wrong, each experiment opens up new holes, but if we don't start those, we will not have decent models. Because experiments just improve our models. We will not have decent models that allow us to make sensible decisions about how this could work.

Jason Jacobs:                I think that's a great place to end because it's illustrative of not only the fact that we need research, but really getting to a good real world example of why.

David Keith:                  And that research is completely doable by agencies like NASA, by combinations and we're doing a very tiny early version of it here called Scop Ex, we want to do, but that is the thing that needs to get done and it's completely inside the mainstream of normal tools of stratospheric and broadly aerosol and climate science. But we need to turn those tools on, and if we don't, we simply will not learn.

Jason Jacobs:                David, thank you so much for coming on the show.

David Keith:                  Thanks very much. It was a pleasure.

Jason Jacobs:                Hey everyone, Jason here. Thanks again for joining me on My Climate Journey. If you'd like to learn more about the journey, you can visit us at Note, that is .co not .com. Someday, we'll get but right now, .co. You can also find me on Twitter @jjacobs22 where I would encourage you to share your feedback on the episode or suggestions for future guests you'd like to hear. And before I let you go, if you enjoyed the show, please share an episode with a friend or consider leaving a review on iTunes. The lawyers made me say that. Thank you.