C2GTalk: An interview with Ken Caldeira

Should scientists be allowed to do outdoor research on solar radiation modification?

9 March 2022

This interview was recorded on 26 January 2022 and is available with interpretation into 中文, Español and Français.

Over the last two decades solar radiation modification has gone from an intellectual experiment to something people are seriously considering, says pioneering climate scientist Ken Caldeira during a C2GTalk. The world needs to understand what would happen if somebody felt the need to cool the Earth rapidly, and that requires the ability for scientists to do more research. “There is a case to limit knowledge acquisition if it would lead to imminent harm,” says Mr Caldeira, but this is not the case for solar radiation modification experiments.

Ken Caldeira is Senior Staff Scientist (emeritus) with Carnegie Institution for Science, and world famous for his work on the global carbon cycle and climate change. He was a lead author for the Intergovernmental Panel on Climate Change’s fifth assessment report, a co-author of the 2010 US National Academy America’s Climate Choices report, and participated in the UK Royal Society’s geoengineering panel in 2009. He is also Senior Scientist at Breakthrough Energy, which supports innovation to reach zero carbon emissions.

Below are edited highlights from the full C2GTalk interview shown in the video above. Some answers have been edited for brevity and clarity.

You have been studying climate change for a few years now and have played a prominent role in informing efforts to tackle it.  How would you describe the moment we have reached in 2022 both in terms of the science and our understanding of climate change and how humanity is responding to that science to limit its impacts?

That’s a whole tangled-ball- of-yarn-type question there.  I started studying climate science in the 1980s, and I remember saying, “Well, right now the signal of climate change is in the noise of natural variability, but sometime in the 1990s that signal will start rising out of the noise;” and indeed it did with Ben Santer and the IPCC (Intergovernmental Panel on Climate Change) saying there was a discernible human influence on the climate system.

Marty Hoffert and I and others in 1998 wrote a paper in Nature magazine putting out the scale of what would be needed to stabilize atmospheric greenhouse gas concentrations or CO2 (carbon dioxide) concentrations and pointing out that it would mean a massive transition to carbon-emission-free power at scales that are orders of magnitude greater than what was being deployed then, unfortunately.

Another point was I remember doing a congressional briefing on ocean acidification in 2005, and at that briefing I was asked by some members of Congress: “What should the temperature target be or the CO2 stabilization target be?”

I said: “Oh, I don’t think we should think in terms of stabilization targets.  I think we should think in terms of emissions targets.”

They said: “What should the emissions target be?”

I said: “Oh, it should be zero, in the same way that if you ask what’s the goal for our rate of mugging little old ladies you try to reduce it as far as you can.”  Members of Congress laughed at that, and it was seen as being out of the sense of reasonableness.  It is really interesting to me to see here we are 17 years later and the target of zero emissions is pretty broadly accepted.  So, in terms of what people say, we have come a long way.

Where we have come much less far is in terms of what people do.  It is true that solar power has become a lot cheaper, wind has become cheaper, and there is increased production of renewables, but here even in California we are still building natural gas plants.  The rate at which we would need to roll out carbon-emission-free energy technology needs to be — I don’t know the exact number — say ten times bigger at least than what we are doing now.  I think there is increased recognition of what we need to do, but the social system hasn’t really embraced the scale of the effort that is required.

In terms of the science and how it is presented to policymakers, some have questioned the continuing utility of the Intergovernmental Panel on Climate Change, at least in its current form.  What are your thoughts on that?  What are the key ways in which science is needed to inform policy today, and how could the Intergovernmental Panel on Climate Change (IPCC) help in that?

First of all, I think the IPCC, especially Working Group I, has done a tremendous service.  At least around the time of the first report — I forget when it came out, 1991 or 1992, something like this — there really was a consensus among the physical scientists about the basic physics and biogeochemistry of climate change, and there was a bunch of noise, some of it promoted by the usual vested interests, trying to pretend that there wasn’t a scientific consensus.  I think that the IPCC, especially the physical science component, did a tremendous service in demonstrating that there really was a scientific consensus despite the people who were trying to suggest otherwise.

Then, after a while, the IPCC added Working Group II on impacts and adaptation and then Working Group III on climate change mitigation.  Those provided useful information, but really there is less consensus.  Everybody agrees on the laws of physics pretty much, but not everybody agrees on what technologies may or may not play out in the future or what technologies may or may not be accepted by societies.

Anyway, I think the utility of the physics side has been huge, and the utility of the other reports has also been large as an information source.  Even today I needed something on carbon capture and storage and I went to an IPCC report to find it, so as a reference source it is valuable.  For me, I guess the question is: Is the amount of time that it is taking up of research scientists commensurate with the social return on what comes out of the reports?

I guess there is another factor too, and that is when people were saying, “Oh, we have to stop smoking indoors,” it wasn’t always saying, “Oh, it’s the latest science that says we have to stop indoor smoking.”  Basically people said, “We have known for decades that this causes cancer and we’re subjecting children to carcinogens.”  I also think this is true of the climate system, that we have known now for decades that we basically have to eliminate our emissions if we want to stop the planet from warming and that we should want to stop the planet from warming.  This kind of saying, “Oh, there is a new round of reports and it’s the new round of reports that says we have to do something” — no, it’s the stuff we have known for decades that means we have to do something.

I would actually like to see the IPCC move to something more efficient.  Maybe there is an encyclopedia, and maybe each cycle they update the chapters, but they don’t start ab initio.  Maybe every once in a while you need a new chapter or a chapter is so out of date that you just remove it.

When I was a kid in the pre-Wikipedia days, we had the Encyclopædia Britannica in the house, and you used to get these yearbooks of updates to the Encyclopædia.  I almost feel like this kind of model of updating an encyclopedia might be more efficient.

But I think the IPCC has done a tremendous service.  It acts as an excellent reference source, and it’s really a question as to whether those benefits could be achieved with less investment.

I wanted to pick up the point you made earlier about talking to Congress about zero.  We have seen a proliferation over the last couple of years of countries and organizations talking about “net-zero” goals.  Obviously the world is quite a long way of working out what that means in practice, and we have seen rising concerns that the “net” in net-zero means loopholes for companies and countries to keep emitting.  Can you share your thoughts on the relative value of net-zero as an approach versus real zero, and to what extent do people understand the difference between the two?

I am big fan of carbon dioxide removal as a research project.  I am a little skeptical of incorporating it too deeply into decarbonization plans.  Back to mugging little old ladies — that’s a politically incorrect thing to say — I think we basically need to head for as close as we can get to zero emissions, not just net emissions but gross emissions, from human activities.  That should be the goal.

There are certain activities where that is going to be really expensive to do or just problematic.  Let’s say long-distance aviation, flying from New York to Sydney; right now liquid hydrocarbon fuels are pretty much the only way to do that.  You could in principle get some carbon from a biomass facility and then take electrolytic hydrogen from non-zero-emitting electricity sources and make synthetic liquid hydrocarbons; but if it’s cheaper to use fossil hydrocarbons and then remove the CO2 from the atmosphere later, well, then, by all means, do whatever is cheapest, assuming the other externalities are similar.  So I think there might be a role for carbon dioxide removal, but the idea that we can just go on emitting vast amounts of carbon and the assumption that we can clean it up through carbon dioxide removal —

Also there are two levels of — it’s one thing to say I’m going to fly a plane today burning fossil hydrocarbons and simultaneously I’m going to be running a direct air capture plan — that I can buy.  The other one where, “Oh, we’re going to fly a plane today and somebody a few decades from now or someone later is going to remove our CO2” — that one seems disingenuous at best.

You touch on some pretty crucial issues there.  As people get to grips with this — what do we focus on and so forth — there is this idea of a mitigation hierarchy that has emerged, that we should prioritize avoiding and minimizing emissions before removal.  At the same time, assuming that it will be tough to abate residual emissions and all approaches will likely be needed in some form to achieve these goals within the time that we have left to achieve them, there is clearly a lot of work that needs to be done now on carbon dioxide removal.

What are your thoughts on how you go about that in practice without undermining the urgency of emission cuts, without creating mitigation deterrence of the emission cuts, the “moral hazard question” that some people refer to it as?

I am a physical scientist who observes the policy process, but I don’t pretend to great policy expertise.  As an informed physical scientist the idea of a carbon tax always seemed appealing to me.  I have listened to economists saying how it’s economically efficient and all this kind of thing.

Politically it seems hard to get a carbon tax whereas just regulating what kinds of technologies people are allowed to build seems more socially acceptable.  If you tell people “You can’t build a natural gas plant” or “You can’t build a coal plant” but you let them build a wind plant, a solar plant, or maybe a nuclear plant — that people want the electricity, so there is local benefit to building this carbon-emission-free system — basically all you have to do is ban what is bad, and then, because people want the energy services, they will build the carbon-emission-free energy systems.

In contrast carbon dioxide removal has no direct local benefit.  It has lots of direct local costs, and the benefit is to the rest of the world or to the entire world and for decades and centuries into the future; so you need a system of incentives and regulation and so on to be put in place to make sure that people do it.  If you just go to the example of sulfur scrubbers on coal plants — I heard this hearsay, but I heard that in China a bunch of plants had built sulfur scrubbers; but it was cheaper to pay off the inspectors than it was to run the sulfur scrubbers, so even though the coal plants had sulfur scrubbers they weren’t using them.

For an average gigawatt-scale facility, the costs of carbon capture are going to be hundreds of millions of dollars a year — I believe; I might have those numbers off — unless you have really strong governance keeping that system operating in an uncorrupted way.

I think the game theory of it, avoiding emissions through effectively banning technologies, which I know the economists don’t like so much because it’s not economically efficient, but it seems like it might be socially efficient in the sense that we might actually be able to get it done.

Anyway, I am concerned about will society really develop the appropriate regulatory and policing structures to govern carbon dioxide removal.  One of the things we see right now is some removal — say through physical and chemical means with geologic storage — is expensive.  People have given different numbers — $400/ton, $600/ton CO2.  Meanwhile there are people selling forest offsets for $10 or $15 or something like this.  To have something that is permanent storage and really is a reversal of taking fossil fuels out of the ground and throwing them into the atmosphere, that really are taking the carbon out of the atmosphere and throwing it back into the ground, versus some kind of storage in forests that may or may not be there decades or a century from now, or there might be a forest fire or who knows what, and how the relative values of those different kinds of carbon storage get reflected in markets and all this is super-complicated.

I think carbon dioxide removal can play an important role in our models for that last little bit.  For example, we see in the models as you ramp down the CO2 constraints, you start with natural gas, then it might use natural gas with carbon capture, usage, and storage, but for that last little bit, if you have a peaker plant that is running once or twice a year, it’s cheaper to run that peaker plant once or twice a year with no carbon capture; and then you have another plant that has a carbon capture facility running 24/7, so it has a high utilization, where if you are only using all this carbon capture stuff once or twice a year, that is a lot of capital costs that you are not using.  It’s a really tough regulatory problem.  It could be a big contribution, but I am glad I am not in the meeting rooms to design that.

You keep on stressing that you are a physical scientist.  You alluded to potential nature-based and more technological geochemical approaches to carbon removal, and actually some people might think the nature-based approaches have a lot of co-benefits; but also, there are challenges around permanence, land use, and all the rest of it. Do you think there is still some sort of intrinsic preference to using nature rather than technology, if there is such a contradiction, and does that make sense through the lens that you look at these things?

Let me say a preface before getting to the question. think humans are fairly malleable and adaptable, and if we could organize ourselves we could protect the people who are most vulnerable; but ecosystems and things like ice sheets and things like this have a much less adaptive capacity than we do, I believe.  

So a lot of the reason I want to avoid climate change is to protect the existing ecosystems.  People, including myself, have a positive association with natural systems.  They just seem less dangerous to us or less scary.  As you mentioned, reforestation especially has huge co-benefits; if it’s done the way I would be most happy, you would both be restoring a natural ecosystem and absorbing carbon, and I would actually look at the protection of the ecosystem as primary and the co-benefit as the carbon storage.

In a way things, I think, have gotten turned around, in that it’s hard to sell forest protection for purposes of just environmental protection, ecosystem protection, or biodiversity, and so people are using the carbon storage dimension as a means for protecting ecosystems.  Again, were I king of the world, we would be protecting forests because forests are worth protecting in and of themselves, and then we would count the carbon storage as a co-benefit.

On the other hand, while there is an emotional attraction to the nature-based solutions, another paradigm is that we try to do everything in as concentrated a way as we can and as dense a way as we can and ideally, if we can make human activity be as compact as possible, that we leave more of the world available for nature.  Again, I guess with the nature-based solutions my general outlook is to look at the carbon storage as a co-benefit; so if it makes sense to help protect the soil and farmlands and that results in more carbon being in the soil, great. Here’s an example.  We did a study showing that boreal forests, forests that are on snowy ground in the Arctic, have a net warming influence, that even though they store carbon, a snowy field reflects a lot of sunlight to space; whereas the dark forest absorbs the sunlight and absorbing the sunlight of the forest is a stronger effect than the carbon storage.  So we published this paper, and some people asked, “Oh, well, should we cut down the boreal forests?”

I said, “Well, no, I’m trying to prevent climate change to save the natural ecosystem.”  To try to destroy natural ecosystems to prevent climate change is completely wrong-headed from my perspective.  I would say the case of the boreal forests highlights that I think it is the protection of the ecosystem that is primary and carbon storage is a means to that end.

If you are restoring a natural ecosystem, it is one thing, but a lot of these carbon storage efforts are basically planting a tree farm, you are planting a monoculture of some loblolly pine or some fast-growing species.  You might even use Roundup to kill off the things that you don’t like, and maybe we’ll use some insecticides to keep the leaves from being eaten.

Anyway, I am all for carbon storage in natural systems.  A similar thing is protection of mangroves, peat, and so on.  These things are not big carbon sinks.  They are not really absorbing lots of carbon, but they contain a lot of carbon, and you should avoid disturbing that.

You mentioned the reflectivity of the boreal forests or the albedo issue — I am using this as a segue to move onto the next topic — but there is another potential approach being discussed to manage the risks of overshooting the Paris temperature goals, known collectively as solar radiation modification or solar geoengineering, essentially the idea that humanity might intentionally reflect back some sunlight to reduce temperatures. You were involved in the Royal Society report back in 2009 that identified and explored many of the key issues around this.  Has the understanding of these approaches and how to govern them advanced significantly since then; and, if so, how?

Yes, there have been a lot of advances. Let me just say a little bit of history.  I used to work at the Lawrence Livermore National Laboratory, and Edward Teller and Lowell Wood were proponents of researching solar geoengineering.  Even though both Lowell Wood and I were both working at Lawrence Livermore Lab, I had not met him there.  We were at a meeting in Aspen, Colorado, and David Keith was there, and Lowell was making excessive claims on behalf of solar geoengineering, but nobody had done any real climate model simulations.  Both David Keith and I said: “Oh, that’ll never work because CO2 works around the whole planet all the time and sunlight is just in the daytime and it is mostly at the equator and mostly in the summer.”

I went back to my office and, with my colleague Govindasamy Bala, we did the first climate model simulations of solar geoengineering using a three-dimensional climate model, and it worked.  Originally our idea was to show that it wouldn’t work, and it worked in the model much better than we ever anticipated.  Part of what happened was that the climate system feedbacks are so powerful in governing the climate system’s response to changes in forcing.  A doubling of atmospheric CO2 traps around 4 watts/m2 of outgoing energy.  If you have sea ice or ocean, that can change 100 watts/m2 of reflectivity.  Also, ice on top of the ocean insulates the ocean from the overlying atmosphere and prevents the ocean heat from warming the atmosphere.  What we found was that if you more or less cooled the Earth down enough so that the sea ice returns to where it was status quo ante, that more or less you would get some approximation of the previous climate.

Since that time, first of all, there have been lots of studies that have more or less confirmed that basic result.  There have been a lot more advances in understanding the differential effects on the hydrological cycle versus temperature, and that is the climate physics part with which I am more familiar.  There have also been a lot of advances in understanding how aerosol particles get transported and interact and related chemistry in the stratosphere, and that is the part on which I am not particularly expert.  But I don’t think that anything has changed any fundamental pictures over the last two decades.

For one thing, we have had big volcanoes like Mt. Pinatubo or Mt. Agung.  Mt. Pinatubo was more or less the size of what a full-time solar geoengineering deployment would be, and so there is some relevant experience to suggest that the models are not too far off.

What may have changed, if not so much the understanding, is the context in which these ideas are being presented, the sense of urgency.  What do you think the likelihood is now?  What is your feeling as that sense of urgency rises that some organization or group, even with a lack of social agreement, will feel climate change acutely enough to attempt to actually do this, to try some form of solar radiation modification (SRM)?  What could precipitate that kind of action?

As you point out, when we did that first study — which was published in 2000 but we started I think in 1998 — for us it was just a thought experiment, an idealized test of a model that was sort of like a science fiction story that we were doing for fun, and we never really thought that large numbers of people would take it seriously as something we might actually want to do.

I think you are right that over the last two decades solar geoengineering has gone from sort of a novelty, a fun thing to think about, to something where people are thinking seriously: Well, we might want to do this, and what would we need to do?  When I say “we,” I mean somebody might want to do this, and what would we want to know about in that event?

Again, I don’t claim clairvoyance, but the scenario that seems most plausible to me for actual use of solar geoengineering would be if temperatures in the tropics really start causing massive crop failures and potentially famines and so on.  There was a paper a year or two ago, an estimate that said basically to have enough solar geoengineering to cool the Earth by 1°C would cost around $18 billion per year.  You can probably multiply or divide that by a factor of five or something, but let’s say in that kind of $18 billion a year ballpark, which is little enough money that individual tropical countries or coalitions of them could muster that. 

I think, given advanced social systems, farming, and so on, there is enough food in the world; but there are already famines or near-famines in various parts of the world today, so social systems are not necessarily responding appropriately to today’s food security threats. 

I should also point out that there have been a number of studies that suggest, at least in the high-emission scenarios, that substantial parts of the tropics could become essentially unlivable outdoors at least some of the time where, if the heat and humidity gets beyond a certain point, then you can no longer cool your body through sweating; and it is projected that it is at least a possibility that substantial portions of the tropics could be in that situation by the end of the century.

So let’s just imagine that this situation happens and there are crop failures and so on accompanying that.  The biggest reason why I am in favor of researching solar geoengineering is that solar geoengineering is the only approach known that can cause the Earth to start cooling in our lifetimes, in the political careers of political leaders.  So if there is a crisis where there is ongoing famine year after year from ongoing crop failure and you are the leader of a country and you think, I could potentially save millions of lives not only in my country but throughout the tropics, and we just have to make this $18 billion a year investment, and we can do it in a coalition of countries that are similarly affected, that seems at least to me a plausible scenario.

I think it could also be used initially not as an actual deployment but as a threat that says, “If you don’t give us aid and address our food security needs, we’re going to have to do this.”  I think the fact that solar geoengineering becomes a credible threat by tropical countries, the idea that it would get used to try to induce increased aid first as opposed to actual deployment — but again, if you are a leader of a country and you have not been able to industrialize your economy so you don’t have your population working indoors and so you have an economy that is based on outdoor work and you were facing widespread famine, I would think a political leader would be remiss not to consider solar geoengineering deployment.

I was at a meeting in Berlin — I won’t mention names — but there was some European who was talking about how solar geoengineering was capitalist, to protect the oil companies, and was more colonialism, colonial capitalism, or whatever, the North oppressing the South, and so on.  There was a guy there from Ghana who said: “Look, if we thought this could help our country, we might be interested in it.”  Those are just two individuals not representing anything other than themselves, but I think there has been a narrative about how solar geoengineering is in the interests of the rich and the powerful.  I think the fact that it is something that is effective and low-cost transfers a lot of power to people who are marginalized.

There was a campaign recently launched January 17 on the likelihood of academics and researchers calling for an agreement on the non-use of solar geoengineering and a number of ideas attached to that, including no public funding and no outdoor experiments, essentially to address what they deem to be an unacceptable risk.

You recently wrote a blog outlining some of your thoughts after being invited to sign up for that.  Can you share some of the arguments that you gave?

Yes. First of all, I think there should be a presumption of unfettered freedom of scientific exploration.  I guess the classic case — and nobody wants to compare themselves to Galileo or anything like this — obviously the findings of Galileo interfered with some of the teachings of the Catholic Church, and he was proscribed from doing experiments — nobody thought the experiments that he was doing, rolling balls down inclines and dropping balls off of buildings, were particularly risky, but they were concerned about what might come out of the knowledge gained.

I think we can contrast that with, let’s say, somebody who is developing a nuclear weapon, where if they learn this one bit of physics that will allow them to make this nuclear device that they could, say, bring to Times Square in New York City and destroy the entire city.  So I think there is a case to be made for preventing knowledge acquisition when that knowledge would enable somebody to do great harm and also where there is some likelihood that somebody so enabled might actually do it and that there is no other reasonably easy way to prevent that from happening.  So, if there is some terrorist group that is operating in secret building a nuclear weapon and the easiest way to prevent them from achieving their goals is to prevent the knowledge acquisition, then I am all in favor of preventing that knowledge acquisition.  So I am not 100 percent dogmatic on this issue.

But if we think about what a realistic solar geoengineering operation looks like, you would need a fleet of airplanes operating continuously from an airbase.  Those planes would need to get fuel, be reloaded, and there would be a variety of mechanisms, ranging from political to economic to military, to prevent that from continuing as an ongoing operation.  And, even if somebody started it today and did it for a couple of months before the operation was taken down, it’s not going to be the end of the world.  It would be like a small volcano or something.  Maybe it’s not good, but it’s not catastrophic.

So I think because there is no risk of rogue deployment that is not relatively easily countered by conventional means, it just doesn’t fall into that category where the knowledge acquisition leads to imminent harm that is not easily countered by other means.  The idea that we’re better off being ignorant about something —

First of all, let’s go to the case that I was talking about before, where parts of the tropics are becoming uninhabitable and famines are becoming more widespread and they are seeming like they are getting worse and worse year after year.  The political pressure to do something about it for political leaders could get extremely intense, as we saw even with the coronavirus vaccines, where people were saying: “Oh, let’s just start using the vaccine before it has fully gone through its testing because we’re in an emergency situation and we have to roll something out.”  You could easily see somebody wanting to deploy something at scale before full understanding has been developed and then, if there really is some showstopper that leads to something really catastrophic, we will be sorry that we didn’t learn about it ahead of time.

There is basically one means known to cause the Earth to start cooling within our lifetimes or within the careers of current politicians, and if we really take climate threats seriously, we might consider that we might want to start the Earth cooling within our lifetimes.  I am not saying that this will happen, but it just seems to me that if you really take climate threats seriously, you would want to understand what would happen if somebody felt the need to cool the Earth rapidly.

The open letter says: “Speculative hopes about the future availability of solar geoengineering technologies threaten commitments to mitigation.”  Do you think there is validity in their evidence of that?

That has not been my experience.  I have seen it go the other way.  Again, I don’t want to name names here, but there are people who I would consider kind of right-wing people who were skeptical about climate science and skeptical about energy system transition and were thinking: Oh, let’s at least investigate solar geoengineering just as a backup, just in case there really is something to this climate change.

I think in a way solar geoengineering acts as a gateway drug to learning more about the climate system, and then they start looking at the model results and say: “Look, if people were just cooking up the models to give the answers they want, why would they say that this works so well?”  Then they start looking into the physics, and they say, “Oh, there really is physics here.”  Then they start to say, “If you’re going to believe how the solar geoengineering affects the climate system, why shouldn’t you believe how the CO2 affects the climate system without the solar geoengineering?”

Then people start realizing, Oh, if really the CO2 continues to accumulate in the atmosphere and we are ramping up the solar geoengineering, that end state is pretty ugly, so even if we have to do solar geoengineering, we are still going to have to transition off of fossil fuels, and that it is really not a substitute for an energy system transition.  It is something that you might want as some palliative care or I don’t know what.  You might want it to reduce adverse effects while you are doing the energy system transition, but you still have to do that energy system transition.  Anyway, I have seen several people move from skepticism on climate energy system transition to entering the problem through the geoengineering lens and ending up being advocates of energy system transition.

One of the critical points this campaign makes is they say the current global governance system is unfit to develop and implement the far-reaching agreements needed to maintain fair, inclusive, and effective political control over solar geoengineering deployment.  How valid a critique is that in pursuing research?

Again, I am no expert but I assume that’s true. I think there is a big difference between solar geoengineering research and solar geoengineering deployment, admitting that there is a fuzzy zone between the two things.  But, at least at the scales being envisioned today, again if there is a full-scale deployment, it’s an air force that is ongoing for many years, and there are many ways to deal with air forces that are engaged in multiyear operations.

Scientific tests tend to be of limited resources.  They are very limited in time.  They are limited in space.  I have done experiments in the marine environment in Australia where we added both alkalinity and CO2 to seawater and we had to go through a permitting process.  It was harder on the CO2 one because we acknowledged that putting some CO2 in the water would harm the reef but that there would be knowledge acquisition because the whole reef would be exposed to higher CO2 waters later in the century.  In the permitting process you say: “We are doing this.  There is going to be some harm to the reef.  We are throwing anchors down, we are walking on the reef, we are putting chemicals on the reef, but we’re getting some knowledge out of this.”

The regulatory authority does balance the knowledge acquisition versus the potential harm, so that if you wanted to do the same thing and there was zero expected scientific return, they would ask, “Well, why are you doing this harm to the reef for zero return?”  I understand that a regulatory environment, even one that is based on physical harms, has to ask, “Well, does this knowledge acquisition justify the damage or harm that you’re doing?”  I think that is really the question, not what is the danger of the knowledge acquisition, but what is the actual physical harm caused by the experiment itself?

One of the famous ones — I know there were all kinds of patent issues with it — was the Stratospheric Particle Injection for Climate Engineering (SPICE) experiment, more or less somebody just wanted to put a hose to a balloon and spray some water in the sky.  You could say, “Oh, yes, there was a risk of the hose falling down and somebody getting hurt” or something like this, but basically nobody thought the experiment posed any substantial direct harm.

It was the idea that, “Oh, this is a solar geoengineering experiment.”

So I guess that there are two arguments for banning that type of experiment: (1) that the knowledge gained is itself harmful and (2) we need to prevent this knowledge acquisition.

You raise a different issue, which is maybe a better argument, that since there is a continuum between one hose in the sky and an air force operating 24/7 over many years, that we better draw the line early.  If we know we don’t want what’s at the end of that road, then we should prevent anybody from taking the first steps down that road.

I guess what I would reject is the hubris in assuming that we know where we want to end up.  It might be that climate change is a lot worse than I think it will be.  What if the big ice sheets are breaking up really rapidly and we start getting meters of sea level rise that is unexpected, and what if big swaths of the tropics start being uninhabitable?  It might end up being worse than we think, and we might want to use it.  When I say “we,” I mean humanity.  I don’t expect to have any role in the decision.

It is not that just that would we want to use it, but would anybody want to use it, and would we know how to respond appropriately to that?  One of the justifications for the United States doing direct injection of CO2 into the ocean experiments was that the Japanese were interested in it and so the U.S. government should understand it to understand how to respond to the Japanese proposals.  I think the Japanese scientists were saying the same thing to their leaders.

Even if you think it’s bad, I think they would be able to show why it’s bad.  Do the experiment to show why it’s bad.

You have used the terms “know” and “knowledge” a number of times in your responses.  Of course, getting society’s agreement on what we know, all of the facts, is pretty challenging and can become even more so with the way the Internet works, conspiracy theories, and all of this.  We do have the Covid-19 pandemic, to take a different example.  We saw pretty clearly the divisive consequences of disinformation, inadequate information, and misunderstanding of information, so much so that the World Health Organization coined the term “the infodemic” as it went alongside the pandemic.  What have we learned from that experience, and I guess also the history of what we know around climate change in general, in terms of how we would go about actually establishing and sharing a willing trust in what we know about solar radiation modification?

This is obviously a tough question.  If I had to say how my thinking has changed over the last five or so years, I used to have pretty much this almost Lockean view of humans as basically rational actors.  Maybe rationality was clouded by emotions, but Homo economicus was some kind of reasonable representation of human beings.

Now I am thinking, Oh, we evolved in small groups of hunter-gatherers, and probably the worst thing for us was to be banished to the forests by ourselves — really the centrality of group identity for human psychology, and we are basically willing to believe anything to avoid being rejected by our group.  Not to be overly controversial, but I think this is like religions, that if you want to be a member of the group, then you better share these religious beliefs; so no matter how crazy the religion is, we will believe it if lets us stay with the group. 

We see with the response to coronavirus how people’s views on empirical facts closely align with their group identity.  How to surmount this and get a more rational assessment is the challenge of the day, not just with solar geoengineering but with the whole rest of our political system.

I guess there are a few things that I have been trying to do personally to try to help, although I am not always successful.  I think we need to be much more supporting what we think might work and be a little more generous to what other people are doing that we think isn’t going to work.  I think this climate challenge is plenty tough, but the climate community — whether you are for or against nuclear power, you are for or against solar geoengineering, or you are for or against carbon capture and storage — I feel like being against something has very limited utility.  Tell us what you think will work or what is useful for us to do, and let’s try to widen the pie and get more resources so that we can develop all of these pathways.

I have been trying to, when somebody says things that I disagree with, rather than say, “Oh, that’s a bunch of bull,” to phrase my objection in terms of a question: “How would you deal with this concern?” or “How would you deal with that?”

I think there is something in civility and generosity and that we just need to start being — I know it’s a hard road to get to this point, but I kind of feel like after 9/11 when the World Trade Center came down and the United States responded, I thought we could respond magnanimously and say: “We know these people did terrible things, but yes, there is real injustice in the world and inequality that needs to be addressed.”  There was an opportunity there, but instead we responded with kidnapping, torture, violence, and basically acted on the same level as the people who were attacking us.

I think it’s the same thing.  I think that we need to take the high road and try to argue in favor of the facts and try to be positive, and when somebody says something we think is ridiculous, don’t just say “You’re a jerk,” but ask, “How would you deal with this?”

I know this is an inadequate answer and may be insufficient, and I am not saying the forces of darkness won’t win, but I think we just have to try to stick to the high road.

You talk about staying positive and you also mention the “forces of darkness.”  Climate change can be a pretty bleak problem to deal with, where you can start to see things in that light,; and it can take a toll on professionals who study it and also find themselves caught up in these debates.  How do you — and maybe we will finish on this — personally maintain some sense of agency, hope, and enthusiasm whilst not kidding yourself about the sheer scale of the challenge ahead?

First of all, I have to say this.  I have been involved in trying to deal with climate change now for over four decades.  I first started getting involved in 1979, which was a pretty long time ago.  It basically has felt mostly like hitting your head against a brick wall.  Maybe there has been a little motion, but again the amount of motion compared to what there needs to be is in the single-digit percents.

I guess there are a few different things.  One is I get to work with superintelligent post-docs, these people who are motivated, smart, and nice people doing interesting work.  I get to talk to all kinds of interesting people.

I think a lot of our personal happiness has to do with our social interactions and not our intellectual beliefs, but I am constantly in a state of existential anxiety over what can I do to be effective.  I feel like I am in a better position to be effective than 99.99 percent of the people on the planet in that I have been fortunate enough to help bring information to Bill Gates, I get to communicate with other people, and I feel like, given the resources I have and the connections I have, I should be a lot more effective than I am.  I constantly feel like I am underperforming.

I think the people who are easily satisfied with their own performance probably don’t accomplish so much.  One of the things of trying to accomplish a lot is feeling like you’re always falling far short of your ambition.  If I knew what I could do to be more effective, I would do it, and every day I try to think: Oh, man, what could I do that would actually make a difference to somebody? 

This is maybe part of the thing of aging.  I still have a good healthy ego and like to promote myself.  I am much more now getting more satisfaction in helping other people and acting as a facilitator to other people and doing some things in the background a little more.

We haven’t solved the climate problem, we haven’t addressed climate challenges in a substantive way, so this is again why I am less critical of other people’s strategies and saying: “It’s not like my strategy has been successful or your strategy has been successful, so who am I to criticize somebody else who has an unsuccessful strategy?  Let’s just try it anyway.” 

I don’t know what to do with this, but it feels like hitting your head against the wall.  Luckily I have good social relations because the amount of progress on addressing climate challenges has been disappointing.

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