Interview: Confronting the Riddle of Geoengineering

Climate change expert Rob Bellamy believes that solar geoengineering has enormous potential, but the risks are real.


BY DAN FALK
02.16.2024

THERE’S NO QUESTION that our planet is warming as the result of human activity. One obvious strategy to slow down this warming is to reduce greenhouse gas emissions — something that has thus far garnered more talk than action. It has been eight years since nearly 200 nations signed the Paris Agreement to limit the global temperature increase to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels, a feat that experts believe is unlikely to be achieved, as many nations remain reliant on fossil fuels, and emissions remain high. Meanwhile, 2023 was the hottest year on record.

So what else can be done? One provocative idea that’s been floated for several decades is geoengineering — basically, large-scale technological interventions to change the Earth’s environment or atmosphere to counter the effects of global warming.

Rob Bellamy specializes in the interaction between climate and society, and he’s particularly interested in how solutions to climate change are perceived, evaluated, and governed.
Visual: Courtesy of Rob Bellamy

Geoengineering proposals have come in various forms, but the most talked-about ideas involve solar geoengineering: reducing the amount of solar radiation that reaches the Earth by reflecting some of the sun’s light back into space, or by allowing more heat to escape the atmosphere. One way of doing that would be to inject a chemical such as sulfur dioxide into the atmosphere, increasing the atmosphere’s reflectivity (sometimes called stratospheric aerosol injection). Other ideas under this umbrella have also been put forward — for example, spraying seawater aerosols into clouds above the ocean (“marine cloud brightening”) or spraying silver iodide into high cirrus clouds, triggering precipitation which in turn would thin the clouds and allow more heat to escape (“cirrus cloud thinning”).

Such tinkering with Earth’s climate has always been controversial; last September, a panel of experts called for a moratorium on geoengineering efforts. At the same time, others have suggested the idea at least needs to be researched, so that if it one day becomes necessary, scientists will better understand its possible effects.

Rob Bellamy, a lecturer in climate and society in the geography department at the University of Manchester, specializes in the interaction between climate and society; he’s particularly interested in how solutions to climate change are perceived, evaluated, and governed. He’s also playing a leading role in an effort called Co-CREATE, a three-year European Commision-funded project investigating strategies for responsible research into geoengineering.

Our interview was conducted over Zoom and has been edited for length and clarity.

Undark: As concerns over climate change become more urgent, is interest in geoengineering increasing?

Rob Bellamy: Yes, I think it is. It tends to go through waves. So there was this whole interest in it, recently, I suppose, kicked off by the Nobel Laureate Paul Crutzen in 2006, when he published a quite influential article on climatic change, when he was arguing that we should be looking at stratospheric aerosol injection.

I think in the last two or three years, there has been an increase — a resurgence — in solar geoengineering again. So there’s a whole bunch of projects and things that are going on in this space.

And this is in response to things like the 1.5 degree target. The chances that we will stay below 1.5 are really quite low, if not impossible.

And that immediately starts opening up questions around solar geoengineering, because at this point in time, the only thing that really could — if you really wanted to reduce the Earth’s temperature very quickly and significantly — solar geoengineering is the only thing that can do that.

UD: How much sulfur dioxide would have to be released to slow down global warming significantly?

RB: A good example is the Mount Pinatubo eruption, which is often used as a kind of natural analog for solar geoengineering. Stratospheric aerosol injection is often thought of as like doing a volcano deliberately, if that makes sense.

Volcanoes release sulfur into the atmosphere all the time. So you say, “Oh, why don’t we do that ourselves?” And so if you were going to do a continuous injection rate of between 8 and 16 trillion grams [about 9 to 18 million tons] of sulfur dioxide a year — that’s approximately equivalent to the amount that Mount Pinatubo erupted in 1991 — and would reduce global temperature by about 1 degree [Celsius].

If you’ve got to offset one and a half degrees, you probably want to do one and a half Mount Pinatubos worth of stratospheric injections.

UD: Do we have the technology to actually do that?

RB: Yes, we do. There are a whole bunch of ways you could do it. One of the most popular suggestions is to fly aircraft and release it at high altitudes in the stratosphere. And that should be fairly straightforward, technically speaking.

The other options include firing missiles, or having a balloon with a pipe attached to it. There was actually a project in the U.K. called the Stratospheric Particle Injection for Climate Engineering project, or SPICE for short, which was taking place back in the early 2010s. And there was a plan to do a testbed for that technology where they were going to do a 1/20th scale model, where they’d have this balloon going up a kilometer [0.6 miles], and a pipe.

With the real thing, you’d pump up sulfur dioxide, but they just wanted to pump up a bathtub load of water, just to see if you could get it up there, and to stress-test the pipe and the balloon under different wind conditions. It didn’t go ahead in the end, because of the controversy.

And then there are various conventional means; other people have suggested building a space elevator, which is a bit more science fictiony, and probably quite impractical. But in theory, you could technically do it quite soon.

Now, if you think about these things not purely in a technical sense, but see them instead as what we like to call “socio-technical systems” — so combinations of technical objects and the social arrangements that go along with them, and without which they wouldn’t work, thinking about things like policies, people, procedures, things like that — they’re actually very hard to do.

UD: You’ve described some of the ways these aerosols can be released into the atmosphere — would such a release be a one-off affair, or would it have to be done repeatedly?

RB: I think the idea would be that it would be a kind of a repeated thing. They often talk about doing continuous injections, over a period of time. But I suppose the thing is, once you start doing these injections, you’re committed to doing it for as long as is needed to reduce carbon dioxide in the background.

Because this links to one of the big risks associated with several geoengineering technologies, including stratospheric aerosols, and this is called “termination shock.” It’s the idea that if you were doing these injections over time, and in the background you haven’t been reducing your emissions so they’re kind of continuing to build up, and then for whatever reason — a technical failure, or a terrorist attack, or something like that — if for whatever reason, aerosol injections stopped, then you would see a very sudden rise in the Earth’s temperature in line with the amount of carbon dioxide that had been building up in the background.

So that’s one of the really big concerns. These technologies offer quite quick and very effective means of reducing the Earth’s temperature in principle, but you can’t do it on its own without massive risks.

UD: What are some of the other risks?

RB: There’s quite a lot. One of the other big ones, I suppose, is disruption to regional weather patterns around the world. So in particular, there have been several studies that have looked at the impact of the Indian monsoon quite significantly changing, potentially. So it could affect precipitation patterns in quite dangerous ways.

That has knock-on effects on things like agricultural production, ecosystems, things like that. Coral reefs could also be affected — potentially in a positive way, in terms of reducing heat stress. Lots of potential disruption to circulation patterns.

And there’s another one: With the stratospheric aerosol injection, in particular, there’s a concern about the depletion of ozone in the atmosphere, which is obviously another global environmental problem that we’re trying to try to deal with. So it wouldn’t necessarily help with that. Acid rain, obviously sulfur, when it falls out of the atmosphere again, would come down as acid rain in places.

UD: Is there also a danger that a program like this could lead to complacency?

RB: Yes. You may have heard of the term “moral hazard,” or “mitigation deterrence” — the idea that if we have a so-called technical fix, or technological fix, that’s available to us, then we might think, “OK, well, problem solved. We don’t need to do any of that hard work around reducing our emissions or anything like that.” So there’s a real concern that having this technology even available to us as an option before you even think about deploying it — even just the idea could be a deterrent to more stringent climate policy.

Now, there is a whole debate about whether or not this is a thing. There have been quite a lot of studies that have been looking at how the presence of these kind of technologies as an option would affect how people think about climate policy. Some studies have shown that solar geoengineering does induce kind of moral-hazard-type thinking, in the sense that people think a bit more, “OK, well, everything’s fine; we don’t need to do those emissions reductions.”

On the other hand, there’s plenty of evidence that also shows it doesn’t do that. And actually, there is reason to think that these technologies being available — and indeed being under serious consideration — could actually have a galvanizing effect on climate policy because people think, “Well, wow, if people are considering things as scary as this, then it must be serious.”

And then there’s plenty of evidence that says it’s not really going either way. So it’s really mixed.

UD: How reliable are the models that scientists have been using to judge the effects of geoengineering programs?

RB: I should caveat this by saying I’m not a modeler.

I think if you ask a lot of the other folks who are doing the modeling work in this space, they’d be quite confident that they’re doing a good job of predicting the effects and indeed some of the risks as well.

I mean, technically speaking, when you think about — just putting the models aside for a second — if you think about it in terms of the natural analogy of the volcanoes, I can say we know pretty well that putting sulfur into the atmosphere will cool the planet; we know that from volcanoes. If you look back in the climatic record, every time there’s a big volcanic eruption, there’s a big dip in the global temperature. So we know that it would work in that sense.

UD: If there are questions about how accurate the models are, I suppose that could lead people to suggest that that’s some kind of real-world testing is necessary.

RB: Yes, absolutely. And I think that’s actually where we’re at, now, in terms of this whole debate. We’ve had quite a lot of research in the social sciences and the natural sciences modeling work over the last decade or two, and I think this is one of the things that’s underpinning this new resurgent interest in the area: If we are going to make progress in this space, and figure out whether or not it is something that we may or may not want to do, then we’re going to have to start doing some kinds of experiments.

That’s actually what this project that I’m involved in is — it’s a European funded project, where we’re going to be trying to look at this exact question as to how, if at all, we can proceed with doing experiments in a responsible way.

UD: Tell me about that project.

RB: We’re working within the frame of an area called “responsible innovation,” where we’re trying to address things that we know are areas of significant concern across different types of new science and technology. So you look at all sorts of different controversial areas, like AI or biotechnology, climate technologies, there’s all sorts of things. The same kinds of concerns from people tend to come up time and again.

And so this framework we’re using is all about trying to address these concerns, anticipating the kinds of impacts that might come from using these technologies. Thinking about the different ways in which the research might be framed as well. Obviously, the way in which you frame your research questions will frame the kinds of answers that you get out of it. And that speaks as well to the modeling — the kinds of questions that you ask, the information you put into your research, will pretty much determine what comes out the other end.

Another key aspect of this work is, and this is the work I’m leading on, is societal engagement stuff. So we’re trying to get a wide range of voices involved in thinking about this. I suppose, to date, the whole debate has been very dominated by a quite a small clique of individuals in the natural and social sciences, who have basically been having this debate for 15 years or so. And often you’ll find that they make claims on behalf of other people, quite often vulnerable communities or the Global South in particular.

It’s argued that solar geoengineering could offer a way of alleviating some of the risks and harms that are being posed to those who are most vulnerable to the effects of climate change. But at the same time, you could argue that this technology could place those very same people at elevated risk from the use of this technology, and the different impacts that it might bring about.

But very few people have actually gone to these communities to ask them what they think. So that’s one of the things we’re quite keen to do — to really broaden this conversation.

UD: It seems like the very idea of geoengineering is international. What rules or laws ought to govern it?

RB: This area has been described as being a kind of governance black hole. So there is there is a need for governance here, and it’s a very contested space. You may have seen in the last couple of years, there’s been whole debates around whether or not there should be a ban, certainly on deploying solar geoengineering technology, but also whether or not there should be a ban on doing even research.

It’s a very contentious area. I can kind of see both sides of the argument. I think one thing most people would agree on is that there should be a moratorium or a ban on immediate deployment, because I think everyone would agree we just don’t know enough about the effects yet to be able to do it at a global scale.

That said, when it comes to research, it’s much more divisive. On the one hand, people argue that if we don’t research this, then we’ll remain ignorant about what we’re currently ignorant of. And on the other hand, people would argue that remaining ignorant about these things would save us from the folly of pursuing something as outlandish as solar geoengineering.


Dan Falk (@danfalk) is a science journalist based in Toronto and a senior contributor to Undark. His books include “The Science of Shakespeare” and “In Search of Time.”