Designing the program
What is the best-case scenario for geoengineering? Scientists often laugh when I ask them that. “I would say the best-case scenario is if we figure out a way not to do it,” replied Ben Kravitz, which is actually most people’s first answer. “Barring that, I would say the best-case scenario is that we do it in an intelligent way, where we are designing geoengineering so that it will do what the politicians want it to do, minimizing side effects, and that there is an appropriate government structure … and just people working in a way that I believe they can work. Not the way they usually do.” He adds, “We could go out and do geoengineering tomorrow, really poorly. That’s what scares me.”
Doug MacMartin has a similar view, sketching out a hypothetical scenario where the world manages mitigation that curbs warming to two and a half degrees, and uses solar geoengineering for a century to bring temperatures down to one and a half degrees. “We do that in a way where adjusting aerosol injection at different latitudes balances all sorts of different climate impacts. So that in principle, almost nobody on the planet is actually harmed [by geoengineering itself], and that there is strong international trust in whatever organizations are involved in making decisions, so that everybody on the planet feels that their voice has been heard, and accepts the fact that this limited deployment of solar geoengineering is better in some aggregate sense than not having had any geoengineering, and so it doesn’t result in conflict.”
“Geoengineers” are often caricatured as being in bed with fossil fuel companies, stranding us in the business-as-usual era; or otherwise, as gritty realists who lack the imagination to see the social transformation that’s truly possible. Yet in the best-case articulation of many researchers, solar geoengineering does represent a rather-utopian dream. You have to believe that people are really capable of long-term thinking and cooperation to even articulate these scenarios—much less spend your time researching them. MacMartin adds that a best-case scenario, socially speaking, would frame geoengineering as a conscious acceptance of responsibility for the climate, rather than simply an effort to control it. “Accepting responsibility for it, I think, speaks to a maturation, and a way of expanding one’s moral sphere further. Expanding one’s moral sphere to the rest of the planet to future generations, to nonhumans, and saying we actually have responsibility for the betterment of all them. It’s certainly possible that a hard discussion about solar geoengineering could push humanity in that direction.”
While climate engineering researchers don’t tend to interpret this question of a “best-case” climate scenario through the lens of a comprehensive, long-term solar geoengineering program, they do have a sense about what a climate engineering program might look like—contingent on what society is doing with mitigation and carbon removal. Ideally, solar geoengineering would be limited in scope. And it would be limited in time.
“Would a marginal deployment of geoengineering harm anybody?” Peter Irvine, an atmospheric scientist based at Harvard University, is trying to help answer this empirical research question. He explains that modelers often look at a scenario where all warming is offset, and evaluate who wins and loses in this extreme scenario. “Would offsetting 0.1 Celsius with geoengineering dial anything back, or would it amplify certain things? Does a marginal deployment help or hinder? … How many more increments of cooling can you add before you start running into new issues that come with geoengineering?” Irvine and colleagues’ work looks at what happens when just enough stratospheric aerosols are used to offset half of a doubling of CO2 in the atmosphere for a hundred years. They find that using this smaller amount could avoid many of the previously reported impacts of aerosol geoengineering upon the hydrological cycle, such as extreme or decreased precipitation. With halved warming, everything seems to scale up without major hazards. “Beyond half … some of the real differences start popping out a bit more.” I asked Irvine about his best-case scenario for using solar geoengineering, and like most scientists, he says the best case is strong emissions cuts. “Against that backdrop … I think some deployment carefully, carefully scaled up, little by little, over the course of a decade or two. … Gradually halving the warming, possibly halting the rate of warming some decades in, against the backdrop of trying to cut emissions and then bringing them back down.”
Even though Irvine is a climate scientist who thinks about the temporal aspects of a solar geoengineering system, he doesn’t necessarily take a long-term, programmatic view. “You’ve got to think kind of decade by decade. Like, what do we do now, in this decade?” Irvine asks: “Who are we to say what the 2100 climate policy should be?” He thinks it is possible to have a climate policy that includes solar geoengineering but not negative emissions, where it would be decided decade by decade whether to ramp back the solar geoengineering or continue it, and points out that the same questions apply to making policy around negative emissions. “How quickly should we get to zero, and how quickly should we go negative? I think these are questions that, it’s a bit daft to impose what we think… to basically, to meet some arbitrary 2°C target or 1.5°C target people in 100 countries agreed on in one meeting somewhere, and to assume that it’s going to bind people 100 years from now.”
Many scientists see solar geoengineering as a temporary measure that could be phased out if carbon removal was succeeding. Oliver Morton, in The Planet Remade, calls this temporary geoengineering scenario the “breathing-space approach,” in that it allows incremental use of solar geoengineering to create breathing space for decarbonization.7
This intuition that solar geoengineering is a temporary intervention develops, I think, not only from an engineering perspective that thinks about resilient systems, but also from a moral sensibility. Kravitz says that solar geoengineering is not a permanent solution: “It’s not something that we want to just do forever, or at least I don’t, because I think too much can go wrong.” Similarly, MacMartin thinks we’d eventually want to restore the climate using carbon removal, in order to have an exit strategy and avoid inflicting an implied commitment to solar geoengineering on future generations. Most stratospheric aerosol scenarios last 200 years, he says, and there’s probably no deployment scenario that’s less than a hundred years (with the caveat that it’s possible that someone will find a really cheap way to pull CO2 out of the atmosphere during that time period). Kelly McCusker, a climate modeler who has studied what happens when a solar geoengineering program is ended abruptly, also emphasizes that solar geoengineering will need to be done in combination with carbon dioxide removal or mitigation. “That’s my feeling, but I don’t necessarily have a good basis for that. I mean, in part, it’s like you can look at these plots and just know it would be completely immoral to do it on its own.”
The scientific consensus around this feeling is reflected in the IPCC’s Special Report on 1.5°C, which explicitly assesses solar geoengineering in terms of its potential to limit warming to this amount “in temporary overshoot scenarios as a way to reduce elevated temperatures and associated impacts.” It states that “if considered, SRM [solar radiation management] would only be deployed as a supplement measure to large-scale carbon dioxide removal.”8 This report actually reflects quite closely the views MacMartin, Kravitz, and others have already published, and their sense of how the practice might be best used, given that the aim of the report is to summarize the existing literature—and these researchers are the ones who wrote the existing literature. At the same time, this consensus on how it should be used might not be shared by politicians or industry leaders, who are often thinking on much-shorter timescales, and with different considerations in mind.
Why, exactly, is it so important that geoengineering be temporary? One issue is that of “termination shock,” mentioned at the beginning of this book—the phenomenon in which if solar geoengineering was suddenly ceased, temperatures would shoot back up to a level commensurate with the greenhouse gas concentration of the atmosphere.
Some scientists argu
e that the risk of termination shock is not as high as portrayed in the media or academic literature. For a termination shock to happen, the geoengineering intervention would have to be large: as Oliver Morton writes, if solar geoengineering were “a relatively modest affair, the termination shock would be more a termination shudder.”9 Likewise, Andy Parker and Pete Irvine argue that a sudden termination is unlikely, and preventable.10 Because solar geoengineering is cheap, they argue, it would take a pretty massive catastrophe to halt it and keep it turned off. For instance, 70 percent of GDP of the United States or China could be wiped out, and they could still deploy solar geoengineering for less than 1 percent of their post-catastrophe GDP. When it comes to such external forces, Irvine says: “If we’re talking large-scale nuclear war, everything else that we’re technologically dependent on is going to kill us first. I mean, the fact that I don’t know how to grow food or catch food or hardly even look after myself … I think that’s what’s going to do us in, rather than a slightly greater warming off the back of your mushroom cloud–induced nuclear winter.” It’s true that people could choose to stop geoengineering, but Irvine finds this similarly unlikely, because for termination shock to be a big issue, you’re already have to be decades into the program. “You’re a generation into this. It’s normal. It’s as normal as, you know, irrigation and rivers. It’s everyday … If you start to run through this story line, and put yourself in the perspective of a world that’s thirty, forty years in … I think it would be as unthinkable as international shipping or aviation ending.” Parker and Irvine also add that it would take months for a disruption to a solar geoengineering program to have any effect upon temperatures, because the aerosols would take months to thin out. “This is crucial for analysing the risks of termination shock, as it means that humanity would have a period of several months in which to resume deployment of SRM in the event of a disruption,” they write. They point out that even if solar geoengineering was used to offset a large amount of warming, it could be slowly phased out over the course of decades without a shock. They also suggest criteria for a solar geoengineering system that would be robust against termination shock: it would need to be geographically distributed, affordable enough for multiple actors to maintain independent systems or backup hardware, and slow to lead to damages following disruption. “If back-up deployment hardware were maintained and if solar geoengineering were implemented by agreement among just a few powerful countries, then the system should be resilient against all but the most extreme catastrophes,” they write.11
Other researchers, however, view the risk a bit differently. In one study, ecologist Christopher Trisos and colleagues modeled the consequences of solar geoengineering termination on other species.12 Their study looked at the “climate velocity” of different species, which is the rate at which plants and animals have to move to keep their climate the same. Basically, if solar geoengineering was started and then stopped, many species would not be able to move quickly enough to keep up, threatening extinction for corals, mangroves, amphibians and land mammals. I caught up with Trisos one spring day in Washington, DC, to hear more about his research. “To the extent that risk is probability times consequence,” he explained, “even if that probability is tiny, if the consequence is worse than anything we could conceive of over a similar time period of climate change without geoengineering; then for me, it’s big enough of a risk to really think twice about the geoengineering discussion. Essentially, if we are exposing ourselves to that level of planetary risk, should we even think about geoengineering anymore in the first place?” Trisos thinks that the extreme severity of a termination shock, even if unlikely, raises the bar for geoengineering researchers to show that termination “is not a risk, or at least a low, low probability.”
Atmospheric engineering on an ocean planet
There’s another key reason that solar geoengineering would need to be nested within carbon removal: we live on an ocean planet. Ocean acidification has been called the “other CO2 problem,” and solar geoengineering wouldn’t directly help ocean acidification much. (Solar geoengineering would likely affect ocean acidification through a host of other secondary effects—temperature effects on terrestrial biomass, hydrological cycle changes, changes in marine productivity13—but it doesn’t directly address the issue of increased CO2.)
Solar geoengineering may help mitigate sea level rise, though there are some limitations. Sea level rise has two drivers: ocean heating (because warmer waters expand), and melting ice. To stop the former, we’d have to address the energy imbalance in the ocean, which would mean returning it to roughly preindustrial conditions. Imagine that temperatures rose, but then we did geoengineering to lower temperatures back down half a degree, suggests Pete Irvine: this would reduce the direct atmospheric-driven, temperature-driven effects, such as heat waves. However, the ocean has layers. The surface ocean can respond to solar geoengineering in decades, but the deep ocean takes hundreds or thousands of years to respond. For example, if we reached two degrees Celsius and did geoengineering to come back to 1.5, the rate of heating would slow, but the ocean would not necessarily stop heating. “It’s going to take thousands of years to reach a new balance.”
By bringing temperatures down, one could stop ice from melting in places like Greenland, Irvine notes, which is otherwise going to experience a slow runaway feedback loop in which it loses mass over thousands of years. But in parts of Antarctica, on the other hand, staving off melting might not be possible, since Antarctica has points that become unstable with only a little bit of warming. “Because of the way the glaciers meet the ocean, when they start to retreat, they have kind of a runaway retreat. Again, very slow, like a couple of centuries. Five centuries. But once it starts, it’s not a temperature-driven thing; it’s a dynamic-driven thing … Once the ice shelf is sheared off or melted away, it’s not there to hold the ice sheet back and there’s this kind of dynamic response.” Irvine explains that some ice may have crossed that tipping point already: “Quite big chunks of West Antarctica may have already crossed this threshold, and it might not be possible to dial them back. But there’s other parts that may trigger a little later. Or may trigger much later …” It’s not like everything is safe below 1.5 Celsius, and then there’s a sudden step change when the world reaches 1.5. “I think there’s lots of little mini steps. And the sooner you arrest warming, the fewer of these steps you cross.” Some things are not reversible by solar geoengineering. Irvine continues: “You could imagine quite easily if that migrant species’ last refuge gets pushed off the top of a mountain because it’s getting too warm, well, it can’t come back because it’s dead. So I think there are examples where you could say, the atmosphere can respond back and we can dial it back. We can dial it back five decades later and get it back to where it was.” But some aspects of the ice sheet response can’t be dialed back. “And obviously if certain harms and damages have occurred, things have died, glaciers have melted away permanently … You know, there’s certain things you can’t take back.”
Best-case solar geoengineering: A temporary measure for conservation?
One of the best reasons to consider solar geoengineering, in my view, could be to preserve species during an overshoot—but would this even be possible? I asked Christopher Trisos, the ecologist, about this. He’s hesistant to say that geoengineering could save species, he says, because while some ecological impacts could be forecast, they really depend on the social choices that are made around geoengineering, and Trisos’s impression is that “the scenario’s uncertainty is still so big that ecologically, it is just anyone’s game.” There are areas that could be investigated, though, such as biome changes or wildfires, as well as disease vectors like mosquitoes, which we know a fair bit about. “What happens to the insects that are vectors for a lot of really nasty diseases like malaria, chikungunya, Zika? Is a geoengineered world better or worse for Zika in the Americas?” Or would it be worse for cholera in Asia? I wonder. It could be the opposite; m
aybe the conditions it sets in place climatologically are more preventative than promotive. We don’t know. “A geoengineered world with potentially more Zika, more cholera, more malaria … I’d much rather take climate change without geoengineering.”
There’s so much that’s unknown, but to me, it’s noteworthy that not very much research has been done on the ecologies of geoengineered worlds. I ask Trisos to speculate on this gap. He hypothesizes that ecologists don’t want to lend the idea credibility. “The 30,000-foot view of what geoengineering could mean for ecosystems—my sense is a lot of people are reluctant to do that, or just not interested, because they view it more as the sci-fi fringe with the crazy people at climate conferences, and the real work of ecologists is to try and show how bad climate change can be. To promote greenhouse gas emission reductions. And also, I think in a normative way, geoengineering goes against what a lot of ecologists hold dear about promoting resilience of the planet, and natural recovery of ecosystems, and giving things space and time to have an adaptive capacity. The idea of putting your thumb on the thermostat of the planet is antithetical to that.” The study of speculative futures under geoengineering is on the cutting edge of climate change ecology research, Trisos adds, which also makes it a tough sell for ecologists. “If you’re going to push that research frontier forward, they would rather focus on a conventional climate change scenario than look at the more unconventional, potentially fringe ones like geoengineering.”
After Geoengineering Page 25