Solar Geoengineering: Risk of ‘Termination Shock’ Overplayed, Study Says

Clouds over Llanymynech, Wales, UK. Dave McGlinchey / Flickr

By Robert McSweeney

Solar geoengineering, or "solar radiation management" (SRM), is perhaps the most controversial of the different ways of limiting human-caused climate change.

A commonly voiced objection to the technique is the risk of "termination shock"—the rapid rebounding of global temperatures if SRM is deployed and then suddenly stopped.

But a new research article, published in Earth's Future, argues that this risk has been "significantly overestimated." There are numerous ways to prevent termination shock from occurring, the researchers say, and also to ensure that an SRM program is resilient to physical, political or economic interruptions in the first place.

However, despite their findings, the best way to protect against termination shock is "to cut CO2 emissions rapidly so that SRM is not needed for managing climate risk," the lead author told Carbon Brief.

Preventing a Shock

SRM describes an array of methods—all of which remain hypothetical—for artificially reducing how much sunlight reaches the earth's surface in order to dampen global warming. These include "seeding" clouds, spraying aerosols into the atmosphere, or blocking sunlight with mirrors in space.

Implementing SRM would require overcoming a series of technical, political and ethical challenges, which have been the subject of robust debate for some time. Just last year, SRM was one of the main topics under discussion at a four-day conference in Berlin.

One of the potential risks of implementing SRM is "termination shock." This could happen because SRM masks the warming caused by greenhouse gases rather than reducing the concentration of gases in the atmosphere. In effect, it is treating the symptoms of climate change rather than curing the underlying condition.

A study from earlier this year found that the rate of change in temperature after terminating SRM could be as much as four times larger than those caused by climate change itself. This would likely leave many species unable to cope with the sharp change in conditions.

But the researchers behind the new paper feel that termination shock is often given as a reason not to try SRM without giving proper consideration to what the term actually means. Andrew Parker, lead author and honorary senior research fellow at the University of Bristol, explained to Carbon Brief:

"It's common for commentators to say that once you start SRM you can't stop it. Some then conclude that you should never start. But it's just not accurate to say that once you start SRM you can't stop it."

There are several ways in which termination shock could be avoided, the researchers argue in their paper.

First, SRM could be employed to offset just a portion of human-caused warming. The paper suggests that a cooling impact of around "a few tenths of a degree" could be stopped suddenly without risking termination shock. Considering the difference in potential impacts between 1.5°C and 2°C of warming, using SRM for a relatively small reduction in temperatures would still have clear benefits, the paper notes.

Second, SRM could be phased out gradually. For example, using SRM to limit 0.2C of warming per decade could be phased out gradually over 50 years without a shock, the paper says.

And third, if SRM was interrupted, there would be a window of "a few months" to restart it before an appreciable rise in temperatures would occur. For example, aerosols already released into the stratosphere would continue to have an effect, the researchers say, and it would take the earth system a while to readjust to any change.

Co-author Dr. Peter Irvine, a postdoctoral research fellow at the Harvard John A. Paulson School of Engineering and Applied Sciences, explains more in the video below:

Potential Causes of Shocks

The risk of termination shock is also affected by what causes an SRM program to end suddenly, the authors say.

The study focuses on one proposed type of SRM, known as a "stratospheric aerosol injection," which involves sending up substances to the stratosphere that are known to have a cooling effect on the climate.

Using high-flying jets has been judged a "feasible" way of doing this, the researchers say. And based on estimates from other studies, the researchers assume implementing SRM on a large scale would cost an initial outlay of $50 billion and then $12.5 billion a year to deploy.

Aerosols have a limited lifetime in the stratosphere and would need to be released at regular time intervals in order to be effective. The researchers looked at what might cause an SRM program to be interrupted.

There are two main reasons why an SRM program would be terminated early, the paper suggests: because something forced it to stop, or because people made a decision to stop it.

The former might include a terrorist attack (either physical or cyber) or some sort of catastrophe (either natural, economic or political). The latter could be caused by a change of political will, or if SRM was causing unintended impacts that resulted in calls for it to be stopped.

The researchers ran through all these scenarios, plotting out how they might result in termination of an SRM program. Their results suggest that "people had been underestimating how robust an SRM system could be and, thus, overestimating the risks that it could suddenly be terminated," said Parker.

"Some things that people had been assuming could disable an SRM system—such as terrorist attacks or political demands—would probably not be able to do so unless the system was terribly designed. In fact, a well-designed system should be able to withstand most suggested events that might cause termination shock."

A well-designed system would include, for example, maintaining backup infrastructure—such as additional airfields and jets for releasing aerosols into the stratosphere, said Parker. This should be "easy" to do, the paper argues. Similarly, if multiple countries around the world were capable of deploying SRM, the system would be "resilient against all but the most disastrous of global calamities."

Making sure that deployment of SRM is legitimately and widely agreed would also help prevent political grievances, Parker added.

Wider Debate

The new paper identifies an important gap in the SRM discussion, said Dr. Ben Kravitz, a climate scientist focusing on climate feedbacks and geoengineering at the Pacific Northwest National Laboratory in Washington, who was not involved. He told Carbon Brief:

"One extreme [of termination shock] is a lot of geoengineering, abruptly ceased, permanently. But what does that middle ground look like? At what point does phasing out geoengineering look like a 'shock'? I think this is an important thing to look at and quantify, and I'm glad the authors took the first steps toward doing that."

The paper is a "welcome input into the overall debate" on SRM, added Janos Pasztor, executive director of the Carnegie Climate Geoengineering Governance Initiative (C2G2) and former assistant UN secretary-general.

But while it might be "easy" to build the physical systems needed to backup an SRM programme, organizing how it might be governed is not so straightforward, said Pasztor:

"Some say stratospheric aerosol injection systems are ungovernable. I don't believe that is the case, but it will be challenging. So many different voices will need to be heard. Creating global consensus for deciding whether or not to use and then, if yes, how to make it happen—including how to minimize termination risks—will be a massive undertaking."

For example, one gap in the paper is what happens if one group goes ahead with SRM without international agreement, noted Dr. Anthony Jones, an associate research fellow at the University of Exeter, who led a recent study on the regional impacts of SRM. He told Carbon Brief:

"One issue the paper doesn't cover is the consequences of a group of countries or a single country deciding to implement solar geoengineering without global consent and participation, which would increase the risk of early termination. Although international opposition would make unilateral deployment unlikely, it is still a scenario worth discussing."

The policy options put forward in the paper do not require decision-makers to "behave with perfect rationality," the authors note, but that they "must just avoid wanton irrationality."

Although this may seem reasonable, said professor Alan Robock of Rutgers University, "unreasonable policy decisions are made all the time." He asked: "Can we count on future political actors to be reasonable?"

It is also worth remembering that the potential for termination shock is just one of many other potential risks and concerns with SRM, he told Carbon Brief:

"Even if termination shock were less likely, there are still many reasons why SRM would not be a robust policy option."

That said, Robock "completely agrees" with the last paragraph of the paper, which argues that the solution to global warming is mitigation and adaptation so that SRM is not necessary in the first place:

"Our final conclusion is the most obvious and important. The best way to avoid termination would be to avoid a situation where a large amount of SRM would be needed to reduce committed climate risks. Strong action on mitigation would reduce the amount of SRM necessary to maintain a stable global temperature.

The development of safe and scalable CO2 removal techniques could reduce the cooling needed from SRM after deployment, and strong adaptation investment would reduce the suffering from the residual climate impacts to which Earth is already committed."

Reposted with permission from our media associate Carbon Brief.

EcoWatch Daily Newsletter

Fabian Krause / EyeEm / Getty Images

By Elizabeth Streit, MS, RDN, LD

Paprika is a spice made from the dried peppers of the plant Capsicum annuum.

Read More Show Less
Water protectors of all persuasions gathered in talking circles at Borderland Ranch in Pe'Sla, the heart of the sacred Black Hills, during the first Sovereign Sisters Gathering. At the center are Cheryl Angel in red and white and on her left, Lyla June. Tracy Barnett

By Tracy L. Barnett

Sources reviewed this article for accuracy.

For Sicangu Lakota water protector Cheryl Angel, Standing Rock helped her define what she stands against: an economy rooted in extraction of resources and exploitation of people and planet. It wasn't until she'd had some distance that the vision of what she stands for came into focus.

Read More Show Less
Hedges, 2019 © Hugh Hayden. All photos courtesy of Lisson Gallery

By Patrick Rogers

"I'm really into trees," said the sculptor Hugh Hayden. "I'm drawn to plants."

Read More Show Less
BruceBlock / iStock / Getty Images

By Jillian Kubala, MS, RD

Thanks to their high concentration of powerful plant compounds, foods with a natural purple hue offer a wide array of health benefits.

Read More Show Less
Environmental Investigation Agency

By Genevieve Belmaker

Last week, the Peruvian Palm Oil Producers' Association (JUNPALMA) promised to enter into an agreement for sustainable and deforestation-free palm oil production. The promise was secured by the U.S. based National Wildlife Federation (NWF) in collaboration with the local government, growers and the independent conservation organization Sociedad Peruana de Ecodesarrollo.

Read More Show Less
Jessica Kourkounis / Stringer

The rallying cry to build it again and to build it better than before is inspiring after a natural disaster, but it may not be the best course of action, according to new research published in the journal Science.

"Faced with global warming, rising sea levels, and the climate-related extremes they intensify, the question is no longer whether some communities will retreat—moving people and assets out of harm's way—but why, where, when, and how they will retreat," the study begins.

The researchers suggest that it is time to rethink retreat, which is often seen as a last resort and a sign of weakness. Instead, it should be seen as the smart option and an opportunity to build new communities.

"We propose a reconceptualization of retreat as a suite of adaptation options that are both strategic and managed," the paper states. "Strategy integrates retreat into long-term development goals and identifies why retreat should occur and, in doing so, influences where and when."

The billions of dollars spent to rebuild the Jersey Shore and to create dunes to protect from future storms after Superstorm Sandy in 2012 may be a waste if sea level rise inundates the entire coastline.

"There's a definite rhetoric of, 'We're going to build it back better. We're going to win. We're going to beat this. Something technological is going to come and it's going to save us,'" said A.R. Siders, an assistant professor with the disaster research center at the University of Delaware and lead author of the paper, to the New York Times. "It's like, let's step back and think for a minute. You're in a fight with the ocean. You're fighting to hold the ocean in place. Maybe that's not the battle we want to pick."

Rethinking retreat could make it a strategic, efficient, and equitable way to adapt to the climate crisis, the study says.

Dr. Siders pointed out that it has happened before. She noted that in the 1970s, the small town of Soldiers Grove, Wisconsin moved itself out of the flood plain after one too many floods. The community found and reoriented the business district to take advantage of highway traffic and powered it entirely with solar energy, as the New York Times reported.

That's an important lesson now that rising sea levels pose a catastrophic risk around the world. Nearly 75 percent of the world's cities are along shorelines. In the U.S. alone coastline communities make up nearly 40 percent of the population— more than 123 million people, which is why Siders and her research team are so forthright about the urgency and the complexities of their findings, according to Harvard Magazine.

Some of those complexities include, coordinating moves across city, state or even international lines; cultural and social considerations like the importance of burial grounds or ancestral lands; reparations for losses or damage to historic practices; long-term social and psychological consequences; financial incentives that often contradict environmental imperatives; and the critical importance of managing retreat in a way that protects vulnerable and poor populations and that doesn't exacerbate past injustices, as Harvard Magazine reported.

If communities could practice strategic retreats, the study says, doing so would not only reduce the need for people to choose among bad options, but also improve their circumstances.

"It's a lot to think about," said Siders to Harvard Magazine. "And there are going to be hard choices. It will hurt—I mean, we have to get from here to some new future state, and that transition is going to be hard.…But the longer we put off making these decisions, the worse it will get, and the harder the decisions will become."

To help the transition, the paper recommends improved access to climate-hazard maps so communities can make informed choices about risk. And, the maps need to be improved and updated regularly, the paper said as the New York Times reported.

"It's not that everywhere should retreat," said Dr. Siders to the New York Times. "It's that retreat should be an option. It should be a real viable option on the table that some places will need to use."


By Manuella Libardi

Leaked documents show that Jair Bolsonaro's government intends to use the Brazilian president's hate speech to isolate minorities living in the Amazon region. The PowerPoint slides, which democraciaAbierta has seen, also reveal plans to implement predatory projects that could have a devastating environmental impact.

Read More Show Less

Hope may be on the horizon for the world's depleted coral reefs thanks to scientists who successfully reproduced endangered corals in a laboratory setting for the first time, according to Reuters.

Read More Show Less