CLIMATEWIRE | A controversial idea for cooling the earth’s climate through artificial means would likely require a much longer global commitment than policymakers and the public understand, according to a recent study that raises new questions about the potential for using solar geoengineering.

If world leaders decide to use solar geoengineering to meet international climate goals, they could be locked into it for a century or more, the study suggests. The potentially long timeframe further complicates the debate about geoengineering and its viability.

Geoengineering is “often communicated as temporary, a stopgap measure — so it implies being relatively short, and short in the sense of a couple of decades,” said lead study author Susanne Baur, a doctoral candidate at the European Centre for Research and Advanced Training in Scientific Computation in France. “And so when we started looking at these pathways, and we extrapolated them a bit longer, we saw that in many cases, it’s actually not that short.”

The public may not realize the scope of a commitment solar geoengineering — or its risks, including the need for long-term international cooperation.

“If we have to keep up a system like this for such a long time, that just increases the possibility of something bad happening,” Baur said.

Solar geoengineering refers to a kind of climate geoengineering aimed at manipulating the amount of solar radiation that hits the planet. The most commonly discussed strategy involves spraying special reflective aerosols into the atmosphere to beam sunlight away from the earth, lowering global temperatures.

It’s just an idea for now. And it’s highly contentious. Solar geoengineering risks and side effects range from possible damage to the earth’s ozone layer to inadvertent changes in global precipitation patterns.

Once started, it would be dangerous to stop unless enough carbon had been sucked out of the atmosphere to lower the earth’s temperatures below a safe threshold. Otherwise, a sudden halt to geoengineering could cause temperatures to skyrocket, potentially faster than life could adapt, a concept known as “termination shock.”

The risks have prompted scientists to urge international discussion and agreement about regulating geoengineering experiments and deployments.

The new study, published March 28 in the journal Earth System Dynamics, analyzes how solar geoengineering could be used to meet climate targets and how long the world would have to maintain the practice to meet the targets.

The time frames range vastly, the study finds. If nations quickly reduce emissions and atmospheric carbon, solar geoengineering could be unnecessary.

But based on the carbon-cutting commitments nations have made under the 2015 Paris Agreement, solar geoengineering would likely have to persist for at least a century to keep global warming within a threshold of 1.5 degrees Celsius, the study found.

The study modeled hundreds of potential geoengineering scenarios to account for factors such as how quickly global emissions fall, how much carbon is removed from the atmosphere each year and how the climate system physically responds, which is still uncertain.

Although the projected timelines range from no geoengineering to hundreds of years, few scenarios resulted in a timeline of less than 100 years. Those scenarios generally assume extremely aggressive climate action.

The study also found that if nations met their climate goals under the Paris Agreement, solar geoengineering would be needed for at least a century before the world could safely stop and ensure that global temperature increases would remain below 1.5 C.

The threshold is the Paris Agreement’s most ambitious goal. And it’s becoming more elusive. The most recent report from the U.N.’s Intergovernmental Panel on Climate Change, released in March, warns that the world could exceed the temperature target within a decade. Even with immediate cuts in carbon emissions, the world will likely overshoot the 1.5 C threshold at least temporarily, the report says.

Overshoot doesn’t have to be permanent. Nations could use various technologies to suck carbon dioxide out of the atmosphere, lowering global temperatures in the process. But some consequences of climate change, such sea-level rise, are irreversible on human time scales and can’t be undone.

Solar geoengineering could prevent overshoot by temporarily cooling the earth’s climate, keeping global temperature increases below 1.5 C while world leaders work to cut emissions and remove carbon dioxide to cool the climate on a long-term basis.

Eventually, after global emissions hit net zero and enough carbon is removed, the world could stop using geoengineering without global temperatures shooting back up. But it’s uncertain how long it would take to reach that point.

Few studies have sought to determine how long geoengineering would be needed, according to Baur, even though the question is essential. Longer uses of geoengineering increase potential risks — and the need for international cooperation, which could be unpredictable over long periods.

“Keeping up this international cooperation on such a technology, where geopolitical interests are involved, is just very risky,” Baur said.

Chris Field, an earth-system scientist at Stanford University who was not involved in the study, said plenty of long-term frameworks for international cooperation on other matters have succeeded for decades. Still, he said, “It makes total sense to me that concerns about long-term governance are legitimate.”

Field chaired a committee for the National Academies of Sciences, Engineering and Medicine that released a report on solar geoengineering in 2021. The report suggested that the concept deserved more scientific research and urged the U.S. government to develop a well-funded national research program, emphasizing careful governance and regulation in the process.

The new study “highlights the need for that research agenda to be broad-based and address issues like the long-term governance challenges and how long the governance challenges will persist,” Field said.

There’s often more scientific and public interest in experiments that investigate the physical effects of solar geoengineering than there is in questions about ethics and logistics, he added.

“Sometimes the enthusiasm for those [issues] runs ahead of the enthusiasm for the other kinds of research on unintended consequences, on the social license, on the issues with governance that are likely to be really really important,” Field said.

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2023. E&E News provides essential news for energy and environment professionals.