A Cool Debate About a Heated Topic

At the panel event, “Is solar geoengineering a viable tool in the climate policy arsenal?” experts discussed what’s known and what’s unknown about the controversial technology.

Vanessa Schipani
Vanessa Schipani

Vanessa Schipani is a PhD Candidate in Philosophy at Penn and prior to the PhD was a journalist for over 10 years, including for FactCheck.org.

Is solar geoengineering a viable tool in the climate policy arsenal? The short answer is – we don’t know. In the face of such uncertainty, debate about the subject in the public sphere often becomes, well, heated. But at a panel event on April 19th, three experts – Michael Mann, Shuchi Talati and Michael Weisberg – debated the topic calmly and coolly. As Mann, the Director of the Penn Center for Science, Sustainability and the Media (PCSSM), put it, “One of the great things about the environment we have here at Penn is that we can have different viewpoints and discuss them civilly and rationally.”

The event – jointly organized by the PCSSM, the Kleinman Center for Energy Policy and the Perry World House – was moderated by Stacy-Ann Robinson, the Lightning Scholar at Perry World House and Assistant Professor of Environmental Studies at Colby College. Robinson posed questions to the panelists that elucidated why we can’t even decide whether solar geoengineering should be used as a tool to fight climate change. Robinson posed her first question – What is solar geoengineering? – to Talati, a Visiting Scholar at Kleinman Center for Energy Policy and a scholar in residence with the Forum for Climate Engineering Assessment at American University.

Talati explained that there are two methods of solar geoengineering – stratospheric aerosol injection (SAI) and marine cloud brightening (MCB) – both of which aim to reflect solar radiation, or sunlight, back into the atmosphere to cool the planet. SAI mimics the effects of volcanic eruptions by injecting sulfur or other aerosol particles into the stratosphere. MCB involves spraying sea salt into low-lying rain clouds. While SAI would affect the entire planet’s temperature and precipitation patterns, MCB could be used regionally or globally.

But the physical, social and geopolitical risks involved with solar geoengineering remain largely uncertain, Talati added. We just don’t know how the climate and the people living on it will react to the deployment of the technology. This is because research on solar geoengineering has been limited to computer simulations and accidental experiments, such as the Mount Pinatubo eruption in 1991. After that eruption, the average global temperature dropped about 0.5°C for over a year. To significantly reduce uncertainty about the risks, especially the climatic ones, we’d have to conduct more controlled, real-world experiments.

Why haven’t we conducted these experiments? Because they might run into some of the risks that deployment of solar geoengineering itself entails. In this way, experimentation, especially on a larger scale, involves a bit of a catch-22. This was well articulated by Weisberg, Professor and Chair of Philosophy at UPenn and Senior Faculty Fellow and Director of Post-Graduate Programs at Perry World House: “We’re in a bind because part of the reason that people have been reluctant to do a lot of research about solar geoengineering is because of the uncertainty, but the reason there’s so much uncertainty is because there’s very little research that’s been done.”

Robinson also asked the panelists their viewpoints on what governance structures might be needed to both debate and regulate the technology. In response, Talati pointed out that most of the conversation about solar geoengineering has occurred in the Global North, despite the fact that climate change disproportionally affects the Global South. This needs to change, she argued. “Often when we talk about solar geoengineering, we focus on outcomes, but the critical question to me is how we make decisions and who gets to be involved,” she said.

Mann agreed. He also raised another reason why we need to put more effort into creating better governance on the issue: Rogue actors might deploy the technology without prior agreement from others. For this reason, we should set up international agreements sooner than later, he said. But Weisberg was more skeptical. He supported creating more governance when it came to debating solar geoengineering, but he argued it might be hard to avoid rogue action if things get really dire. This is partly why we need to do more real-world research on the subject, he said, so we have a better idea of what to expect in these kinds of cases.

At the end of the event, an audience member raised the worry that even considering the use of solar geoengineering could give polluters an excuse to continue with business-as-usual. This so-called ‘moral hazard’ argument against the technology might have been the issue where the panelists disagreed the most. Weisberg and Talati argued that, at present, this isn’t a worry, given the risks of the technology. The moral hazard argument might be more applicable to carbon recapture technology, which aims to suck carbon out of the air, than to solar geoengineering, they agreed. But Mann, who has experienced first-hand how low fossil fuel companies can stoop to avoid losing profits, was less optimistic.

Another audience member also crucially asked – Can we even stabilize warming at 1.5 or 2°C without the use of solar geoengineering? Weisberg explained that you could answer that question in two ways: from a scientific perspective and from a political perspective. Scientifically, we could, in theory, avoid 1.5 or 2°C without the use of solar geoengineering, he said “If we hit 50 percent reduction in greenhouse gas emissions by the end of the decade and net zero by 2050, 1.5°C is possible according to the laws of physics and chemistry,” Weisberg explained.

It should come as no surprise that the answer to the question is more complicated from a political perspective. If all countries met their nationally determined contributions to reducing emissions under the Paris Agreement, which would be conditional on money flowing from the Global North to South, we’d be in the mid 2°C range, Weisberg explained. “If you add to that all the other pledges that everybody’s made, both private and public, you can squint and see around 2°C,” he said.

As a sober reminder, Talati pointed out that even if we hit net zero by 2050, we’re still going to experience increasing impacts of climate change, so the “political nature of solar geoengineering will likely shift” with those shifts in climate, she said. “A 1.5°C world is not a safe world,” Weisberg agreed, with Mann chiming in, “1.2°C, which is where we are now, is not a safe world either.” This is why other geoengineering technologies, such as carbon recapture, will have to be part of the climate policy arsenal. But as already noted, this technology also comes with risks.

“Philosophers like to talk about the distance of possible worlds to the current one,” Weisberg said. The world in which we never have to use solar geoengineering because mitigation succeeds “is a possible world, and it’s not so far away, but we’re not there yet.”