A controversial tactic against climate change

Cloud image by Pahz via Flickr. CC BY-NC-SA 2.0

A scientist studying solar geoengineering hopes for a broad public conversation on the controversial option for slowing global warming.

David Keith has a tool for fighting climate change, and a big challenge: convincing the rest of the world to use it. Speaking to science writers gathered in State College, Pa. on Oct. 28, Keith, a professor of applied physics and public policy at Harvard University, said he understands why some are apprehensive about his approach.

“This topic is controversial,” Keith said, “and it should be.”

Keith spoke during the annual New Horizons in Science briefing presented by the Council for the Advancement of Science Writing as part of ScienceWriters2019.

Most conversation about fighting climate change focuses on managing greenhouse gases in the atmosphere, by reducing the production and emission of carbon and trapping excess carbon. Keith works on solar geoengineering, also known as solar radiation management. His research looks skyward, developing methods to reflect a portion of the sunlight constantly radiating toward Earth and prevent it from heating the planet.

“Solar geoengineering is the idea that humans might deliberately alter the Earth’s radiative forcing — the Earth’s energy balance — to reduce some of the risks of accumulated long-lived greenhouse gases,” he said.

One proposed method would create atmospheric aerosols that would act as artificial clouds, forming a barrier between the sun and Earth. Aerosols are produced naturally during volcanic eruptions, which spray huge amounts of sulfur-containing particles into the atmosphere, forming thick clouds that block sunlight.

Although solar geoengineering is backed by scientifically sound theory, Keith was careful to emphasize that it is not a solution by itself.

“I think that it’s, in fact, naive to imagine there is a ‘one magic bullet’ solution to climate,” Keith said.

Solar geoengineering is meant to be complementary, he said, and used along with other practices including decarbonization (reducing carbon production) and carbon removal (trapping carbon already present). Each technology, he said, offers a partial climate solution. Decarbonization alone will not reduce the effects of climate change, only prevent them from becoming more intense. Similarly, carbon reduction will decrease climate risks, but the planet will still experience massive environmental ramifications before it starts to see improvement. Keith argued that a combination of all three might lead to a smoother reduction in climate effects with less severe outcomes than otherwise.

An apprehensive community

Solar geoengineering appears to work in computer simulations. Using climate models, Keith has shown that its implementation could lead to less extreme precipitation, more uniform water availability, less intense tropical cyclones, and less extreme temperatures. But while the results produced by models show promise, he said, they should be interpreted with care. They “[do] not mean that we know enough to say, ‘we should go ahead and do solar geoengineering.’ I think we absolutely do not,” Keith said. “But it is, in a sense, a reason to take this seriously.”

Solar geoengineering requires more research to understand if and how it might be an effective tool. However, Keith said, concerns about its potential implementation are slowing the research. Possible health risks of spraying aerosols in the atmosphere are still being evaluated. In addition, solar geoengineering has the potential to be misused on an international scale.

All the models showing positive benefits of solar geoengineering assume a balanced distribution of effort across the planet, Keith said. Only a planetary-scale implementation produces a broad, global improvement in climate effects. If solar geoengineering is used in just one hemisphere, the results are “terrible” for the other half of the planet, Keith said. Given the uneven effects of partial implementation, some worry about possible weaponization of the technology. Such concerns are among the reasons organizations including the Climate Action Network have come out in opposition to large-scale research on solar geoengineering.

A more philosophical issue is that of “moral hazard,” a term applied to the debate by Keith himself in the 1990s. Critics worry that even the idea of solar geoengineering as a potential method of fighting climate change will split the hard-earned political capital of the environmental movement. Keith blames this anxiety in part for slowing research on solar geoengineering.

“The underlying concern has been the legitimate fear that even talk about these technologies, let alone deployment, would be used by forces that want to block emissions cuts,” said Keith.

To Keith, overcoming this fear is one of the major hurdles to having a real conversation about solar geoengineering. He thinks that the first step is to emphasize solar geoengineering as only one part of a larger solution involving emission cuts. This approach may even help convince people to adopt more active approaches, he argued, pointing to studies where German citizens were more likely to give money to offset carbon emissions if they were informed about solar geoengineering. However, he was doubtful that politicians and policymakers would be as easily swayed as the layperson.

Convincing the world

The global logistics involved in planning and carrying out a climate change mitigation strategy involving solar geoengineering would require navigating complex geopolitical relations and building a foundation of global trust. Neither of these is easy, Keith said.

But there must be a starting point. Who should be first to start researching large-scale solar geoengineering? Because “cost is not a big barrier to implementation,” there could be “profound consequences,” said Keith. A single country conducting solar engineering alone could lead to other nations experiencing even stronger effects of climate change, without their knowledge or consent.

International coordination is therefore essential, said Keith. He envisioned a future in which the United Nations would facilitate relationships between countries committed to transparency and noncommercialization of new technology, as well as encourage foundational research and discourage active deployment of solar geoengineering before it is better understood. Since the technology is relatively inexpensive, even countries in the developing world could spearhead the initial research, allowing them to lead the cultural charge.

Such plans rely on the immediate reduction of carbon emissions and the implementation of active carbon removal methods that would work in conjunction with solar geoengineering. If those efforts started now, Keith estimates that solar geoengineering technology would need to be deployed within the next 10 to 20 years in order to be effective.

Achieving such a timeline would require not only a massive, concerted effort into solar geoengineering research, but also clearer evidence that the technology would actually work in the real world. If Keith’s conviction is any measure, scientists are ready to investigate; only the political will power appears lacking.

“There is no scientific right answer,” Keith said. “This is a social choice.”

Charlie Crowe is a PhD candidate at Pennsylvania State University, where he studies phase-separated emulsions as artificial cells. He is also the co-editor-in-chief of Chembites and tweets about SciComm, grad school, and exciting chemistry developments at @CharlesDCrowe. Charlie wrote this story as a participant in the ComSciCon-SciWri workshop at ScienceWriters2019.