Can solar geoengineering save the world?

The concept of solar geoengineering—blocking the sun’s radiation to slow Earth’s warming—is no longer just the realm of science fiction. In 2023, the U.S. government and the UN released reports on the topic. Whether or not solar geoengineering can save the world is up for debate, and Tony Harding, an assistant professor in the School of Public Policy, is contributing to the conversation.

Harding is an alumnus of the School of Economics and returned to Georgia Tech after a postdoc at Harvard University. He studies the impact of innovative technology on climate change policy and governance, focusing on solar geoengineering. In the eight years he’s been researching it, Harding said it’s the scale of the conversation that’s changed the most: not what the researchers are speaking about, but who they’re speaking to.

“A lot of people in the climate policy and academic realms were hesitant to talk about solar geoengineering, and I think that’s starting to change,” Harding said. “There’s definitely wider acceptance of at least talking about it, and in that way, pathways to having spaces to talk about it and research funds are opening up.”

As the idea of solar geoengineering picks up steam, Harding invites everyone to join the conversation, starting with learning about what it is, how it works, and whether or not this once-niche proposition really can save the world.

What is solar geoengineering?

The most commonly proposed method of solar geoengineering, which also goes by names such as solar radiation modification or climate intervention, uses sulfate aerosols. When injected into the Earth’s stratosphere, they reflect a small amount of the sun’s radiation—less than 1%—and reduce Earth’s surface temperature.

This option is the most popular, and the one Harding studies, because we have natural examples, he explained. Volcanoes release sulfates when they erupt, and the largest ones are strong enough to push them into the stratosphere.

“So we have evidence from the past that if sulfate aerosols make it up to the stratosphere, there’s a cooling effect,” he said. “This natural analog gives us a bit more belief that it’s going to work at least in some of the ways we expect it to in the real world and not just on a computer.”

The other two types of solar geoengineering researchers consider most seriously are marine cloud brightening to reflect incoming sunlight and Cirrus cloud thinning to let light escape more easily. Each one has pros and cons. For example, marine cloud brightening would only occur over the deepest and darkest parts of the ocean, Harding said, “which would have a non-uniform cooling effect and could lead to certain adverse outcomes.”

Stratospheric aerosol injection has a more uniform distribution and cooling effect that better mimics the warming we’re experiencing. However, it comes with its own concerns, one of which is that the cooling isn’t permanent.

“If something happened to stop the deployment of the aerosols, whether it was for political or technological reasons, we would bounce right back and experience a rapid heating that we’ve never experienced before, and could have catastrophic impacts,” Harding said.

What are the costs and benefits of solar geoengineering?

This question is where Harding’s research makes the most impact. As an economist, he examines the costs and benefits of solar geoengineering to highlight the tradeoffs involved. Harding has published articles on how solar geoengineering could impact other climate change mitigation policies, how it affects income inequality, and the value of reducing uncertainty around solar geoengineering.