What is Stratospheric Aerosol Injection (SAI)?

Climate Reflections: The SRM360 Podcast

On June 15th, 1991, the densely populated island of Luzon in the Philippines awoke to an explosion that would turn out to be the second largest volcanic eruption of the 20th century. Mount Pinatubo had erupted, releasing a huge cloud of volcanic ash, hundreds of kilometers across and 40 kilometers high. As satellites tracked the ash cloud spread around the globe several times over, atmospheric scientists noted that over the next year, the Earth's global temperature had decreased by as much as half a degree Celsius. The eruption had added around 17 million tons of sulfur dioxide into the stratosphere, a layer of the atmosphere between 10 and 50 kilometers above the surface. And this sulfur had gone on to form countless tiny aerosol particles. In the lower atmosphere, these particles would have been washed out in days, but because the stratosphere is dry and stable, these particles lasted for several years, reflecting light, and cooling the Earth.

Could the climate cooling effect of this eruption be replicated as a way to help tackle climate change? In this episode, we focus on the basics of the sunlight reflection method known as Stratospheric Aerosol Injection, or SAI, an SRM idea that looks like it could offer a practical means of halting or even reversing global warming within a few years. What is SAI? What would it take to cool the planet? And who could do it?
Featuring Dr. Daniele Visioni, an Assistant Professor of Earth and Atmospheric Sciences at Cornell University and Dr. Joshua Horton, a Senior Program Fellow at the John F. Kennedy School of Government at Harvard University.

Climate Reflections is a production of SRM360, a non-profit knowledge hub supporting an informed, evidence-based discussion of sunlight reflection methods. For more information and the latest research on SRM, visit SRM360.org.
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