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How did the 1991 eruption of Mount Pinatubo inspire stratospheric sulfur injection proposals?

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Illustration of various geoengineering techniques to address climate change, including carbon capture and storage methods like artificial trees, industrial scrubbers, and deep ocean CO2 storage, as well as solar reflectance strategies such as sulfur aerosols, reflective crops, cloud whitening, and orbital mirrors. The scene shows these interventions applied to land, sea, and atmosphere, with labeled features explaining each process. — Geoengineering Various geoengineering proposals designed to increase solar reflectance or capture and store carbon.

The 1991 eruption of Mount Pinatubo is widely cited as the primary inspiration for stratospheric sulfur injection proposals because it demonstrated the cooling potential of volcanic aerosols on a global scale.12

During the eruption, approximately 17 million tons of sulfur dioxide (SO₂) were injected into the stratosphere. These gases formed an aerosol layer of sulfate droplets that circled the globe, effectively scattering incoming solar radiation and preventing it from reaching the troposphere. This natural event resulted in a measurable cooling of Earth’s average surface temperature by approximately 0.4–0.5 °C (0.7–0.9 °F) for several years.314

Proponents of geoengineering suggest that humans could intentionally mimic this process to mitigate global warming. By using cannons, balloons, or aircraft to disperse sulfur particles into the stratosphere, scientists theorize that we could create an artificial aerosol layer to increase the planet's solar reflectance and lower global temperatures.12