When Mount Pinatubo erupted in the Philippines in June 1991, it delivered the second-largest volcanic explosion of the 20th century. Beyond localized devastation, the volcano blasted approximately 20 million tons of sulfur dioxide gas into the stratosphere, reaching altitudes over 20 miles high. In the upper atmosphere, sulfur dioxide reacted with water vapor to form tiny aerosol droplets of sulfuric acid.
This stratospheric haze acted as a planet-wide mirror, bouncing roughly 10 percent of incoming solar radiation back into space. Within months, global surface temperatures dropped by about 0. 5 degrees Celsius (0.
9 degrees Fahrenheit). This temporary cooling effect effectively reversed multi-decade global warming trends between 1992 and 1993 until the heavy aerosol particles settled out of the atmosphere. The event provided scientists with a massive real-world experiment that validated climate computer models and inspired modern solar radiation management geoengineering proposals.