bo’s 1991 eruption pumped volcanic gases high into the atmosphere. The gases interacted with water vapor to form a reflective shade of aerosol particles (top graph) that stretched far beyond the Philippines, where the volcano is located. The global average temperature dipped half a degree Celsius until the particles (sulfates) cleared a few years later. Scientists test and refine global climate models by comparing model predictions of temperature change after events like the eruption to actual observations (bottom graph). When models reliably match observations, scientists gain confidence that the models accurately represent Earth’s climate system