Volcanoes produce ash and prodigious amounts of sulfur dioxide, a colorless gas with a pungent odor. Sulfur dioxide interacts with air to produce sulfate aerosols. Volcanoes can launch sulfates high into the stratosphere, where they can persist for years. Global temperature fell by half a degree when just one volcano—Mount Pinatubo—erupted in 1991 and produced large amounts of light-reflecting sulfates, which act like a mirror over Earth, reflecting radiation away from the surface.
Image Information: Astronauts snapped this image of Mount Etna, a volcano in Sicily, erupting in 2002. For more details, please visit this Gateway to Astronaut Photography page. Credit: NASA/Johnson Space Flight Center/Image Science & Analysis Laboratory
--Adam Voiland, Goddard Space Flight Center