Volcanologists and climatologists are watching the impending eruption of Mount Agung in Bali closely to see how soon it might erupt and how strong the eruption might be. Agung last erupted in 1963 and caused several years of below-normal weather following the strong eruption. The most recent large tropical volcanic explosion was Mount Pinatubo in the Philippines in 1991.

Climatologists are concerned because strong volcanic eruptions, particularly those in equatorial regions, can lead to cooler conditions (and spectacular sunsets) for several years following the eruption. The cause: reflection of sunlight back to space from small sulfuric acid droplets that are lofted high into the atmosphere. These drops, which act like the reflective glass beads in stop signs, reduce the amount of solar radiation that reaches the earth’s surface, effectively cooling it off until the droplets fall out over time. Known eruptions with climate effects include Mount Pinatubo in 1991 and Mount Tambora in 1815 (“The year without a summer”). If Agung erupts, climatologists will be watching closely to see if this new eruption will put out enough sulfuric acid droplets to cause impacts on climate. You can read more about the effects of volcanoes on climate at https://earthobservatory.nasa.gov/Features/Volcano/ or for a  more detailed and scientific look, at https://climate.envsci.rutgers.edu/pdf/ROG2000.pdf.