When did the 1991 eruption of Mount Pinatubo occur?

Mount Pinatubo in the Philippines erupted catastrophically on 15 June 1991 after months of unrest and warning signs. It was one of the largest eruptions of the 20th century and injected vast amounts of sulfur dioxide into the stratosphere. That aerosol cloud cooled global average temperatures for about 1 to 2 years by a few tenths of a degree Celsius. Because scientists helped forecast the eruption, it became a landmark case in successful volcanic hazard mitigation.