Which Volcanic Eruption Most Recently Affected Global Climate?

Mount Pinatubo erupted on 15 June 1991 in the Philippines, injecting about 20 million tonnes of sulfur dioxide into the stratosphere. The SO2 converted to sulfate aerosols that reflected sunlight, lowering global average temperatures by about 0.5 degrees Celsius for approximately two years. It was the second-largest eruption of the 20th century (after Novarupta/Katmai, 1912). The Hunga Tonga eruption on 15 January 2022 was the most powerful volcanic explosion recorded by modern instruments (generating a pressure wave that circled the Earth multiple times and a tsunami), but it injected an unusual amount of water vapour rather than SO2, which actually contributed to slight warming rather than cooling. For historical comparison, the 1815 Tambora eruption (Indonesia) caused the "Year Without a Summer" in 1816, with crop failures across the Northern Hemisphere. Scientists monitor volcanic activity closely because a future large eruption could temporarily mask (or reset) global warming trends.