How Major Volcanic Eruptions Can Temporarily Cool Earth

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Large volcanic eruptions can briefly change Earths climate in a surprising way. When a powerful eruption sends sulfur dioxide high into the stratosphere, the gas reacts with the atmosphere and forms tiny sulfate particles. These particles scatter and reflect some incoming sunlight back into space, reducing the amount of solar energy that reaches the surface. The result can be a measurable drop in global surface temperatures for a year or more. The effect is temporary because the particles eventually settle out of the atmosphere. The 1991 eruption of Mount Pinatubo is one of the clearest modern examples. It injected roughly 20 million tons of sulfur dioxide into the stratosphere, and global temperatures fell by about 0.6 degrees Celsius for roughly two years. The impact is not simply a matter of volcanic ash blocking the Sun. Ash usually falls out relatively quickly, while sulfur compounds that reach the stratosphere can remain there much longer. Volcanoes can also release carbon dioxide, which has a warming effect, so the climate response depends on what an eruption puts into the atmosphere and where it reaches. An unusual example came from the 2022 underwater Hunga Tonga eruption, which injected an exceptional amount of water vapor into the stratosphere. That water vapor behaves differently from sulfate aerosols and can contribute to warming, showing why volcanic eruptions do not all produce the same climate response.