Did an Ancient Volcano Freeze Earth?

One fine day about 74,000 years ago, a giant volcano on Sumatra blew its top. The volcano, named Toba, may have ejected 1000 times more rock and other material than Mount St. Helens in Washington state did in 1980. In the process, it cooled the climate by at least 10°C, causing a global famine. But could the aftermath have been even worse? A new study puts to rest questions about whether Toba plunged Earth into a 1000-year deep freeze and whether an equivalent event today could jump-start a new, millennia-long ice age.

Giant volcanic eruptions such as Toba briefly cause the opposite of global warming. Although eruptions do emit greenhouse gases such as carbon dioxide, volcanoes also spew sulfur dioxide. Combined with water vapor, sulfur dioxide forms sulfate aerosols, which can spread around the globe, blocking solar radiation and chilling the air before becoming acid rain and snow.

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