From: Phil Berardelli, ScienceNOW Daily News
Published July 8, 2009 10:12 AM

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, millennium-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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Paleoclimate evidence suggests that the Toba eruption, which occurred during the last ice age, emitted lots of sulfur dioxide--vastly more than Mount St. Helens did. The eruption also seems to have coincided with the start of a 1000-year period of even colder temperatures. Some scientists have suggested that Toba caused the deep freeze and that perhaps such an event happening today could bring on a new ice age. But models developed by NASA and the National Center for Atmospheric Research in Boulder, Colorado, argue otherwise.

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