Volcanoes and the Little Ice Age

We wrote in SuperFreakonomics about how past volcanic eruptions have resulted in a temporarily cooler planet, thanks to the release of sulfuric ash into the atmosphere. New research indicates that a series of volcanic eruptions may have caused the Little Ice Age:

The study, led by the University of Colorado Boulder with co-authors at the National Center for Atmospheric Research (NCAR) and other organizations, suggests that an unusual, 50-year-long episode of four massive tropical volcanic eruptions triggered the Little Ice Age between 1275 and 1300 A.D. The persistence of cold summers following the eruptions is best explained by a subsequent expansion of sea ice and a related weakening of Atlantic currents, according to computer simulations conducted for the study.

According to Bette Otto-Bliesner, one of the study’s co-authors, the volcanic eruptions may have “triggered a chain reaction”:

The model showed that sustained cooling from volcanoes would have sent some of the expanding Arctic sea ice down along the eastern coast of Greenland until it eventually melted in the North Atlantic. Since sea ice contains almost no salt, when it melted the surface water became less dense, preventing it from mixing with deeper North Atlantic water. This weakened heat transport back to the Arctic and created a self-sustaining feedback on the sea ice long after the effects of the volcanic aerosols subsided, according to the simulations.

(HT: Naked Capitalism)