Previous studies have suggested that Indonesia's Toba supervolcano, when it erupted about 74,000 years ago, triggered a 1,000-year episode of ice sheet advance, and also may have produced a short-lived 'volcanic winter,' which drastically reduced the human population at the time. Previous climate model simulations of the eruption have been unable to produce the glaciation, and there are no climate observations to support the volcanic winter.
     To investigate additional mechanisms that may have enhanced and extended the effects of the Toba eruption, as well as the volcanic winter, Robock et al. conduct six climate model simulations using state-of-the-art models that include vegetation death effects on radiation budgets, and stratospheric chemistry feedbacks that might affect the lifetime of the volcanic cloud. The authors use a wide variety of aerosol injection volumes, ranging from 33 to 900 times that of the 1991 Mount Pinatubo injection. They find that none of the models initiate glaciation. Nonetheless, they produce a decade of severe volcanic winter, which would likely have had devastating consequences for humanity and global ecosystems, supporting the idea that the Toba eruption produced a genetic bottleneck in human evolution.

Source: ScienceDaily (6 July 2009)