six additional climate model simulations with two different climate models, . . . in two different versions, to investigate additional mechanisms that may have enhanced and extended the forcing and response from such a large supervolcanic eruption.
While "none of the runs initiates glaciation" and, in all cases, their simulations revealed that "the climate recovers over a few decades", nevertheless,
A second study, conducted by Stanley Ambrose and Martin Williams, was recently (Nov. 2009) reported in Science News:
the “volcanic winter” following a supervolcano eruption of the size of Toba today would have devastating consequences for humanity and global ecosystems. These simulations support the theory that the Toba eruption indeed may have contributed to a genetic bottleneck. (my emphasis)
Ambrose and his colleagues pursued two lines of research: They analyzed pollen from a marine core in the Bay of Bengal that included a layer of ash from the Toba eruption, and they looked at carbon isotope ratios in fossil soil carbonates taken from directly above and below the Toba ash in three locations in central India.The investigators concluded that there was
"incontrovertible evidence" that the volcanic super-eruption of Toba on the island of Sumatra about 73,000 years ago deforested much of central India, some 3,000 miles from the epicenter . . . The bright ash reflected sunlight off the landscape, and volcanic sulfur aerosols impeded solar radiation for six years, initiating an "Instant Ice Age" that -- according to evidence in ice cores taken in Greenland -- lasted about 1,800 years.When we combine such reports of Toba-induced devastation with Petraglia's findings, strongly suggesting the presence of modern humans in South Asia at the time, the possibility of major population bottlenecks downwind from the volcano seems strong indeed. While stone artifacts were found both above and below the Toba ash, indicating that at least some humans survived (I'm wondering, though, whether these items may have leeched to the surface while the ash was molten), we can assume that any survivors would have been struggling very hard in an environment radically different from the one that first greeted them. And while the presence of the artifacts suggests that they survived the immediate effects of the disaster, this does not mean they were able to survive its long-term effects.
As both the archaeological and genetic evidence suggests, much of the Indian subcontinent, especially the east coast, directly in the path of the volcanic plume, could have been depopulated, only to be repopulated at a later time from the East, as Oppenheimer suggests, by people who would also have been affected by the disaster, but to a lesser extent. It is these Toba survivors who would most likely have experienced severe population loss, resulting in bottlenecks, both genetic and cultural. Populations even farther to the east and southeast, and also farther to the north (assuming there were any at that time) would also have suffered, but to a much lesser extent, and would thus show fewer signs of genetic, morphological and cultural change. This does indeed seem to be the case, though the situation is obscured by the considerable movement of various peoples into and out of this region for many thousands of years since.
It's possibly for this reason that "some of the best, if not the only archaeological evidence for dating the beachcomber's trek along the coast of the Indian Ocean, comes not from India, South Arabia, or Africa, but from the later parts of the trail -- the Malay Peninsula, New Guinea, and Australia" (The Real Eve, 159), those areas least affected by the volcanic fallout.