[10] The ignimbrite phase is characterized by low eruption fountain,[11] but co-ignimbrite column developed on top of pyroclastic flows reached a height of 32 km (20 mi).

[19] The outflow sheet originally covered an area of 20,000–30,000 km2 (7,700–11,600 sq mi) with thickness nearly 100 m (330 ft), likely reaching into the Indian Ocean and the Straits of Malacca.

Greenland stadial 20 (GS20) is a millennium-long cold event in the north Atlantic ocean that started around the time of Toba eruption.

[28][29] It is the stadial part of Dansgaard–Oeschger event 20 (DO20), commonly explained by an abrupt reduction in the strength of the Atlantic meridional overturning circulation (AMOC).

[38] Northern Hemisphere ice sheets embarked on significant expansion and surpassed the extent of the Last Glacial Maximum in eastern Europe, Northeast Asia and the North American Cordillera.

South China Sea marine records of climate, sampled at every centennial interval, shows 1 °C (1.8 °F) cooling above the Toba ash layer for a thousand years but the authors concede that it may just be GS20.

[49] Environmental records from a Middle Stone Age site in Ethiopia, however, shows that a severe drought occurred concurrently with the Toba ash layer, which altered early human foraging behaviours.

[15] The modeled climate effects of the Toba eruption hinges on the mass of sulfurous gases and aerosol microphysical processes.

Modeling on an emission of 8.5×1014 g of sulfur, which is 100 times the 1991 Pinatubo sulphur, volcanic winter has a maximum global mean cooling of 3.5 °C (6.3 °F) and returns gradually within the range of natural variability 5 years after the eruption.

[55] The Toba catastrophe theory holds that the eruption caused a severe global volcanic winter of six to ten years and contributed to a 1,000-year-long cooling episode, resulting in a genetic bottleneck in humans.

[63][64] Subsequent research on the differences in human mitochondrial DNA sequences dated a rapid growth from a small effective population size of 1,000 to 10,000, sometime between 35 and 65 kyr ago.

[65][66][67] In 1993, science journalist Ann Gibbons posited that population growth was suppressed by the cold climate of the last Pleistocene Ice Age, possibly exacerbated by the Toba super-eruption which at the time was dated to between 73 and 75 kyr near the beginning of glacial period MIS 4.

[70] In 1998, anthropologist Stanley H. Ambrose of the University of Illinois Urbana-Champaign hypothesized that the Toba eruption caused a human population crash to only a few thousand surviving individuals, and the subsequent recovery was suppressed by the global glacial condition of MIS 4 until the climate eventually transitioned to the warmer condition of MIS 3 about 60,000 years ago, during which rapid human population expansion occurred.

[56] At least two other Homo lineages, H. neanderthalensis and Denisovans, survived the Toba eruption and subsequent MIS 4 ice age, as their latest presence is dated to ca.

Recent analyses apply Markov models to the complete set of genetic material to infer human population history.

As a small group with a size of a few thousand people migrated from the African continent into the Near East, the drastic reduction in numbers imprinted on non-African genomic diversity.

This event of closely timed selections is named the "Arabian Standstill" and may have been caused by the severe cold arid conditions from the onset of MIS 4 and exacerbated by the Toba super-eruption.

[77][78][89] This 1 million year old bottleneck is thought to have been caused by severe ice age MIS 22 which marked the mid-Pleistocene climate transition with widespread aridity across Africa.

This age gap is suspected to be due to the removal of post-eruption sediments or decimation of the local population until re-occupation at 55 kyr.