Overview of the various models for ice ages in the recent past (3 MYBP to present) - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 215

As Figure 8.1 shows, the Earth typically returns to normal behavior about
three years after a fairly major volcanic eruption. However, Robock (2000) raised
the question whether longer term climate changes could be induced or enhanced
by either (a) the impact of an extremely large volcano (e.g., Toba at VEI 8) or
(b) the cumulative effect of a series of large volcanoes (VEI >

5 to 6) over some
extended time period. Figures 4.6 and 4.7 show that after the Eemian interglacial
from about 135 to 115 kybp , there was a period from 115 to 74 kybp of
meandering Greenland temperature that tended downward, but this 40-year
period lacked the wild oscillations that followed from about 74 to 20 kybp . Two
very high amplitude oscillations occurred around 74 and 70 kybp in which the
Greenland temperature varied by about 20 C in about a millennium. These are
also evident in Figures 4.16 , 5.2 , 5.4 , and 5.5 . The ice core records suggest that
the two wild climatic oscillations from 74,000 to 70,000 ybp provided a pivotal
turning point when the climate went from a mild phase to a full glacial world.
Could the eruption of Toba be implicated in this transition? Burroughs (2005)
discussed this possibility. Toba was the greatest known volcanic eruption in the
past million years. Rampino and Self (1992, 1993) presented model calculations to
investigate the possible climatic effects of the cloud that lofted more than 10 12 kg
of material to heights of over 30 km. We actually know a good deal more about
the Tambora eruption in 1816 than we do about the Toba eruption. Tambora
produced about one fifth as much aerosol material as Toba, and it is estimated
that this led to a decrease of about 0.7 C decrease in average Northern
Hemisphere temperature. Using linear scaling they estimated that volcanic dust
and aerosols from Toba may have produced a hemispheric temperature decrease
of up to 3-5 C for several years, which could have ''accelerated the shift to glacial
conditions that was already underway, by inducing snow cover and increased sea
ice extent at sensitive northern latitudes.'' But the effect of Tambora was amplified
at high northern latitudes. Tree ring data from northern Quebec suggest that mean
summer temperatures after Tambora were lowered by 3.5 C, indicating a fivefold
amplification of NH average temperature decrease. Thus, summer temperature
decreases produced by Toba at high northern latitudes could have been as high as
15 C adjacent to regions already covered by snow and ice. The Toba eruption was
dated by a number of investigators to be 74,000 3,000 ybp . While the effect of an
individual volcano is not long-lasting, it is conceivable that the impact of a very
large volcano or series of

large volcanoes could trigger a nonlinear climate

response.
Robock et al. (2009) revisited the question of whether the Toba eruption
might have contributed to the budding Ice Age 74,000 years ago. They investi-
gated how the Toba eruption may have affected the Earth's climate by using a
climate model. Robock et al. (2009) were not certain how much SO 2 was injected
into the stratosphere so they parameterized this quantity as a multiple of the
known amount emitted by Pinatubo, a much smaller volcano. Pinatubo released
approximately 0.02Gt of SO 2 . Robock et al. (2009) considered the possibility
that Toba emitted 33, 100, 300, and 900 times this amount without interactive
chemistry and 300 times with interactive chemistry.