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 216

Figure 8.2. Global temperature change after the Toba eruption (smoothed) for various mag-
nitudes times Pinatubo (adapted from Robock et al., 2009).
Using a model that did not include full interactive atmospheric chemistry, they
found that a Toba-size eruption produces a severe impact on global climate with
huge amounts of global cooling (up to 15 C for 300 Pinatubo) and reduced
precipitation (up to 45% reduction). However, these effects only lasted for a
limited time and diminished after about a decade (as shown in Figure 8.2 ).
Irrespective of the amount of SO 2 assumed, there was no evidence for ice age
initiation. Although snow persisted for several summers in the mid-latitudes of the
Northern Hemisphere, it melted as aerosols left the atmosphere and full insolation
returned. When they used a model with full atmospheric chemistry for 300
Pinatubo, they found a larger ( 18 C temperature anomaly) and longer lasting
response (more than 20 years), but still no evidence of ice age initiation. They
then answered the question of whether a Toba-like eruption could produce an ice
age today, and the answer was in the negative. Nevertheless, they pointed out that
a ''volcanic winter following a supervolcano eruption of the size of Toba today
would have devastating consequences for humanity and global ecosystems.''
What Robock et al. did not answer was whether an Earth leaning toward
glaciation might have been driven toward further glaciation by an eruption of
such a large volcano. As they put it:
''Clearly, a volcanic eruption is not required to produce a glaciation, so it is
obvious that if the climate system was poised to cool dramatically anyway, a
slight nudge could have sped it along. With lower CO 2 concentrations, different
solar activity, or even different vegetation patterns producing a different
planetary albedo, the sensitivity of the climate system to massive radiative forcing
might have been higher and maybe more prone to switch.''