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 214

Figure 8.1. Direct and diffuse solar irradiance measured at Mauna Loa following volcanic
eruptions at a solar zenith angle of 60 corresponding to the passage of sunlight through the
two Earth air masses (adapted from Robock, 2000).
in diffuse irradiance is roughly 70% of the decrease in direct irradiance, producing
a maximum deficit in TSI of about 40W/m 2 for both El Chicho´ n and Pinatubo.
This produces global cooling. Although the Pinatubo eruption's input to the
stratosphere was greater, the center of the El Chicho´ n cloud passed directly over
Hawaii, while only the side of the Pinatubo cloud was observed there (Rapp,
2008).
The reduction in net TSI (and surface temperature) produced by a major
eruption is huge and produces a very strong reduction in solar forcing. If the
reduction in TSI (and surface temperature) observed during the first year after an
eruption persisted for many years, the Earth would almost certainly enter an ice
age. Fortunately, the heat capacity of the Earth is great enough that the reduction
in global temperature produced by a Pinatubo-like eruption (VEI ¼ 6) is only
about 0.3 C. However, regional temperature reductions can be greater. The
Tambora eruption of 1815 led to the year without a summer (1816) in the NH.
The greatest known eruption of the past 100,000 years was the Toba eruption
of about 71,000 years ago on the island of Sumatra. While the principal effects of
Pinatubo lasted only about two years, it is probable that the effects of Toba may
have lasted for about six years. Individual large eruptions certainly produce global
or hemispheric cooling for a few years.