Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 42

Figure 2.10. Smoothed data from the Vostok ice core. The dust and solar scales are arbitrary.
The solar curve represents midsummer solar intensity at 65 N (adapted from C&L).
sensitivity by comparing the LGM with pre-industrial times. They asserted: ''One
of the uncertainties in the radiative forcing calculation during the LGM to the
Holocene transition is the radiative forcing due to increased aerosol optical depth
during the peak of the last ice age.'' In their analysis they used the LGM to pre-
industrial transition and the cooling period between the warm period around
42,000 ybp and the LGM to deduce the change in aerosol radiative forcing and to
estimate climate sensitivity. It was assumed that climate sensitivity was the same
for both periods.
Chylek and Lohmann (2008) (C&L) utilized data from the Vostok ice core for
transitions between two time periods:
(i) Warm period around 42,000 years ago ) LGM (about 20,000 years ago)
(ii) LGM ) pre-industrial period (about 200 years ago).
The smoothed data from the Vostok ice core used by C&L are shown in
Figure 2.10 .
Based on these data, C&L estimated temperature differences and forcing due
to greenhouse gases as shown in Table 2.1 .
The radiative forcing due to surface albedo changes (extent of ice sheets, sea
ice and snow cover, exposure of new land in a low sea level state, change in
surface characteristics and vegetation cover) for the LGM ) pre-industrial transi-
tion was estimated to be roughly 3.5W/m 2 , but C&L used a range of values from
3.0 to 4.0W/m 2 .
C&L pointed out that the dust measurements in the Vostok ice core suggested
that aerosol concentration differences from 42 kybp to the LGM were about 53/58
as great as aerosol differences from pre-industrial time to the LGM. However,