The astronomical theory and data compared - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 298

In contrast, they argued that millennial-scale variability cannot be attributed
to CO 2 variations and, hence, they posed the question: ''Can two such disparate
views both be correct?'' However, there is no evidence that long-term temperatures
are controlled by CO 2 levels; indeed, there is no possible mechanism to cause the
CO 2 level to independently rise and fall every 100,000 years or so of its own
volition and, thus, create ice ages. So the very thesis of Toggweiler and Lea (2010)
does not make much sense.
Toggweiler and Lea (2010) further asserted:
''A close look shows that Antarctica and the polar north did not warm and
cool at the same times; the two hemispheres became warm together over the
longer cycles but only after the big transitions in Antarctica had already
occurred. Both kinds of transitions, millennial and long term, seem to involve
displacements of heat that allow the south to warm at the expense of the north.''
This assertion, like many others made by Toggweiler and Lea (2010), has little
basis in fact. Toggweiler and Lea (2010) drew the following conclusions:
''The whole Earth did not warm and cool together during the big transitions
of the ice ages. The south warmed, in particular, while the north remained cold.
The north also became very cold toward the ends of the glacial stages long after
the south had reached its glacial minimum. The big transitions took place when a
resurgent precessional cycle produced inputs of melt water to the North Atlantic
that lasted for thousands of years. The melt water inputs suppressed the AMOC,
flattened the temperature contrast between the hemispheres, and produced a
redistribution of heat from north to south that warmed Antarctica and the
Southern Ocean. The same factors caused the level of CO 2 in the atmosphere
to rise along with the temperatures in Antarctica.
Atmospheric CO 2 was important during the ice ages because it varied with
such a long time scale. The long time scale allowed the oceanic CO 2 system and
northern ice sheets to interact in ways that gave rise to large temperature changes
in the Earth's polar regions. The long time scale also allowed the variability in
northern ice volume to enhance the variability in atmospheric CO 2 , and vice
versa. Without the long time scale for CO 2 , the overall level of climate variability
during the ice ages would have been much smaller.''
These claims do not seem to have any experimental basis. Unless Toggweiler
and Lea (2010) have powers of perception beyond those of this writer, they appear
to represent supposition and speculation. As we pointed out in Section 4.3, the
data in Figure 4.16 suggest that during the most recent ice age each sudden
increase in temperature in Greenland was preceded by a rather slow moderate
temperature rise in Antarctica for a few thousand years. This led to a number of
scientists proposing that the connection between these events lies in heat transport
known as the ''bipolar seesaw'' (see Section 4.3) between the south and the north