The astronomical theory and data compared - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 297

Figure 10.14. Relative peak solar input to 65 N and 65 S showing the two time periods during
which both solar inputs increase simultaneously (see arrows).
was concluded that it is ''an open question'' as to whether deglaciation is initiated
in the north or the south.
Stott et al. (2007) utilized a high-resolution chronology of surface-dwelling
planktic formanifera and bottom-dwelling benthic formanifera in a tropical loca-
tion to establish the relative timing of high-latitude vs. low-latitude climatic
change at glacial terminations. They found that the onset of deglacial warming
throughout the Southern Hemisphere occurred long before deglacial warming
began in the tropical surface ocean. In a second paper (Timmermann et al., 2009)
this group carried out modeling that suggested the likely cause of initiation of
deglaciation after 20 kybp was the increase in southern insolation coupled with
the sea ice-albedo feedback as the sea ice went into retreat. As the CO 2 concentra-
tion rose, this presumably added another warming feedback. They also showed
that each of the last four major ice age terminations were associated with increases
in solar input to the far SH. Solar input to the far SH during the austral spring
period when the ice pack is at a maximum may be a major factor in initiating
deglaciation. As before, however, this may be a necessary condition but might not
be sucient.
Toggweiler and Lea (2010) distinguished between millennial-scale temperature
variability (over thousands of years) and long-term records over hundreds of
thousands of years. They claimed that long-term temperatures are controlled by
CO 2 levels:
''Hence, it is natural to assume that the CO 2 -temperature relationship in the
long records from Antarctica is causal, i.e., that the increases in atmospheric CO 2
warmed Antarctica and the rest of the planet.''