Summary of climate variations - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 208

that previously brought heat to northern latitudes via ocean circulation. At the
end of the Younger Dryas, both the warming and the drop in dust content appear
to have occurred over a period of a few decades. Broecker (2002) cited evidence
that these climate changes, detected in Greenland ice cores, were reflected in
climate changes worldwide, except that temperature records from Antarctica do
not follow the Greenland pattern.
North-south synchrony The relationship between climate variations in the NH
and the SH can be elucidated by comparing the chronologies of the Greenland and
Antarctic ice cores. This requires an accurate means of putting both ice core records
on a common chronological basis. It is not necessary that the chronologies be exact
on an absolute basis—only that the two chronologies must be accurately matched.
The preferred means for doing this is to compare CH 4 time series in the Greenland
and Antarctic ice cores. The results are shown in Figures 4.15 and 4.16 . There
appears to be a correlation between major climate changes in Greenland and
Antarctica. Sudden temperature increases in Greenland were preceded by rather
slow moderate temperature increases in Antarctica for a few thousand years. Each
sudden rise in Greenland occurs near the end of a more protracted rise in Antarctica.
If there is a causal relationship between these events, it seems likely to involve the
thermohaline flow of the oceans.
Carbon dioxide and methane The patterns of CO 2 and CH 4 concentration vs.
time are similar to those of temperature vs. time with the concentrations of
greenhouse gases rising with rising global temperature and vice versa. In particular,
CO 2 seems to vary from about 180-190 ppm at the height of glaciation to about
280-290 ppm during interglacial periods. The CO 2 vs. time curve lags the tempera-
ture vs. time curve by about 1,000 years. These changes cannot simply be explained
in terms of changing solubility in the oceans with temperature. Evidently, the process
is far more complex.