Summary of climate variations - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 205

Figure 7.1. Copy of Figure 4.10 for Vostok ice core data showing the spacing between rapid
terminations in millions of years.
by the closure of the Isthmus of Panama. It is not clear whether this event is tied to
the advent of subsequent ice ages. It may well be that additional moisture was
provided to higher northern latitudes, allowing ice sheets to build up in the north
when other factors dictated glaciation should advance. The ''other factors'' are
widely believed to be variable solar input to higher latitudes. This is discussed in
Chapters 9 and 10.
As Figure 5.6 shows, the climate of the Earth became unstable and subject to
cycles with the advent of glaciation. Initially (until about 1 mybp ) the oscillations
were rapid (period 40,000 years) and of moderate amplitude. In the past million
years, the oscillation period gradually increased to about 100,000 years and the
amplitude increased significantly.
The past 800,000 years Over the past 800,000 years, the Earth has undergone
approximately eight major cycles of glaciation and deglaciation spaced at roughly
100,000-year intervals. These cycles are shown in Figures 4.10 , 4.12 , 5.1 , 5.2 , 5.4 , 5.5 ,
5.7 , and 5.8 . The trend has been for long slow accumulation of ice in northern ice
sheets while the Earth cooled, followed by rather sudden warming back to inter-
glacial conditions and a warm hiatus for several thousand years before a new cooling
trend began. During each cooling period, which may have lasted 50,000 to 100,000
years, there were frequent significant short-term violent fluctuations in the climate.
As Figure 7.1 shows, the spacing between cycles has been increasing over the
past 800,000 years by roughly 5,000 years per cycle (with some non-uniformities).
Oscillation amplitudes increased significantly over that period.
The most recent ice age and its aftermath The most recent ice age and its
aftermath are recorded in the Greenland ice cores ( Figure 4.7 ). This figure shows
the end of the penultimate ice age with a warming trend starting around 145 kybp ,
leading to the so-called Eemian interglacial from about 135 to about 115 kybp ,
followed by a buildup of ice sheets in the last ice age from about 115 to about
20 kybp . This ice age was permeated by numerous very sharp but short-lived