Ice core data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 165

Figure 4.26. Sudden climate change events at Greenland and Antarctica. Numbered peaks are
D-O events. Heinrich events are shown as h-numbered minima. Warming in Antarctica is
shown as a-numbered events (adapted from Alley, 2007).
beginning of the Younger Dryas seems to have occurred within fewer than 100
years. After about 1,300 years of cold and aridity, the Younger Dryas seems to
have ended in the space of only a few decades when conditions became roughly as
warm as they are today (Adams et al., 1999; Adams, 2002).
The start of the present warm phase (i.e., the Holocene) followed the sudden
ending of the Younger Dryas, about 11,500 years ago (see Figure 4.4 ) . Forests
quickly regained the ground that they had lost to cold and aridity. Ice sheets
again began melting though, because of their size, they took about 2,000 more
years to disappear completely. The Earth entered several thousand years of con-
ditions warmer and moister than today; the Sahara and Arabian Deserts almost
completely disappeared under vegetation cover, and in northern latitudes forests
grew slightly closer to the poles than they do at present. This phase, known as
the ''Holocene Optimum'' occurred between about 9,000 and 5,000 years ago,
although the timing of the warmest and moistest conditions probably varied some-
what between different regions. Other fluctuations during the Holocene have been
reported (Adams, 2002).
A number of sudden climate transitions occurred during the Younger Dryas-
Holocene stepwise change around 11,500 years ago, which seems to have occurred
over a few decades. Of particular note is the event at 8,200 ybp (see Figures 4.3
and 4.4 ) . The speed of these changes is probably representative of similar but
less well-studied climate transitions during the last few hundred thousand years.
These events almost certainly did not take longer than a few centuries. Various