Overview of the various models for ice ages in the recent past (3 MYBP to present) - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 222

albedo would reflect more of the incoming solar radiation, further amplifying the
cooling. Depending on the strength and duration, this process could lead to an
episode of relatively cold climate over the North Atlantic region, perhaps lasting
from a few years up to decades. But if it were su ciently strong and durable, it
could set the stage for the global climate to return to full glacial conditions.''
8.6.2 Sudden climate change: the consensus view
In Section 4.6 we showed that the Earth's climate is subject to rapid extreme
climate change, particularly during glacial periods. In the aftermath of a glacial
period, when the great ice sheets are breaking up, abrupt climate changes also
take place. In addition, there is some evidence that rapid climate changes may
have occurred during the previous (Eemian) interglacial period. Many studies
have focused on these rapid gyrations in the Earth's climate, and the literature in
this field is extensive. Two important review articles provide overviews of this
work (Adams et al., 1999; Alley, 2007). This section relies heavily on these articles
and the classic book by Broecker (2002).
Two impressive aspects of abrupt climate change are (1) they can occur in
short time periods (centuries to decades) and (2) the changes in temperature can
be a significant fraction of the long-term secular change in temperature observed
in the 70,000-year evolution of an ice age. The impact of such violent climate
changes on primitive humans was undoubtedly significant.
Various mechanisms—involving changes in ocean circulation and biotic
productivity, changes in atmospheric concentrations of greenhouse gases and haze
particles, and changes in snow and ice cover—have been proposed to explain
sudden climate change. Some changes such as the Younger Dryas and Heinrich
events might only occur during glacial periods when large ice sheets and more
extensive sea ice cover are prevalent.
Adams et al. (1999) discussed several sources of evidence that significant rapid
climate changes occurred during the previous (Eemian) interglacial period. They
concluded:
''The combined sources of evidence suggest that there was a cold and dry
event near the middle of the Eemian, at about 122 kybp , which was characterized
by a change in circulation of the North Atlantic, a several-degree decline in the
Nordic seas and Atlantic sea-surface temperatures, and an opening up of the west
European forests to a mixture of steppe and trees.''
As the most recent ice age settled in over the past 100,000 years, numerous
sudden climate changes took place (as shown in Figure 4.26 and discussed in
Section 4.6).
In the mid-1980s, Wally Broecker developed a concept that the Earth's climate
may have two or more stable modes and may shift almost discontinuously
between them. Broecker (2002) emphasized that the concentrations of continental
dust and sea salt in Greenland ice were more than an order of magnitude higher