Life and climate in an ice age - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 1

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Life and climate in an ice age
What was the global impact of the growth of large ice sheets in the far north
during past ice ages? What were the climates of the various continents 20,000
years ago at the height of the Last Glacial Maximum? Why was there a greater
diversity of species, higher numbers of animals, more large animals, and larger
animals? How did climate changes impact the evolution and migration of humans,
animals, and vegetation? These are questions that have been pondered and studied
by many researchers. Several scenarios have been put forth. However, it is dicult
to draw firm conclusions. All we can do is provide a few fragmentary insights.
1.1 CONTINENTAL CLIMATES DURING THE ICE AGE
As we will show in subsequent chapters, based on geological evidence, and data
from ice cores and ocean sediments, we know that the Earth was immersed in an
ice age over the past 100,000 years that peaked about 20,000 years ago, began to
wane about 15,000 years ago, and ended roughly 10,000 years ago. The immensity
of the ice sheets is dicult to comprehend. The maximum volume of the ice
sheets—about 18,500 years before the present ( ybp )—was about 57 10 6 km 3 .
This huge volume of ice resulted in a lowering of sea level of about 110m (Zweck
and Huybrechts, 2005). 1 Assuming that this ice sheet was built up over 60,000
years, that would imply that ice was added to the ice sheets at the average rate
of about 10 12 m 3 per year. The lowering of sea level exposed large areas of con-
tinental shelves that were (at least initially) barren and susceptible to wind erosion.
Ice core data from Greenland and Antarctica indicate that the atmosphere
was heavily laden with dust and salt during periods of high glaciation, suggesting
1 The removal of water from the oceans was actually about 50m greater than this because the
crust below the ocean rebounded about 50m when water was removed at the LGM.