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the long residence time for ice in Antarctica listed in Table 2.2 .) The mass of
the Greenland ice sheet is about one order of magnitude smaller than that of
the Antarctic ice sheet.
More than 67,000 smaller glaciers are spread throughout the world, includ-
ing the tropics high in the Andes Mountains and on African topography. Kili-
manjaro Glacier, for example, is located only 3° of latitude from the equator in
East Africa. Glaciers exhibit significant change on decadal time scales and lon-
ger. A glacier's mass balance is the difference between its accumulation and ab-
lation rates. A positive mass balance indicates a growing glacier, and a negative
mass balance indicates glacial retreat. With only a few exceptions, the world's
smaller glaciers are currently in retreat as the climate warms ( Fig. 2.33) .
Glaciers are invaluable recorders of climate. As the fallen snow compresses
and turns into ice, air bubbles are trapped within the glacier. These air bubbles
are samples of the atmospheric composition at the time of ice formation. Ice
cores from Vostok, in East Antarctica, are drilled to a depth of over 3.5 km and
record 400,000 years of climate history. In the Northern Hemisphere, the lon-
gest cores are drilled in the Greenland ice. The ice at the bottom of these cores,
at more than 3 km depth, formed more than 200,000 years ago.
In addition to providing air samples, ice cores yield information about past
temperature and precipitation through isotopic analyses. Sediment deposited
(a)
(b)
5
-1
0
0
-5
1
-10
2
-15
3
-20
4
Europe
Andes
Arctic
Asian high mountains
NW USA + SW Canada
Alaska + coast mountains
Patagonia
Europe
Andes
Arctic
Asian high mountains
NW USA + SW Canada
Alaska + Coast mountains
Patagonia
-25
5
-30
6
-35
7
1960
1970
1980
1990
2000
1960
1970
1980
1990
2000
Year
Year
Figure 2.33 Mass balance since 1960 for small glaciers around the world. Units “mm
SLE” are the number of millimeters of sea level rise (sea level equivalent) associated
with the mass balance. Adapted from Kaser, G., J. G. Cogley, M. B. Dyurgerov, M. F.
Meier, and A. Ohmura, 2006: Mass balance of glaciers and ice caps: Consensus
estimates for 1961-2004. Geophysical Research Letters 33:L19501.
 
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