Geoscience Reference
In-Depth Information
Note that the physical processes determining water vapor concentrations
in the atmosphere have nothing to do with the ability of air to “hold” water.
This characterization of the dependence of the saturation vapor pressure on
temperature is misleading.
2.4 THE CRYOSPHERE
From the Greek word
kryos
, meaning cold,
cryosphere
refers to the frozen
parts of the climate system and includes sea ice, freshwater ice, ice shelves, ice-
bergs, snow, glaciers, frozen ground, and permafrost. About 11% of the plan-
etary surface is covered by permanent ice, and about 14% of the land surface
has permanently frozen soil.
Table 2.2
provides an estimate of how frozen water is distributed within
the earth system. The vast majority of the ice is sequestered on land in
glaciers
,
which form in regions where the winter's snowfall does not melt completely
over the summer. The minimum defined area for a glacier is 0.1 km
2
. Ice in
glaciers flows from an
accumulation area
, where the ice mass is increasing
by snowfall, to an
ablation area
, where ice mass is being lost by melting or
calving.
Ice sheets
are large areas of glacial ice, covering 50,000 km
2
or more,
formed over thousands of years. There are two ice sheets in today's climate,
covering Antarctica and Greenland. Together, they contain more than 99%
of the earth's fresh water. The Antarctic ice sheet is, by far, the largest mass of
ice on the planet. Rates of snowfall onto the Antarctic continent are quite low
(~150 mm/yr), so the buildup of ice is a millennial time scale process. (Note
Table 2.2 Estimates of the distribution of snow and ice in the earth system
Mass
(10
15
kg)
Area
(10
6
km
2
)
Flux
(10
15
kg/yr)
Residence
time (yr)
Ice type
Antarctic
ice sheet
26,400
12.0
2.2
12,000
Greenland
ice sheet
2,660
1.7
0.54
5,000
Glacial ice
Smaller
glaciers
150
0.64
0.67
200
Ground ice
~4,000
21
~6
~700
Sea ice
35
26
33
1
Seasonal snow
10.5
72
~25
~0.4
Icebergs
7.6
64
2
4
Ice in the atmosphere
1.7
510
390
0.004
