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The Cryosphere
Learning Objectives
After reading this chapter, students should be able to:
• Understand the importance of the cryosphere to the climate system.
• Understand how ice forms on land and in the ocean.
• Know how glaciers and sea ice move and understand what controls ice dynamics.
• Recognize that an understanding of the cryosphere will be important later in the text for
understand projected patterns of greenhouse warming.
Review Questions
1.) How does a snow cover affect overlying air temperature?
2.) How does the snow cover affect soil temperature?
3.) How do snow crystals form?
Snow forms as ice crystals in clouds. In the same way that water droplets form
around cloud condensation nuclei (Chapter 4), small ice crystals also form around
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4.) What is permafrost?
5.) Why might melting permafrost be important for future climate change?
Melting permafrost results in lakes and water-logged soil with anaerobic (low
oxygen levels) conditions that create an environment in which methane producing
6.) Explain how snow is transformed into glacier ice.
If snow cover persists through the summer and starts to accumulate over time, the
snow cover increases in thickness, but also undergoes various transformations.
Temperature gradients in the snow pack, together with differences in the size and
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7.) Explain how glaciers move.
Most of us are familiar with small blocks of ice—ice cubes that you put in drinks.
That ice is brittle; when it is stressed (if you hit it with something hard) it will
8.) Explain the difference between the way glaciers and sea ice accumulate ice.
Glaciers accumulate ice through snowfall on the glacier surface in the
9.) What role do ocean currents play in the distribution of sea ice?
The asymmetric nature of the ice margin in the Arctic Ocean reflects the influence
of the continental configurations and the ocean circulation: the ice margin extends
10.) What are the two primary ways sea ice affects climate?
The ice cover modifies the atmospheric and oceanic temperatures and
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Critical Thinking Problems
1.) The first decade of the 21st century has been characterized by significant
reductions in the extent of summertime Arctic sea ice. Given what you know of
ice-climate interactions and what you learned about the climate system in chapter
4, explain what effect you think continued decreases in North Atlantic ice cover
may have for European climate.
In summer, the ice margin moves northward as does the polar front zone. The
result is that low pressure systems track toward the north and the open ocean
allows evaporation. The result is relatively mild conditions and rainfall in
northern Europe (see Figure 4-26 in the main text). Increasing the amount of
summer time open water around the margins of the Arctic Ocean could enhance
this present pattern, possibly reducing rainfall over southern Europe and
increasing it in Scandinavia and the coastal margins of Siberia if low pressure
systems track further north into the Arctic Basin. The impact would be even more
noticeable if we were to have a significant decrease in wintertime ice extent, with
a corresponding movement north of the polar front zone in this region.
Using the density for ice (that you can find in the text) and assuming an ice
thickness of 130 m and a surface slope of 5o, calculate the basal shear stress under
the glacier. The number you obtain is a typical value for a glacier. If the surface
slope changes, the thickness of the ice will change. Assuming that the basal shear
stress remains the same, how thick will the ice be if the slope increased to 10°?
What does this tell you about the relationship between surface slope and glacier
thickness?.
If we use 900 kg m-3 as the density of the ice, then the shear stress (
τ
) in Pascals
(Pa) is given by the density x gravity (g = 9.8m sec-1) x the ice thickness in
meters (h) x sin of the slope (
α
):
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