Geoscience Reference
In-Depth Information
Figure 12 uses a simple ice sheet model to show how the GIS might
jump from a large to a small ice sheet. 15 This fi gure shows two sets of
lines. The solid upper line shows the equilibrium volume of the sheet for
different global temperatures, starting from today's temperature and ice
sheet. You can follow the upper arrows to see the sequence of warming.
If the world warms 1 degree, the GIS shrinks about 2 percent; at 2°C
the shrinkage is 4 percent; up to 5°C, where the shrinkage is about 15
percent. When the globe warms just a little beyond the 5°C threshold,
the unstable dynamics of warming, lowering of elevations, darkening,
and melting enter a downward spiral, so that at 6°C the ice sheet melts
completely. In other words, at a certain point, the equilibrium jumps
down the steep slope to a new and drastically smaller size. If the jump
occurs quickly, it might lead to several feet of sea-level rise in a short
time.
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Global temperature change (°C)
Figure 12. Illustration of a tipping point for the Greenland Ice Sheet. This fi gure shows a
calculation from the GRANTISM model of the response of the Greenland Ice Sheet to
different temperatures.
 
 
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