Environmental Engineering Reference
In-Depth Information
FIGURE 4.25 Estimates of the net mass balance of the Antarctic Ice Sheet since 1992 (Allison et al., 2009b).
The horizontal dimension of the boxes shows the time period for which the estimate was made, and the
vertical dimension shows the upper and lower limits of the estimate. The colors represent the different
methods that were used: black is satellite radar altimetry, orange is aircraft laser altimetry, red is the flux
component method, and blue is satellite gravity.
future is unknown. Currently there is no dynamic ice sheet model that can
predict the response of the Greenland ice sheet for a warmer climate. We
can constrain a possible upper bound of SLR contribution from Greenland
assuming a doubling in ice discharge and a continued increase in surface
melt using the AR4 A1B scenario (Pfeffer et al., 2008). The total contribution
to SLR would be about 0.16 m by 2100, with 0.09 m contribution from ice
dynamics, and 0.07 m from surface melt (Pfeffer et al., 2008).
The Antarctic ice sheet shows a pattern of near balance for East Antarc-
tica and mass loss from West Antarctica and the Antarctic Peninsula since
2003 (Cazenave et al., 2009). However, the uncertainties of these measure-
ments are large (Figure 4.25) and there is no strong evidence for increasing
Antarctic loss over the period shown.
However, there is a region in West Antarctica that shows increasing
ice loss in recent years (Figure 4.25, most of this signal comes from West
Antarctica). The Amundsen Coast Basin, including Pine Island ice and
Thwaites Glacier, is not confined by large ice shelves, and these marine-
based ice masses, which are potentially unstable, contain about 1.5 m
sea level equivalent. The average ice velocity in this region is 2 km y
-1
,
which is considerably higher than the average velocity of all Antarctic ice
streams (0.65 km y
-1
) (Pfeffer et al., 2008). If this ice discharge continues to
increase, SLR contribution from West Antarctica cannot be ignored. Pfeffer
