Environmental Engineering Reference
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FIGURE 4.24 Estimates of the net mass budget of the Greenland 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, purple is aircraft/
satellite laser altimetry, red is the flux component method, and blue is satellite gravity.
of the mass balance of the Greenland ice sheet that have been made since
the early 1990s. 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 dif-
ferent methods that were used: black is satellite radar altimetry, orange is
aircraft laser altimetry, purple is aircraft/satellite laser altimetry, red is the
flux component method, and blue is satellite gravity. The dashed green box
represents the estimated Greenland balance of the IPCC AR4 assessment.
These data indicate that mass loss from the Greenland ice sheet may be in-
creasing, although it is also clear that the various estimates are frequently not
in agreement. Greenland lost roughly 150 Gt y -1 since 2000, increasing to
180±50 Gt y -1 (0.5±0.14 mm y -1 SLR) for the time period 2003-2007. More
than 50% of the current ice loss is caused by increase in ice discharge and
ocean interaction of tidewater glaciers, the remaining part can be explained
by the increase in surface melt due to warmer summer temperatures (Hanna
et al., 2008). The interior of the ice sheet is expected to be less vulnerable
to future changes than the edge regions. Current discharge rates may repre-
sent a transient instability, and whether they will increase or decrease in the
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