Environmental Engineering Reference
In-Depth Information
Figure 1
Ice shelves: (a) Ross ice shelf, Antarctica; (b) major shelf
features in cross-section; (c) possible late Pleistocene ice shelf,
retreating grounding lines (1 and 2) and drumlin fields in the Irish
Sea basin.
limit of the ice shelves polewards. This probably led to the collapse of the Prince
Gustav and parts of the Larsen ice shelves after 1994. The 2001 IPCC assessment
suggests that total Antarctic iceberg production of some 2,612 × 10
12
kg yr
−1
exceeds ice
accumulation of 1,843 × 10
12
kg yr
−1
on the shelves, giving a net loss of 769 × 10
12
kg
yr
−1
(with wide margins of error). The entire Greenland ice sheet may have a net deficit
of 44 × 10
12
kg yr
−1
(although with over 100 per cent margin of error) due to increased
calving and it, too, contains enough ice to raise sea levels by 6-7 m.
Ice shelf sensitivity to sea-level rise is the most alarming scenario of all. Sea level rise
renders shelves prone to accelerated calving, since it moves grounding lines inland and
undermines their pinning effect. A catastrophic shelf collapse could - literally - put the
skids under the ice sheet, leading to its draw-down by surging glaciers and rapid
disintegration. The IPCC assessment is 98 per cent certain there will be no collapse by
2100 and that atmospheric warming of 10° C would be necessary to induce its collapse.
By comparison, the East Antarctic Ice Sheet is far more stable. Twenty degrees' warming
would be needed to change this and the region has not been so warm for over 15 Ma. It is
thought that a smaller scale ice shelf collapse took place in the northern Irish Sea basin
