Environmental Engineering Reference
In-Depth Information
Melting Ice Sheets, Mountain Ice Caps and Mountain
Glaciers
Ice sheets: There are two major ice sheet systems in the world. The largest covers most of
Antarctica (about 14 million square kilometres) and contains 30 million cubic kilometres
of freshwater ice. This amounts to 61% of all the freshwater on Earth. The second is the
Greenland ice sheet, which contains about 2.93 million cubic kilometres of freshwater ice.
According to the NSIDC, a complete meltdown from the Greenland and the Antarctic ice
sheets would produce a total global sea level rise of about 6 metres (20 feet) and 60 metres
(200 feet), respectively. Given our knowledge of GHGs and global warming, should we be
worried about the stability of these ice sheets?
Yes, we definitely should be worried. As this section will show, the Arctic reservoirs
of ice are melting. The 2005 ACIA and the 2011 SWIPA reports include two integrative as-
sessments of the state of knowledge of the Greenland ice sheet and of the 402,000 square
kilometres of mountain glaciers and mountain ice caps that exist in the Arctic. They are well
worth a careful study because like all AMAP products, they provide a peer-reviewed syn-
thesis of an enormous amount of the published scientific literature.
The Greenland ice sheet is a massive accumulation of ice mainly resting on bedrock.
Snow accumulates at higher altitudes, where it is gradually compressed into ice by the
weight of subsequent snowfalls. On the flanks, an altitude is reached - known as the equilib-
rium line altitude (ELA) - at which the rates of ice accumulation and loss are roughly equal.
Below the altitude of the equilibrium line is the ablation zone, which experiences a net loss
of ice. The puzzle in answering our question as to the fate of the Greenland ice sheet is re-
lated to the balance between the rate at which new ice is being added (by the compression of
new snow) relative to the rate at which ice is lost. This is known as the total mass balance . It
tells us whether the ice sheet is in equilibrium, is growing or is receding. A simplified sum-
mary of the ice dynamics of the Greenland and Antarctic ice sheets is shown in Figure 10.8 .
Search WWH ::




Custom Search