Geoscience Reference
In-Depth Information
probably amount to between 30% and 40%
of the total global sea level rise of around
3.2 mm (0.13 inches) per year. The rela-
tive importance of the contribution of ice
sheets to sea level rise is expected to rise
significantly in this century.
In 2010 a joint team of United States and
Dutch researchers headed up by D. B. Dias
concluded that previous measurements of
ice loss from Antarctica and Greenland had
overestimated the rate of ice loss, which
was only half of current estimates. Accord-
ing to these authors, the rebound, or up-
ward movement, of the land surface due to
the loss of glacial ice weight was incorrectly
accounted for in previous measurements.
The authors admit that more field evidence
is needed to substantiate their results.
If all the ice on Greenland melted tomor-
row, sea levels would rise twenty feet or
so. Estimates of the sea level rise potential
of melt water from the West Antarctic Ice
Sheet range from 3.7 to 5.2 meters (12 to
17 feet). If all three ice sheets melted com-
pletely, sea level would rise by 67 meters
(220 feet). Obviously, if this were to hap-
pen coastal cities around the world would
be destroyed. In any case these cities are
potentially in serious trouble, even with
very much smaller sea level rises.
warming of the atmosphere, but the melt-
ing of the West Antarctic Ice Sheet is more
complex, and its future melt water contri-
bution to the sea is not necessarily directly
related to global warming. The rate of melt-
ing of all of the ice sheets is accelerating.
The rate of flow from the Greenland Ice
Sheet is controlled first and foremost by the
slope of the land and friction at the base
of the ice mass. The release of water to the
sea occurs as individual glaciers calve into
ocean waters and as the surface and base
of the glacier melt. During the summer the
surface melt waters form shallow ponds
and streams of water that plunge spectacu-
larly through cylindrical moulins that lead
through the glacier to its floor, lubricating
the base of the glacier and speeding its sea-
ward flow.
The complexity of the melting of Antarc-
tica's ice sheets and the continent's status
as the coldest place on Earth make it diffi-
cult to predict its contribution to the future
of sea level rise. The same mechanisms at
work on the Greenland glaciers also work
here, but there are important additional
factors. Many of the individual Antarctic
glaciers that make up the margins of the
ice sheet are grounded on the continental
shelf, sometimes butting up against is-
lands or other topographic irregularities.
As a glacier thins from melting or retreats
from calving into the sea, it may become
detached from the shelf, causing a sudden
acceleration of the ice flow into the sea.
Other Antarctic glaciers are buttressed
up against ice shelves along the seaward
how the Ice Sheets Work
The Greenland and Antarctic ice sheets are
quite different. The Greenland Ice Sheet
melts more or less in proportion to the
