Antarctic Glaciers
In Retreat
By AFP
23 April, 2005
Agence France Presse
Scientists have issued a fresh warning
about the effect of climate change on Antarctica, saying that more than
200 coastal glaciers are in retreat because of higher temperatures.
Of the 244 marine
glaciers that drain inland ice on the Antarctic peninsula, a region
previously identified as vulnerable to global warming, 87 percent have
fallen back over the last half century, according to research by British
experts.
Using 2,000 aerial
photos dating back to the late 1940s and 100 satellite pictures, experts
from the British Antarctic Survey (BAS) compiled a record of glacier-ice
shelves and tidewater glaciers along the peninsula -- the tongue of
land that juts 800 kilometers (500 miles) northwards out of continental
Antarctica.
Glacier-ice shelves
are floating glaciers on the shoreline that are still connected to the
land glaciers from which they flowed.
Tidewater glaciers
rest on rock and break off into the ocean when they reach the water's
edge.
Over the last half
century, during which time regional temperatures have risen by around
2 C (3.6 F), these glacier fronts have reversed direction, the authors
note in a study published on Friday in the US weekly journal Science.
Until the mid-1950s,
most of the glaciers advanced. For the next decade after that, they
were roughly stable. Since then, though, most have been shrinking.
In the past five
years, the retreat has accelerated, and the pattern of retreat is widening.
It started in the warmer northern tip of the peninsula and is heading
progressively to the colder south as atmospheric temperatures rise.
"Fifty years
ago, 62 percent of the glaciers that flowed down from the mountains
to the sea we looked at were slowly growing in length, but since then
this pattern has reversed," said lead author Alison Cook.
The average retreat
of the 212 shrinking glaciers has been 600 metres (yards) over 50 years.
But this does not
take into account a dramatic acceleration in recent years, exposing
numerous islands that were once ice-smothered.
Sjogren Glacier,
at the northern tip of the peninsula has fallen back eight kilometers
(8.5 miles) since 1993, while Widdowson Glacier, on the west coast of
the peninsula, has been retreated at 1.1 kms (0.6 miles) per year over
the past five year.
As for the cause,
the BAS team caution against a leap to judgement.
At present, it is
unclear that the man-made "greenhouse effect" -- the burning
of fossil fuels which disgorged carbon dioxide into the atmosphere,
trapping solar heat -- is entirely to blame, they say.
They note that over
the past 50 years, a minority (32) of glaciers has grown, by an average
of 300 metres (yards), and that key data on local ocean temperatures
and circulation remain scarce.
Antarctica's geology
is split into three main regions: East Antarctica, which comprises the
bulk of the continent; West Antarctica, which has two huge ice shelves
on either side; and the Antarctic Peninsula, which juts out of West
Antarctica.
Previous research
had already identified the peninsula as a vulnerable "hot spot"
for global warming, although the reasons for this are debatable.
In February, BAS
researcher Chris Rapley presented evidence that ice flows into the Southern
Ocean from three big inland glaciers were accelerating, spurred by the
loss of the vital shelves of floating glacial ice at the coast.
Like a cork released
from a bottle, the lost shelves let the icy river flow swiftly into
the sea, causing sea levels to rise by some 1.8 mm (0.07 inches) per
year.
The new study repeats
that warning, although without giving figures. It says the erosion of
floating glacier ice could spur glacier flow from inland and "make
a substantial contribution" to rising sea levels.
Antarctica, the
fifth largest continent in the world, contains more than 90 percent
of the world's ice, most of it above sea level.
If even a small
part of this cap melts, rising sea levels could drown low-lying island
states, cities and deltas.
Copyright ©
2005 Agence France Presse