Arctic Summer Ice Melt Shocks Scientists
Pastor Dale Morgan
Arctic Summer Ice Melt Shocks Scientists*
Paris, France (ESA) Sep 20, 2006
Satellite images acquired from 23 to 25 August 2006 have shown for the
first time dramatic openings - over a geographic extent larger than the
size of the British Isles - in the Arctic's perennial sea ice pack north
of Svalbard, and extending into the Russian Arctic all the way to the
North Pole.
Observing data from Envisat's Advanced Synthetic Aperture Radar (ASAR)
instrument and the AMSR-E instrument aboard the EOS Aqua satellite,
scientists were able to determine that around 5-10 percent of the
Arctic's perennial sea ice, which had survived the summer melt season,
has been fragmented by late summer storms. The area between Spitzbergen,
the North Pole and Severnaya Zemlya is confirmed by AMSR-E to have had
much lower ice concentrations than witnessed during earlier years.
Mark Drinkwater of ESA's Oceans/Ice Unit said: "This situation is unlike
anything observed in previous record low ice seasons. It is highly
imaginable that a ship could have passed from Spitzbergen or Northern
Siberia through what is normally pack ice to reach the North Pole
without difficulty.
"If this anomaly trend continues, the North-East Passage or 'Northern
Sea Route' between Europe and Asia will be open over longer intervals of
time, and it is conceivable we might see attempts at sailing around the
world directly across the summer Arctic Ocean within the next 10-20 years."
During the last 25 years, satellites have been observing the Arctic and
have witnessed reductions in the minimum ice extent - the lowest amount
of ice recorded in the area annually - at the end of summer from around
8 million km in the early 1980s to the historic minimum of less than 5.5
million km in 2005, changes widely viewed as a consequence of greenhouse
warming.
Satellite observations in the past couple of years have also shown that
the extent of perennial ice is rapidly declining, but this strange
condition in late August marks the first time the perennial ice pack
appears to exhibit thinner and more mobile conditions in the European
sector of the Central Arctic than in earlier years.
Both sets of images were taken by two different satellite instruments -
ASAR on the left and AMSR-E on the right. In the coloured AMSR-E images,
ice cover, or the concentration of ice, is represented by the colour.
Pink represents pack ice and the colour blue open water. Intermediate
colours orange, yellow, and green indicate lower ice concentrations of
70%, 50% and 30%, respectively. In the ASAR images, ice cover is
represented by the uniform grey area which extends radially-outwards
from the North Pole, represented by the central black hole.
The set of images on the top were both acquired on 24 August 2005, while
the bottom left ASAR image was acquired on 23 August 2006 and the AMSR-E
on 24 August 2006. In 2005, the uniform grey area in the ASAR image and
the pink colour in the AMSR-E image are both consistent all the way
around the pole (black hole), indicating pack ice with 100% ice
concentration.
However in 2006 there is a significant extent of leads - fractures and
openings in the sea-ice cover - just below the pole in both the ASAR
image, seen as splashes of dark grey and black, and the AMSR-E image
(with British Isles shown for scale), seen by the high concentration of
yellow, orange and green colours, signifying low ice concentrations.
In the last weeks, what was open water has begun to freeze, as the
autumn air temperatures over the Arctic begin to fall. Although a
considerable fraction of darker leads can still be seen in the area
using ASAR, the AMSR-E sensor no longer shows openings.
ASAR is an active microwave instrument which sends periodic radar pulses
toward the Earth and measures the signals return. AMSR-E is a passive
microwave instrument which does not send radar pulses down but receives
radiation naturally emitted from the Earth. Passive microwave data
contain a certain amount of ambiguity in interpretation of ice types,
particularly in mid summer during melting. However, this ambiguity is
removed in high resolution active microwave data.
Though the reason for the considerable change in the ice pack
configuration is still unknown, it is likely due to the stormy weather
conditions in August that characterised the month.
The effect stormy conditions have on ice is illustrated in this ASAR
image, taken on 25 August 2006, as the ice in the red circle is
divergent as a consequence of a low pressure system centred on the North
Pole.
"As autumn freeze-up begins, the current pattern will undoubtedly
precondition the ice situation in the Central Arctic for the subsequent
ice season," Drinkwater said.
ICE WORLD
Arctic Ice Meltdown Continues With Significantly Reduced Winter Ice Cover
Greenbelt MD (SPX) Sep 14, 2006
As far as temperatures drop in the Arctic winter - on average to -34C
(-29F) - a new study shows that in the last two years sea ice is
shrinking on the surface of Arctic waters to record low levels. Using
satellite data, scientists have observed unusually warm wintertime
temperatures in the region and a resulting decline in the length of the
Arctic ice season.
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