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Retour a la fonte des glaciers :Ice shelves melting



      INTERNET POUR INTERNET
Home      Changements climatiques      Ice shelves melting
 Retour a la fonte des glaciers :Ice shelves melting

 
On pense que les méfaits du changement climatique sont loin de notre génération. GRAVE ERREUR! Lisez cette étude anglosaxonne.
 
 
 

 

 

Ancient ice shelf breaks free in Canadian Arctic

 

Breakaway may 'signal the onset of accelerated change,'
researchers say

IMAGE: BREAKUP OF AYLES ICE SHELF
 
 
NASA via AP
 
This NASA satellite image shows the Ayles Ice Shelf collapse, center and below the open water, on Aug. 13, 2005. Within days of breaking free and becoming an island, Ayles drifted about 30 miles before freezing into the sea ice seen here along top of photo.
 
 

 
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updated 7:40 p.m. ET Dec. 29, 2006

 

 

TORONTO - A giant ice shelf has snapped free from an island
south of the North Pole, scientists said Thursday, citing
climate
change as a “major” reason for the event.

 

 

The Ayles Ice Shelf — about the size of Manhattan — broke
clear
16 months ago from the coast of Ellesmere Island, about 500
miles
south of the North Pole in the Canadian Arctic.

 

 

Scientists discovered the event by using satellite imagery.
Within
one hour of breaking free, the shelf had formed as a new ice
island,
leaving a trail of icy boulders floating in its wake.




 
 
 
 

 

 

 

Warwick Vincent of Laval University, who studies Arctic
conditions, traveled to the newly formed ice island and
couldn’t believe what he saw.

 

 

“This is a dramatic and disturbing event. It shows that we
are losing remarkable features of the Canadian North that
have been in place for many thousands of years,” Vincent
said.
“We are crossing climate thresholds, and these may signal
the onset of accelerated change ahead.”

 

 

The ice shelf was one of six major shelves remaining in
Canada’s Arctic. They are packed with ancient ice that is
more than 3,000 years old. They float on the sea but are
connected to land.

 

 

'Consistent with climate change'
Some scientists say it is the largest event of its kind in
Canada in nearly 30 years and that climate change was a
major element.

 

 

“It is consistent with climate change,” Vincent said, adding
that the remaining ice shelves are 90 percent smaller than
when they were first discovered in 1906. “We aren’t able to
connect all of the dots ... but unusually warm temperatures
definitely played a major role.”

 
 




Laurie Weir, who monitors ice conditions for the Canadian Ice Service, was poring over satellite images in 2005 when she noticed that the shelf had split and separated.

 

 

Weir notified Luke Copland, head of the new global ice lab at the University of Ottawa, who initiated an effort to find out what happened.

 

 

Using U.S. and Canadian satellite images, as well as seismic data — the event registered on earthquake monitors 155 miles away — Copland discovered that the ice shelf collapsed in the early afternoon of Aug. 13, 2005.

 

 

Copland said the speed with which climate change has
affected the ice shelves
has surprised scientists.

 

 

“Even 10 years ago scientists assumed that when global
warming changes occur that it would happen
gradually so that perhaps we expected these ice shelves
just to melt away quite slowly,” he said.

 

 

Instead, satellite images showed the 9-mile long crack,
then the ice floating about a half mile from the coast within
about an hour, Copland said.

 

 

“You could stand at one edge and not see the other side,
and for something that large to move that quickly is quite
amazing,” he said.

 

 

Copland said the break was likely due to a combination of
low accumulations of sea ice around the mass’s edges as
high winds blew it away, as well as one of the Arctic's
warmest  temperatures on record. The region was 5.4
degrees
F above average in the summer of 2005, he said.

 

 

Ice shelves in Canada’s far north have decreased in size
by as much as 90 percent since 1906, and global warming
likely played a role in the Ayles break, Copland said.

 

 

“It’s hard to tie one event to climate change, but when you
look at the longer-term trend, the bigger picture, we’ve lost
a lot of ice shelves on northern Ellesmere in the past
century and this is that continuing,” he said. “And this is
the biggest one in the last 25 years.” 

 

 

Shipping hazard possible
Derek Mueller, a polar researcher with Vincent’s team,
said the ice shelves get weaker and weaker as temperatures
rise. He visited Ellesmere Island in 2002 and noticed that
another ice shelf had cracked in half.

IMAGE: ISLAND THAT USED TO BE AYLES ICE SHELF
 
 
 
Warwick Vincent / Laval University file
 
 
Part of what was the Ayles Ice Shelf is surveyed last summer by Denis Sarrazin, a researcher with the Center for Northern Studies at Laval University in Quebec City, Canada. Sarrazin and other researchers visited what is now an island as part of an expedition within a program called ArcticNet.
 

“We’re losing
our ice shelves
and this a
feature of the
landscape that
is in danger of
disappearing
altogether from
Canada,” Mueller
said.

 

 












Within days of breaking free, the Ayles Ice Shelf
drifted about 30 miles offshore before freezing into
the sea ice. A spring thaw may bring another concern:
that warm temperatures will release the new ice
island from its Arctic grip, making it an enormous
hazard for ships.

 

 

“Over the next few years this ice island could drift
into populated shipping routes,” Weir said.

 
 
 
 
 
 
 
 
 
 
 
   


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