July 30, 2008

Canadian Ice Shelf In Pieces

Eight square miles worth of giant ice sheets broke off an ice shelf in the Canadian Arctic last week, and scientists said on Tuesday that global warming could be to blame.

Experts say temperatures in large parts of the Arctic have increased far faster than the global average in recent decades.

In one of the northernmost parts of Canada, the ice broke away from the shelf on Ward Hunt Island, which is a small island just off giant Ellesmere Island.

It was the largest fracture of its kind since 2005, when 25 miles of the nearby Ayles ice shelf broke away.

Scientists had already found deep divisions in the Ward Hunt shelf, which measures around 155 square miles. The shelf is one of five along Ellesmere Island in the northern Arctic.

Trudy Wohlleben of the Canadian Ice Service said, "Because the break-off occurred between two large parallel cracks they're thinking more could go this summer before the freeze sets in."

Asked to be more specific, she speculated, "More could be a piece as large as the Ayles ice shelf."

In the past, Ellesmere Island was home to an enormous ice shelf totaling around 3,500 square miles.

Now, all that's left of that shelf are five much smaller shelves that in total cover fewer than 400 square miles.

Warwick Vincent, director of the Centre for Northern Studies at Laval University in Quebec, said much of the remaining Ward Hunt ice shelf is now in a vulnerable state.

"It underscores the fact that each year we're now crossing new thresholds in environmental change in the High Arctic, and of course our concern in the longer term is that these may signal the onset of serious change at all latitudes, much further to the south, for example," he said.

Wohlleben said, "The break-off is consistent with other changes we've seen in the area, such as the reduction in the amount of sea ice, the retreat of the glaciers and the break-up of other ice shelves."

She said the shelf could have fallen away because of a strong wind from the south.

Derek Mueller, an Arctic ice shelf specialist at Trent University in Ontario, said he was worried about the fast moving changes in the High Arctic over the last few years.

"It's a bit of a wake-up call for those people who aren't yet affected by climate change that there are places on earth that are, and the same could be true for them if you fast-forward a decade or two or three," he said.

Mueller first though 1.5 square miles of ice had broken off the shelf. However, upon a closer look at the data, he increased that figure to eight square miles.

"Whatever has kept this ice shelf in balance for 3,000 years is no longer keeping it in balance," he said.

Wohlleben said the ice shelves contained unique ecosystems that had yet to be studied; she believed they would not be replaced because they took so long to form.

"Once they've broken off they're gone," she said.


Image Caption: A 2006 satellite image of the Ward Hunt ice shelf in the Canadian Arctic. Giant sheets of ice totaling almost eight square miles broke off the ice shelf last week and more could follow later this year, scientists said on Tuesday. (Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC)