The largest ice shelf in the Arctic -- an 80-foot-thick slab of ice nearly the size of Lake Tahoe -- has broken up, providing more evidence that the Earth's polar regions are responding to ongoing and accelerating rates of climatic change, researchers reported Monday.
The Ward Hunt ice shelf, located 500 miles from the North Pole on the edge of Canada's Ellesmere Island, has broken into two main parts and a series of ice islands. A massive freshwater lake long held back by the ice has drained away.
"Large blocks of ice are moving out. It's really a breakup," said Warwick Vincent, a professor of biology at Laval University in Quebec and co-author of the report, which will be published in an upcoming issue of the journal Geophysical Review Letters. "We'd been measuring incremental changes each year. Suddenly in one year, everything changed."
While far larger shelves of ice have cracked off the edges of Antarctica, this is the largest ice separation in the Arctic, occurring in an area of the eastern Arctic long thought to be more protected against the gradual warming of the planet.
"This type of catastrophic [event] is quite unprecedented," said Martin Jeffries, a professor of geophysics at the University of Alaska Fairbanks and co-author of the report.
Because of their longevity and sensitivity to temperature, ice shelves are considered "sentinels of climate change." In recent years, scientists have seen ice shelves the size of Rhode Island break off of western Antarctica as it warms and have measured glaciers' retreat in response to warmer temperatures throughout the western Arctic.
Weather data recorded at the nearby military station Alert on Ellesmere Island show that temperatures there have been warming since 1967 at the same rate as in western Antarctica: about one degree Fahrenheit per decade. The average July temperature of recent years of 34 degrees was above the temperature -- 32 degrees -- at which ice shelves are known to break up.
The researchers said they considered the weakening of the ice additional evidence of climate change in the high Arctic and said the report fit with studies that show global warming trends are connected to the human production of greenhouse gases. Those trends have been seen first and amplified in the Arctic.
But they said other factors, including ocean circulation and atmospheric patterns that can last for decades, could be contributing to the changes in the ice.
