The permanent Arctic sea ice that is home to the world's polar bears and usually survives the summer has all but disappeared, a Canadian researcher said Friday.
University of Manitoba Arctic researcher David Barber said experts around the world believed the ice was recovering because satellite images showed it expanding, but the thick, multiyear frozen sheets have been replaced by thin ice that cannot support the weight of a polar bear.
"Polar bears are being restricted to a small fringe of where this multiyear sea ice is. As we went further and further north, we saw less and less polar bears because this ice wasn't even strong enough for the polar bears to stand on," said Barber, who just returned from an expedition to the Beaufort Sea.
The deterioration has far-reaching consequences for the North and its iconic mammal. Polar bears that rely on the permanent ice to survive the summer have fewer and fewer places of refuge, Barber said.
Scientists also said Friday that shrinking Arctic sea ice may be forcing some hungry polar bears to cannibalize bear cubs.
At least seven cases of mature male polar bears eating bear cubs have been spotted this year among the animals around Churchill, Manitoba, said Ian Stirling, a retired Environment Canada biologist who specializes in the Churchill bears.
Stirling said evidence suggests the cubs are being killed for food, not just so the male can mate with the sow.
He said the Hudson Bay sea ice, which the bears use to hunt the seals they consume to fatten up for winter, isn't appearing until weeks later than it used to.
Barber said permanent ice, which is normally up to 10 meters (30 feet) thick, was easily pierced by the research ship.
The team finally reached what it thought was stable ice, only to watch a crack appear just as researchers were preparing to descend onto the floe.
"As I watched, over the course of five minutes, the entire multiyear ice floe broke up into pieces. This floe was 10 miles across," said Barber, who holds the Canada research chair in Arctic science at the University of Manitoba. Ten miles equal about 16 kilometers.
The ice is unable to withstand battering waves and storms because global warming is rapidly melting it at a rate of 70,000 square kilometers (27,000 square miles) each year, he said.
Multiyear sea ice used to cover 90 percent of the Arctic basin, Barber said. It now covers roughly 19 percent. Where it used to be up to 10 meters (33 feet) thick, it's now 2 meters (6 feet) at most.
The findings, which are soon to be published in the journal Geophysical Research Letters, come as a shock to experts worldwide. Although northern sea ice hit a record low in 2007, researchers believed it was recovering because of what they were seeing on satellite images.
But the satellites the experts relied on were misleading because the rotten ice looked sturdy on the surface and has a similar superficial temperature, Barber explained.
"The satellites give us only part of the story. The multiyear ice is disappearing and it's almost all gone now from the northern hemisphere."
The lack of sea ice may be good news to some who want to see the North opened to industry. Without thick ice blocking the way, ships can more easily gain access to the Arctic's natural resources.
"We were doing almost the same speed we'd do in open water through what we thought was multiyear sea ice," Barber said. "Transportation and all the issues of navigation across the pole all become very real when you no longer have any multiyear sea ice."
(This version CORRECTS ADDS other researcher's reports on polar bears. corrects metric conversion, graf 12. For global distribution.)