Reuters: The incredibly rapid rate at which Canada’s Arctic ice shelves are disappearing is an early indicator of the "very substantial changes" that global warming will impose on all mankind, a top scientist said on Wednesday. Researchers announced late on Tuesday that the five ice shelves along Ellesmere Island in the Far North, which are more than 4,000 years old, had shrunk by 23 percent this summer alone. The largest shelf is disintegrating and one of the smaller shelves, covering …