Two ice shelves that existed before Canada was settled by Europeans diminished significantly this summer, one nearly disappearing altogether, Canadian scientists say in newly published research.The loss is important as a marker of global warming, returning the Canadian Arctic to conditions that date back thousands of years, scientists say.

Floating icebergs that have broken free as a result pose a risk to offshore oil facilities and potentially to shipping lanes. The breaking apart of the ice shelves also reduces the environment that supports microbial life and changes the look of Canada's coastline.

Luke Copland is an associate professor in the geography department at the University of Ottawa who co-authored the research published on Carleton University's website. He said the Serson Ice Shelf shrank from 79.15 square miles (205 square kilometres) to two remnant sections five years ago, and was further diminished this past summer.

Copland said the shelf went from a 16-square-mile (42-square-kilometre) floating glacier tongue to 9.65 square miles (25 square kilometres), and the second section from 13.51 square miles (35 square kilometres) to 2 square miles (7 square kilometres), off Ellesmere Island's northern coastline.

This past summer, Ward Hunt Ice Shelf's central area disintegrated into drifting ice masses, leaving two separate ice shelves measuring 87.65 and 28.75 square miles (227 and 74 square kilometres) respectively, reduced from 131.7 square miles (340 square kilometrrs) the previous year.

"It has dramatically broken apart in two separate areas and there's nothing in between now but water," said Copland.

Copland said those two losses are significant, especially since the Ward Hunt Ice Shelf has always been the biggest, the farthest north and the one scientists thought might have been the most stable.Copland, who uses satellite imagery and who has conducted field work in the Arctic every May for the past five years, said since the end of July, pieces equaling one and a half times the size of Manhattan Island have broken off. Co-researcher Derek Mueller, an assistant professor at Carleton University's geography and environmental studies department, said the loss this past summer equals up to three billion tons. Copland said their findings have not yet been peer reviewed since the research is new.

Scambos said the loss of the Arctic shelves is significant because they are old and their rapid loss underscores the severity of the warming trend scientists see now relative to past fluctuations such as the Medieval Warm Period or the warmer times in the pre-Current Era (B.C.).

Ice shelves, which began forming at least 4,500 years ago, are much thicker than sea ice, which is typically less than a few feet (meters) thick and survives up to several years.Canada has the most extensive ice shelves in the Arctic along the northern coast of Ellesmere Island.

Courtesy: AP