Canada's ice shelves suffered massive erosion over the summer, losing almost one-quarter of their area, researchers have found.

The ice shelves on the north coast of Ellesmere lost 214 square kilometres over the summer, or an area three times larger than Manhattan Island, said a group of researchers from Ontario, Quebec and the United States on Tuesday.

The entire Markham ice shelf broke away in early August and is now adrift in the Arctic Ocean, carving away 50 square kilometres. Two large sections of the Serson ice shelf also broke off, shrinking it by 122 square kilometres or about 60 per cent. The Ward Hunt ice shelf lost 22 square kilometres.

"These substantial calving events underscore the rapidity of changes taking place in the Arctic,” said Dr. Derek Mueller, who has been studying the shelves at Trent University, in a statement. “These changes are irreversible under the present climate and indicate that the environmental conditions that have kept these ice shelves in balance for thousands of years are no longer present.”

Unusually high air temperatures were the main cause of the cracking, the researchers said, and the disintegration trend is likely to continue. Canada's most northerly national park, Quttinirpaaq, is therefore likely to lose its last remaining ice shelf as the largest one remaining, Ward Hunt, continues to crack up.

The disintegration will have an effect on local ecosystems, the researchers said. The Serson ice shelf, for example, had been damming a large freshwater lake, which is now threatened.

"The extent of their loss this season is significant," said Dr. Warwick Vincent, director of Laval University's Centre for Northern Studies, who collaborated on the study. "Unique ecosystems that depend on this ice are on the brink of extinction.”

The Ellesmere ice shelves are made up of ancient sea ice and snow and are up to 4,500 years old. Scientists have measured them to be about 40 metres thick.

More than 90 per cent of Canada's ice shelves have been lost over the past century, with most melting during a warm period in the 1930s and 1940s.

Temperatures are higher now than they were then, researchers said, which had led to accelerated breakup since 2002.