Two ice shelves in Canada's far north had lost massive sections in the past month, while a third was now adrift in the Arctic Ocean, researchers said yesterday, blaming climate change.

The entire 50sqkm Markham Ice Shelf, off the coast of Ellesmere Island broke away early last month and is now adrift, while two sections of nearby Serson Ice Shelf detached themselves, reducing its mass by 60per cent or 122sqkm.

Ward Hunt Ice Shelf, which halved in size two months ago, has lost an extra 22sqkm.

A polar scientist at Trent University in Peterborough, Ontario, Derek Mueller, said, ''These changes are irreversible under the present climate and indicate that the environmental conditions that have kept these ice shelves in balance for 4000 years are no longer present.''

Canada's ice shelf losses over this northern summer now total 214sqkm almost the size of Manhattan and about 1/11th the size of Canberra and suburbs.

The director of Ottawa University's cryospheric research lab, Luke Copland, said extensive cracks in Ward Hunt, the largest remaining ice shelf, meant it would continue to disintegrate in the coming years.

Professor Copland blamed ''very warm temperatures'' and ''reduced sea ice'' for the crumbling of the ice shelves.

The sea ice usually braced the shelves and, without it, wind and waves broke them apart more easily, he said.

The coast of Ellesmere Island had also warmed by an average of 2degrees in the past 50 years, he said. In winter, temperatures were now 5 degrees warmer, making it more difficult for ice lost in summer to re-form in winter.

''We see that warming is concentrated in the winter,'' Professor Copland said. ''It's part of global warming. When we warm up the planet it gets concentrated close to the poles.

''Usually the ice shelves would use the winter to recover from the previous summer.

''They would reform ... but the ice shelf can't recover in the winter any more.

''We have now reached a threshold where [the environment] is too warm for these ice shelves to exist any more. What it tells us is that the Arctic is changing.''

Dr Mueller, from Trent University, said, ''It underscores the rapidity of the changes, how quickly things are moving along in the Arctic.

''It's not just the ice shelves that are changing: these changes are occurring in concert with sea ice reduction and other indications of climate change.''

AFP