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Even though this summer's ice melt hasn't approached last year's record conditions, the once-frozen Northwest Passage through Canada's Arctic is expected to open again soon, for only the second time in recorded history.

Already, a shallower, more southern route has freed up, according to high-resolution sea ice charts extracted from satellite microwave imagery by German researchers at the University of Bremen's Institute of Environmental Physics.

The more traditional Northwest Passage route, further north, is still clogged but it could be ice-free later this month, said Mark Serreze, a senior researcher at the University of Colorado's National Snow and Ice Data Center.

"Our view is that it may well open in the next few weeks," he said in an interview yesterday.

Ice remains from west of Cornwallis Island in Nunavut to east of Banks Island in the Northwest Territories, he said. "There is only a fairly small plug in there right now and it's showing signs it's melting away."

Beyond questions of trade, ship navigation and Arctic sovereignty raised by the repeated unlocking of the fabled waterway, Dr. Serreze said, the phenomenon is further proof that humankind might witness an ice-free Arctic Ocean within decades, with resulting unpredictable weather patterns.

"It really is just one more indication how quickly we're losing the sea ice cover. ... The sea ice cover is in a downward spiral, it's essentially in a death spiral right now."

The polar ice cap is now so thin that, even though this summer has been somewhat cooler than the previous one, large portions will disappear. "It really almost doesn't matter any more. We know we'll get a big loss of ice this year simply because we have so much thin ice," Dr. Serreze said.

Scientists are still unclear how the disappearance of the Arctic ice will influence weather elsewhere in the world. Some studies show that the western part of North America will suffer extended drought. Others suggest there will be changes to storm tracks and precipitation patterns over Western Europe.

"It's the sort of thing that we're just starting to get a handle on. It's a new area of research because we weren't thinking we would lose sea ice this quickly. Compared to what our climate models said, we're 20, 30 years ahead of schedule in terms of ice loss. This kind of caught us by surprise and the researchers are just starting to catch up."