Just a week after Canada and the U.S. agreed to disagree over the ownership of the Northwest Passage, this summer’s record melt of Arctic sea ice has unlocked the fabled polar shipping route more completely than ever before, the U.S. National Snow and Ice Data Center has announced.

“It’s open,” Mark Serreze, a senior scientist with research institute based in Boulder, Colo., said in an interview Tuesday. “It’s unprecedented. Theoretically you could take a ship from Tokyo through the Northwest Passage to Boston. Not an easy sail, not a Sunday cruise, but it has started to happen.”

Describing the phenomenon as clear proof that global climate change in underway, the centre says on its website that “analysts at the Canadian Ice Service and the U.S. National Ice Center confirm that the passage is almost completely clear and that the region is more open than it has ever been since the advent of routine monitoring in 1972.”

Environment Canada scientist Lionel Hache, a senior forecaster with the Canadian Ice Service in Ottawa, says a navigable route across the country’s Arctic archipelago has opened a few times since 1998. This year, he notes, “you could go through the Northwest Passage with a sailing boat without any problems, without seeing any ice.”

The record melting of the passage comes two weeks after the NSIDC and two other ice-monitoring agencies in the U.S. and Japan declared that the Arctic Ocean ice cover has shrunk to its smallest size since regular satellite imaging of the polar cap began in 1979.

And what particularly concerns scientists is that the thawing of Arctic ice typically continues until mid-September, virtually ensuring that next summer’s melt season will begin with a much-reduced base of what used to be called “permanent” ice.

The ice “is going to remember that next year,” said Serreze. “Everything seems to be ahead of schedule and the models are all too slow. We’re on the fast track.”

The accelerated annual loss of Arctic ice prompted Serreze to predict that the entire polar region, including the North Pole, could witness a total summer melt by 2030.

The rapid degradation of the ice cover has been a key factor in the growing interest among — and friction between — Russia, Canada, the U.S. and other northern nations in securing seabed territory, resource claims and shipping rights in the Arctic.

On Aug. 2, a Russian mini-sub planted a flag at the North Pole seabed as part of a controversial bid to prove that Russia’s continental shelf extends far from the Siberian coast and encompasses the potentially lucrative oil reserves of the high Arctic seafloor.

At the time, former foreign affairs minister Peter MacKay ridiculed the Russian move as “a show” of bravado and pressed Canada’s own seabed claims in the Arctic.

Days later, Prime Minister Stephen Harper reasserted Canadian sovereignty in the North during a high-profile Arctic tour that added a $100-million deep-water seaport on Baffin Island and a new military training centre at Resolute Bay to a previous $3-billion promise of at least six new Arctic patrol ships.

Danish- and American-led research expeditions to the Arctic followed, fuelling the sense that an Arctic land grab and oil rush are underway.

For centuries, European explorers sought a clear shipping route through the Northwest Passage as a shortcut to Asia. Canada’s vast possessions in the Arctic are largely the result of 19th-century British voyages in search of the passage, which was not traversed until Norwegian explorer Roald Amundsen completed a three-year crossing in 1906.

Canada and the U.S. have been at odds for decades over the legal status of the Northwest Passage, the tension highlighted in 1985 by the unauthorized transit of the U.S. icebreaker Polar Sea.

Despite recent statements by former U.S. ambassador to Canada Paul Cellucci that the U.S. should cede control of the waterway to Canada, U.S. President George W. Bush said during his visit to Canada last week that “we believe it’s an international passage… We’ll manage the differences, because there are differences on the Northwest Passage.”

Harper responded: “Canada’s position is that we intend to strengthen our sovereignty in the Arctic area.”