NORTHWEST PASSAGE?: The fabled shortcut to Asia from Europe has been open water in recent years but dangerous ice chunks still lurk in the coveted shipping lane of the McClure Strait, pictured here.
ESA

It is said that the Inuit have many words for snow, but when it comes to the Northwest Passage only one type of frozen water matters: multiyear ice. It can slice through the hull of a ship like a knife through butter and it persists in the passage's waters despite unprecedented warming in the Arctic Ocean, thwarting shippers in search of a shortcut between Europe and Asia.

The fabled Northwest Passage has made headlines ever since it thawed last year for the first time. For three centuries the quest for an expedited route between the Atlantic and Pacific oceans rivaled today's space race, with European superpowers vying for the prize. Hundreds of sailors and countless expeditions ventured into Canada's Arctic waters, including such naval luminaries as Sir Francis Drake, Captain James Cook and the ill-fated Henry Hudson, who left his name—and lost his life—on the Canadian bay that marks its entrance.

Slide Show: View satellite images of the possible Northwest Passage

Now, with the Arctic's sea ice shrinking at a rate of 10 percent per decade, this coveted shipping lane has opened for business—but shippers are not rushing to use it. The reason: as fate would have it, global warming appears to also be increasing the amount of potentially deadly multiyear ice chunks lurking in the newly opened pathway.

Sea of Ice
"The thing is, the Canadian Arctic has a totally different ice regime than the Arctic Ocean," says Stephen Howell, a climatologist at the Interdisciplinary Center on Climate Change at the University of Waterloo in Ontario.

In fact, the Canadian Arctic Archipelago acts as a "drain trap" for ship-wrecking multiyear ice, Howell says. This year, for example, when the first-year ice in the passage had melted, it opened the way for multiyear ice (MYI) from the Queen Elizabeth Islands to flow into and clog the Northwest Passage. "We call it a 'MYI invasion' and that's going to be the threat as we transition to an ice-free summertime Arctic," he says.

"The first-year ice, that's sort of like Swiss cheese and you can just plow through it," Howell says. This ice freezes over a winter and is seldom thicker than three feet (one meter). Often, first-year ice melts the summer after it's frozen, but if it doesn't, it becomes thicker the following winter and becomes multiyear ice. "The multiyear ice isn't like Swiss cheese; it's solid and trouble" for ships that collide with it, he says.

"In places it was three meters (nearly 10 feet) thick, but in other places we had a five-meter (16.5-foot) drill bit and we still did not reach the bottom," says Bruno Tremblay, an atmospheric and oceanic scientist at McGill University in Montreal, who was taking ice cores of multiyear ice in the Canadian territory of Nunavut's Viscount Melville Sound last year.

"It's very dangerous," adds Ivana Kubat, an engineer at the National Research Council's Canadian Hydraulics Centre in Ottawa. "If a lower type of vessel hits a piece of multiyear ice, then the vessel can sink depending on the speed and damage." One study showed that multiyear ice was to blame for 74 percent of the damage suffered by ships traveling in the Canadian Arctic between 1976 and 2007.

A Route to Dodge Danger?
Still, there are several ways through the Northwest Passage. The southern, shallow and circuitous route through Peel Sound in Nunavut has been open the past three summers, thanks to warmer temperatures. "That's because that region is mostly first-year ice so with warmer temperatures it melts and it clears," Howell says.