It was the lure of a Northwest Passage through the ice that once drew Henry Hudson and John Franklin to Canada's Far North. Instead, both explorers found only hunger and death.

But the icy door they once beat against in vain is now creaking open, thanks to man-made global warming.

Climate models differ on exactly when the Arctic Ocean will be ice-free in summer. The U.S. navy has estimated it could occur as early as this year. More conservative models put the event closer to mid-century, or even later.

But whenever it occurs, the Arctic is already becoming more open to both commercial shipping and international fishing fleets, and that is why the Arctic portion of accords between the U.S. and Canada announced Thursday could be so important in the future.

Along with commitments to joint action to address climate change, U.S. President Barack Obama and Prime Minister Justin Trudeau pledged to protect the Arctic from overfishing and development.

Last great unexploited fishery?

Factory-freezer trawlers and drift-netters now routinely fish on the other side of the world from their home waters. In the Southern Ocean, which has never been as ice-bound as the North, fleets from Japan, Taiwan and mainland China are already scouring the seas of toothfish, icefish, shrimp and even krill.

While the fisheries in both the western Arctic and the eastern Arctic are fairly well regulated, the high seas part of the Arctic Ocean beyond the 200-mile limits claimed by the U.S. and Canada has no real protection other than the ice that covers it.

"In the Canadian and U.S. Arctics on the western side, we have instituted closures to commercial fishing, and are really taking quite a precautionary approach," says Sabine Jessen of the Canadian Parks and Wilderness Society. "On the eastern side, it falls under NAFO [the North Atlantic Fisheries Organization] which controls the fishing along the eastern side of Baffin Island."

"Then we've got the centre part of the Canadian archipelago where there is no policy. In the High Arctic, there is an agreement between the five countries that border the Arctic not to exploit that fishery until we know more."

The problem, says Jessen, is that the agreement does nothing to prevent the Taiwanese or other roving fleets from sailing in and scooping up marine life.

"I think there are a variety of different kinds of companies and interests that are looking to the opportunities in the Arctic with the changing ice and melting ice. And we have to be ready. If we're not proactive about it, then the initiatives to get up there and exploit resources are going to overtake our ability to manage them."

In a joint statement issued Thursday in Washington, Trudeau and Obama committed to protect those fish and ensure that any new shipping corridors are "low impact."

Prime Minister Justin Trudeau and U.S. President Barack Obama held a joint news conference in the Rose Garden at the White House on Thursday. In a joint statement, the leaders pledged to protect the Arctic. (Paul Chiasson/Canadian Press)

Under the heading "Abundant Arctic Fish," the two leaders "call for a binding international agreement to prevent the opening of unregulated fisheries in the central Arctic Ocean to preserve living marine resources and promote scientific research in the region. Canada offers to host the next round of negotiations, to continue momentum and build on a precautionary, science-based principle to commercial fishing that both countries have put in place in their Arctic waters."

The two leaders also pledged to create a pan-Arctic marine protection area network, including at least 10 per cent of their Arctic waters and 17 per cent of their Arctic land mass, committing to "substantially surpass these national goals in the coming years."

And they promised to be strict about licensing any kind of Arctic development, and to "set a world-class standard by basing development decisions and operations on scientific evidence."

U.S., Canada haven't always co-operated

It's a new departure for two countries that have often jockeyed for control over their shared Arctic waters.

During the negotiations leading up to the drafting of the UN Charter on the Law of the Sea, Canada argued that the Northwest Passage was not a true strait, and that therefore the rules that guarantee the right of passage through international straits (such as the Strait of Gibraltar or the Strait of Hormuz at the mouth of the Persian Gulf) do not apply.

The United States responded in 1985 by sending an icebreaker, the Polar Sea, to traverse the Arctic from Greenland to Alaska. Declining to ask Canada's permission, the U.S. government merely notified Canada of the Polar Sea's journey between Canada's Arctic islands.

Stung by criticism that it was failing to defend Canada's Arctic sovereignty, the Mulroney government ordered increased patrols and the construction of a new fleet of Arctic icebreakers. The U.S. blinked first, and in 1988 signed an accord in which Washington agreed to ask Canada's permission before making such a voyage in future.

That incident prompted Canada to declare its sovereignty over the entire Arctic archipelago and all the waters within it.

But recently the issue of Arctic sovereignty has resurfaced as countries have made vast territorial claims based on underwater exploration of their continental shelves.

In the past 18 months, Russia has made a claim for 1.2 million square kilometres of Arctic waters, and Denmark has claimed 900,000 square kilometres. Both claims overlap with Canadian claims and include the North Pole.