For centuries, a harsh climate and ice-choked seas dashed the dreams of sailors attempting to cross the Canadian Northwest Passage between Asia and Europe. Now, thanks to climate change and reduced ice cover, the trip isn't nearly so daunting. Last month the Crystal Serenity, a luxury cruise ship, carried a record thousand-plus passengers and crew through the passage. Next year, it'll do the same.

Does this mean that the age-old vision of a time-saving, money-making Arctic passage for the world's shippers is finally coming true? Don't bet on it.

In theory, it's a terrific idea. Traveling from Shanghai to Rotterdam via the Northwest Passage is about 3,540 km shorter than going through the Panama Canal. In 2013, the Nordic Orion became the first bulk cargo carrier to traverse the passage. Bound for Finland from Vancouver, it shaved more than 1,600 km — and $200,000 — off a more typical route. Not long after, officials at China's Polar Research Institute predicted that 5 percent to 15 percent of China's international trade would use the Northeast Passage, which skirts the Russian Arctic, by 2020.