Shortly after pulling away from the pier at Longyearbyen, the main town on the Arctic archipelago of Svalbard, Norway, we saw our first sea ice. Three milky dots moving in the stillness proved to be a mother polar bear and two cubs. But that was the last significant sea ice we were to encounter as we continued north, halfway between Norway and the North Pole.

I had come to the Arctic to learn what the people who live and work there think about the talk of geopolitics—land-grabs, hidden oil wealth, and strategic shipping lanes—now that global warming is opening the region. I wanted to see what the threats really looked like on the ground. And, of course, I hoped to see the Arctic ice sheet, the frozen top of the planet that I had dreamt of setting foot on since I was a child.

What I discovered surprised me. As we sailed north over a week last June, there was no sea ice in sight. And rather than signs of international maneuvering or preparations for oil drilling, I encountered a sort of stunned silence among the people who have long lived in the "high north" and are still coming to terms with the region's rapid, climate-induced changes. Everyone I spoke to was far more concerned about the fragility of the region's wildlife than any competing national interests. The Inuit, who call the circumpolar Arctic their homeland, are concerned about the peril to their distinct culture and way of life.

In June 1818, the ill-fated polar explorer, Sir John Franklin, ventured north from Svalbard, the last bit of Europe before the pole. He was on his first failed expedition to find an Arctic sea route between the Atlantic and Pacific oceans. The ship's halyards were fat with ice, and soon the sea was thick with it, too—much of it many years old, stretching beyond the northern horizon.

"Where Franklin found ice I found nothing but open water"

I set sail on the same route 200 years after his voyage with a group of artists in a square-rigged barquentine not very different from his ship, the Trent. But where Franklin found ice I found nothing but open water, blue and flat as far as the eye could see. The ice cover around Svalbard had dropped 40 percent below a four-decade summer average, and our captain, a Dutchman, reported that the frozen edge of the Earth's ice cap was 100 miles farther north than we had time to sail.

Everyone knows the Arctic is melting. But the stark reality of an ice-free sea—well beyond where Franklin managed to navigate two centuries earlier—was startling nonetheless. The volume of Arctic sea ice, both in thickness and extent, has decreased more than 70 percent since the late 1970s.

The polar ice cap at the end of the summer melt season, roughly the size of the contiguous United States 40 years ago, has shrunk to an irregular semicircle covering about two-thirds of that area today. It hugs Greenland and Canada's Arctic shore, but in August, open water appeared on Greenland's northern coast for the first time on record as the ice there unexpectedly broke up—an ominous development. Some scientists predict that there will be no summer ice in little more than a decade and that the Arctic Ocean will freeze only in winter.