ILULISSAT, Greenland — On a clear day in August, a helicopter set me and a few companions down on the northern end of the Jakobshavn Glacier in Western Greenland, about 150 miles north of the Arctic Circle. The ground under our feet seemed almost lunar: gray silt and dust, loose rocks and boulders and, at the edge of the glacier's face, mud so deep, it nearly ate my boots. To the south, the calving front of the glacier known in Greenlandic as Sermeq Kujalleq periodically deposited enormous slabs of ice, some more than 100 feet high, into the open water.
I asked the pilot to give me a sense of how much the glacier had retreated since he had been flying the route. He pointed to a distant rocky island in the middle of the fjord.
"That's where the glacier was in 2007," he said.
Over the course of the 20th century, the Jakobshavn Glacier retreated about 10 to 15 kilometers. Over just the next eight years, it retreated about the same amount, according to oceanographer Josh Willis of NASA's Jet Propulsion Laboratory. Later, the front advanced a little — a function of complex dynamics partly involving ocean currents — before resuming its retreat.
For anyone who has entertained doubts about the warming of the planet, a trip to Greenland serves as a bracing corrective. Flying low over the vast ice sheet that covers most of the island, I immediately noticed large ponds of cerulean meltwater and dozens of fast-flowing streams rushing through gullies of white ice and sometimes disappearing into vertical ice caverns thousands of feet deep. Such lakes, scientists report, have become far more common over the past two decades, occurring earlier in the year at higher elevations. Last year, it even rained at the highest point of the ice sheet, some 500 miles north of the Arctic Circle. That's a first since record-keeping began in the 1980s.
Closer to the coast, at the point where the sheet approaches the darkly colored mountains that ring the island, lies a distinctive beige trimline of barren earth, ranging in width from hundreds to thousands of meters. Like the bathtub rings in the depleted lakes and reservoirs of the American West, it shows where the ice once reached and how far it has receded. History also records that Greenland's great 19th-century explorers — men like Fridtjof Nansen of Norway and Robert Peary of America — had to climb steep glacial walls merely to get onto the sheet itself. Now it is easy to spot places where the ice meets the dry land on flat ground.
And then there's the testimony of the market.
In the coastal town of Ilulissat, I had dinner with Bo Møller Stensgaard, a geologist and the CEO of Bluejay Mining, which plans to mine for copper, nickel, cobalt, zinc and ilmenite.