On July 18th, 2005, around four in the morning, a research ship called the Arctic Sunrise was slowly making its way south along the eastern coast of Greenland. It was already bright out, and very still. An ice scientist named Gordon Hamilton stood on deck, watching the rocks and eddies along the water's edge. The rest of the crew was still sleeping below. There was a helicopter on the deck, painted bright orange so it could be spotted easily if rescue were needed, and Hamilton saw its pilot, the only other person awake so early, coming down a nearby staircase. They had plans to fly to a massive glacier called Kangerdlugssuaq later that afternoon, to measure its speed and to see whether the warming climate had forced this part of the world into dramatic changes. The pilot asked if Hamilton wanted to take a quick flight over to the glacier now, to scout out a good landing spot. "Sure," Hamilton said. He went below deck to collect his maps.
Most of the ice in the world is contained in two great, ancient ice sheets, each of them the size of a continent: One covers Antarctica and the South Pole, and the other, not nearly as big, covers Greenland. Both of these formations slope gently from high interiors down to the coast, with ice edging outward in vast frozen rivers known as glaciers. Snowfall at the top of the slopes presses down on the glaciers, helping gravity propel them toward the edges of the continent. There, when it meets the warmer water, some of the ice melts slowly into the ocean. Until a few years ago, scientists like Hamilton thought of the ice sheets as changing only imperceptibly, on the time scale of centuries. But as the planet has warmed, they have come to see the ice as far more volatile and nimble. The ice sheets no longer seem static; they are mysterious, complicated dams that help hold back entire continents, keeping coastal cities free from flood. If you understand the ice sheets, and how they might melt, you can understand the future of the oceans — how much they might swell, and on what schedule. And if you understand the oceans, you might be able to get a more accurate fix on the future of the world's coasts, and of the civilizations they hold.
Hamilton and the pilot took off from the ship's deck and flew toward the coast, heading for the fjord where Kangerdlugssuaq empties into the ocean. At the time, ice scientists were trying to resolve a strange and disturbing anomaly. A glacier called Jakobshavn Isbrae — the largest in Greenland, on the other side of the continent from Hamilton's ship — had begun to thin rapidly, according to recent data collected by NASA, and to send far more ice into the sea than was normal. Nobody knew exactly what to make of this. If some change in the climate was responsible, then this accelerated melting should have shown up at other glaciers, but so far it hadn't. Hamilton had with him a sketch based on satellite images of Kangerdlugssuaq taken 10 months earlier, and it showed that the normal processes here were in balance. The glacier seemed to be at equilibrium.
As the helicopter headed toward the coordinates on the glacier where Hamilton wanted to land, he gazed out the window. His mind drifted absently across the landscape. The steep rock of the fjord rose above the dark, pooling water below, the glacier still miles upstream. Suddenly, Hamilton was startled out of his grogginess by a squawking in his headphones: The pilot was trying to tell him something. Hamilton asked the man to repeat himself. "We're here," the pilot said.
Hamilton looked down. They were over open water. The glacier had vanished.
Confused, Hamilton picked up the satellite image. Perhaps he had given the pilot the wrong coordinates. In the sketch, he could see two tributary glaciers that emptied into Kangerdlugssuaq right where he had wanted to land. He looked out the window. There were the two tributary glaciers. But they were emptying into the sea. In the few months since the image had been taken, the front end of Kangerdlugssuaq had disappeared. "It was here for more than 50 years," Hamilton says. "And now it was gone."
Returning to the Arctic Sunrise, Hamilton found the graduate student who was working with him, Leigh Stearns, and asked her to return to the glacier with him. On the way, he was purposely vague about what he'd seen; he still thought he might have missed something. Now, flying through the fjord a second time, Hamilton saw evidence of the disappeared glacier that he had missed earlier that morning. Along the sides of the fjord, like a ring on a bathtub, were icy smears that had been left on the rock when the glacier calved into the water. Higher up, he could see dirt mounds that suggested how high the missing glacier had risen. This section of Kangerdlugssuaq had vanished in only 10 months — a pace most scientists had thought impossible. Perhaps the ice sheets weren't battleships, massive and inert, but catamarans, nimble, bending to the wind. The question now was, how fast were the glaciers moving?
The answer, Hamilton knew, could have profound implications for the world's coasts. A report being put together at the time by the U.N.'s Intergovernmental Panel on Climate Change, a collection of the world's leading climate experts, estimated that global sea levels would rise no more than a foot and a half in the next century. But over the past five years, as more discoveries like Hamilton's have emerged, those numbers have come to seem obsolete. "The estimates are now clustering around a rise in sea level of three feet by the end of the century," says Richard Alley, a geoscientist at Pennsylvania State University — double the previous estimates. "Nature has begun to resolve some of these arguments for us." The new science indicates that by the end of the century, rising seas could turn as many as 153 million people into refugees. Most of New Orleans, and large swaths of Miami and Tampa, are likely to be underwater, along with some of the world's largest cities: Manila, Lagos, Alexandria. A full quarter of the developing world's coasts will be battered by more frequent hurricanes and tsunamis; roughly half of Bangladesh, a country of 160 million people, will be subject to regular flooding. If Hamilton was right, then within the ice sheets something truly cataclysmic had begun.
Flying over the water where Kangerdlugssuaq once stood, Hamilton and Stearns found the new edge of the glacier, sliding furtively down between a pair of hills. Once the pilot spotted a stable landing spot and touched down, they worked quickly. With an electric drill, they bored a hole into the ice and dropped a pole into it, with a small GPS receiver mounted on top. Then they flew off, found another steady landing spot and repeated the process. By the end of the afternoon they had installed six receivers along the glacier's edge, enough to get an idea of the ice's overall speed.
Back on the ship, Hamilton collapsed onto his bunk, exhausted. Stearns opened her laptop and started downloading data from the monitors. When she was done, the speed was so implausible that she checked her calculations five times to make sure she had the math right before she showed her boss. Kangerdlugssuaq, when it was stable, moved toward the sea at a rate of about three miles a year. Now, Stearns' calculation showed, it was moving nearly nine miles. "It was faster than any glacier had ever been measured," Hamilton says. "We hadn't thought glaciers could achieve those speeds." The continent was shifting, the planet shrugging its shoulders, sending the edges of the ice sheet racing into the sea.
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