"In March of 2000 I was sitting at this computer," she said. "Another analyst, Mary Keller, was sitting at the next one, and suddenly she said, ÔMy God! It's a huge iceberg!' A huge piece had broken off a shelf in the B quadrant since we'd last checked a day or so before. There had been no stress fractures visible in the ice sheet; the calving was completely unexpected. This iceberg was the 15th in B, so we labeled it B-15. I had never seen a berg that size. It was awesome—158 by 20 nautical miles. After it broke off it kind of ratcheted itself along the coast, sliding on each low tide, slowly moving from where it began, and in the process it eventually split into two pieces, one of about a hundred miles long and another of about 80. B-15 was the most exciting iceberg I've watched since I've been here."

Shaffier and I spent hours looking at computer images that hopscotched the icy places of the globe. Some of the pictures were visible-light photographs; some were made by infrared imagery that indicated different ice temperatures by color. Iceberg ice is 20 or 30 Celsius degrees colder than sea ice, old sea ice is a few degrees colder than new sea ice; in general, the colder the ice, the more difficult it is to navigate through. In passing, we checked up on B-15A—the giant was partly blocking the entry to West Antarctica's McMurdo Sound, apparently stuck on underwater rocks.

"Let's look at the Larsen Ice Shelf, or what's left of it," Shaffier said. "Did you hear what just happened to Larsen B? The Larsen Shelf is in a part of West Antarctica where local temperatures have gone up four or five degrees over the past decades, and a few years ago a big part of the shelf, Larsen A, disintegrated almost completely. People said that the rest of the shelf, Larsen B, would probably go in the next two years. Well, a few weeks ago, it went. Over a thousand square miles of ice—poof. One day the shelf was there, the next day it started to break up, and 35 days later the satellite images showed nothing but dark water and white fragments where solid white ice used to be. In about a month this major geographic feature of Antarctica ceased to exist."

Later, a glaciologist I talked to explained how the breakup of Larsen B probably occurred: Higher surface temperatures created pools of meltwater that accumulated on the ice during the summer months until the water flowed into ice crevices; once in the crevices, the water became a hydraulic wedge, forcing its greater weight down through the ice and cracking it apart. When pieces of the ice broke off, they pushed over the pieces next to them, like books falling on a shelf. The process had a swiftness and a magnitude glaciologists had never seen before, and it created the largest movement of ice in a single event in recent times. Unlike the calving of giant icebergs, the Larsen Shelf breakup occurred because of a sharp rise in local temperatures, which scientists believe was almost certainly the result of global warming.

"Actually, I've never seen an iceberg except in pictures," Shaffier told me. "The only ice on my computer screen I've ever seen in person was ice on Lake Erie near Brook Park, Ohio, where I used to live. Next fall I might get a place on the supply ship going down to McMurdo. I'd love to do that. I want to see the ice up close, but even more, I want to hear it. The images on my screen are silent, of course. But think about when an iceberg 200 miles long by 21 miles wide breaks off Antarctica. Think what that sound must be."

According to scientists, probably no one has ever heard that sound, or been present when a giant Antarctic iceberg calved. Whether that event is even accompanied by sound audible to humans, no one can yet say. Instruments that listen for underwater oceanic sounds sometimes pick up vibrations like a cello bow across strings—only much lower, below human hearing—which are believed to come from the friction of giant icebergs, though none of the vibrations have yet been matched to a specific calving. When giant icebergs run into something, however—when they collide with the ocean bottom or the land—they cause seismic tremors that register at listening stations halfway around the world.

I WANTED TO SEE AN ICEBERG myself. Like Judy Shaffier, I had never seen one live. I took a cab from my house in New Jersey to Newark Airport and flew to Halifax, Nova Scotia, one of those far northern airports where connecting passengers half-sleepwalk in a twilight of individual time zones. From Halifax I flew to St. John's, Newfoundland, on an uncrowded plane over the coastline and then across ocean that was mailbox blue. I had my face close to the window, craning my neck to scan. A finger of Newfoundland appeared directly below the plane. In the other direction, on the ocean far to the east, I saw a blip of white. It got bigger as the plane approached, and I could make out what seemed to be two white oil-storage tanks rising from the ocean's surface. They looked so plausible, I was sure that was what they were. At slightly closer range, the deception fell away, and I saw they were both parts of a single iceberg; and moreover, one of the dry-dock kind I'd read about. This sighting excited me beyond all measure. From home to iceberg was about two hours of flying time.
The plane banked to the west and descended to land at St. John's, and at about a thousand feet it came over a high bluff above a fjordlike little bay, and in the middle of it was a large, tent-shaped iceberg. The plane passed over the iceberg in a second, and five minutes later was at the gate. I hurried to the luggage claim, got my bag, picked up my rental car, and drove back to the bay where the iceberg was. At a turnout by the road skirting the bay, I got out. The berg rode there, rotating slightly back and forth, about 200 yards away. Its top had a sort of spinal effect, with knobs in a curving row like vertebrae. Small waves broke around it, and it seemed to give off a mist.

Icebergs are really white. Usually you don't see this kind of white unless you've just been born or are about to die. It's a hazmat-suit, medical-lab, hospital white. There are some antiseptic-blue overtones to it, too, and a whole spectrum of greens where the berg descends into the depths out of sight. In these latitudes, sea and land and sky wear the colors of hand-knit Scottish sweaters: the taupes, the teals, the tans, the oyster grays. Surrounded by these muted shades, icebergs stand out like sore thumbs, if a sore thumb could gleam white and rise five stories above the ocean and float.