The Vanishing Ice Sheets

Page 6 of 6

In the past few years, scientists have begun to worry that the world's glaciers have entered what they call a "runaway feedback mode," in which the dramatic changes to the water and wind and ice caused by global warming have not only accelerated but have themselves begun to alter the climate, creating a dynamic that could be irreversible. Both Antarctica and Greenland are now losing ice at twice the rate they were in 2002 — as much as 400 billion tons each year. In July, after the planet's six warmest months on record, a giant crack opened up overnight in the Jakobshavn Glacier; for the first time ever, scientists monitoring satellite data were able to observe in real time as an iceberg covering 2.7 square miles broke off and floated into the sea. Three weeks later, an even larger iceberg — four times the size of Manhattan — cleaved away from another glacier to the north of Jakobshavn, stunning scientists who study the ice sheets. "What is going on in the Arctic now," says Richard Alley, the geoscientist at Penn State, "is the biggest and fastest thing that nature has ever done."

Scientists say that oceans have long memories. The water reflects the slow-spreading response to events that took place a month, a year, a hundred years ago. An earthquake in the Arctic. A cyclone in the Bay of Bengal. A particularly strong El Niño summer, a decade and a half in the past. These memories are not all known, and their physics are not perfectly mapped, so the movements of the oceans are not well understood. "The ice sheet," Bindschadler says, "really is just the tail of the dog." There remains the chance that cutting carbon emissions might, in the long term, prevent more warm water from getting into the Amundsen Sea, where it is melting the ice shelves. If the atmospheric system really does have dials, in other words, then perhaps they can be turned to more comfortable settings. "That may be the saving grace," Bindschadler says. But even if we reduce emissions, he warns, there is no way to get the heat that is already in the ocean, melting the ice, back out.

"If you look at all these dramatic changes, water is doing it all," he says. "The vulnerability the ice sheets have to heat from the ocean is the key to all of this. And there's orders of magnitude more than enough heat in the ocean to kill the ice sheet, on whatever time scale the ocean and atmosphere conspire to deliver that heat. It's not at all about subsequent warming or future warming of the oceans. We don't have to warm up the ocean any more at all. The vulnerability is really from climate change altering the atmospheric circulation and how much that's going to alter the ocean circulation. The ice sheets have no defense against warm water. They don't really stand a chance."

At the end of last year, Bindschadler took a trip down the Atlantic seaboard, stopping at various points where the land sloped gently away to the sea, the places most vulnerable to the rising waters. He wanted to explain to local officials the dimensions of the threat they faced and to elucidate, as clearly as he could, what science could and couldn't say about the coming flood. In Norfolk, Virginia, only one or two city planners bothered to show up, leaving him to address a room of worried environmentalists and academics. Preacher, he thought, meet choir.

But when he arrived in Wilmington, North Carolina, Bindschadler found himself in a small room at city hall, equipped with his PowerPoint slides, explaining the state of things to a sizable gathering of local planners and politicians. The officials told him that they were planning a highway extension that would snake along the coast near the banks of the Cape Fear River, and it had been designed to come close to the water's edge — a foot above sea level in some places, two feet in others. Their question was simple: Did climate change mean that they should move the highway?

Bindschadler looked at the maps — the elevation figures for the ground, the route of the proposed highway. He imagined the seas rising here in a progression. Based on the science, he could picture what might happen here in 20 years, in 100, in 200. He looked up from the maps and turned to the officials.

"Well," he asked them, "how long do you want the highway to last?"

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