Arctic Ice Thinning
At An Alarming Rate
By Jack Hamann - CNN Environment Unit

(CNN) -- He's an expert on Arctic ice ... but he's never been to the North Pole.
Drew Rothrock says he's a "digital guy:" the sort of scientist who would rather pour over data on a computer screen than get his feet wet in the field. (Or, in the case of Arctic tundra, get his feet frozen.)
Dr. Rothrock and two colleagues from the University of Washington's Polar Research Center recently published a 4-page paper in a relatively obscure journal called Geophysical Research Letters []. But the findings in that brief paper won worldwide attention in media like the New York Times, Washington Post, Christian Science Monitor and CNN. Not bad for data jockeys.
Why all the attention? Turns out, Arctic ice is getting pretty thin.
Thawing decades of data
For most of the 1990s, Rothrock and his partners have been studying measurements of North Pole ice taken by U.S. Navy nuclear submarines. The Arctic Ocean is fairly deep in many places, and military submarines regularly glide beneath the ice, trying to remain strategically invisible to competing navies, while taking sonar soundings of the ice pack above. Since the end of the Cold War in 1990, the military has been increasingly willing to let scientists use their vessels, vehicles and aircraft to study the planet.
Arctic ice is very different than the stuff found on land, like glaciers. For starters, ice formed in seawater never gets all that thick. Most of the actual freezing takes place on the bottom of the ice sheet, where ice contacts the ocean. Ice traps air, which acts as an insulator, which eventually slows down the ice-forming process. (Icebergs, by contrast, can be huge -- they are formed on land, and break off into the sea and float around).
Even in the sub-freezing temperatures of midwinter, Rothrock commonly finds Arctic ice measurements only a few inches thick, although in some places it can pile up to 10 feet or more. The Navy numbers from the '90s seemed to show a disturbing trend, however: on average, the thickness seemed to be decreasing about 4 inches (10 cm) a year.
Rathrock's data shows that arctic ice is thinning at an alarming rate
Were these measurements yet another sign that our planet is getting warmer? Or were they simply a small slice of natural global fluctuations?
The Navy has been recording ice data for decades, but like most Cold War calculations, the information has been top secret. If an unfriendly nation gets a hold of just where and when submarines had taken their measurements in the past, they might be able to guess where those subs would travel in the future.
But -- like the Arctic ice itself -- military secrecy seems to be thawing. About a year ago, Rothrock convinced Navy brass that measurements taken in the 1950s could be helpful in figuring out whether the data from the '90s was statistically significant. Armed with a pile of new numbers, Rothrock guessed that they might show that the polar cap had shrunk perhaps 18-20 inches over the past half century.
He was wrong. The actual shrinkage left him astonished.
On average, the University of Washington team found that ice had thinned by four feet (1.3 meters) ... a 40 percent decrease since 1953. The "trend" of the 1990s seemed to be an indisputable fact.
Scientists fear Gulf Stream diversion
When Arctic ice melts, it does not raise the level of the ocean, threatening coastal communities with flooding. Like an ice cube in a drinking glass, sea ice only displaces ocean water, merely changing form when it melts. By contrast, land-based ice does pose a threat to coastlines if it melts too dramatically.
But there is still reason to pay attention. Water from the Arctic Ocean plays an important role in Northern Hemisphere weather. The powerful Gulf Stream current moves warm water from the tropics past the east coast of the United States and Canada and Northwestern Europe. If the Arctic continues to melt, some scientists fear the Gulf Stream will be diverted. Without that warm water, heavily populated areas around the northern Atlantic might suffer bitterly cold winters.
Could global warming be the cause of Arctic melting? And could that melting, ironically, make some places colder?
Rothrock won't go that far. His own theory is that a cyclical pattern of Arctic winds has stayed strong longer than expected, and that those winds have hastened the normal seasonal breakup of polar ice. He does not say -- as many environmentalists do -- that global warming is the culprit. But he also cannot say why those Arctic winds have stayed so strong.
A nuclear submarine churns through arctic ice
The folks at the Polar Science Center say they need even more data. On the one hand, they are expanding their relationship with the Navy, as more and more scientists are allowed to travel on submarines and conduct experiments. On the other, they are gently pressuring the Pentagon to release even more of the mountains of Cold War data, enabling them to piece together a more complete picture of changes in ice thickness over time.
Of all the places where submarines sneak around, the statistics at one precise point are already fairly well-established. No matter what the date or the mission, any submarine that gets permission to surface through the ice almost always surfaces ... right at the North Pole. By tradition, the lucky sailors who are allowed to frolic at 90 degrees North play a game of softball.
Rothrock, however, doesn't care whether he ever plays in one of those games. He's content to simply analyze the numbers they bring back ... and perhaps play a digital softball game on his computer.


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