Arctic Ice Cap
INTRO: In late July, tourists and even some scientists aboard a Russian cruise ship were shocked to discover open water at the North Pole. A New York Times article reported the open water as one of the most important signs yet of global warming. But as Doug Schneider reports in this week's Arctic Science Journeys Radio, scientists who study the Arctic say open water at the North Pole isn't unusual.STORY: When University of Washington oceanographer Dr. Drew Rothrock read in his New York Times last week that the ice cap over the North Pole was melting, his first reaction was to dismiss the report. According to Rothrock and other scientists who study the Arctic, open water at the pole is a common occurrence.
ROTHROCK: "There's a lot of open water, a lot of crack of this size they describe in the sea ice in the summer. So in and of itself, that doesn't seem so bizarre. I think they played it up as something a little bigger than it actually was. It seemed to me that mostly, it was a disappointment to the people who wanted to step out and say they stood on the North Pole."
In fact, at any given time during the summer, 10 to 15 percent of the Arctic Ocean is not covered by ice, says Dr. Mark Johnson, a physical oceanographer at the University of Alaska Fairbanks. Johnson spends a great deal of time modeling the ever-changing dynamics of the ice cap. He says the six-mile-long opening in the icecalled a leadthat tourists saw, sounds about right for this time of year.
JOHNSON: "If the bridge height or the height from where people were looking at this open water was anywhere from 30 to 60 feet high, you can see an area that would have from 6 to 9 square nautical miles of open water. That can be arranged in almost any pattern, but if it's all in one area that's a significantly large area that you could find at any time during the summer."
The reason there is open water at the North Pole is because the ice cap is not, as some people might think, a stable, unchanging sheet of ice. Far from it, says Rothrock.
ROTHROCK: "It's a big ocean up there at the North Pole. It has floating sea ice covering it, which is typically about ten feet thick. It's not like an ice sheet or glacier on land, which is the situation at the South Pole. Sea ice is pretty mobile stuff. It moves around. It cracks. It breaks. It piles up. It's always on the go."
This isn't to say that the Arctic ice cap hasn't undergone some dramatic changes. Dr. Igor Polyakov is a physical oceanographer at the International Arctic Research Center in Fairbanks. He says the open water tourists saw is more the result of wind and ocean currents than climate change. He also says sea ice thickness varies according to large-scale ocean-atmosphere oscillations that take decades to unfold.
POLYAKOV: "We found a 60- to 70-year cycle with many Arctic parameters, such as surface temperature, air pressure, and ice thickness variability. And we believe this signal comes from the North Atlantic and is induced by very slow anomalies in the circulation in the North Atlantic. We believe that this cycle is very important for the Arctic environment, because all major parameters show this slow variability."
That seems to fit with records from about 1930 to 1960 that show sea ice in the high Arctic was thick and widespread. It also seems to mesh with data from 1960 to 1990, which shows that sea ice became 40 percent thinner overall, according to Rothrock's research.
ROTHROCK: "We've published results from submarine cruises, where they have upward-looking sonar and they are able to determine ice thickness. We took data taken from cruises in the 1990s that we had been party to and compared it to older data from the '50s, '60s and '70s and found quite a large difference."
Not to worry, however. Polyakov and others say the cycle shows signs of shifting back toward a colder Arctic climate.
POLYAKOV: "I would be very careful with forecasts. But available data suggests that we are very close to the situation when everything will go to a cold climate regime, with thicker ice, colder air temperature, higher atmospheric pressures and colder water in the ocean."
For the moment, many scientists believe that natural cycles are exerting a more powerful influence on the Arctic's ice cover than are the impacts of global warming. But, says Johnson, scientists shouldn't let their guard down.
JOHNSON: "The question of what happens should there be more open water is an incredibly complex one to answer. The question that needs to be asked is how much of these changes are "global warming" or "global change" versus the natural variability that's been going on for hundreds and hundreds and hundreds of years? And that's an enormously difficult question because our records are, of course, incomplete over the long haul."
OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.
Thanks to the following individuals for help preparing this script:
Dr. Mark Johnson, physical oceanographer
Dr. Igor Polyakov
Dr. Peter McRoy, physical oceanographer
Dr. Drew Rothrock
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
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Satellite image of North Pole, 7/26/00
State of the Cryosphere, National Snow and Ice Data Center
Listen to a radio clip from NPR about the melting pole story