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| Deep freeze: A view through the heads-up display of a US Air Force C-17 cargo plane as it leaves Antarctica. Ted S. Warren/AP/FILE |
As arctic ice melts, South Pole ice grows
Scientists are puzzled, but the phenomenon seems to fit the latest global-warming models.
from the January 10, 2008 edition
Page 2 of 3
'Antarctic sea ice is such a different animal'
For some commentators, the out-of-sync trends in sea ice at the two poles is evidence that warming isn't global and doesn't deserve the international angst it triggers.
Not so fast, many researchers respond. Northern and southern sea ice shouldn't necessarily act in lock-step. "Antarctic sea ice is such a different animal," says Douglas Martinson, another polar-ice specialist at Lamont-Doherty. Geographic and oceanographic differences – a virtually landlocked ocean in the north versus an open ocean in the south – encourage the buildup of thick, long-lasting, multiyear ice in the Arctic Ocean. Antarctica's sea ice, by contrast, is largely thin and seasonal. In winter, Antarctic sea ice covers an area nearly twice the size of Europe. By the end of summer, it shrinks to one-sixth of its winter extent. These wide swings make it difficult to tease out long-term trends in ice cover there.
The first big advance in monitoring Antarctic sea ice came in 1972, when the federal government launched a satellite with a microwave device to monitor ice 24/7, regardless of cloud cover.
The results were eye-opening, says Claire Parkinson, a researcher who tracks sea-ice trends at the Goddard Space Flight Center in Greenbelt, Md. During three of the first four years the instrument gathered data, an enormous open area in the ice, or polynya, appeared in the Weddell Sea – a phenomenon no one has seen there since. (A grocery-store tabloid had the obvious explanation: that scientists had discovered evidence of an undersea base run by space aliens – heat from the alleged facility had melted the ice. "It was one of our images," says a bemused Dr. Parkinson. "But it wasn't our interpretation.")
Since 1978, the satellite record shows that Antarctica's sea ice has expanded by about half a percent a year. Declines in sea ice recorded between 2000 and 2002 have significantly moderated the overall rise.
These long-term data have let scientists tease out relationships between Antarctic sea ice and natural climate variations, such as swings between El Niño and La Niña in the tropical Pacific. Recent modeling work has given scientists a sense that they are on the right track as they explore the processes affecting sea ice. Dr. Yuan, who uncovered Antarctica's coherent response to El Niño, has developed a seasonal sea-ice forecast model for key regions that scientists now use to plan expeditions.
The ice also plays a key ecological role in the region, some of which bears on the exchange of CO2 between the atmosphere, ocean, and ice, and on cloud formation.
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