Antarctica May Be Melting
By Keay Davidson
San Francisco Examiner
Scripps Howard News Service
New evidence strengthens fears that Antarctica might be melting, threatening to raise sea levels and flood low-lying areas around the world.
At worst, scientists say, global sea levels might rise by about 20 feet over the next few centuries. Such a disaster would drown many coastlines and submerge some Pacific islands.
Last month, in several articles in science and nature magazines, scientists reported new data suggesting that parts of the Antarctic ice are falling apart faster than once thought.
The main object of concern is the West Antarctic Ice Sheet, or WAIS. It floats above water, like an extension or "shelf" projecting from the Antarctic continent.
Among the scientists' findings:
Space satellites have detected Antarctic ice changes that might, at worst, "be a first step toward the collapse of the entire West Antarctic Ice Sheet," according to the July 24 issue of Science.
The European research satellites, known as ERS 1 and ERS 2, use radar to map the distribution of ice in Antarctica. The satellite data show that the so-called grounding line -- the boundary between floating ice and ice atop the Antarctic continent -- "has been retreating inland at a rate of more than a kilometer (0.6 mile) per year," reports the Science article by Richard Kerr.
Why? "Presumably because the glacier is losing mass by melting at its base," Kerr says. His article summarizes research, published in the same issue, by Eric Rignot of the Jet Propulsion Laboratory in Pasadena, Calif. Rignot was unavailable for comment.
The West Antarctic Ice Sheet is unstable over geological time, judging by new evidence that it "wasted away to a scrap" at some unknown time in the last 1.3 million years, according to researchers in Sweden and Southern California.
The scientists base the finding partly on fossilized marine organisms, diatoms, which they recovered from deep within the West Antarctic ice. The find shows that the ice-covered area was free of ice in the geological past.
The finding is reported in the July 3 issue of Science by Reed Scherer of Uppsala University in Sweden and Slawek Tulaczyk of Caltech, and their colleagues.
"Now the question is when the WAIS might disintegrate again as the world warms -- and how rapidly it might flood low-lying coasts," says a Science story accompanying the Scherer report.
Slick, fine-grained sediments beneath Antarctic coastal ice might accelerate its outflow, speeding the rise of global oceans, according to research published in the July 2 issue of Nature. The researchers are at numerous universities and are led by R.E. Bell of Columbia University.
Environmentalists have worried about Antarctica's fate for decades.
In the 1970s, a few researchers warned that "global warming" might melt part of the Antarctic ice sheet, which is several miles thick. As a result, they said, sea levels could rise globally.
Ever since, glaciologists -- scientists who study the world's vast outcroppings of glacial ice, from Greenland to Antarctica -- have warred over what's really happening in the southernmost continent.
They fall into two camps. One argues that Antarctic ice has been relatively stable over millions of years, and is unlikely to undergo major collapse as the planetary temperature rises, according to geophysicist Alan Cooper of the U.S. Geological Survey at MenloPark, Calif.
Another camp, Cooper says, argues that at least parts of the West Antarctic Ice Shelf are highly unstable, and could rapidly fall apart during a major warming. By "rapidly," they mean a few centuries, extremely fast in geological terms.
Cooper -- who declines to side with either camp -- says the public can learn more about Antarctic ice dynamics at a Web site:
While concerned by Rignot's observations, experts caution against jumping to conclusions.
"Eric Rignot's observation does not mean that the (Antarctic ice) collapse has started; it does not mean sea level will be 20 feet higher in 100 years," says Richard Alley of Pennsylvania State. "The easiest reason (for saying this) is that he hasn't watched (the glacier) very long."
Conceivably, Alley said, the glaciers might be undergoing some very dramatic, but normal, changes that are unrelated to global warming.
"Glaciers do odd things sometimes. They flow fast, then slowdown. ... You could anthropomorphize them and say they have a mind of their own," says Alley, who calls for further research.
The new evidence impresses at least one veteran skeptic, Barclay Kamb, a noted glaciologist at Caltech.
Originally, Kamb said, "I was rather skeptical of this idea of (Antarctic ice sheet) disintegration, it seemed (to me) like a play for attention, like grandiosity."
But now, he says, the evidence for rapid ice changes is good enough that the worst case scenarios are worth worrying about.
If the ice sheet disintegrated, "sea level would rise by about five meters, that is, about 20 feet," Kamb says. "You'd produce a lot of these huge 'tabular' icebergs, some as big as the state of Connecticut."
Scherer's work impresses John Barron, a USGS-Menlo Park geologist who studies diatoms.
"I think (Scherer has) proven his case" that the ice sheet changes substantially over time, Barron says. "What has been lacking is direct evidence.
"And now he has provided direct evidence that at some time in the last 1.3 million years, there was no ice sheet over those sites."
Meteorologist Mark Fahnestock of the University of Maryland at College Park thinks it's too early to say whether the ice sheet is disintegrating over the centuries, or is just undergoing routine variations in shape and size.
But if the ice continues to melt at high speed, he says, "then maybe we will get to the point where we would call it a warning signal."