Antarctic ice melt traced to 10,000 years ago

Melting of the West Antarctica ice sheet may have begun long before human-induced climate change

October 9, 1999
Web posted at: 5:32 p.m. EDT (2132 GMT)

In this story: Role of global warming debated Disintegration may be unstoppable RELATED STORIES, SITES

From staff and wire reports

SEATTLE (CNN) -- The meltdown of a huge ice sheet in the West Antarctic began about 10,000 years ago -- well before any human-induced climate change -- says a new study published in the journal Science.

The leader of the team of scientists responsible for the research, Howard Conway of the University of Washington, told the Associated Press:

"Collapse appears to be part of an ongoing natural cycle, probably caused by rising sea level initiated by the melting of the Northern Hemisphere ice sheets at the end of the last ice age."

Role of global warming debated

Conway added, "Global warming could well speed the process. Our study doesn't address that problem."

Dan Lashof, of the Natural Resources Defense Council, said, "Global warming could actually accelerate this melting, which would potentially double or triple the rate of sea level rise compared to the best estimates that had previously been made."

But scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, have kept track of the icecap using satellite technology, and they say global warming may not be a factor.

"There doesn't appear to be a direct connection at this time between rapid flows that have been observed and the warmer temperatures in Antarctica, for instance," said Mark Drinkwater of the Jet Propulsion Laboratory

The report by Conway's research team is one of three about the Antarctic ice sheet in the current issue of Science.

Another team of scientists, using satellite images, found the flow of Antarctic ice into the sea is dictated by the underlying contours of land, rather than temperature.

Conway's study found that the melting of the ice sheet, about half the size of Alaska, is on schedule to raise sea levels about 20 feet, or slightly more than six meters, over the next 7,000 years

Although climate changes may influence the rate of meltdown, the future of the ice sheet "may have been predetermined when the grounding line retreat was triggered in early Holocene time," about 10,000 years ago, according to the report.

The grounding line is the boundary between floating ice and ice that reaches to the sea floor. Scientists determined the line has receded about 800 miles since the last ice age, withdrawing at an average of about 400 feet per year for the last 7,600 years.

Conway's team calculated the movement of the grounding line using evidence gathered from raised beaches and radar imaging of subsurface ice structures. The timing of the melting was determined by carbon-14 dating of samples found on raised beaches.

Disintegration may be unstoppable

The report concludes that continued shrinking of the ice sheet, perhaps even complete disintegration, "could well be inevitable."

The ice sheet's meltdown is of concern because of estimates that its disappearance could swamp low lying coastal communities around the world.

Icecap melting increases sea level worldwide, which is presently rising by about 1.5 milimeters (.06 inches) every year.

The report was made public Friday, a day after U.S. environmental groups unveiled plans for a multimillion-dollar campaign to raise public awareness of global warming.

West Antarctica is the section of the continent south of the tip of South America.

Correspondent Jim Hill and The Associated Press contributed to this report.

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