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Antarctica gets heavier every year

New York, May 20: The eastern half of Antarctica is gaining weight, more than 45 billion tonnes a year, according to a new scientific study.

Data from satellites bouncing radar signals off the ground show that the surface of eastern Antarctica appears to be slowly growing higher, by about 1.8 cm a year, as snow and ice pile up.

The gain in eastern Antarctica snow partly offsets the rise in sea level caused by the melting of ice and snow in other parts of the world. The finding also matches expectations that the earth’s warming temperatures would increase the amount of moisture in the air and lead to greater snowfall over Antarctica.

“It’s been long predicted by climate models,” said Curt H. Davis, a professor of electrical and computer engineering at the University of Missouri and the lead author of a paper that was published on the website of the journal Science yesterday. “This is the first observational evidence.”

The accumulation occurring across 2.75 million square miles of eastern Antarctica corresponds to a gain of 45 billion tonnes of water a year or, equivalently, the removal of the top 0.12 mm of the world’s oceans. “This is the only large terrestrial ice body that is likely gaining mass rather than losing it,” Davis said.

The data, from two European Space Agency satellites, cover 1992 to 2003, but because the satellites do not pass directly over the South Pole, they did not provide any information for a 1,150-mile-wide circular area around the pole. Assuming that snow was falling there at the same rate seen in the rest of Antarctica, the total gain in snowfall would correspond to a 0.18-mm-a-year drop in sea levels.

The data also deepen a mystery: Satellite measurements show that the level of the world’s oceans has been rising about 3 mm a year in recent years, and scientists cannot figure out where all of the water is coming from.

Because water expands when it warms, the rise in global temperatures by itself causes sea levels to rise about 1 mm a year. The melting of glaciers in Greenland, Antarctica and elsewhere appears to account for another mm or so.

That leaves “at least a missing millimetre a year to explain,” said Robert Thomas, a glaciologist who works with Nasa. “This is perhaps another reason to suggest the information that Curt has presented doesn’t include the entire picture.”

Thomas said that there could be as-yet-unseen melting of ice along the edges of Antarctica, where the satellites could not map the steeper coastal topography.

The new study is “another piece of the puzzle that we’re still putting together,” said Waleed Abdalati, head of the cryospheric sciences branch at Nasa’s Goddard Space Flight Centre in Maryland.

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