JIJITANG2014-09-11 4:47 PM

ANTARCTICA IS LOSING 159 BILLION TONS OF ICE EVERY YEAR

New precise measurements taken by satellite show that the Antarctic ice sheet is losing 159 billion tons of ice each year—twice as much as when it was last measured.

Scientists used the European Space Agency’s CryoSat-2 satellite mission, which carries an altimeter, to produce the first complete assessment of Antarctic ice sheet elevation change.

In sharp contrast to past altimeter missions, CryoSat-2 surveys virtually all the Antarctic continent, reaching to within 215 kilometers of the South Pole and leading to a fivefold increase in the sampling of coastal regions where current ice losses are concentrated.

Overall, the pattern of imbalance continues to be dominated by glaciers thinning in the Amundsen Sea sector of West Antarctica. However, the improved capabilities of CryoSat-2, show that the rugged terrain of the Antarctic Peninsula are also problem areas.

On average West Antarctica lost 134 gigatons of ice, East Antarctica three gigatons, and the Antarctic Peninsula 23 gigatons in each year between 2010 and 2013—a total loss of 159 gigatons each year.

The polar ice sheets are a major contributor to global sea level rise and, when combined, the Antarctic losses detected by CryoSat-2 are enough to raise global sea levels by 0.45 millimeters each year alone.

In West Antarctica, ice thinning has been detected in areas that were poorly surveyed by past satellite altimeter missions.

POINT OF NO RETURN

These newly mapped areas contribute additional losses that bring altimeter observations closer to estimates based on other approaches.

But the average rate of ice thinning in West Antarctica has also increased, and this sector is now losing almost one third (31 percent) as much ice each year than it did during the five-year period (2005-2010) prior to CryoSat-2’s launch.

“We find that ice losses continue to be most pronounced along the fast-flowing ice streams of the Amundsen Sea sector, with thinning rates of between 4 and 8 meters per year near to the grounding lines of the Pine Island, Thwaites, and Smith Glaciers,” says lead author Malcolm McMillan from the University of Leeds.

This sector of Antarctica has long been identified as the most vulnerable to changes in climate and, according to recent assessments, its glaciers may have passed a point of irreversible retreat.


SEES THROUGH CLOUDS

Launched in 2010, CryoSat carries a radar altimeter that can “see” through clouds and in the dark, providing continuous measurements over areas like Antarctica that are prone to bad weather and long periods of darkness. The radar can measure the surface height variation of ice in fine detail, allowing scientists to record changes in its volume with unprecedented accuracy.

“Thanks to its novel instrument design and to its near-polar orbit, CryoSat allows us to survey coastal and high-latitude regions of Antarctica that were beyond the capability of past altimeter missions, and it seems that these regions are crucial for determining the overall imbalance,” says lead author Andrew Shepherd.

“Although we are fortunate to now have, in CryoSat-2, a routine capability to monitor the polar ice sheets, the increased thinning we have detected in West Antarctica is a worrying development. It adds concrete evidence that dramatic changes are underway in this part of our planet, which has enough ice to raise global sea levels by more than a meter. The challenge is to use this evidence to test and improve the predictive skill of climate models.”

“The increasing contribution of Antarctica to sea-level rise is a global issue, and we need to use every technique available to understand where and how much ice is being lost,” says Professor David Vaughan of the British Antarctic Survey, who was not involved in the study.

“Through some very clever technical improvements, McMillan and his colleagues have produced the best maps of Antarctic ice-loss we have ever had. Prediction of the rate of future global sea-level rise must be begin with a thorough understanding of current changes in the ice sheets— this study puts us exactly where we need to be.”

The full report is published in Geophysical Research Letters.


Original Article:

Increased ice losses from Antarctica detected by CryoSat-2, Published on Journal 《Geophysical Research Letters》in Jun 9, 2014.


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