Antarctic buffers sea level rise

The ice sheet covering the interior of Antarctica is thickening, researchers report in the journal Science.

This bulge, which was recorded by satellite, may temporarily buffer rising sea levels, they believe. Antarctica's "weight gain" is due to extra snowfall, caused by rising temperatures, the US-UK team thinks.

However, the scientists worry the overall mass of the Antarctic may be decreasing because ice near the coasts is melting, possibly at a greater rate.

Understanding Antarctica
The Antarctic contains the bulk of our planet's ice, so understanding its growth or shrinkage is critical to predicting future sea level changes.

Scientists fear that if the planet's oceans swell significantly, there could be devastation on populated low-level islands and coastal regions.

Sea levels are currently rising at about 1.8mm per year, largely because ice sheets in polar regions are melting, the Intergovernmental Panel on Climate Change (IPCC) has said.

However, the panel also predicted that global warming would lead to an increase in snow fall over the Antarctic, because warmer air leads to more evaporation and precipitation.

Scientists from both sides of the Atlantic tested this theory by analysing the thickness of Antarctica's central ice sheets, using satellite radar altimetry measurements.

They discovered that East Antarctica thickened at an average rate of 1.8cm per year between 1992 and 2003.

The region, which covers 75% of Antarctica's total land area, holds 85% of the total ice volume.

"The East Antarctic ice sheet absorbed ocean mass in the form of snowfall so, as a result, it slowed sea level rise," Curt Davis, of the University of Missouri, US, told the BBC News website.

"It is a modest slowing, but it is somewhat surprising because all the other terrestrial ice masses are contributing to sea levels. This is the only one that is absorbing mass rather than contributing to it."

Although Greenland may also be experiencing increased precipitation, Professor Davis says, the result is not the same.

"In Greenland we are getting more snowfall but Greenland is a lot warmer," he explained. "So whenever you get an increase in temperature in Greenland, you also get increased melt."

Finite effect
Even though Antarctica is, at the moment, taking the edge off the effects of a warming global climate, we should not take too much comfort, say the researchers.

Snowfall over East Antarctica will not continue to increase indefinitely in a warming world but, conversely, ice melt will accelerate proportionately with every degree of rising temperature, swelling oceans further.

"The effect will only work for a finite period of time," Professor Davis said. "Eventually, the snow will start to melt."

Also, the overall mass of Antarctica may be decreasing, because coastal melt may be happening faster than internal ice sheet gain.

"Since sea levels are rising, that would be a reasonable assumption to make, although we don't know for sure," added Professor Davis.

The instruments used in this particular study were unable to monitor the coastal regions because they could not cope with the steep terrain.

However, the European Space Agency satellite CryoSat, due to be launched in the next year, should be up to the task, Professor Davis believes.

"CyroSat has some special processes that allow it to do a better job," he said. "Over the next few years we should get a more definitive answer."

Source: news.bbc.co.uk