Date: December 26 2012
A MASSIVE ice shelf in Antarctica is warming at twice the rate previously thought, raising concerns about the speed and scale of future sea level rises, new research shows.
Temperatures at the remote Byrd Station in western Antarctica have risen 2.4 degrees between 1958 and 2010, three times the average global rate.
This follows recent studies showing increasing melting in the same region, including landmark Australian research that found the continent's net loss of ice amounted to about 69 billion tonnes a year.
The new findings, published this week in the journal Nature Geoscience, are considered significant because the warming is taking place on and around one of the world's biggest ice sheets. It contains enough frozen water to raise global sea levels by more than three metres, should it eventually melt entirely.
''Our record suggests that continued summer warming in west Antarctica could upset the surface mass balance of the ice sheet, so that the region could make an even bigger contribution to sea level rise than it already does,'' the report's lead author, Professor David Bromwich of Ohio State University, said.
''Even without generating significant mass loss directly, surface melting on the [west Antarctic ice sheet] could contribute to sea level indirectly, by weakening the west Antarctic ice shelves that restrain the region's natural ice flow into the ocean.''
Historically, measuring temperatures across western Antarctica has been fraught with problems. At Byrd Station, sizeable chunks of the data is missing, partly because of power failures over the Antarctic winter.
The researchers attempted to fill the gaps in data with climate models, then refined the models until they accurately matched the empirical measurements.
The findings could then be cross-checked against other weather stations in the region, as well as from results from bore holes drilled into the ice, which can be used to estimate past temperatures.
Earlier this year, a team of scientists from the British Antarctic Survey announced results from a drilling program that was attempting to compare current warming to past trends.
They discovered that gradual warming had been taking place over the past 600 years but that the rate had accelerated markedly over the past century, and especially over the past 50 years, as the effects of growing human greenhouse gas emissions were superimposed over natural climatic variations.
The Nature Geoscience paper found that average winter and spring temperatures in western Antarctica had risen the most quickly, but summer temperatures were also up.
However, the region is still bitterly cold - summer temperatures hover at about minus-10 degrees.
Run-off from the melting ice sheet has a relatively minor impact on sea levels, of about 0.2 millimetres a year, Professor Bromwich said. This is about a 15th of the annual average rate of three millimetres.
Researchers at the University of Tasmania examined the Antarctic thaw in research published in October, finding that although some parts of eastern Antarctica ice were growing, this was more than offset by melting in the west.
The Australian team, led by Professor Matt King, developed a new analytical model that matched satellite data to ground-based observations.
As ice melts from the continent's surface, the weight on the ground beneath the ice is reduced and the land rises at the rate of about two millimetres a year. The scientists refined earlier models to better fit the existing data and showed that the net ice loss in recent years was an average of 190 million tonnes a day.
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