| | |  Editorials | Environmental | April 2009 
Antarctica: Another Ice Shelf Falls Away
 Marcela Valente - Inter Press Service
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Buenos Aires - Accelerated warming in the Antarctic Peninsula has caused the loss of over 85 percent of the ice shelves surrounding the northern half of the peninsula in the last 20 years, experts say.
The latest collapse occurred on the weekend. The Wilkins ice shelf, an ice sheet up to 250 metres thick located on the southwestern side of the peninsula - the northernmost part of the mainland of Antarctica - had already shrunk from a surface area of 16,000 to 13,700 square kilometres.
Finally the slender ice bridge attaching it to an offshore island collapsed, releasing a considerable portion of the ice shelf to sea, where it is breaking up.
"It was expected, because of the condition it was in. The remaining fragment of the ice shelf was unstable, and we did not know whether it would go this (southern hemisphere) summer or next," biologist and expert glaciologist Hernán Sala, of the Argentine Antarctic Institute (IAA), told IPS.
A recent study indicated that the ice shelves located in the southern portion of the peninsula were under threat of breaking up, he said. Summer temperatures in that area average -1.5 degrees Celsius, so most of the ice shelves that remain in the region are found there.
The snapping of the ice bridge was confirmed by the British Antarctic Survey, based on satellite images provided by the European Space Agency (ESA). But Sala and glaciologist Pedro Svarka, also of the IAA, have been warning about ice shelf fragmentation for a long time.
The ice shelves become degraded and break up gradually. Their surface becomes covered with meltwater, and eventually they cannot withstand the motion of the sea, which breaks the bridges that join them to the land mass.
The event contributed to the campaign on climate change in Antarctica organised by the World Wide Fund for Nature and the Fundación Vida Silvestre Argentina (Argentine Wildlife Foundation, FVSA) to raise global awareness of the problem.
As ministers of the Arctic Council - a forum of Arctic countries and peoples - and the signatories to the Antarctic Treaty on peaceful use of and scientific research on the southern continent hold their first ever joint session this week in the U.S. city of Baltimore, Maryland, environmental organisations are warning that "time is running out."
In an interview with IPS, FVSA's Juan Casavelos said that the ministers, who began to meet Monday on the 50th anniversary of the Antarctic Treaty, were also expressing their concern about the impact of climate change on the earth's polar regions.
"The average global temperature has risen by 0.8 degrees Celsius, but at the poles it has increased by more than 2.5 degrees," he said. "We hope that the disintegration of the Wilkins ice shelf will help draw attention to the situation."
According to the IAA, over the past half-century surface air temperatures on the Antarctic peninsula, located 1,600 kilometres southeast of the southernmost tip of South America, have risen by an average of 2.5 degrees Celsius. The last two decades were the region's warmest in one hundred years of record-keeping.
In contrast, the eastern part of the frozen continent is experiencing colder temperatures than usual, also regarded as a probable result of climate change caused by greenhouse gas emissions.
The most dramatic transformation on the continent, according to experts, is the collapse of the ice shelves around the Antarctic peninsula. Already over 30,000 square kilometres of glacier-derived ice have floated off to sea as giant icebergs.
According to Sala, 85 percent of the ice shelves on the east and west sides of the northern portion of the peninsula have broken off and eventually melted.
The Wilkins ice shelf is further south, and had a surface area equivalent to the U.S. Pacific island of Hawaii. Previously, the Larsen A and B ice shelves and the Prince Gustav Channel, Müller, Jones, Wordie and George VI (North and South) ice shelves had all collapsed.
Sala said that the IAA's hypothesis, for which evidence has been increasing with each of these events, is that when an ice shelf disintegrates, the glaciers feeding it speed up their flow into the sea.
This is not the case with the Wilkins ice shelf, which was fed by snowfall on the ice platform, but it did describe what happened with the Larsen A and B ice shelves, he said. After their collapse, the tributary glaciers began to flow up to eight times faster, became narrower, and retreated.
Ice that was previously landlocked causes sea levels to rise when it enters the ocean and melts, unlike floating ice shelves that already displace their own weight. "So far this trend, although worrying, is affecting only the Antarctic peninsula rather than the entire continent, and does not contribute very much to rising sea levels," Sala said.
However, if the Larsen C ice shelf were to disintegrate, an enormous wall holding back vast masses of ice on the continent of Antarctica would be lost, and the sea level would rise around its coasts, the IAA maintains.
Ice sheets reflect the sun's rays, whereas sea water absorbs them and their heat, so that the melting of the polar ice caps has a multiplier effect, further accelerating global warming. Casavelos said that scientists "are extremely concerned at the pace of change caused by the impact of global warming on the polar regions," and announced that the Scientific Committee on Antarctic Research (SCAR) will publish a report on the phenomenon in a few months.
"Ice sheets the size of small countries are collapsing, and the latest evidence shows that the effects of global warming are accelerating this process in Antarctica, where the Wilkins ice sheet has just disintegrated," Casavelos said. |
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