200-metre thick Antarctic ice shelf melts
The Guardian, March 20, 2002
LONDON - Scientists from the British Antarctic Survey said yesterday the speed of the complete disintegration of the 200-metre thick, 3,250 square kilometer Larsen B ice shelf was "staggering." They had predicted the collapse of the continent's northernmost ice shelf four years ago following evidence of the retreat of many glaciers on the Antarctic Peninsula, but the final break up of the whole shelf took just 31 days and has shocked glaciologists with its scale and speed.
The shattered ice has formed a plume of thousands of icebergs, adrift in the Weddell Sea, east of the peninsula. The collapse is believed to have dumped more ice into the Southern Ocean than all of the previous half century's icebergs combined.
Yesterday the UK environment minister Michael Meacher said the collapse of the Larsen B shelf was "a great cause of concern and a wake-up signal to the whole world."
A spokesman for Greenpeace international said yesterday that the current melting trend was an acutely disturbing sign of global warming, and it may be the precursor for more dangerous events. "This area and that of the western Arctic off Alaska are the two most rapidly warming places on the globe. The trends of melting ice shelves is now clear," said Steve Sawyer, a climate change scientist.
A further fear of international climate scientists is that the disappearance of large quantities of ice means the Antarctic could warm up more quickly because 80% of the heat and light of the sun is reflected back into space from ice or snow. With a loss of sea ice and ice shelves, reduced albedo, or reflective power, causes a change in the absorption of heat and carbon dioxide, which means more warming.
A Rhode Island-size piece of the floating ice fringe along a fast-warming region of Antarctica has disintegrated with extraordinary rapidity, scientists said yesterday.
The loss of floating ice does not contribute to rising sea levels, just as melting ice cubes floating in a glass do not cause it to overflow. But the researchers said this was the first time in thousands of years that this part of Antarctica — the east coast of its arm-shaped peninsula — had seen so much ice erode and temperatures rise so much.
While it is too soon to say whether the changes there are related to a buildup of the "greenhouse" gas emissions that scientists believe are warming the planet, many experts said it was getting harder to find any other explanation.
"With the disappearance of ice shelves that have existed for thousands of years, you rather rapidly run out of other explanations," said Dr. Theodore A. Scambos, a glaciologist at the National Snow and Ice Data Center at the University of Colorado, which has been monitoring the loss of ice in the Antarctic along with the British Antarctic Survey.
Other parts of Antarctica have experienced different trends, including a cooling of the continent's interior in recent decades.
The latest ice breakup occurred in the Larsen B ice shelf, which has probably existed since the last ice age. "There's no evidence of any period in the last 12,000 years where there was open water in the area that has now been exposed," Dr. Scambos said.
For years, researchers hiking on the ice and using satellites have been watching pieces of the shelf slowly break away, but the disintegration over the last month was on a vastly greater scale, several experts said. "The speed of it is staggering," said Dr. David Vaughan, a glaciologist at the British Antarctic Survey.
Starting in February, satellites recorded the event as the ice sheet fragmented into thousands of floes.
Scientists say the likely culprit is rapidly warming summer air temperatures. Along that part of the peninsula, temperatures have risen 4.5 degrees in five decades, and hundreds of small ponds of meltwater have formed on the surface of the Larsen shelf and others nearby.
The surface water migrates into tiny cracks in the ice, steadily deepening and widening them until the monumental structure starts to fall apart, Dr. Scambos said.
Antarctic ice shelf breaks apart
An Antarctic ice shelf that was 200 metres thick and with a surface area of 3,250 square kilometers has broken apart in less than a month.
UK scientists say the Larsen B shelf on the eastern side of the Antarctic Peninsula has fragmented into small icebergs.
Researchers from the British Antarctic Survey (Bas) predicted in 1998 that several ice shelves around the peninsula were doomed because of rising temperatures in the region - but the speed with which the Larsen B has gone has shocked them.
"We knew what was left would collapse eventually, but the speed of it is staggering," said Dr David Vaughan, a glaciologist at the Bas in Cambridge, UK.
"[It is hard] to believe that 500 billion tonnes of ice sheet has disintegrated in less than a month."
The climate on the peninsula has changed rapidly in the last 50 years. The region has experienced a 2.5 degree Celsius rise in average temperatures - an increase greater than for any location in the Southern Hemisphere.
However, the picture generally in Antarctica is a complicated one with temperatures in the interior actually falling over the same period. There is also some evidence that the retreat of the West Antarctic Ice Sheet, on the other side of the peninsula to the Larsen B shelf, has halted.
The Larsen B was one of five ice shelves - huge masses of ice that are floating extensions of the ice sheets covering the land - that had been steadily shrinking because of climate change, Dr Vaughan said.
But the break up of the ice mass would not raise sea levels because the ice was already floating, he added. Sea levels would only be affected if the land ice behind it now began to flow more rapidly into the sea.
The UK scientists were first alerted to the Larsen B collapse by US colleagues studying images from the American space agency's Modis satellite.
The British Antarctic Survey then dispatched its research ship RRS James Clark Ross to the area to obtain photographs and samples.
Scientists hope the data gathered on site will help them determine when such an event last happened and which ice shelves are threatened in future.
The US-based National Snow and Ice Data Center (NSIDC) said on Tuesday: "This is the largest single event in a series of retreats by ice shelves in the peninsula over the last 30 years.
"The retreats are attributed to a strong climate warming in the region."
US scientists also reported on Tuesday that an iceberg more than nine times larger than Singapore had broken off Antarctica.
The National Ice Center said the berg, named B-22, broke free from an ice tongue in the Amundsen Sea, an area of Antarctica south of the Pacific Ocean.
It is more than 64 kilometers (40 miles) wide and 85 kilometers (53 miles) long, and covers an area of about 5,500 square kilometers.
Icebergs are named for the section of Antarctica where they are first sighted. The B designation covers the Amundsen and eastern Ross seas and the 22 indicates it is the 22nd iceberg sighted there by the US National Ice Center.
The Boston Globe,March 19, 2002
LONDON (AP) A large Antarctic ice shelf in an area that is warming faster than the global average has collapsed with ''staggering'' rapidity, British scientists said Tuesday.
The shelf designated as Larsen B, 650 feet thick and with a surface area of 1,250 square miles, has collapsed into small icebergs and fragments, the British Antarctic Survey said. Before breaking apart, the ice shelf was about the size of Rhode Island.
The collapse was first detected on satellite images earlier this month by Ted Scambos of the National Snow and Ice Data Center at the University of Colorado.
''In 1998, BAS predicted the demise of more ice shelves around the Antarctic peninsula. Since then, warming on the peninsula has continued and we watched as piece-by-piece Larsen B has retreated,'' said David Vaughan, a glaciologist at the British Antarctic Survey.
''We knew what was left would collapse eventually, but the speed of it is staggering. Hard to believe that 500 million billion tons of ice sheet has disintegrated in less than a month.''
In the past half century, the Antarctic Peninsula has warmed by 4.5 degrees Fahrenheit, much faster than average global warming, the Survey said. As a result, five ice shelves which extend out over the ocean have retreated. The peninsula is nearest to southern Argentina and Chile.
Two months ago, however, the journal Science reported new measurements showed the ice in West Antarctica was thickening, reversing earlier estimates that the sheet was melting. The Antarctica Peninsula extends from West Antarctica.
Those flow measurements for the Ross ice streams, using special satellite-based radars, indicate that movement of some of the ice streams has slowed or halted, allowing the ice to thicken, according to a paper in the Jan. 18 issue.
Researchers Ian Joughin of the California Institute of Technology and Slawek Tulaczyk of the University of California, Santa Cruz, said the thickening, if not merely part of some short-term fluctuation, represented a reversal of the long retreat of the ice.
Their finding came less than a week after a separate paper in Nature reported that Antarctica's harsh desert valleys long considered a bellwether for global climate change have grown noticeably cooler since the mid-1980s.
Air temperatures recorded continuously over a 14-year period ending in 1999 declined by about 1 degree Fahrenheit in the polar deserts and across the White Continent, that paper said.