Wednesday, 26 March 2008
Have you ever hated to be right?
The Wilkins Ice Shelf covered an area of 16,000km2 (the size of Northern Ireland). Having been stable for most of the last century it began retreating in the 1990s. A major breakout occurred in 1998 when 1000km2 of ice was lost in a few months.
Satellite images processed at the US National Snow and Ice Data Center revealed that the retreat began on February 28 when a large (41 by 2.5 km) iceberg calved away from the ice shelf's south-western front. In a series of images, the edge of the shelf proceeded to crumble and disintegrate in a pattern that has become characteristic of climate-caused ice shelf retreats throughout the northern Peninsula, leaving a sky-blue patch spreading across the ocean surface compose of hundreds of large blocks of exposed old glacier ice (see pictures). By 8 March, the ice shelf had lost just over 570 km2, and the patch of disintegrated Antarctic ice had spread over 1400km2. As of mid-March, only a narrow strip of shelf ice was protecting several thousand kilometres of potential further break-up.
The recent break out leaves a thin strip of ice between Charcot and Latady islands on the Antarctic Peninsula.
Climate warming has increased the volume of summer meltwater on glaciers, which has weakened ice shelves. Sea ice, which protects ice shelves from ocean swell, has reduced also as a result of warming temperatures.
The collapse of the 32502 Larsen B Ice Shelf took place in 2002. During the past 40 years the average summer temperatures in this region of the north-east Peninsula has been 2.2°C. The western Antarctic Peninsula has showed the biggest increase in temperatures (primarily in winter) observed anywhere on Earth over the past half-century.
The Antarctic Peninsula is an area of rapid climate change and has warmed faster than anywhere else in the Southern Hemisphere over the past half century. Climate records from the west coast of the Antarctic Peninsula show that temperatures in this region have risen by nearly 3°C during the last 50 years – several times the global average and only matched in Alaska.
Ice sheet – is the huge mass of ice, up to 4 km thick, that covers Antarctica's bedrock. It flows from the centre of the continent towards the coast where it feeds ice shelves.
Ice shelf – is the floating extension of the grounded ice sheet. It is composed of freshwater ice that originally fell as snow, either in situ or inland and brought to the ice shelf by glaciers. As they are already floating any disintegration (like Larsen B) will have no impact on sea level. Sea level will rise only if the ice held back by the ice shelf flows more quickly into the sea.
Regular satellite images of Wilkins Ice Shelf were obtained using NASA's Modis instruments and the International Polar Year 'Polar View' project which uses the European Space Agency Envisat satellite. Polar View operates to provide timely images of the Antarctic sea ice and shelves to assist science and operations in the Southern Ocean. Further information and images are available at www.polarview.aq
This discovery follows the recent UNEP report that the world's glaciers are continuing to melt away. Data from 30 reference glaciers in nine mountain ranges show that between the years 2004-2005 and 2005-2006 the average rate of melting and thinning has more than doubled.
The Cambridge-based British Antarctic Survey (BAS) is a world leader in research into global environmental issues. With an annual budget of around £40 million, five Antarctic Research Stations, two Royal Research Ships and five aircraft BAS undertakes an interdisciplinary research programme and plays an active and influential role in Antarctic affairs. BAS has joint research projects with over 40 UK universities and has more than 120 national and international collaborations. It is a component of the Natural Environment Research Council.JIM ELLIOT, BRITISH ANTARCTIC SURVEY.
Posted by Rev. Peter Doodes at 10:16