Wilkens ice shelf rapidly melting

Ice shelf succumbs to warming

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Wednesday, 26 March 2008

A large chunk of an Antarctic ice shelf has disintegrated over the last month, with scientists saying it's further evidence of the warming effect of human greenhouse gas emissions.

Satellite images show a 160-square mile area of the 5000-sq.m. Wilkins Ice Shelf in the south-west Antarctic below South America has broken up and a much larger area is at risk of falling away, according to the National Snow and Ice Data Center at the University of Colorado.

Lead scientist at the Center, Ted Scambos, told Reuters that half the entire shelf could disappear within a few years after being a permanent fixture for hundreds of years. The way it is shattering is consistent with previous ice shelf losses that subsequent studies have put down to global warming, he said.

The dramatic collapse of the Larsen B Ice Shelf in Antarctica over just a month in 2002 helped raise awareness of climate change around the world and the British Antarctic Survey has since said human greenhouse emissions are responsible.

The collapse of the Wilkins Ice Shelf comes toward the end of the Southern Hemisphere summer and follows record ice-melt of the Arctic ice cap last Northern summer. Scientists have been surprised by the rate of polar thawing and say that global warming is occurring fastest in polar regions.

A separate study has concluded that soot particles falling on polar and mountain ice cover around the world may explain higher rates of ice thaw and overall global warming in recent years than had been predicted. Another study concluded that the high polar melt rates were due to a combination of factors, including natural events, not just the effects of human greenhouse gas emissions.

Reuters 25/3/08, Environment News Service 16/10/06

Related stories:
Arctic thaw natural and manmade
Soot the dark horse in global warming

Images of Wilkins Ice Shelf Breakup

Source: Breakup of the Larsen B Ice Shelf: 15 February 1998 - 18 March 1999

NSIDC has monitored the Wikins ice shelf for signs of retreat for several years. A review of historical data and older satellite images indicates that retreat rate along the northern edge of the Wilkins began to pick up in the mid to late 1980's. In the last few years, several small break-up events have occurred, with long narrow icebergs calving from the shelf front and then becoming entrapped in thick sea ice in front of the shelf.

In March of 1998, AVHRR images recorded what appeared to be a large break-up event along the northwestern front. The shelf appearance changed from solid white to mottled in images of reflectance, from a uniformly cold temperature to a mixture of warm and cold surfaces in thermal imagery. Recently, SAR data gathered in August of 1998 was examined, and it revealed that this event was a major retreat of nearly 1100 km².

Ordinarily, ice shelves calve relativly large bergs from their fronts; i.e., the majority of the area lost to maintain equilibrium is lost in a few major calving events. In the Larsen B, and as vividly illustrated here for the Wilkins, the retreating Peninsula ice shelves are calving thousands of bergs at once, suggesting that they are shattered in place before being dispersed by storms, currents, or wave action. A mechanism in which meltwater enhances ongoing, natural fracturing in the shelf was suggested many years ago by several scientists: current data supports the theory very well.

AVHRR: 28 January 1996

AVHRR: 20 November 1998

The breakups come as temperatures continue to rise and the melt season lengthens on both sides of the Antarctic Peninsula in the 1990's. Melt ponds are visible in other SAR images in the northeastern area of the Wilkins, and other field work by the British Antarctic Survey suggests that the snow on the shelf is saturated with water.

The lower image is an enhanced synthetic aperture radar (SAR) image acquired by Radarsat and provided by the Alaska Satellite Facility.

SAR Image: 16 August 1998

Also see:

Antarctic Meteorology and Climatology (Cambridge Atmospheric and Space Science Series) by J. C. King See all pages with references to "synoptic environment". Excerpt - on Page 39: " ... and surrounding sea areas. With so few in situ observations, this imagery is the only means of monitoring the broad-scale synoptic environment over the ... " Key Phrases: Weddell Sea, Antarctic Peninsula, Southern Ocean, Bellingshausen Sea, East Antarctica, Northern Hemisphere, katabatic layer, katabatic stream, katabatic jumps, mesocyclone activity, circumpolar trough, katabatic circulation (see more) Key Phrases: Weddell Sea, Antarctic Peninsula, Southern Ocean, Bellingshausen Sea, East Antarctica, Northern Hemisphere, Meteorological Office, New Zealand, Ross Sea, West Antarctica, Faraday Station, South Polar, South Pacific, Terra Nova Bay, South America, Cape Denison, Transantarctic Mountains, Marie Byrd Land, Ronne Ice Shelf, Australian Bureau of Meteorology, Tasman Sea, Dronning Maud Land, Month Figure, Rothera Station, Pacific Ocean, katabatic layer, katabatic stream, katabatic jumps, mesocyclone activity, circumpolar trough, katabatic circulation, longitude tessera, strong surface temperature inversion, katabatic drainage flow, katabatic outflow, strong katabatic flow, mesoscale cyclogenesis, barotropic low, frequent cyclogenesis, katabatic surges, katabatic wind regime, persistent katabatic winds, water vapour imagery, synoptic environment, water vapour budget, climatological investigations, cyclogenesis events, unfrozen ocean, mesoscale weather systems, mean virtual temperature (see less)

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Predictability of Weather and Climate by Tim Palmer See all pages with references to "synoptic environment". Key Phrases: Weather Rev, Met Office, Cambridge University Press, Tim Palmer, Renate Hagedorn, Monte Carlo, Southern Oscillation, North American, Academic Press, Shinfield Park, Technical Memorandum, Martin Ehrendorfer (see more)