The Guardian, March 26, 2015
The ice around the edge of Antarctica is melting faster than previously thought, potentially unlocking metres of sea-level rise in the long-term, researchers have warned.
A team of US scientists looked at 18 years’ worth of satellite data and found the floating ice shelves that skirt the continent are losing 310km3 of ice every year. One shelf lost 18% of its thickness during the period.
The loss of ice shelves does not contribute much directly to sea level rise. But they act like a cork in a bottle at the point where glaciers meet the sea – jamming the flow of ice from the massive ice sheets of east and west Antarctica.
Professor Andrew Shepherd, director of the Centre for Polar Observation and Modelling at the University of Leeds, said the rates of ice loss were unsustainable and could cause a major collapse. This is already occurring at the massive Pine Island glacier, where ice loss has doubled in speed over the last 20 years as its blocking ice shelf has melted.
“This is a real concern, because such high rates of thinning cannot be sustained for much longer, and because in the places where Antarctic ice shelves have already collapsed this has triggered rapid increases in the rate of ice loss from glaciers above ground, causing global sea levels to rise,” he said.
The new research, published in the journal Science on Thursday, discovered for the first time that ice shelf melt is accelerating.
Dr Paul Holland, a climate scientist at the British Antarctic Survey (BAS), said the loss of the shelves would speed the complete collapse of the west Antarctic ice sheet, which would eventually cause up to 3.5m of sea level rise. But he said it was highly unlikely this would occur this century. He said the “worst case scenario” for 2100 was that ice sheets would contribute an additional 70cm to the sea level rise caused by the warming of the ocean.
The UN’s climate science body has not previously included the ice sheets of Antarctica and Greenland in its predictions for future sea level rise because scientists are not certain how fast they will slide into the ocean.
Holland said: “What humanity needs to know is what’s the sea level rise in 2100 and the biggest source of uncertainty in that is what’s going to happen to the ice sheets.”
Over the past decade the loss of ice shelf volume in Antarctica increased from 25km3 to 310km3 every year.
It is unclear whether the loss of ice is directly related to man-made climate change or a cyclical change in ocean currents. But the extra sea level rise from ice sheets will exacerbate the rise caused by the expansion of oceans as the world warms.
Professor David Vaughan, director of science at BAS, said the findings would help scientists to make more accurate predictions about future sea level rise.
“The rate of ice loss, especially when considered in terms of the percentage of ice lost in the last two decades, is dramatic. This research is a significant step towards improving our ability to predict the future of the Antarctic ice sheet and its contribution to global sea level rise.”
The western coast ice shelves contributed the majority of the ice loss. The rate of loss increased by 70% in the last decade. Two shelves in this region could completely disappear within a century. Conversely, there were some areas in east Antarctica where the shelves stayed stable or grew slightly. Vaughan said the regional variations were predicted by previous studies.
Holland said it was important not to confuse floating ice shelves, which can be up to 2km thick, with the much thinner sea ice. The one metre thick layer of sea ice around Antarctica has been expanding in recent decades, which some scientists think is because of increasing polar winds, which push the ice further out.