NASA: West Antarctic ice sheet collapse unstoppable

Ice is melting in the western Antarctic at an "unstoppable" pace,scientists said Monday, warning that the discovery holds major consequences forglobal sea level rise in the coming decades.The speedy melting means that prior calculations of sea level rise worldwide madeby the Intergovernmental Panel on Climate Change will have to be adjustedupwards, scientists told reporters."A large sector of the West Antarctic ice sheet has gone into a state of irreversibleretreat. It has passed the point of no return," said Eric Rignot, professor of Earthsystem science at the University of California Irvine."The retreat of ice is unstoppable," he said, noting that surveys have shown there isno large hill at the back of these glaciers that could hold back the melting ice.Scientists have been warning about this so-called weak underbelly of westernAntarctic for decades, but only since the 1990s have scientists been able to gatherdetailed information on this remote area.The results are included in pair of published studies that document observationalchanges in the Antarctic in recent years, and predict the future behavior of the melting ice through computer models."This retreat will have major consequences for sea level rise worldwide," Rignotadded, anticipating the melting will take place largely in the next two centuries."It will raise sea level by 1.2 meters or four feet," said Rignot, whose paper appearsin the peer-reviewed Geophysical Research Letters, a journal of the AmericanGeophysical Union.- Melting over hundreds of years -Rignot, a glaciologist at NASA's Jet Propulsion Laboratory, said his study compileddata from satellites, airplanes, ships and ground surveys in the west Antarctic icesheet.Retreat of the area's Pine Island glacier has slowed in recent years, but scientistssaid that was likely to due to the very rapid retreat it went through early on.The nearby Thwaites glacier has been speeding up since 2006, and the long termtrend toward faster melting is clear.A separate study published in the journal Science on Monday found that Thwaitesglacier is melting fast and that its collapse could raise global sea level nearly two feet (60 centimeters).That study was based largely on computer modeling to predict future conditions,along with airborne radar measurements of the West Antarctic ice sheet that allowedscientists to map the underlying bedrock. Study author Ian Joughin, a glaciologist at the University of Washington, said theprocess is now expected to take between 200 and 1,000 years.He also found that such a collapse may be inevitable."All of our simulations show it will retreat at less than a millimeter of sea level riseper year for a couple of hundred years, and then, boom, it just starts to really go,"Joughin said- More sea level rise -Current projections of sea level rise, agreed upon by international surveys, do notaccount for the Antarctic ice sheet melting, experts said.Sridhar Anandakrishnan, professor of geosciences at Pennsylvania State University,said that studies like these show the Antarctic is undergoing "enormous change,"and will cause the United Nations to revisit their projections."The number for 2100 will almost certainly be revised and revised upwards, and myguess is toward what is now their upper limit of something like 90 centimeters,close to three feet," said Anandakrishnan, who was not involved in the new reports. He said that the rise in sea level is widely accepted to be a result of human-causedclimate change, driven by the burning of fossil fuels."As glaciers and ice sheets flow faster, that water has nowhere to go but in theocean and once in the ocean this results in a rise in sea level around the globe," hetold reporters.In the past, Greenland has been the source of most melting glaciers, but thatappears to be changing, with more and more output coming from the South Pole.The western Antarctica ice melt is particularly bad because much of the bottom ofthe ice is below sea level, compared to the rest of the Antarctic where the ice bed isabove sea level, Anandakrishnan said.