Uncontrollable ice-melt? Uncorking East Antarctica could yield unstoppable sea-level rise, simulations show

The melting of a rather small ice volume on East Antarctica's shore could trigger a persistent ice discharge into the ocean, resulting in unstoppable sea-level rise for thousands of years to come. This is shown in a study now published in Nature Climate Change by scientists from the Potsdam Institute for Climate Impact Research (PIK). The findings are based on computer simulations of the Antarctic ice flow using improved data of the ground profile underneath the ice sheet

"East Antarctica's Wilkes Basin is like a bottle on a slant," says lead-author Matthias Mengel, "once uncorked, it empties out." The basin is the largest region of marine ice on rocky ground in East Antarctica. Currently a rim of ice at the coast holds the ice behind in place: like a cork holding back the content of a bottle. While the air over Antarctica remains cold, warming oceans can cause ice loss on the coast. Ice melting could make this relatively small cork disappear -- once lost, this would trigger a long term sea-level rise of 300-400 centimeters. "The full sea-level rise would ultimately be up to 80 times bigger than the initial melting of the ice cork," says co-author Anders Levermann.

"Until recently, only West Antarctica was considered unstable, but now we know that its ten times bigger counterpart in the East might also be at risk," says Levermann, who is head of PIK's research area Global Adaptation Strategies and a lead-author of the sea-level change chapter of the most recent scientific assessment report by the Intergovernmental Panel on Climate Change, IPCC. This report, published in late September, projects Antarctica's total sea level contribution to be up to 16 centimeters within this century. "If half of that ice loss occurred in the ice-cork region, then the discharge would begin. We have probably overestimated the stability of East Antarctica so far," says Levermann.

Emitting greenhouse-gases could start uncontrollable ice-melt

Melting would make the grounding line retreat -- this is where the ice on the continent meets the sea and starts to float. The rocky ground beneath the ice forms a huge inland sloping valley below sea-level. When the grounding line retreats from its current position on a ridge into the valley, the rim of the ice facing the ocean becomes higher than before. More ice is then pushed into the sea, eventually breaking off and melting. And the warmer it gets, the faster this happens.

Complete ice discharge from the affected region in East Antarctica takes five thousand to ten thousand years in the simulations. However, once started, the discharge would slowly but relentlessly continue until the whole basin is empty, even if climate warming stopped. "This is the underlying issue here," says Matthias Mengel. "By emitting more and more greenhouse gases we might trigger responses now that we may not be able to stop in the future." Such extensive sea level rise would change the face of planet Earth -- coastal cities such as Mumbai, Tokyo or New York are likely to be at risk.

ARCTIC ICE DECREASING AND ANTARCTIC ICE INCREASING

         Much attention is paid to melting sea ice in the Arctic. But less clear is the situation on the other side of the planet. Despite warmer air and oceans, there is more sea ice in Antarctica now than in the 1970s- a fact often pounded on by global warming sceptics. The latest members suggest the Antarctica sea ice may be heading toward a record this year.

           A researcher of the University of Washington says the reason lie in the winds. A new modelling study to be published in the Journal of Climate shows that stronger polar winds lead to an increase in Antarctic sea ice, even in a warming climate.

           “The overwhelming evidence is that the Southern Ocean is warming”, said the author Jinlun Zhang, an oceanographer at the UW Applied Physics Laboratory. “Why would sea ice be increasing? Although the rate of increase is small, it is a puzzle to scientists.”

            His new study shows that stronger westerly winds swirling around the South Pole can explain 80% of the increase in Antarctica sea ice volume in the past three decades.

           The polar vortex that swirls around the South Pole is not just stronger than it was when satellite records began in the 1970s, it has more convergence, meaning it shoves the sea ice together to cause ridging. Stronger winds also drive ice faster, which leads to still more deformation and ridging. This creates thicker, longer-lasting ice, while exposing surrounding water and thin ice to the blistering cold winds that cause more ice growth.

         In a computer simulation that includes detailed interactions between wind and the sea, thicker ice- more than 6 feet deep– increased by about 1% every year from 1979 to 2010. While the amount of thin ice stayed fairly constant. The end result is a thicker, slightly larger ice pack that lasts longer into summer.

         When the model held the polar winds at a constant level, the sea ice increased only 20% as much. A previous study by Zhang showed that changes in water density could explain the remaining increase.

       “People have been talking about the possible link between winds and Antarctica sea ice expansion before, but I think this is the first study that confirms this link though a model experiment.” Said by Alex Schweiger, a polar scientist at the UW Applied Physics Lab. “This is another process by which dynamic changes in the atmosphere can make changes in sea ice that are not necessarily expected.”

     The research was funded by the National Science Foundation.

   Though, it is still a mystery why the southern winds have been getting stronger, some scientist have theorized that it could be related to global warming or to the Ozone depletion in the southern hemisphere or just to natural cycles of variability. Difference between the two poles could explain the opposite behave. Surface air warming in the Arctic is more uniform. Another difference in the Arctic is that, the Northern hemisphere is protected basin, while the Antarctic sea ice floats in open oceans where the ice can expand freely. Many of the models are unable to explain why the Antarctic ice increases.

“If the warming continues, at some point the trend will reverse

WORLD NOT ON TRACK OVER CLIMATE CHANGE

           One of the top UN official said that international leaders are failing to fight global warming, appealing directly to the world’s voters to pressure their politicians into taking tougher action against the build up of green gases.

Halldor Thorgeirsson told the journalists Tuesday that, “We are failing as an international community” and that the world is “not on track” to prevent potentially catastrophic climate change.

           Thorgeisson, a senior director with UN framework convention on climate change, was speaking with two hours left to go before the world powers gather in Paris for another round of negotiation over the future of the world’s climate. Which scientists warn will warm dramatically unless action is taken to cut down on greenhouse gas emissions.