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Is east Antarctic ice melting?

Daniel Cressey; cross-posted from The Great Beyond

antarctica top down.jpgThe ice sheet covering east Antarctica may have been melting since 2006, according to new research, contradicting previous suggestions that it has remained stable or even grown in mass.

Using measurements for 2002 to 2009 from a twin pair of satellites, researchers at the University of Texas at Austin in Austin, Texas, say east Antarctica is losing mass at about 58 gigatonnes a year. Most of the loss appears to be from coastal regions and to stem from increased ice loss post 2006.

Previous studies have generally used satellites to measure elevation or movement of ice. The new study – published in Nature Geoscience – instead looks at the Earth’s gravity field and uses that to work out how much ice is there. It also suggests that 132 Gt of the total annual ice loss of 190 Gt per year is coming from the west.

Although there are uncertainties in the data, the new estimates of ice loss are on average consistent with previous calculations, “but, in contrast to previous estimates, they indicate that as a whole, Antarctica may soon be contributing significantly more to global sea-level rise”, the researchers write in their paper.


The finding is significant because the east of the continent has traditionally been seen as the more stable half. It is also the bigger half so if it is melting it could contribute more to sea level rise.

“We felt surprised to see this change in east Antarctica,” says study author Jianli Chen (BBC, Guardian). “If the current trend continues or gets worse, Antarctica could become the largest contributor to sea level rises in the world. It could start to lose more ice than Greenland within a few years.”

Jonathan Bamber, of the University of Bristol, told Bloomberg he was also surprised, as those previous studies have suggested the East Antarctic Ice Sheet really wasn’t changing that much. “This result really confirms that there are very substantial inconsistencies between different estimates,” he says. “The margins of error are so large that it can be difficult to draw strong conclusions.”

Image: Antarctic continent surrounded by sea ice / NASA/Goddard Space Flight Center / Scientific Visualization Studio, Canadian Space Agency, RADARSAT International Inc.

Comments

  1. Report this comment

    Larry Sheldon said:

    “East Antarctic”?

    Or “East Anglia”?

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    zanardm said:

    Re: A testable model addressing the issue of East Antarctica ice sheet stability?

    As above: If the Isthmus of Panama were opened by significant rising sea level, then Gulf of Mexico waters might egress to Pacific. This would then seem to disrupt the Gulf Stream. Hence one could also obtain sea bed cores from south more proximal aspect of Stream to see if there has been disruption of flow. This could be compared to Panama Isthmus findings, and also could serve as a proxy for significant sea level increase from East Antarctica dissolution.

    For record of foraminifera for http://www.nature.com/nature/journal…ture01089.html Northern ice sheet formation would seem dependent on warm water with higher evaporation and subsequent percipitation. http://www.nature.com/nature/journal…ture01089.html Thus a history of cycles of northern ice sheets would seem consistent with persistence of Gulf Stream; and hence consistent with persistence of closure of Isthmus of Panama. Such persistence of Isthmus of Panama (84 ft elevation) would seem consistent with no sea surface elevation of ~180 ft. Hence cycles of glaciation, persistence of Gulf Stream, would seem consistent with no complete melting or dissolution of East Antarctica. Thus via indirect evidence, East Antarctica would seem to be historically stable.

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    Mike Pope said:

    Discovery of numerous lakes having formed on the surface of the East Antarctic ice sheet indicates it is subject to similar dynamics to those evident in Greenland. There, water from surface lakes has leaked down to bedrock providing lubricant, enabling the ice sheet to become mobile and stressed.

    In Greenland it has also been found that water has eroded the lake bed and tunnelled through the ice until it has discharged into the ocean This has also weakened and stressed parts of the ice sheet where it has occurred. It can be expected to occur in Antarctica.

    The East Antarctic ice cap is land based, unlike the western cap which is a marine ice sheet largely resting on the seabed and subject to rapid disintegration. Unlike the western cap, it covers land which rises from sea level at the coast to over 3,000m inland. The effects of surface lake water leaking to provide a lubricant at the ice base will eventually prove significant as a cause for ice loss.

    A more immediate cause for ice loss is exposure of the vast East Antarctic coastline to warming ocean currents and air streams. Their initial effects will produce seasonal melting and thinning of sea ice, permitting glaciers to discharge directly into the ocean, significantly increasing their rate of discharge and annual rate of ice loss.

    It is likely that these factors will result in the present loss of ice from the east Antarctic cap doubling within 5 years and probably doubling again within a further 5 years. The length of continental coastline exposed to the influences of global warming is much greater than in Greenland and by 2030 it is likely that the East Antarctic ice cap will be contributing far more to sea level rise.

    Current estimates are that sea level rise will be in the order of 1.1 – 1.5m by 2100. Given the likely contribution to rising sea level due to melting of the East and West Antarctic ice caps, those estimates appear to be an under estimation. A sea level rise of about 1.1m is more likely to occur by 2050 with a rise of at least 2.4m by 2100.

    The effect this will have on coastal populations is already known. In view of the reluctance of the worlds major emitters of greenhouse gases to reduce their emissions sufficiently to prevent a 2C rise in global temperatures, it would be prudent to plan for dealing with increasing coastal inundation from 2030 onwards.

    There is of course a limit in dealing with rising sea level. Cities such as New York and Shanghai can not be protected or moved out of the reach of a 2m rise in sea level, nor can the people who inhabit them or the densely populated major food producing river deltas. We either curtail greenhouse gas emissions and population growth or suffer the consequences.

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    Andrew Sheldon said:

    Does this research take into consideration continental loading caused by ice. i.e. As ice melts or thins, the continent is going to bounce back. This will affect gravity readings I suspect. I don’t think you can simply say that gravity change is attributable to ice melting, but also geostatic rebound might play a part.

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