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Greenland ice sheet is melting at an accelerating rate

Warming in the Arctic has now reached the northernmost sections of the Greenland ice sheet. After a long period of stability (more than 25 years), we have found in a new study of the region that the northeast…

The receding edge of the Greenland ice sheet. Hannes Grobe, CC BY-SA

Warming in the Arctic has now reached the northernmost sections of the Greenland ice sheet. After a long period of stability (more than 25 years), we have found in a new study of the region that the northeast section of the ice sheet is no longer stable. This means global sea levels may rise even faster than was previously anticipated.

The Greenland ice sheet is a vast body of ice covering roughly 80% of the surface of Greenland. The northeast portion has one of the longest ice streams (rivers of ice) and drains a huge area. It was previously thought to be very cold and therefore stable.

Our new study shows how, over the past eight years, it has actually lost an increasing amount of ice. Satellite images show that the ice loss rate here is now the second largest in Greenland – only exceeded by the Jakobshavn Glacier.

Pointing out mis-predictions

This means that other models have underestimated the total mass loss and thus Greenland’s future contributions to global sea level change. To date, calculations of future rises in sea levels have not accounted for the large contribution of ice flowing into the ocean from this part of Greenland. Published in Nature Climate Change, our new study points out this mis-prediction.

Many modelling approaches used to assess future sea level rises have suggested that the northeastern sector of the ice sheet is relatively stable and therefore not contributing to any significant ice mass loss. They have used data from the last decade to model the Greenland ice sheet’s contribution to sea level rise by 2100, but they assume no mass loss in northeast Greenland, which is incorrect.

Declines in the ice sheet can be seen in recent years. Shfaqat A. Khan et al

Our study used a combination of old aerial photographs from 1978, and modern satellite observations to measure the thinning of Greenland’s glaciers. Together, they show that the thinning from 1978 to 2003 in the northeast was very limited. But, since 2006 there has clearly been a sustained mass loss in this section.

This increased loss is due to a combination of warmer summer air temperatures and warmer sea temperatures. This regional warming has reduced the extent of sea ice around the ice sheet, which has a stabilising effect on the glacier margins.

Unlike other large glaciers in Greenland, the Northeast ice sheet has an ice stream, which reaches more than 600km directly into its interior. This implies that changes at the marginal can affect the mass balance deep in the centre of the ice sheet. The fact that this ice loss is associated with a major ice stream that channels ice from deep in the interior of the ice sheet does add additional concern about what might happen. Due to the huge size of the Northeast Greenland ice stream, it has the potential to significantly change the total balance of the ice sheet overall in the near future.

New and surprising

The fact that the overall decline of the Greenland ice sheet has generally increased over the past few decades is well known. But the increasing contribution from the very cold northeastern part of the ice sheet during the last seven to eight years is new and very surprising. Over the past decade the front of the glacier has retreated by about 20km from the coast. This compares with a 35km retreat of the Jakobshavn glacier in warmer, western Greenland over the last 150 years.

The Greenland ice sheet has contributed more than any other ice mass to sea-level rise over the past two decades. It accounts for an increase in average levels around the world of 0.5mm per year, out of a total increase of 3.2mm per year. If completely melted, the ice sheet has the potential to raise global sea level by more than seven metres.

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9 Comments sorted by

  1. Smudge Martens

    Engineer

    "This increased loss is due to a combination of warmer summer air temperatures and warmer sea temperatures."

    Can you comment on the speculation that geothermal heat is a major contributor, in essence the theory is:

    "The temperature at the base of the ice, and therefore the current dynamics of the Greenland ice sheet is the result of the interaction between the heat flow from the earth's interior and the temperature changes associated with glacial cycles,"

    http://phys.org/news/2013-08-earth-mantle-contributes-greenland-ice.html

    -Cheers

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    1. David Arthur

      resistance gnome

      In reply to Smudge Martens

      While geothermal heat is a major contributor to basal ice-cap melt as stated by Petrunin et al ("Heat flux variations beneath central Greenland’s ice due to anomalously thin lithosphere", Nature Geoscience 6, 746–750 (2013) doi:10.1038/ngeo1898) - the original source for the phys.org news report - it has not been sufficient to prevent accumulation of the Greenland ice-cap over the last ~3 million years.

      If the ground surface beneath Greenland's glaciers is relatively warm due to geothermal activity, then rate of glacier flow may be limited by adjacent sea temperatures.

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    2. David Arthur

      resistance gnome

      In reply to Alice Kelly

      Gday Ms Kelly, I'm sorry for any ambiguity in the second paragraph of my previous comment.

      If we think of a glacier as a gravity-driven river conveying a high-viscosity form of water (ice) from high to low elevation, than its flow can be retarded either by high friction along its bed ie along the rock channel it's grinding out, or by a blockage at its point of discharge (for Greenland and Antarctic glaciers, this is the coast).

      The blockage at the coast may be a big lump of ice, or a wall of…

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    3. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to David Arthur

      That's what I thought, water towards water downhill, disregarding a temperature difference between the two bodies of water, it seems has become unblocked by large bodies of ice (plug) towards the 'mouth', at least according to the ABC article, and this is what is happening now. It's free, and velocity has increased significantly. The inland area connected to this river is massive. And must constitute a large area of the basin sitting in the middle of Greenland. Thanks

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  2. Alice Kelly
    Alice Kelly is a Friend of The Conversation.

    sole parent

    Around 2006 ice discharge increased, if this is because of diminishing ice thickness, faster speed and localise glacial valley shapes this is sad.
    http://www.sciencenewsline.com/articles/2014031022190016.html
    And if the blockage at the mouth of this stream, became un-blocked due to higher temperatures after 2006, this is even sadder. If as Smudge says, the lithosphere is thinner in central greenland, then what is being seen due to warmer temperatures of both the atmosphere and ocean un-plugging the mouth can get worse.
    http://www.abc.net.au/news/2014-03-17/global-warming-melts-greenland-ice-sheet/5324848

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  3. David Travers

    professional

    It is clear that the ice sheet on Greenland is melting. Where does archeology fit in to the mix? During the medieval warm period the Vikings lived in Greenland and raised livestock.

    As the climate changed and things cooled they switched their diet back to fish but it appears they were unable have the success of the Intuit. They looked down on the Intuit and did not adopt their fishing methods.

    Eventually their settlements failed. There are many climate lessons in history in our short span of time as the dominate species on Earth. Underwater archeology is another neglected aspect of climate history.

    This may be a normal cyclical event.

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    1. David Arthur

      resistance gnome

      In reply to David Travers

      I think you'll find, Mr Travers, that Greenland was inhabitable for pastoralists in Mediaeval times because the Mediaeval Warm Period was a largely North Atlantic phenomenon - I understand that at that time, heat transfer from the Caribbean courtesy of the Gulf Stream was particularly pronounced.

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