New Study Suggests Antarctic Glacier Melting May Be Irreversible

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The Thwaites Glacier, Antarctica

The Thwaites Glacier, Antarctica. Image credit: NASA

What’s happening to the world’s ice?

The loss of Arctic sea ice and the plight of the polar bears often makes headlines (and cute pictures) but what’s happening elsewhere in the cryosphere (the planet’s ice sheets and ice caps) is at least as important.

Monitoring and research from NASA and the University of California adds increasing evidence to the contention that what’s happening in the Antarctic is something we should be worried about.

Why the Antarctic Ice Sheet Matters

Though lacking permanent habitation (except for its scientific bases) the Antarctic is crucial to humans because of its role in climate. Its area, at around 5.4 million square miles, is, as the National Snow and Ice data centre (NSIDC) observes, “roughly the area of the contiguous United States and Mexico combined” and the volume of the ice sheet includes around 7.2 million cubic miles of ice.

That’s a lot. And one of the reasons it’s important is that it’s land ice rather than sea ice. Sea ice is frozen sea water and has no impact upon sea level. But land ice, when it melts, becomes additional water in the oceans – and if all the water locked up in the Antarctic ice sheet were to melt, it would release enough water to increase global sea level by up to 200 feet.

It isn’t just sea level. The existence of such a large area of extreme cold on the surface of the planet means that the Antarctic ice sheet is already a key player in global climate. Climate is influenced by heat transport by winds and by ocean currents; the polar ice caps are key drivers of the latter, affecting the transport of the sun’s heat from low to high latitudes.

What’s Happening at the Bottom of the World?

The planet's ice sheets contain a vast quantity of water. Image credit: NASA

The planet’s ice sheets contain a vast quantity of water. Image credit: NASA

Although the fluctuations of Arctic sea ice are a key media focus, climate scientists have been studying the characteristics of the Antarctic ice sheet (and Decoded Science reports regularly upon their findings). Ice sheets are dynamic and climate changes naturally; but studies are showing unusual changes within the ice sheet – changes which may have key implications for sea level change.

Ice is moved from the ice sheet by massive glaciers which discharge into the oceans; and the rate at which these glaciers move is determined by a number of factors, including the underlying topography. A study from NASA and the University of California focussed upon a selection of glaciers in a part of the continent known as the West Antarctic Ice Sheet (WAIS).

Using a variety of techniques (including satellite radar altimetry), the team, led by Professor Eric Rignot of University of California Irvine, mapped changes in the point at which the glaciers lift from the sea bed (the grounding line) based on data from 1992-2001. Professor Rignot told Decoded Science the key findings of the study were: “The fast retreat rate of the grounding lines and the high resolution reconstructed bed that shows no bed barrier.” The lack of an upstream barrier being crucial in that it offers no means to stop the retreat.

The West Antarctic Glaciers

Map of the key West Antarctic Glaciers. Image credit: Eric Rignot

Map of the key West Antarctic Glaciers. Image credit: Eric Rignot

As glaciers retreat they become thinner and lift up, allowing sea water to get beneath them and increase the rate of melting – an example of a positive feedback mechanism. The changes which the team mapped for the half dozen glaciers they studied are, to say the least, alarming. Over the study period one, the Smith/Kohler glacier retreated by 35km, the Pine Island Glacier retreated by 31km and the Thwaites Glacier by 14km.

This is not an unprecedented rate of retreat,” said Professor Rignot, “but for the West Antarctic ice sheet, this is what you might refer as a tipping point.” In other words, the retreat of the ice may have become so rapid and so significant that it cannot be reversed and the melting of this part of Antarctica, at least, may now be inevitable.

And with that come implications for sea level. “The evolution of this sector will contribute to push sea level toward the upper part of IPCC projection for 2100 (90cm) and even beyond (more like 120cm)” warns Professor Rignot.

The Longer Term Perspective

The WAIS makes up just part of the Antarctic Ice Sheet as a whole – and a range of studies have shown that melting rates are lower elsewhere on the continent (although overall the mass of ice is decreasing). But NSIDC data suggest that the wasting off the WAIS glaciers contributes to a loss overall of 136 ± 60 gigatons in 2006, most of it in the WAIS.

The volume of ice locked up in Antarctica is so large that even at rapid rates of melting it would take many hundreds, possibly thousands, of years before it all melted. But even a minor increase in sea level, such as the 90-120cm projected by the IPCC, will have significant impacts on low-lying coastal areas – including some of the world’s major cities.

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© Copyright 2014 Jennifer Young, All rights Reserved. Written For: Decoded Science
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Comments

  1. Decoded ScienceDecoded Science says

    Hi, Gail! Thanks for your comment, you bring up some great points! Just to be clear, however, this article is an explanation of the following research:
    Rignot, Eric, et al. Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011. (2014). American Geophysical Union.
    We appreciate you taking the time to share your thoughts!

  2. Gail Combs says

    1. You forgot about the fact an active volcano is under the ice that is melting and that the melting is only in that one area.

    2. Antarctic Sea Ice is at record levels.

    3. The Sea level High Stand was thousands of years ago and the earth is now cooling off in the last stages of the Holocene.

    Holocene sea-level change and ice-sheet history in the Vestfold
    Hills, East Antarctica
    Dan Zwartz ) , Michael Bird, John Stone, Kurt Lambeck

    Abstract
    A new Holocene sea-level record from the Vestfold Hills, Antarctica, has been obtained by dating the lacustrine–marine and marine–lacustrine transitions that occur in sediment cores from lakes which were formerly connected to the sea. From an elevation of ; 7.5 m 8000 yr ago, relative sea-level rose to a maximum ; 9 m above present sea-level 6200 yr ago. Since then, sea-level has fallen monotonically until the present….

    The Holocene interglacial is now 11,717 years old….. That’s two centuries or so beyond half the present precession cycle (or 23,000/2=11,500). Only one interglacial , MIS-11, since the Mid-Pleistocene Transition has lasted longer than about half a precession cycle.

    Any hope that the Holocene would go long was shot down by Lisiecki and Raymo in 2005 in their rebuttal of Loutre and Berger, 2003.

    http://large.stanford.edu/publications/coal/references/docs/Lisiecki_Raymo_2005_Pal.pdf

    Recent research has focused on MIS 11 as a possible analog for the present interglacial [e.g., Loutre and Berger, 2003; EPICA community members, 2004] because both occur during times of low eccentricity. The LR04 age model establishes that MIS 11 spans two precession cycles, with #18O values below 3.6h for 20 kyr, from 398{418 ka. In comparison, stages 9 and 5 remained below 3.6h for 13 and 12 kyr, respectively, and the Holocene interglacial has lasted 11 kyr so far. In the LR04 age model, the average LSR of 29 sites is the same from 398{418 ka as from 250{650 ka; consequently, stage 11 is unlikely to be arti cially stretched. However, the June 21 insolation minimum at 65#N during MIS 11 is only 489 W/m2, much less pronounced than the present minimum of 474 W/m2. In addition, current insolation values are not predicted to return to the high values of late MIS 11 for another 65 kyr. We propose that this effectively precludes a \double precession-cycle” interglacial [e.g., Raymo, 1997] in the Holocene without human in influence.

    Since then no one in Quaternary Science has rebutted Lisiecki and Raymo. Not a fact to give one warm fussy feelings.

    If you think the Medieval Warm Period and the current Modern Warm Period negates the possibility of the Holocene ending think again.

    Boettger et al 2009 (Quaternary International 207 [2009] 137–144) http://www.sciencedirect.com/science/article/pii/S1040618209001475 (paywalled)

    In terrestrial records from Central and Eastern Europe the end of the Last Interglacial seems to be characterized by evident climatic and environmental instabilities recorded by geochemical and vegetation indicators. The transition (MIS 5e/5d) from the Last Interglacial (Eemian, Mikulino) to the Early Last Glacial (Early Weichselian, Early Valdai) is marked by at least two warming events as observed in geochemical data on the lake sediment profiles of Central (Gro¨bern, Neumark–Nord, Klinge) and of Eastern Europe (Ples). Results of palynological studies of all these sequences indicate simultaneously a strong increase of environmental oscillations during the very end of the Last Interglacial and the beginning of the Last Glaciation. This paper discusses possible correlations of these events between regions in Central and Eastern Europe. The pronounced climate and environment instability during the interglacial/glacial transition could be consistent with the assumption that it is about a natural phenomenon, characteristic for transitional stages….

    And just in case you were wondering the “Polar Vortex” of last winter coincides with the same land area as was covered by the Laurentide Ice Sheet of the Wisconsin Ice age, the earth’s last ice age.

    Even if the earth does not descend into an interglacial, the climate during the solar insulation lows between the two solar insolation peaks of MIS 11 was quite the rough ride since it was near the solar insolation transition boundary.

    A fall 2012 paper “Can we predict the duration of an interglacial?” gives the calculated solar insolation values of several glaciations:
    Current values are insolation = 479W m−2

    MIS 7e – insolation = 463 W m−2,
    MIS 11c – insolation = 466 W m−2,
    MIS 13a – insolation = 500 W m−2,
    MIS 15a – insolation = 480 W m−2,

    MIS 17 – insolation = 477 W m−2, CO2 = 240 ppmv

    To give you a feel for how close to glaciation we are, you can look at the calculations from NOAA:
    http://www1.ncdc.noaa.gov/pub/data/paleo/climate_forcing/orbital_variations/berger_insolation/insol91.jun
    depth of the last ice age – around 463 Wm−2
    NOW (modern Warm Period) 476 Wm-2
    Holocene peak insolation: 522.5 Wm-2

    The earth is a heck of a lot closer to glaciation than it is to peak warming. Remember ALL the energy comes from the sun not from Greenhouse gases that just retard the escape of the sun’s energy.

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