Weighing change in Antarctica

GRACE data are still being collected but the mission has now begun to rundown. With a much-needed GRACE follow-on mission expected to launch around 2017, observation and modelling of the Antarctic GIA will continue to give us insights into the ice sheet history – from LGM through to the present – and hence provide the context for any future changes.

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31 comments on this post.
  1. Russell:

    Satellite images indicate Earth’s cryospher occupies > 10% of its surface , or some fifty million square kilometers.

    But that tenth of the planet’s area has an albodo typically in the 60-85% range, making it locally three to five times more reflective than the continental average , and an order of magnitude brighter than the oceans , and amplifies the radiative impact of ice recession at the cryosphere margins accordingly.

  2. Chris Dudley:

    Just to check, the acceleration of about -14 Gt/yr/yr found be Rignot et al. (2011) for Antarctica is not in question here, just when the mass balance changed sign?

  3. CM:

    Just for reference, we went over some of this ground here last year, discussing Rignot 2011 (and Wu 2010).


  4. Kevin McKinney:

    Very interesting. If my quick search is correct, this paper’s result is roughly comparable to Greenlandic mass loss rates, right? And this should be susceptible to meaningful consideration within the context of SLR measurements/modeling.

  5. KR:

    Does this lower estimate of Antarctic contribution to sea level rise (from melt) indicate that the thermosteric component (expansion from warming) is larger than previously estimated? That more energy is going into the oceans, more warming, than previous calculations indicated?

  6. CM:

    Chris #2, I looked it up:

    Ice mass loss acceleration, all Antarctica, in Gt/yr/yr:
    – Rignot 2011: -14.5 (±2) (1992-2010, mass budget method)
    – Rignot 2011: -13.2 (±10) (2002-2010, GRACE)
    – King 2012:      -4   (±16) (2002-2010, GRACE, with new GIA model)

    So King et al., unlike Rignot et al., find the acceleration is not statistically different from zero for Antarctica as a whole. They do find significant acceleration in West Antarctica, though. (Someone correct me if I’m reading this wrong or comparing apples with pears.)

  7. Dan H.:

    Your assessment of their conclusions of the AIS is correct. The acceleration of the WAIS is on the edge of significance; 8.4 +/- 8.4 Gt/yr/yr. Most of the calculated ice loss (>90%) is occurring on the Amundsen Sea Coast, while the rest of West Antarctica showed little ice mass loss. Check out some other papers on The Amundsen coast and the Pine Island Glacier:



  8. Chris Dudley:

    CM (#6),


  9. BillS:

    Interesting. Many of the drainage basins in West Antarctica and the Peninsula are quite small. If memory serves, GRACE’s spatial resolution is about 400 km. How were these small basins mapped?

  10. Aaron Lewis:

    In 15 years, when we have data from the GRACE follow on systems, what do you expect to find? How fast can WAIS/EAIS loss/gain change given current weather patterns?

  11. Edward Greisch:

    Thanks much for this article and the references provided by everybody. As you know, the denialists say that ice loss in the Arctic Ocean is matched by ice gain in the “Antarctic Ocean.” This article will be good as a reference to help dispel that nonsense.

  12. prokaryotes:

    What is expected in long term trends? To my understanding, a thaw during deglaciation is typical on earth with a see-saw effect (North/South hemisphere) as for example it happened during the Younger Dryas or can we calculate a more broader, global time frame for the ongoing deglaciation? I assume that the rate of emissions to past emission uptake and following deglaciation is about 300 times faster than in historical records.

  13. prokaryotes:

    Ok, actually i do not know if it is typical for a deglaciation to have a see-saw effect. The wikipedia is very sparse. And the YD is a bad example since it is a glaciation. http://en.wikipedia.org/wiki/Deglaciation

  14. Matt King:

    Kevin (#4) Greenland is losing about 250 Gt/yr over this period so substantially more and with a clearer acceleration pattern over the recent decade or more. That estimate for Greenland seems pretty robust across multiple techniques – see http://dx.doi.org/10.1126/science.1178176

    KR (#5) our results don’t speak to the origins of the very high sea level rise rates in this period other than to suggest this rate was achieved with little input from Antarctica as a whole. One recent compilation by Church et al. in GRL gave 0.43 ± 0.20 mm/yr from Antarctica (1 sigma uncertainties) so our rate is systematically lower but not outside 2 sigma uncertainties.

    Chris (#2), CM (#6), Dan H (#7) just note our sigmas in the paper are reported at 2 sigma throughout. We find the only basin to be seeing *overall* acceleration (at 2 sigma) to be the one containing Pine Is Glacier on the Amundsen Sea Coast of West Antarctica. The reason for the differences in estimated *acceleration* between our study and previous GRACE ones needs further examination but the accelerations seem somewhat sensitive to data period (since the changes are not a perfect quadratic) and how we derive data uncertainties. It’s important to say that satellite altimetry has identified the neighbouring Thwaites Glacier to be accelerating at its front but this is either in the noise of our GRACE results or countered by accelerating snow accumulation higher up in the Thwaites Glacier basin (http://dx.doi.org/10.3189/2012JoG11J118).

    Bill S (#9) – you are right about the resolution of GRACE – but these basins are generally much larger than 400km across. We needed to consider carefully leakage of signal from one basin to the other carefully.

    Edwards (#11) don’t get confused between Arctic sea ice and grounded Antarctic ice. I think the denialists are comparing sea ice with sea ice.

  15. ozajh:

    Does Also Sprach Zarathustra start blaring out when a penguin gets close to that thing . . .

  16. Eli Rabett:

    Many thanks for the work and the explanation

  17. Dan H.:

    Thanks for your response. Regarding the rapidly-moving Thwaites glacier, what do we know about the long-term changes in its movement? Can you answer this in light of the large scale advance and retreat over the past 30 years.

  18. Chris Dudley:

    Matt (#14),

    Thanks for your explanation. Interesting that when taking your rate and acceleration and extrapolating back to when the mass balance was zero, and doing the same with the Rignot et al. GRACE date, you have a higher contribution to sea level by about 2% up to 2010. Your rate is slower, but you are adding to sea level for a longer time, 21 years rather than 11 years. All in the noise of course.

  19. James Staples:

    I was just reading about the antipodal bulge that showed up in the Mars Laser Altimetry experiments opposite the 3 klick thick Tharsis Volcanic Provence…..and, I wonder, if a certain amount of data could not also be extrapolated from observations of the abysal plains beneath the Arctic Ocean.
    Probably not…but, hey, if Canada were antipodal to Antarctica, maybe we’d be in business?

  20. sidd:

    This article might belong on unforced variations, moderators please move it if appropriate.


    Apparently there is a faster than centennial coupling between polar climate and ice volume, last 4 episodes of rapid polar deglaciation/warming all resulted in 1.2 m/century. Hansen, as we know has opined that ice mass waste can be much quicker than gain, this is evidence for that view.

  21. Matt King:

    Dan H. (#17) – I don’t have my finger on the pulse of published work, if any exists, on multi-decadal changes for Thwaites. There is certainly a growing body on Pine Island Glacier.

    Chris Dudley (#18) – Maybe I missed your point, but I think you attributed the duration of the Rignot result to us – we cover 2002-2010 (to round figures) – about 8.5 years. Our rates apply to 2006.9 (in decimal years) so you need to apply any acceleration relative to that time.

  22. Matt King:

    Dan H (#17) – I don’t have my finger on the pulse on what has been published, if anything, on multi-decadal changes to Thwaites, sorry. There is a growing body on Pine Island Glacier though – e.g., http://dx.doi.org/10.1038/ngeo890

    Chris (#18) – I may have missed your point but I think you attributed the Rignot time-period to our study. Our data span 2002-2010 to round figures (about 8.5 years centred on 2006.9). If you wish to apply the accelerations you need to do that relative to rate reference epoch of 2006.9.

  23. Hank Roberts:

    > Dan H.
    > … the large scale
    > advance and retreat
    > over the past 30 years.

    What? a large scale advance?
    “Cycles” again? Citation?


    Widespread rifting and retreat of ice-shelf margins in the eastern Amundsen Sea Embayment between 1972 and 2011

    Authors: Macgregor, Joseph A.; Catania, Ginny A.; Markowski, Michael S.; Andrews, Alan G.

    Source: Journal of Glaciology, Volume 58, Number 209, June 2012, pp. 458-466(9)

    “The major outlet glaciers that drain the eastern sector of the Amundsen Sea Embayment (Smith, Haynes, Thwaites and Pine Island) are among the largest, fastest-flowing and fastest-thinning glaciers in West Antarctica. Their recent ice-flow acceleration is linked to ocean-induced ice-shelf thinning, but may also arise from additional losses of ice-shelf buttressing that are not well understood. Here we present a comprehensive history of coastal change in the eastern Amundsen Sea Embayment between 1972 and 2011 derived mostly from Landsat imagery….”

    Here’s a review from 1998:

    [PDF] Global warming and the stability of the West Antarctic Ice Sheet
    Cited by 269

  24. Hank Roberts:

    Fixed link, if the blog software doesn’t change it:
    Cited by 269

  25. Chris Dudley:

    Matt (#21),

    Rignot et al. used two methods, a mass balance method and their treatment of the GRACE data. I used their GRACE data fit from fig. 2b estimating their rate at 2006 as -100 Gt/yr and reading their acceleration off the figure as -13.2 Gt/yr/yr. For your work I took -69 Gt/yr and -4 Gt/yr/yr from this article and the comments. Looked like the same data period was used in both works. Thus the epoch would be the same. I did add 4 years to the epoch rather than 3.1 to get to 2010, but that change would just favor your analysis as giving a larger contribution to sea level rise.

    Going back just to when Antarctica tipped into ice mass loss is a little arbitrary since it may have retarded sea level rise earlier, it is just amusing that things happened to come out so close.

  26. prokaryotes:

    Can somebody please point me to a good read about general Deglaciation science – from a global perspective, or are there only studies looking at isolated events and the ice cores who show a balanced climate cycle (temps/Co2 levels)?

  27. David B. Benson:

    prokaryotes @26 — Using a web search engine using the phrase general Deglaciation science produces lots and lots of entries, including at least one book and the following review.


  28. prokaryotes:

    David, but is there some science available for free and from the last 1-3 years? I googled “deglaciation” and besides single events, i cannot find a place for a greater look. So for now i guess i have to stick with study papers and different events. Maybe somebody else has another tip for me, thanks.

    On the bottom line i ask public, because others might be interested as well and maybe my comment above motivates to improve the wikipedia page for deglaciation. Cheers.

  29. Adam H:

    Prokaryotes, from a modeling perspective, a few studies come to mind.

    A simple ice sheet model yields realistic 100 kyr glacial cycles
    D Pollard – Nature, 1982

    Sensitivity experiments with a model of the ice age cycle the response to harmonic forcing
    WT Hyde, WR Peltier – Journal of the atmospheric sciences, 1985

    Lev Tarasov and W.R. Peltier, “A geophysically constrained large ensemble analysis of the
    deglacial history of the North American ice-sheet complex ”, Quat. Sci. Rev., 23, 359-388, 2004

    Deglacial rapid sea level rises caused by ice-sheet
    sadle collapses (2012) Nature
    Lauren J. Gregoire, Antony J. Payne & Paul J. Valdes

  30. Perwis:

    Interesting new study in Nature by a team led by Eelco Rohling:
    K. M. Grant, E. J. Rohling, M. Bar-Matthews, A. Ayalon, M. Medina-Elizalde, C. Bronk Ramsey, C. Satow, A. P. Roberts. Rapid coupling between ice volume and polar temperature over the past 150,000 years. Nature, 2012; DOI: 10.1038/nature11593

    I have not yet read it, but it seems to be cutting edge dating of high-res paleo data.

    Given that the previous study by Rohling et al (2008) was used as a basis for the H++ scenario of UKCP of 2.5 meter SLR for year 2100 (Lowe et al 2009), this new study could be very important.

  31. Hank Roberts:

    For Wili

    That’s your search term in Google Scholar, using the “since 2008” button on the left side of the results page.

    After that it’s up to you to dig in — try the “More” button; often you’ll get a HTML page or a link to a library that has it available, or a list of various copies; often one is free from an author’s web page.

    Reposted yet once more again as new readers may not be aware that they can get free copies of most recent science papers — by looking.