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Various estimates of Greenland ice loss

Posted on 28 February 2011 by John Cook

Over the last few weeks, three different papers have been published that all examine ice loss from the Greenland ice sheet. What's interesting is all three papers use entirely different methods to measure the rate of ice loss. Even more interesting is that these three different methods paint a consistent picture of what's happening to Greenland.

Schrama et al 2011 uses gravity measurements from the GRACE satellites to determine any change in mass of the Greenland ice sheet (there's a great article The Riddle of the ice about Ernst Schrama's work). They find from March 2003 to February 2010, Greenland lost ice mass at a rate of 252 gigatonnes per year. A key result from their paper was to confirm that ice loss had spread to the north west of Greenland.

 

Figure 1: Ice mass anomaly of the Greenland ice sheet as measured by GRACE gravity satellites (Schrama et al 2011).

Another paper Zwally et al 2011 uses satellite altimetry to determine the thickness of the Greenland ice sheet. They calculate that over 2003 to 2007, the ice sheet was losing ice at a rate of 171 gigatonnes per year. They then compare this to radar and airborne altimetry data from the 1990s. From 1992 to 2002, Greenland was only losing 7 gigatonnes per year.

Lastly, Rignot 2011 uses the Mass Balance Method to construct a 19 year record of ice loss from Greenland. This involves calculating the amount of snowfall on the surface, the amount of ice mass lost to wind and melt and the amount of ice lost calculated from glacier velocity and ice thickness. Putting all these pieces together gives the total amount of ice lost or gained over the ice sheet.

Over this nearly two decade period, Rignot finds a clear signal of accelerating ice loss. He then compares his results from the Mass Balance Method to results from GRACE data. Both show consistent rates of mass loss. Just as significantly, both are accelerating at similar rates.

Figure 2: Total ice sheet mass balance in Greenland from the Mass Balance Method (black) and GRACE gravity measurements (red). The acceleration is given in gigatonnes per year squared (Rignot 2011).

Out of curiosity, I thought I'd plot the results from all three papers on a single graph to see how the results compared. Each paper covers different time periods so I've indicated the time period (horizontal uncertainty bars) as well as the ice loss uncertainty (when provided). I also included a number of other estimates from recent papers (many thanks to Ernst Schrama for providing a handy summary - saved me some legwork) and Robert Way who pointed me to the IPCC estimates. It was especially interesting to see how the recent Wu et al 2010 estimate compares to the other estimates (it's the blue GRACE data point sitting like an outlier above all the other estimates). Thanks also to Bert Wouters and Ernst Schrama for their advice and feedback.

Figure 3: Various estimates of Greenland ice loss.

While there are a range of estimates on Greenland ice loss, independent lines of evidence all paint a similar picture - Greenland is losing hundreds of billions of tonnes of ice per year and the rate is increasing.

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Comments

Comments 1 to 18:

  1. The Zwally et al (2011) paper is excellent. Figure 8 in particular indicates that it is dynamic thinning that dominates the increase in volume loss. Also note figure 14 indicating the amount of loss around Jakobshavn from dynamic thinning versus melting in the areas beyond the ice stream margin. This is not to say melting has not increased and does lead to mass loss, note the Mittivakkat Glacier, just that is not as significant to date.
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  2. There are multiple aspects of this post that confuse me. The mass in Figure 1 (Schrama's Figure 2) appears linear in time, with a superimposed annual oscillation. The figure doesn't seem consistent with a mean rate of -252 Gt/yr and an acceleration of -22 Gt/yr^2. If I'm wrong, a segment of a parabola with that slope and curvature ought to fit the data well. I read the paper and the figure doesn't seem to match the text or the tabular data. Please ask Schrama to comment.

    Rignot 2011 is a pre-print. Shouldn't it be refereed before its results are used here?

    I think Figure 3 is the mass change rate and the units ought to be Gt/yr. Note that a negative mass loss would be a mass gain.
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  3. Jeff T
    here's the refereed paper, published February 12th.
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  4. Jeff T,
    Rignot et al (2011) is in press at Geophysical Research Letters
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  5. Is it me or melt started around 1995? A consequence of the impredictable non-linear behaviour of climate?
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  6. As discussed here, Greenland’s glaciers double in speed:



    The Yooper
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  7. So one is not allowed to say global temperatures are flatlining after over 10 years of flatlining.

    But when 8 years of greenland ice mass data shows decreasing, you instantly declare "it's accelerating". You do not have the context for that, so you do not know whether it is accelerating (or even melting long term) at all.

    That is absolutely too short period of time.

    Where's the coherence on what can you say on what intervals, and what you can't?

    And shortly calculated, if we pick like 170Gt/a, it makes 0,006% a year, the Greenland is ice free in only 15 000 years. I think that's a rather good reason to sound the alarm.

    And BTW, Greenland temps are just as high as they were in the mid 1900's during the last peak of AMO. Nothing unprecedented on the temps of Greenland either.
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    Moderator Response: [Daniel Bailey] "So one is not allowed to say global temperatures are flatlining after over 10 years of flatlining." You can say it all you want, doesn't make it true:
    GISS, no exogenous factors
  8. We just experienced the warmest decade in terms of global temperature, the largest ice loss from Greenland since observations began in the 1950's, and the largest decade of glacier mass balance loss, no flat lines in sight.
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  9. Flatlining? Even it it were flat, there's still the main issue.

    I suppose I can say I'm standing on a flat surface on each step of a staircase. However, even the most naive acknowledge that it makes a difference whether that "flat" surface is ankle-height above the surrounding level or head and shoulders above that level.

    We're into head and shoulders territory now regardless of the flatness of the terrain.
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  10. We've had Greenland ice loss threads here and here, among others. The conclusion (based on evidence) is always the same. The skeptical(?) response is likewise always the same. "Not listening, not listening."

    To me, this graphic at CCNY's Cryo Processes Lab speaks volumes:



    The figure above shows the standardized melting index anomaly for the period 1979 – 2010. In simple words, each bar tells us by how many standard deviations melting in a particular year was above the average. ... Previous record was set in 2007 and a new one was set in 2010. Negative values mean that melting was below the average. Note that highest anomaly values (high melting) occurred over the last 12 years, with the 8 highest values within the period 1998 – 2010. -- emphasis added
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  11. #10 muoncounter at 11:14 AM on 1 March, 2011
    "Not listening, not listening."

    Let's put recent warming over Greenland into perspective. The conclusion (based on evidence) is always the same.



    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D11105, 2006
    doi:10.1029/2005JD006810
    Extending Greenland temperature records into the late eighteenth century
    B. M. Vinther, K. K. Andersen, P. D. Jones, K. R. Briffa & J. Cappelen

    Years 2006-2009 are added to their supplementary data.
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  12. BP,
    Your link to Vinther et al 2006 doesn't work; your link to 'supplementary data' is a txt data file that ends in 2005. How would a paper published in 2006 have data through 2009?

    In addition, Vinther only looked at the southwest coast. Here's a graph from their monthly data, averaged over summer and fall:



    Both summer and autumn have mild long term warming trends; both seem to turn up in the early '80s. Those seasons seem to be key to understanding Arctic melt: Per Serreze 2009 et al, "it makes sense that the surface warming signal has emerged first in autumn. Less sea ice at summer’s end (September), as observed, has enhanced upward heat fluxes to the atmosphere."

    Here's a more regional study, Box 2002:
    Based on temporal and spatial statistics, distinct and meaningful patterns of temperature are evident in Greenland instrumental temperature records spanning 1873–2001. These include a steady decay of spatial correlation, a lack of correlation between west and east coasts, and the presence of opposite temperature trends between west and east coasts that are themselves not statistically linked.

    So it would seem that no broad conclusions can be drawn from Vinther, which is just the southwest Greenland coast.

    Box (who analyzed 27 stations throughout Greenland) goes a step further:

    The 1873–2001 western Greenland warming trends observed in this study are meaningful in the context of observed Greenland ice sheet melt rates. The mass balance of the ice sheet sector south of 73°N latitude and west of Kap Farvel was negative for the second half of the last century. This appears not to be affected by changes in precipitation, implicating the observed warming and potential ice dynamical changes.

    Yeah, that negative ice mass balance just keeps on rearing its ugly head.
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  13. #12 muoncounter at 14:31 PM on 1 March, 2011
    Your link to Vinther et al 2006 doesn't work

    Sorry, corrected.

    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D11105, 2006
    doi:10.1029/2005JD006810
    Extending Greenland temperature records into the late eighteenth century
    B. M. Vinther, K. K. Andersen, P. D. Jones, K. R. Briffa & J. Cappelen

    How would a paper published in 2006 have data through 2009?

    I have appended recent data from Ilulissat, Nuuk and Qaqortoq, but I've already said that.

    In addition, Vinther only looked at the southwest coast.

    Yes, that's the region for which we have long records. It's easier to talk about regions where no measurements were taken, but somewhat less accurate.
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  14. "I've already said that"
    But you didn't put that data into the txt file you linked. Hopefully its monthly, so the seasonal picture can be extended, particularly as autumn began averaging over 0C at the tail end of the Vinther data in that txt file.

    "easier to talk about regions where no measurements were taken" True, but irrelevant. Box has measurements from 27 stations well-distributed over Greenland. His conclusion: a lack of spatial correlation between east and west coasts.
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  15. Not particularly remarkable when one considers Greenland temperatures through out the Holocene:

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  16. Climatewatcher- what does it mean that the temperatures go up as you go down the right axis. Is the negative sign to be believed? Or does your data show that the medieval warming period was over 1C higher than now?

    To what do you attribute that sharp spike in red on the right side of your graph?
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  17. Climatewatcher @15, that graph is currently being discussed on the Crux of a core thread.

    Essentially its problems for your use are that the most recent temperature from the ice core itself is actually 1855. The red spike at the end is supposed to show global temperature increases to the present, but they do not show global temperatures since 1855, and nor should global temperatures be compared with regional temperatures.

    Based on a recent analysis of Greenland temperature records, the decadal average of temperatures in Greenland has increased by approx 1.5 degrees C since the 1850's, so current tempertures on that graph should be around -30.5 degrees C, or about the peak of the MWP. 2010 temperatures are another degree warmer than that, or about equivalent to the peak of the Roman Warming. That means the current warming in Greenland is unparalleled in magnitude and abruptness in the last 6,000 years.

    What is more, the overall decline in Greenland temperatures evident in your graph has a well known cause, the decline in arctic summer insolation related to the Milankovitch cycles. Summer insolation is still declining. To what, then, do you attribute the sudden reversal of thousands of years of cooling?
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  18. More warming is inevitable (resistance is futile!):



    "Departure of sea surface temperature from average for 2010 from the NOAA Daily Optimum Interpolation SST Anomaly data set for October 2010. Areas colored red are warmer than the 1971-2000 average, areas colored blue are cooler than that average. A large region of record warm water temperatures extended along the west coast of Greenland, leading to record warm air temperatures and record melting along the western portion of Greenland in 2010. Ocean temperatures along the southwest coast of Greenland (60N to 70N, 60W to 50W) computed from the UK Hadley Center data set during 2010 were 2.9°C (5.2°F) above average--a truly remarkable anomaly, surpassing the previous record of 1.5°C set in 2003. Sea surface temperature records for Greenland began in the 1920s."

    The Yooper
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