Mapping the Greenland ice cap thickness

From the University of Copenhagen press release.

IMAGE: This is a map of the ice core drilling locations discussed in the article.

Click for larger image.

Will all of the ice on Greenland melt and flow out into the sea, bringing about a colossal rise in ocean levels on Earth, as the global temperature rises? The key concern is how stable the ice cap actually is and new Danish research from the Niels Bohr Institute at the University of Copenhagen can now show the evolution of the ice sheet 11,700 years back in time – all the way back to the start of our current warm period. The results are published in the journal Nature.

Numerous drillings have been made through both Greenland’s ice sheet and small ice caps near the coast. By analysing every single annual layer in the kilometres long ice cores researchers can get detailed information about the climate of the past. But now the Danish researcher Bo Vinther and colleagues from the Centre for Ice and Climate at the Niels Bohr Institute, University of Copenhagen, in collaboration with researchers from Canada, France and Russia, have found an entirely new way of interpreting the information from the ice core drillings.

“Ice cores from different drillings show different climate histories. This could be because they were drilled at very different places on and near Greenland, but it could also be due to changes in the elevation of the ice sheet, because the elevation itself causes different temperatures” explains Bo Vinther about the theory.

Today the ice sheet is more than three kilometres thick at its highest point and thinning out towards the coast. Four of the drillings analysed are from the central ice sheet, while two of the drillings are from small ice caps outside of the ice sheet itself, at Renland on the east coast and Agassiz which lies just off of the northwest coast of Greenland in Canada.

IMAGE: The ice is approximately 3 km thick in central Greenland and by analyzing every single annual layer in the kilometers-long ice cores researchers can get detailed information about the climate…

Click for larger image.

Small ice caps show the standard

The small ice caps are stable and have not changed in elevation, and even though they lie very far apart from each other on either side of the central ice sheet, they show the same climate history. This means that one can use the small ice caps climate history as a standard reference for the others.

Bo Vinther explains, that the four drillings through the ice sheet would have had the same climate history if there had not been changes in elevation throughout the course of time. It is known that for every 100 meter increase in elevation, there is a 0.6 per mille decrease in the level of the oxygen isotope Oxygen-18, which indicates the temperature in the air. So if there is a difference of 1.2 per mille, the elevation has changed by 200 meters.

By comparing the Oxygen-18 content in all of the annual layers from the four drillings through the ice sheet with the Oxygen-18 content of the same annual layers in the small ice caps, Bo Vinther has calculated the elevation course through 11,700 years.

Temperature sensitive ice sheet

Just after the ice age the elevation of the ice sheet rose slightly. This is because when the climate transitions from ice age to warm age, there is a rapid increase in precipitation. But at the same time, the areas lying near the coast begin to decrease in size, because the ice is melting at the edge. When the ice melts at the edge, it slowly causes the entire ice sheet to ‘collapse’ and become lower.

The calculations show that in the course of about 3,000 years the elevation changed and became up to 600 meters lower in the coastal areas. But in the middle it was a slow process, where the elevation decreased around 150 meters in the course of around 6,000 years. It then stabilised.

The elevations that were found with the help of the Oxygen-18 measurements from the ice cores are checked with other methods, for example, by measuring the air content, which is also dependent upon the elevation.

The new results show the evolution of elevation of the ice sheet throughout 11,700 years and they show that the ice sheet is very sensitive to the temperature. The results can be used to make new calculations for models predicting future consequences of climate changes.

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27 thoughts on “Mapping the Greenland ice cap thickness

  1. The new results show the evolution of elevation of the ice sheet throughout 11,700 years and they show that the ice sheet is very sensitive to the temperature.

    DUH.

    Amazingly…no mention whatsoever of multidecadal [or longer] oceanic cycles.

    “The ice sheet is very sensitive to temperature.”

    Go figure.

    Yeah it is SO sensitive to temperature that Leif’s relatives (not Svalgaard, but Erikson) had a settlement in GREEN-land during the period that officially wasn’t [according to Mann]: The Mideval Climatic Optimum.

    All of that GHG’s that the Vikings were putting out 1000 years ago on Greenland made it sensitively “green” for a while, I guess.

    Of course the ice-sheet is “sensitive to temperature.” DUH!

    Yeah well…we’re all sensitive to temperature. I sweat when its 75 degrees F, and I am in excellent health….just “sensitive to temperature.”

    No rocket science here.

    To the AGW world religion-cult: Climate changes. Deal with it!

    Chris
    Norfolk, VA

  2. Interesting stuff — but that ice is sensitive to temperature is not exactly new. Robert Frost knew a thing or two about this and published his thoughts in 1921, in the poem “A Hillside Thaw.”
    http://www.cs.rice.edu/~ssiyer/minstrels/poems/1284.html

    And we also know that atmospheric temperature is quite insensitive to changes in existing carbon dioxide concentration within this same atmosphere.

    So, what’s the next question?

  3. It sounds like they are suggesting that ancient temperatures derived from the main ice sheet cores would have to be adjusted upward slightly… making present temperatures a little less unprecedented…. I suspect it’s got to be a bit more complicated than that. If 600 meters difference in elevation makes a difference in the chemistry of the ices, just what does that say about a 3 kilometer thick sheet of ice? Are they really good enough to be able to tell us just what the elevation was for each strata as it was deposited? The ice flows down toward the edges, it melts from both above and below, some of it sublimates, and the lower strata get compressed from all the weight above….

    I’m sure the glacier guys have thought of all this, but there are a lot of confounding variables here… color me skeptical still…

  4. Very interesting… They are starting to find that natural variation is a continual phenomenon and at times can be rapid.

    They still haven’t found anything that shows Anthropogenic CO2 is causing the Greenland glacier to melt… Just evidence that it melts and grows, melts and grows…..

  5. “Just after the ice age the elevation of the ice sheet rose slightly. This is because when the climate transitions from ice age to warm age, there is a rapid increase in precipitation.”

    I wonder how slight that increase was, because it is not mentioned in the 3000 to 6000 year period noted in the next paragraph.

    John M Reynolds

  6. in Greenland, where ice in the interior is getting thicker, representing a net gain of ice which then expands outward to send more mass of glaciers into the sea. With increased glaciation the ice will build and flow faster to the sea. Only the latter occurence (faster flow) is seized upon to prove AGW

  7. Hmmm! So how come even the edge cores show 11000 years of data. Where does the MWP figure in this – didn’t the ice melt since it was so sensitive to heat?

  8. “…Just after the ice age the elevation of the ice sheet rose slightly. This is because when the climate transitions from ice age to warm age, there is a rapid increase in precipitation.…”

    …so at least we know now exactly when the last ice-age ended…it was in summer 1942, when two B-17 ‘flying fortresses’, accompanied by six P38 Lockheed – ‘lightnings’ did an emergency landing on the ice. Since then the ice sheet ‘rose slightly’ and covered the aircrafts with aboout 300 feet of ice and snow…;-)

    http://www.lost-squadron.org/cms/

  9. “What we can now say for sure is that 8,000 years ago it was in fact 2-3 °C warmer than now, and it was this 2-3 degrees that actually caused quite a bit of melting,” says Vinther.

    What caused this temperature change 8,000 years ago?

  10. 2009-09-03
    http://www.nbi.ku.dk/english/news/climate_change_is_man-made/
    Climate change is man-made shows arctic research
    New research shows that the temperature of the arctic region fell steadily from over 2000 years ago all the way up to a 100 years ago. The cooling was caused by less solar radiation during the summer and the cold temperatures would have continued undisturbed. But around the year 1900 there occured a dramatic increase in temperature and the new research results therefore provide further evidence of man’s influence on the climate. The results are published in the scientific journal, Science.

  11. bill (03:53:29) :
    Hmmm! So how come even the edge cores show 11000 years of data. Where does the MWP figure in this – didn’t the ice melt since it was so sensitive to heat?

    I am finding, too, that in dealing with AGW adherents simply teaching the name of our current interglacial and the one before it can be a powerful tool. In the case of the Greenland ice sheet, I proceed as follows:

    (1) You live during the Holocene interglacial, which is an interruption of the massive glaciation of the planet.

    (2) The interglacial before the one you are living in was the Eemian. The Eemian was so much warmer than the Holocene that sea levels were 4 to 6 meters higher than they are today.

    (3) Despite the warmer atmospheric temperatures, the Greenland ice sheet came through the Eemian interglacial with no significant thinning.

  12. The ice cores aren’t from the edges, that would be useless since the ice there comes from somewhere else, you don’t know where. The lower-altitude ice cores are from the centres of smaller icecaps (Agassiz, Renland). It is only on the ice-divide that you know that the ice was deposited more-or-less in the same place, and for small ice-caps you also know approximately at which altitude. This is specially true of the Renland cap which for topographical reasons cannot have changed its size much. The only complication is isostasy, but that can be corrected by tracing old sea-levels on nearby coasts, at least for Renland.

  13. “The small ice caps are stable and have not changed in elevation, and even though they lie very far apart from each other on either side of the central ice sheet, they show the same climate history. This means that one can use the small ice caps climate history as a standard reference for the others.”

    One would imagine that smaller masses might be more susceptible to changes than bigger ones…

  14. Antonio San (09:41:47) :

    “One would imagine that smaller masses might be more susceptible to changes than bigger ones…”

    Not in the case of the Renland icecap. This lies on an isolated plateau with very steep sides about 2200 meters above sea level in eastern Greenland. It contains ice all the way back to the last interglacial, so it has never melted completely in 120,000 years. It is about 300 meters thick today, and can never have been much thicker, because the ice then flows over the edges of the plateau.
    It is indeed extremely stable.

    Vinther noted its potential for calibrating the thickness of the Greenland ice in his dissertation (http://www.nbi.ku.dk/english/research/phd_theses/phd_theses_2006/2006/bo_mllese_vinther.pdf/) and did some preliminary estimations there. These can be extended all the way back to the last interglacial:

    “Hence it is probably only the southern part of the Greenland
    ice sheet that experienced significant decreases in thickness during the
    Eemian. In fact it could be argued that a slight increase in the thickness of
    the northern part of the Greenland ice sheet is supported by the 18O data,
    as NGRIP and Camp Century Eemian 18O seems to have increased a bit
    less than the Renland 18O. The contribution to the global Eemian sea level
    rise from a thinning of the Greenland ice sheet is therefore believed to be
    modest, most likely less than 1m.”

    However that part is unlikely to make it into Nature any time soon.

  15. Bill,

    You have cited the recent Kaufmann et al paper. Without wanting to predjudice this research, I am aware that it is the work of the failed Hockey stick team. I believe McIntyre has tried to obtain their raw data and algorithms but they have blocked him. I am also aware that, like the failed hockey stick, it contradicts centuries of Historical and Archeological evidence for Roman and Medievial warm periods as well as the little ice age.

    Only time will tell, but so far, this research has not been independantly verified.

  16. beng (10:17:07) :

    That study is interesting but the results are unrealistic. Their “maximum” reconstruction for the Eemian extent of the ice is perhaps barely compatible with the actual geological data. The other two reconstructions are completely impossible since they have both Dye 3 and Renland (where there is Eemian ice in the ice-cores) ice-free.
    The Holocene reconstruction is also unrealistic. Studies of the distribution of Holocene marine fossils in LIA end-moraines show that the ice never receded more than about 20 km east of its present position in the Disko Bugt. The modelling shows a much larger retreat.

  17. Jari,

    “What we can now say for sure is that 8,000 years ago it was in fact 2-3 °C warmer than now, and it was this 2-3 degrees that actually caused quite a bit of melting,” says Vinther.”

    It matters not what caused the temperature change. Surely the important point is that although the link betwween the GIS and Canadian ice melted the GIS itself did not. So why should we know think a similar rise will have far greater effects?

  18. *****
    Vincent (10:44:36) :
    Bill,

    You have cited the recent Kaufmann et al paper. Without wanting to predjudice this research, I am aware that it is the work of the failed Hockey stick team. I believe McIntyre has tried to obtain their raw data and algorithms but they have blocked him …
    **********
    I’m not kidding when I say no one should seriously consider any “climate change”-related research when it has a bearing on government policy unless ALL data, used and not used by the researchers, is published along with any and all code, equations, or any other data processing techniques. This should be available to ANYONE who wants it, not just the Chosen.

    If the Federal Government funds it an any way, this condition should automatically apply. JMO.

  19. “The results can be used to make new calculations for models predicting future consequences of climate changes” – readers of this article should be aware that Bo Vinther also contributed to the recent ‘Kaufman report’ in Science, see:
    http://www.sciencemag.org/cgi/content/short/325/5945/1236
    The ‘thrust’ of the latter is clearly to dismiss the ‘medieval warming period’ (‘…indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age’).

  20. bill (03:53:29) :
    Hmmm! So how come even the edge cores show 11000 years of data. Where does the MWP figure in this – didn’t the ice melt since it was so sensitive to heat?

    with

    tty (07:22:04) :
    The ice cores aren’t from the edges, that would be useless since the ice there comes from somewhere else, you don’t know where.

    As in all real estate, it’s location – location – location.

  21. Lots of independently varying variablkes changing – or, more properly, NOT assumed to be independently changing.

    All these calculations are dropping back to relative O18/O16 levels in the sampled ice cores, right?

    O18/O16 varies according to elevation above sea level. Fine. IF the O18 production remains the same (no cosmic radiation changes over that period of time? No change in cosmic ray shielding? Solar radiation over time? )

    Then he flip-flops and assumes that the change in O18 production is “related to temperature”, but then determines the changes in Greenland glacier top-of-ice elevation BY the changes in O18 production rate over time, which is apparently therefore related to both elevation of the top-of-ice AND to the temperature of deposition. (Or is he assuming that top-of-ice elevation IS due to changes in temperature only? Clearly not so: He says that top-of-ice changes because precipitation increasing as the Ice Ages end (and glaciers melt, but then these particular glaciers DIDN’T melt at the ends of the various ice ages over the last 120,000 years. So top-of-ice changes due to precipitation when glacier melt – but these didn’t melt; but they change O18 levels due to elevation changes, but these didn’t change; but then nothing else changed to affect O18 production.)

    I don’t buy his theory.

    Not when B-17’s get buried under 300 feet of ice and snow in 50 years. But here he is relating 120,000 years of glacier deposits to changing O18 levels, accurate to 600 foot changes in elevation of the ice.

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