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Arctic Ice Instability

  1. Oct 24, 2009 #1

    Xnn

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    Here's a link to an animation from NASA of melting sea ice:

    http://www.nasa.gov/mov/391782main_sea_ice_concept.mov

    And also, a Science Journal Article on Arctic Ice:

    http://www.sciencemag.org/cgi/reprint/311/5768/1747.pdf

    GHG stands for Greenhouse Gases
    GIS stands for Greenland Ice Sheet
    LIG stands for Last Interglacial (130,000 years ago)

    Finally, here is a link to the current state of Arctic Sea Ice extent:

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.365.jpg

    Notice that while minimum sea ice extent was reached
    in September (as it usually does), the anomaly from the 1979 to 2000 mean
    has accelerated over the last few weeks and is now approximately
    2 million square kilometers low. That's about 3 times the size of Texas.

    The sun set about a month ago, and yet the anomaly has actually grown since then.
    This illustrates to me that the cause is due to the inability of the atmosphere to
    dissipate heat due to greenhouse gas concentrations.

    Figure 2 of the Science article is also fairly interesting because it illustrates that current
    (0kyrs) solar anomalies do not support rapid melting of Arctic ice.
     
    Last edited: Oct 24, 2009
  2. jcsd
  3. Oct 24, 2009 #2

    sylas

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    The setting of the Sun should not really matter. This is an "anomaly", from a kind of climatic mean. That is, they are comparing the extent for late Oct -- after setting of the Sun -- across the available 30 years.

    I have a prediction for you. This anomaly will very shortly reverse, and accelerate rapidly in the opposite direction, to a smaller anomaly again. I expect this to happen within a month or so... and I'll put this on record. You'll soon know whether my guess is right or not.

    Basis for this guess? The summer of 2007 was an extreme standout anomaly. Since then, there has been a quite strong annual cycle. I don't know why and I don't feel competant to guess. Something to do with more "new ice" compared with "old ice", I guess; or possibly a shift in seasonal extremes. After all, the Arctic is warming much more than the rest of the planet; there's something going on up there which is different from elsewhere.

    You can see the long term Arctic anomaly at Northern Hemisphere Sea Ice Anomaly. I'm looking at a strong seasonal signal starting in 2007 and continuing up to the present, and on that basis I'm guessing it will upturn again very shortly.

    The Southern Hemisphere Anomaly looks completely different, further confirming that this is a local regional feature of the changing climate.

    Cheers -- sylas
     
  4. Oct 24, 2009 #3
    If you look closer at the regional anomalies, you can see that the the Kara sea, Laptev sea and the area north of them are late in freezing. The anomalies are certain to disappear, since those areas completely freeze every winter.
     
  5. Oct 24, 2009 #4

    sylas

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    Yes; a strong seasonal cycle in anomalies will be seen if there is simply a delay in the onset of winter.

    Note that there is certainly a strong trend of the anomaly increasing to more and more negative over a scale of decades. The short term acceleration Xnn observed is unlikely to be a part of this longer trend, and is more likely to be part of the short seasonal trends, which are at present showing a seasonal pattern on top of the longer trend.
     
  6. Oct 24, 2009 #5

    Xnn

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    Sylas;

    Fully agree with your prediction;
    didn't intend to imply that the acceleration over the last month should continue.

    Just strange how there is such a seasonal cycle to the anomaly since 2007.
    However, it is consistent with less heat being dissipated since it tends to occur
    after the sun has set.
     
  7. Oct 24, 2009 #6

    sylas

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    Here's another factor which is known to operate and is already part of published work on the matter. Ice cover is an important climate feedback process. This is because ice reflects sunlight particularly well. As ice cover reduces, the Earth gets better at absorbing sunlight, and this amplifies any warming as a positive feedback.

    The effect is particularly strong in the Arctic, because here is where we have major reductions in ice cover. But note that effect of Arctic ice cover changes only applies in the northern summer. As Arctic ice cover reduces, you should expect summer temperatures to increase, with more sunlight being absorbed. In winter, however, there's very little Sun at all, and the effect of Arctic ice cover is weak. The Antarctic ice cover does not show the same strong trends, by the way.

    Upshot is I would expect a reduction in ice cover generally to lead to a larger gap between summer and winter, and hence a reduction in the anomaly as the Sun is removed; and this would contribute to a recovery in the anomaly over the coming months, which is what I expect.

    The years 2007 and 2008 were considerable anomalies with extreme reductions in summer ice cover, beyond what was predicted and well below the trend. 2009 has seen a partial recovery towards the trend... though it is still the third lowest summer ice extent on record. The ice albedo effect should contribute to a more marked seasonal signal in anomaly in these years. I am not claiming this is a complete explanation, but it is a known factor contributing to seasonal anomaly differences.

    Cheers -- sylas
     
  8. Oct 24, 2009 #7

    Xnn

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    Eventually, the Arctic will be ice free during the summer.
    So, what is now a nearly smooth sinusoidal seasonal chart will
    eventually transition to something that looks more like the Hudson Bay
    where there is a much more abrupt freeze period.

    ...At least that is what I suspect will happen
    Here is a link to the Hudson Bay chart:

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.13.html


    Another interesting observation:

    http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter4.pdf

    Since the rest of the year has decreased snow cover, the above
    illustrates another facet of seasonality among an overall reduction in snow and ice.
    The only reason I can think that would drive this in a warming climate is if there were increased precipitation (snow storms) in November and December.
     
  9. Oct 28, 2009 #8
    how high the sea level would rise if all Ice that is left around the poles melted?
     
  10. Oct 29, 2009 #9
    We seem to keep forgetting the cause of the low Arctic ice record of 2005-2007

    Wind

     
  11. Oct 29, 2009 #10

    sylas

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    Not at all. If you look at the posts so far in this thread, you'll see explicit mention of the fact that reductions of ice over this period are anomalous, well beyond a simple linear association with increasing global temperatures. For example, in the second post of the thread, I concluded:
    I have also mentioned the wind factor explicitly in other threads where the Arctic ice reduction is being discussed.

    Thanks for the link! It sheds a bit more light on the matter. Your link is to a NASA press release, and I've followed through to look at the associated paper, and another more recent related publication.

    Your link was to a press release for the research reported by Ngheim et al in 2007. The paper by Simmonds is more recent and gives similar conclusions. These papers confirm what we've also been mentioning so far in the thread, a strong seasonal signal in ice cover. That is, the summer ice reduction (September) is particularly strong; more so than the winter reductions. This shows up in the http://www.arctic.noaa.gov/reportcard/seaice.html [Broken], Update for 2009, at NOAA, for which Ngheim is also a contributing author. Here is figure S2 in this update:
    seaice2009fig2-sml.jpg
    Figure S2. Time series of the percent difference in ice extent in March (the month of ice extent maximum) and September (the month of ice extent minimum) relative to the mean values for the period 1979–2000. Based on a least squares linear regression for the period 1979-2009, the rate of decrease for the March and September ice extents is –2.5% and –8.9% per decade, respectively.
    -- Sea Ice Cover, update for 2009 to Arctic Report Card, NOAA, October 19, 2009 (http://www.arctic.noaa.gov/reportcard/seaice.html [Broken])​
    Note that the difference between March and September trends means that the anomaly is tending to increase in September, and then recover again towards March; a feature Xnn and I have remarked upon in the thread.

    Both papers also mention the significance of these reductions in ice cover for the ice-albedo feedback, which was mentioned in [post=2408973]msg #6[/post]. Both papers note a shift in the Arctic Ocean from perennial (multi-year) ice to seasonal (first-year) ice.

    Simmonds et al (2009) also confirms the importance of changing wind patterns, mentioned also by Nghiem et al. In the discussion, they say:
    We have documented some remarkable changes in September mean cyclone properties which are partially associated with the dramatic decreases in SIE [[strike]Summer[/strike] Sea Ice Extent]. In particular we have seen that informative September Arctic cyclone properties (such as Depth) are related to changes in the Arctic ice in a much more consistent manner than are variations in cyclone counts. ...
    The concluding sentence:
    Our study adds to the evidence which suggests that the decline in Arctic ice thickness and extent has started to render it particularly vulnerable to anomalous cyclonic activity and atmospheric forcing.

    This is, in fact, an example of a positive feedback effect. As climate conditions change, the impact on sea ice further amplifies the changes taking place in the Arctic, by reducing albedo and increasing the absorption of sunlight.

    Cheers -- sylas
     
    Last edited by a moderator: May 4, 2017
  12. Oct 29, 2009 #11

    Xnn

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    Arctic Cyclonic activity!

    Not the number, but the intensity.

    Was only able to read the abstract, but suspect this trend isn't limited to just the month of September. It may very well extend thru December, which is why there has also been a noted trend by the IPCC of increased NH snow extent in the months of November and December. That is big cyclonic storms in the NH during the winter = lots of snow.

    Of course, these storms are the atmosphere's way of redistributing heat.
    They spread snow all over, but also exchange a lot of heat between the polar region and more temperate.
     
  13. Oct 29, 2009 #12

    sylas

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    You are looking at Simmonds and Keay (2009), and the freely available abstract is as follows:
    Dramatic changes have been observed in Arctic sea ice, cyclone behavior and atmospheric circulation in recent decades. Decreases in September ice extent have been remarkable over the last 30 years, and particularly so in very recent times. The analysis reveals that the trends and variability in September ice coverage and mean cyclone characteristics are related, and that the strength (rather than the number) of cyclones in the Arctic basin is playing a central role in the changes observed in that region, especially in the last few years. The findings reinforce suggestions that the decline in the extent and thickness of Arctic ice has started to render it particularly vulnerable to future anomalous cyclonic activity and atmospheric forcing.

    It seems that the paper does specifically single out summer cylones and their properties in September. They hypothesize a positive feedback between ice cover and cyclone intensity, as follows (note that SIE is Sea Ice Extent):
    In this work we test some physical hypotheses as to the connections between September SIE in the Arctic basin (here defined as all ocean points north of 65o N) over the last three decades and aspects of cyclone behavior, with a view to obtaining a more integrated picture of Arctic variability. Septembers with low SIE correspond on average with greater basin-wide surface enthalpy fluxes. (For the data used in this paper the temporal correlation over 1979–2008 between the September SIE and the enthalpy flux is -0.31 (p = 0.10); the flux is dominated by the latent heat flux (LHF), which has a correlation of -0.37 (p = 0.046) with SIE (see Table 1).) From these considerations we suggest that Septembers with low SIE provide increased energy for cyclonic systems, and hence would be associated with the enhanced development of already-existing cyclones. Note also that more energetic cyclones will exert greater mechanical forcing on the ice, with the potential during this month of minimum extent and thickness to disperse ice (moving some into warmer waters) and result, in turn, in less SIE. From these reflections we form the hypothesis (HA1) that reduced September SIE is associated (through mutual interactions) with stronger and larger Arctic basin cyclones. As to the number of summer cyclones, a significant proportion of these originate outside the Arctic basin [Serreze and Barrett, 2008; Löptien et al., 2008]. A second hypothesis is formed (HA2) of no relationship between Arctic September cyclone counts and SIE.

    It looks to me that this more to do with physical movement of ice rather than any heat exchange effects; and least as far as the cause of reduced ice extent is addressed. On the other hand, the reverse part of the feedback loop is that reduced ice extent in September leads to a higher "enthalpy flux" and hence more energy for cyclones. (My bold in the above extract.)

    This mechanical movement of ice is also a feature of the paper by Ngheim et al. From the earlier paper by Ngheim et al (2007)
    The ice loss in January 2007 was also consistent with a northerly wind anomaly of as much as 5 m • s−1, double the January wind averaged over 50 years from the National Centers for Environmental Prediction (NCEP) reanalysis. The loading and enhancement of the TD [Transpolar Drift] had occurred with a much more pronounced short-term effect in September 2005 causing an abrupt ice loss via Fram Strait [Nghiem et al., 2006a, 2006b]. The TD transport of ice in 2005 was accelerated by a strong northerly wind anomaly in September 2005 observed in data from the NCEP reanalysis over the past 50 years along the Greenland Sea [Nghiem et al., 2006b]. On the two different sides of the TD, a pronounced atmospheric low pressure over the Barents Sea, in concert with a strong high pressure over the Canadian Basin, set up the wind anomaly [Nghiem et al., 2006b]. These atmospheric anomalies loaded ice into the TD and accelerated the TD like a runaway train carrying ice out of the Arctic, noted here as the ‘Polar Express’ (PE).
    I like their comparison with a runaway train and the "polar express".

    As a curious sideline; Nghiem et al refer approvingly in their conclusion to the "coordinated research efforts under the International Polar Year Program" for trying to sort out the highly complex problem of forecasting ice cover. We've discussed one of those efforts recently as well.

    In [post=2374600]msg #23[/post] of thread "State of the Climate", mheslep introduced the "Sea Ice Outlook" program, in which researchers participate in an co-ordinated exercise of forecasting ice and comparing with results. Ironically, in 2009, the summer SEI was larger than any group had predicted, thanks to a last minute reversal in weather conditions. Both these paper were written before that 2009 minimum was known. It was still the third lower SEI on record, however. There is further discussion in following posts of that thread.

    The cautionary tale in all these papers is that the polar climate is complicated. The downwards trend in Arctic Sea Ice Extent is unambiguous, especially in the summer, but that's not enough to give good forecasts from year to year.

    Cheers -- sylas
     
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