New Ice Free Arctic Estimate

Volume melt rates are slowing sharply, and I now estimate that the Arctic will be ice-free on September 1, at 9:11 am.

Spreadsheet    Data

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8 Responses to New Ice Free Arctic Estimate

  1. Jackson says:

    Your ‘straight line’ analysis fails to take into account that everything is WORSE than we could have imagined.
    I think the prediction should be for Aug. 30 at 8:47 am to take into account the fact everything is WORSE than we imagined.
    Yes, I am being sarcastic this morning.

  2. mark says:

    Dont know where best to post this, but I hope Tony gets to have a look at it.

    I did a comparison between the NSIDC extent figures, (available and the the JAXA extent figures, available,2223.1050.html).

    In general NSIDC measures extent somewhere between 0.4m and 0.6m km2 above the measurements of JAXA, for whatever reason, (and it would be useful to know how the metrics differ). But in general the two scales then generally match up, in terms of comparative loss or gain of extent on a year by year basis. So for example 2017 was some 0.1m km2 above 2016 on July 16th on both scales. So for example 2015 was some 0.93m km2 above 2011 on NSIDC and 0.81 km2 on JAXA. So for example 2014 was some 0.1 km2 above 2007 on NSIDC and 0.02 km2 on JAXA. All in all a very narrow range of variance.

    That is until one comes to 2018, where the difference in the same calculation suddenly jumps to somewhere between 0.2 km2 and up to 0.36, (2013). 2010 and 2012 are the two years where the difference in ice extent between this year and those years falls back into the same range as the comparison between 2017 and previous years.

    So, for whatever reason, the NSIDC estimation of ice extent is somewhat lower this year than for any year since 2012 in terms of comparing it to JAXA calculation for the same loss/gain ratio when compared to previous years in the records back to 2006.

    This means that 2018 is now reckoned to be the 11th lowest extent according to JAXA’s calculations, and only the 9th lowest according to NSIDC calculations.

    Is this of interest? I hope more qualified contibutors can shed light on this.

    • Steven Fraser says:

      Its been my experience that differences between the numbers produced by the ice estimation groups come down to differences in methodology. Those methodological differences include (in no particular order):

      1) The geographic area covered
      2) The technical mechanism for data acquisition or observation
      3) The timing of observations
      4) The way the observations are organized for analysis
      5) The definition of ‘sea ice’ – typically with a threshold % concentration
      6) The way the analysis is summarized
      7) Changes in a methodology over time

      As an example from the past: In the past, we had no information (observations) from the middle of the Arctic Ice pack. What was known was where the edges were, but only where ships went and made those observations. Those observations were recorded graphically on charts, and aggregated monthly.

      In every aspect, the methodology has incrementally changed. The use of airplanes and submarines gave us information about ice pack continuity and thickness. Photographs taken from satellites were aggregated and analyzed. Microwave sounding and analysis made observations possible at night, especially valuable for NH Winter. Multi-channel microwave sounding added the dimension of ice thickness…

      Along the way, a significant challenge has been to link the current results to the prior ones. For example, in the early years of satellite observations, in a given grid cell, 10% ice coverage in the cell qualified the cell as being ‘ice’ for extent purposes. The results reported in the 1990 IPCC FAR and the 1995 IPCC SAR were produced that way. These days, 15% ice coverage is used for the same purpose.

      All that said, to understand the differences you inquire about, I think it is necessary to compare the NSIDC and JAXA methodology stacks side-by-side to understand their systemic differences. I think you will find your answer there.

      • mark says:

        That’s very interesting, Steven. Thanks.

        What do you think about the discrepancy that has occurred in this year’s managements, where JAXA shows a higher relative figure for 2018 than NSIDC than has been normal.

  3. lance says:

    I liked the graph back a few years ago when ice extent was back rising in the fall/winter, when you projected the earth to be covered in ice by x months..!! Only fair

  4. Steven Fraser says:

    Sea Ice volume numbers for July 17:

    2018 is still #4, up slightly to 111.31% of the 16-year average, and down slightly to 113.37% of the 2004-2013 DMI-charted average.

    2018 retains its position in the upper part of the 1st std deviation for the 16-year average, and the lower part of the 2nd std deviation for the 10-year periods

    Yesterday’s decline was -231 cu km, and #3 year (2003) was -251, so the gap between them narrowed by 20, to 269.

  5. GCsquared says:

    I’m waiting for the black line to turn upward from the dip. Then the projected ice-free days will lie in the past, and we’ll be able to complain about how successfully the coal industry hid the melt!

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