Skip to content

A Tale Of Two Indices

April 2, 2016

By Paul Homewood 




I mentioned the other day that claims of “record low” Arctic ice foundered on the fact that the difference involved was so small to have been well within any margin of error.

Ron Clutz updates the situation, comparing MASIE with the Sea Ice Index, used for public consumption by NSIDC:


Sorry to be serious on April 1.  I am not a fan of ice charts restricted to one month, for reasons illustrated in the post Ice House of Mirrors (some humor there in honor of this day.) But March monthly average sets the baseline for the year’s melt season, and so there is considerable attention and significance attached to the month just concluded.

Here is a chart showing March 2016 compared to the previous ten Marches according to two different indices of Sea Ice Extent: MASIE (Multisensor Analyzed Sea Ice Extent) produced by the National Ice Center and SII (Sea Ice Index) produced by NOAA (both accessed at NSIDC).


MASIE and SII March

It is evident that the March annual maximum is trending slightly upward in MASIE and slightly downward in SII. Note that the indices were quite similar the first five years. Then since 2010, SII has declined quite strongly.

The differences between the two remind us that measuring ice extent is not an exact science.


Read Ron’s full analysis here

  1. April 2, 2016 7:25 pm

    Climate science seems replete with participants looking for trends in data, but I usually remain unconvinced of any significance of the trends. This is a good case in point. Neither of the trends (regressions) done for the two data sets above have basic diagnostics inspiring any confidence. (I just read the numbers off the graphs and entered them into Matlab for fun.) It is just as likely there is no trend in either. Running a vratiotest (in Matlab) indicates similar difficulty rejecting the notion either data set comes from a random walk.
    Arguing about whether the trend is negative or positive seems to be angels on heads of pins. Whenever climate science types talk about trends in data I am reminded of the joke about the psychiatrist, the patient, and ink blot test.

    • It doesn't add up... permalink
      April 2, 2016 11:49 pm

      Here’s Nic Stokes pontificating on just this issue – as he still struggles with the concept that a trend that is not statistically significant cannot be described as a trend (especially when the data exhibit a high degree of autocorrelation):

    • dave permalink
      April 3, 2016 7:55 am


      It is the same old switcheroo.

      At first it is “the Canary in the coal mine” story. The shrinking ice is an early warning.

      Then it is somehow a natural resource which we are in danger of losing!

      Then it is all part of God’s plan for the Universe which we are not allowed to change because that would be presumptuous and bring down his wrath.

      By the way, the maximum number of angels on the head of a pin has been determined.
      It is 42.

      • Broadlands permalink
        April 6, 2016 5:32 pm

        Dave… 42 climatologists? 🙂

    • April 6, 2016 5:25 pm

      I sent a similar comment to Ron, didn’t use Matlab though, just simple observation. There is a great belief that regression proves cause and effect where data are clearly randomly distributed.

  2. AndyG55 permalink
    April 2, 2016 10:37 pm

    For the last 7 or so years the Arctic has been skirting the top turning point of the AMO.

    The Arctic sea ice is behaving exactly as it should be.

    NOTHING unusual is happening in the Arctic except that the sea ice levels are still anomalously high compared to the rest of the Holocene.

    Has it fully recovered from the LIA? Time will tell.

  3. Broadlands permalink
    April 3, 2016 1:32 am

    RE… Trends. Whether statistically significant or random, NOAA uses linear trends, presumably to reveal changes in weather/climate. Temperatures, carefully adjusted and re-adjusted to two decimal places are used. Their linear trends since 1998 are down, in winter especially, currently at minus 0.78°F per decade. Are these trends significant? If not, what is? What metrics, “basic diagnostics”, should be used to find out what’s going on? What is anomalous? or normal?

    • dave permalink
      April 3, 2016 7:44 am

      The first book about Statistics that I read (in 1963) was a volume in the Pelican Series called “Facts from Figures” by the acerbic M.J. Moroney. It was a counter-balance to the rubbish I was being exposed to by the Mathematics Faculty at Cambridge.

      The book had a chapter on Time Series, which the author apologized for including at all. He explained (I paraphrase) that the subject consisted solely of trite observations, and speculative explanations of them, which were trite themselves – or tripe.

      He also wrote that the important thing about trends was that they always came to an end when you had started to rely upon them!

      • April 6, 2016 5:30 pm

        The one that I almost remember is:
        A curve or a line is a trend, but where and how does it bend;
        Does it rise evermore or fall to the floor;
        or just asymptote at the end?

      • Broadlands permalink
        April 6, 2016 5:46 pm

        Dave and Jack… Agree, but again, what metric(s) should be used that can be relied upon? Validly criticizing those in use doesn’t seem to get us anywhere.

        If the global temperature in 1995 was 59.7°F but 58.62°F in 2015 (NOAA)… is that a trend or just two points making a straight line?


      • Broadlands permalink
        April 6, 2016 5:55 pm

        My apologies for the wrong reference to the 1995 global temperatures.

    • It doesn't add up... permalink
      April 3, 2016 9:21 am

      I think they should be required to explain the physics that suggests a linear model is appropriate.

  4. dave permalink
    April 3, 2016 8:23 am

    The DELIBERATE nonsense that we fight (hopelessly) against is exemplified by the left-leaning, mass-market, UK newspaper the Daily Mirror and its headline of yesterday:

    “UK Weather: Sunday will be the hottest day of year as ‘Godzilla El Nino’ brings three-month heat wave.”

    This is THEIR way of reporting/glossing (finger in my mouth) the briefing of the Met Office:

    “For April/May/June the probability the UK average temperature will fall into the warmest of our five categories is 30%”

  5. April 3, 2016 1:46 pm

    even in the last ice age the Arctic was about the same as today.

    “The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout, but like today probably was only covered by relatively shallow ice, subject to seasonal changes and riddled with icebergs calving from the surrounding ice sheets. According to the sediment composition retrieved from deep-sea cores there must even have been times of seasonally open waters”

Comments are closed.

%d bloggers like this: