Analysis of NOAA Arctic Sea Ice extent since 1979

For climate analysis we consider the average monthly extents for March and for September of each year in the satellite record, and the differences (the melt extent). Though we would prefer a longer record, these are currently the most popular data. Several observations:

March averages (annual maximums) do not vary greatly: 15.48 M Km2 is the average extent, with a range of 16.45 to 14.43 M Km2. 2/3 of the years are between 15 and 16M.

September averages (annual minimums) vary much more: 6.40 M Km2 is the average, with a range of 7.88 to 3.63 M Km2. Standard deviation is +/- 1.07 M Km2.


Note: The largest September extent (7.88) in the record occurred in 1996, the same year of the smallest melt extent: 7.25. And the smallest September extent (3.63) occurred in 2012, due to the largest melt in the record, 11.8M. The March extents of those two years were nearly the same.

The Arctic ice extent time series appears to consist of three periods:
1979 to 1996 Annual minimums mostly above average
1997 to 2006 Annual minimums around average
2007 to 2014 Annual minimums below average

Averages March Sept Diff (Melt)
1979 to 1996 15.8 7.2 8.6
1997 to 2006 15.3 6.2 9.0
2007 to 2014 15.0 4.5 10.5

Since 2005 the combination of below average March extents, combined with above average melts has produced September extents below 6 M Km2 each year.

It is now evident that 2012 was an outlier (probably due to the unusual storm activity). That year’s melt of 11.8 was 28% above the average melt of 9.09 and more than 1 M km2 larger than the second largest melt in 2008.

The pivotal decade was 1997 to 2006, preceded by slightly declining extents, and followed by much lower extents. What any of this has to do with CO2 and air temperatures is not obvious.

Data is here:


  1. Geert BAKKER · February 27, 2019

    Does melting of floating arctic ice influence sea level?


    • Ron Clutz · February 27, 2019

      No, it is drift ice already floating on the water.


  2. Geert BAKKER · February 27, 2019

    So the melting of arctic ice is harmless?


  3. Geert BAKKER · February 27, 2019

    Dear Ron,
    Thank you for your answer.
    I understand that the situation is too complicated for short answers to simple questions. Let me try again:
    I was advised to do a simple test: put a handful of ice cubes in a broad glas and fill it with water till the rim and watch what happens while the ice melts. Answer: nothing! Explanation: As we learned at elementary school 10% of an iceberg sticks out into the open and as the ice melts the top of berg sinks back into the water. This is a simple answer to a simple question: the melting of the North Pole sea ice has no effect on sea levels. The yearly melting and freezing is more or less in balance. Of course the South Pole is a different matter because that is mainly land ice.
    The other day I read that icebergs rise above the water while melting because they get lighter; I think that is rubbish.
    Could you please comment again?
    Thank you very much!


    • Ron Clutz · February 27, 2019

      I have no disagreement with what you say. The fuss about rising sea level is about land ice on Greenland and Antarctica.

      It seems to me that Arctic sea ice fluctuations are driven by the 3 Ws: Water, Wind and Weather. The ice extent lessens in relation to warm southern water intruding into the Arctic Ocean basins, most of it coming from the Atlantic by way of Barents Sea. Then the wind blows the drift ice around, causing it to pile up in some places. Those places vary in location depending on whether the prevailing regime is cyclonic or anticyclonic. Then there are weather events like the Great Arctic Cyclone of 2012, and wavy jet streams that bring warm southern air. Not much of a role for CO2.
      I discussed some of this in a post


  4. Geert BAKKER · February 27, 2019

    Thank you, Ron, this will keep me busy for a while; very interesting!


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