the Air Vent

Because the world needs another opinion

Global Sea Ice Trend from Gridded Data

Posted by Jeff Id on February 8, 2009

This post is again about antarctic ice trends. Aside from the recent paper by Eric Steig, I’ve been fortunate enough to be studying the antarctic sea ice trends. The antarctic is quite different from the arctic as far as sea ice due to the fact that the ice melts almost completely every year. What I have done which is different from what you normally find on the internet is to process the actual gridded Antarctic data myself. This includes land masks and individual pixels.

Arctic ice area is defined as the summation of all non-land pixel area times percent ice per pixel. This gives a somewhat more complete estimate of the actual trend in sea ice as compared to extent which is defined as the amount of area containing more than 15% ice.

In my previous post which probably should have come after this one, I looked at the trend in ice for each individual pixel area. It looks like this.


The green square in the bottom left indicates the zero trend line as I stated before. Sorry for the lack of a better scale but the graph is hommade and I’ve spent my time reading papers rather than how to make plots. The plot is therefore a plot of tens of thousands of linear slope fits (one to each ice pixel) in an effort to determine locations of growth and loss in 30 years.

For a more complete description. Gridded Antarctic Sea Ice Trend

I then provide this graph to show the cutoff between positive and negative trend. This is the same as above but intended to provide some form of reference for the interpretation of the above graph.

antarctic-ice-trend3Green indicates an increase over the 30 year measurement time whereas red is a decrease.

How does this translate into total ice area for the antarctic. Ice growth on average for the last 30 years is 24531 Km^2 per year. I don’t see how this can possibly be true with Eric Steigs latest work showing temp increases of 0.176C/decade since 1956. My guess now which is different from before, is that the antarctic is not warming as stated.


Antarctic trend is Arctic Ice looks like this -58983 Km^2/year.

30-yr-ice-area2Global ice area is below and by adding the two graphs with the time offsets was a neagative trend of -29571Km^2 per year.


This doesn’t seem anywhere near the catastrophic headlines we’re constantly bombarded with. It just isn’t reasonable.

I would like to add some more to this but I’m going to go have some fun instead.



The net down slope of global sea ice is therefore 29,000/ 20,000,000 km^2 = 0.00145 x100 = 0.145 percent per year.

About a tenth of a percent per year!

another way

About one thousandth of total global sea ice area was lost per year on average.

Total global ice lost in 30 years = 4.3 percent.

Pretty small change considering that seasonal variation alone runs about 25%.

13 Responses to “Global Sea Ice Trend from Gridded Data”

  1. Layman Lurker said

    Hard to reconcile the two trends. It would have to be a case of the west antarctic anomalies being strongly positive and only partially offset by very weak negative anomalies in the other regions.

  2. jeff Id said

    You know, I want to do an area weighted version of the Steig reconstructed data. I think by area it may turn out that the net trend is negative from his own data. I think he just averaged the stations like Mann does.

  3. Layman Lurker said

    But isn’t the infilling of the reconstruction supposed to consider the location and weight accordingly?

  4. PeterA said

    Ah I see it all! Big Al has connected a line from the winter Arctic sea ice maximum in 1978 to the Arctic summer sea ice minimum in 2008. Extending this line roughly reaches the zero point in 2013.

  5. jeff Id said

    #3 It kind of reads like that. Even RomanM had that impression but as I read it, I think the spatial weighting is handled entirely by the quality of match to the 3 pc’s.

    Pretty nuts eh?

  6. John F. Pittman said

    Jeff, your Nasa Team Global graph looks as though if you did a daily anomoly adjustment, you would get a really nice trend graph, detrended by day of the year. Might be some interesting information hiding in there that would show up.

  7. Jeff Id said


    I wanted to do that also, I spent huge hours this weekend on the Anarctic paper so no time yet.

  8. John F. Pittman said

    I assume you are talking about Steig’s paper? Perhaps that detrended data would be a way to “backlight” Eric’s paper and indicate if there appeared to be a corresponding physical parameter other than their infilled data that supported (or not) the paper. Say, an PDO-like pattern that did or did not show up in their infilled version.

  9. just me said

    hm, 30 x 0,143 = 0,43? I do not think so. 😉

    But, it is true that the global ice numbers are not very helpful because the North and South is quite different. Anyway.

  10. Jeff Id said

    What do you mean? I don’t see anything.


  11. Layman Lurker said

    It would be interesting to compare the evolution of antarctic sea ice area or extent on varying time scales with the antarctic surface temp data (or even the reconstruction) to see what kind of relationship there is. I understand that SST’s would also affect the ice, but perhaps there are some insights here?

  12. Jeff Id said


    I’m no climatologist but it seems to me that the energy content of the water has to be what drives the cycles. I bet different areas would correlate extremely well with ocean temp. I’ve got so many projects going now that are interesting, I may get to this one though.

  13. Have you updated the total sea ice data to 2010?

    Best and thanks for your efforts.

    John Zyrkowski

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