the Air Vent

Because the world needs another opinion

Unique Arctic Sea Ice Plots

Posted by Jeff Id on September 23, 2009

I’ve done some improvement on my Sea Ice plots. I’ve included several graphs I haven’t seen before one of which was the ratio of extent and area suggested by Crashex on the last thread. The plots reveal some interesting and unique aspects of sea ice, and the last two graphs seem to be in opposition to the conclusion that sea ice is melting due to global warming and supportive of a weather pattern change.

This version used some smart filtering to remove points with jumps greater than 100,000km^2 in one day, an improved filtering with a wider window and some other minor improvements. I’ve plotted the data several different ways but I want to start with the improved area and extent value and anomaly plots. I’ve corrected the area plots by adding the satellite hole area in at 100% using only the larger hole from the first satellites so as to not bias the data.

You can see my plot is a near exact match for the Cryosphere version HERE.

arctic ice area

Extent is calculated as all pixels with areas greater than 15% of the pixel.

arctic ice extent

arctic ice area anomaly

You can see most of the big spikes have been removed. Still no significance levels Kenneth, it will take a bit more time.

arctic ice extent anomaly

There are still a few small downward spikes not removed by the 100,000km^2 threshold but the curve is much cleaner. The next graph is a plot of all years overlayed on the average curve displayed in the background. I should mention that all anomalies were calculated over the full length of the data.

arctic ice area each year overlay

It was interesting that I had area (not extent) of 2008 basically equal to the 2007 minimum.

arctic ice extent each year overlay

This is the more familiar extent curve with all NSIDC years plotted. An interesting detail is that the curent extent by NSIDC isn’t higher than 2005 as Jaxa reports. (see where the black line endpoint almost reaches the closest curve directly above it – 2005) I’m interested in this because our current satellite NOAA17 is different from the one used in 2005 which was NOAA13. I believe all of JAXA’s data is from a single satellite and it has what is apparently a higher value for ice levels today than at the same time in 2005. It could be a calibration difference during satellite transitions causing the current years to appear slightly lower in ice levels.
The next plot is Area vs Extent to see if there is a pattern in the annual signal.

extent vs area

The greater than 1 slope means Extent changes just slightly faster than area. The next plot was requested by Crashex.

area divided by extent

I think it shows some interesting trends in the recent years. Where the graph dips is during the summer months and the top values are where the ice packs out the entire ocean in the winter months. I removed the annual anomaly signal and replotted in the next graph.

arctic ice area div by extent anomaly

Then I decided to look at the days at which the ice minimums and maximums occurred. These are not official values and should be determined using heavily filtered data so there is some noise but this is right from the data. If warming were the cause of ice melting rather than weather patterns we would expect the minimum to happen later each year. This meant that if there was a strong trend towards earlier in the year warming wouldn’t be the cause. If it were to shift later in the year over time, either possibility is valid.

Also, it would be reasonable to expect the winter maximum to shift earlier in the year as the higher temperatures would limit ice formation to occur sooner in the season. If it were only weather patterns the shift could be either direction.

ice area minimum day

ice extent minimum day

Wow, that’s a pretty clear uptrend in both graphs. The first wouldn’t survive any trend significance test WRT weather noise but the second might be on the edge. We cannot eliminate temperature as the cause of these curves. What do the maximum’s show

ice area maximum day

This was a little surprising also, the area maximums show more variation than the minimums. There isn’t any clear shifting of the maximum date to earlier in the season though as we would expect if warming were the culprit.

ice extent maximum day
Ok, the strongest trend recorded is from the winter version of the Extent maximums and it’s positive. Again I doubt this trend meets significance compared to the “weather noise” but consider that it is strongly positive meaning that the maximum ice value shifts later in the year by almost 2 days every five years, this is the opposite of what I would expect if ice levels were being reduced by global warming rather than a weather pattern change.
I don’t know where to find official figures on this so it needs confirmation and some improvement in locating an exact minimum but the minimum value in this data is shifting in the opposite direction from what would be expected due to global warming.

13 Responses to “Unique Arctic Sea Ice Plots”

  1. Mike said


    This is important, because KNMI De Bilt is the only temperature station in the Netherlands and for around 150 km in any direction used in GISTEMP (the nearest long-record station is in a suburb of Brussels). Translations are my own work. Apologies for typos.

    1st story:

    KNMI has been measuring the wrong temperature for years

    DE BILT – Weather Institute KNMI has been measuring the years incorrect temperatures on its grounds in De Bilt due to an incorrect setup of a thermometer.

    The instrument stood too close to a line of trees, due to which on average half a degree (Celsius) too high was measured.

    After discovery of the fault the thermometer was moved to an open spot on the measurement field before last summer, the KNMI has confirmed. Due to the change the average measured temperature fell half a degree. This measurement should be reliable.

    The mistake resulted in that the KNMI has announced more “official” summery and tropical days than there were in reality. According to the Institute, the defect has not or hardly influenced the scientific discussion on climate change, because researchers use the data from a large number of weather stations. SUZANNE DOCHTER

    2nd story —

    KNMI has been deaf to criticism for years

    WAGENINGEN – weather Institute KNMI has been deaf to years of criticism from competitor Meteo Consult of its temperature measurements in De Bilt

    Weather specialists from the Wageningen-based Meteo Consult have been expressing their distrust for years, because the KNMI figures in De Bilt were always a bit warmer than in Cabau, 16 km away, where there is also a KNMI thermometer. The position of both places could, according to Meteo Consult, not explain the temperature difference of on average half a degree (Celsius). It was also not taken into account that De Bilt is located in a more built-up, and probably therefore warmer, surroundings than Cabau, near IJsselstein.

    The meteorologists from Wageningen discovered this summer to their amazement that the temperature difference between both places in the KNMI figures had more or less disappeared. On enquiring of the De Bilt employees, it appeared that the thermometer had been moved. Since the intervention, the measurements from De Bilt show not 1/2°, but on average just 2 hundredths of a degree warmer than Cabauw, according to the spokesman of Meteo Consult.

    This summer it appeared that the temperature difference was suddenly resolved. Again discussions blazed between the weather specialists and it was decided to closely compare the measurements between Bilt and Cabauw. “It was thus discovered that last summer in De Bilt was still 1/2° warmer and this year there was just a difference of 0.02 degree Celsius”, explained a spokesman of Meteo Consult.

    The organisation decided to call the KNMI and heard that the “weather cabin”, in which the thermometer is located, had been moved. According to the KNMI the measuring instrument stood too close to a row of trees. Because the trees continued to get taller, the wind began to influence the temperature measurements too much. Now the “weather cabin” has been moved 200 m away, to a more open spot on the measurement field of De Bilt. KNMI employee Cees Molenaars cannot say how much influence the old placement of the thermometer has had on weather reports. “We must investigate that. We only regret is that we did not keep Meteo Consult and other parties informed of the movement.”

    The thermometer of De Bilt is the official measurement used for determining heatwaves, cold waves, and summery days. To speak of a heatwave it must be at least 25°C released 5 days. Also it must be warm than 30° for 3 days. At 25° one can talk about a summery day.

    With a cold wave, freezing temperatures must be measured for 5 adjoining days at De Bilt, with also 3 days with a hard frost. “The differences in minimum temperature between de Bilt and Cabauw were much smaller,” said the spokesman of Meteo Consult. “The chance that a cold wave is missed, is thus smaller.”

    The thermometer in De Bilt has less influence on KNMI weather predictions. These are performed on the basis of the data of tens of measurement stations. Further, for scientific purposes, such as climate change research, the central Dutch temperature was brought to life long ago. For this, data from various stations is used [NOT TRUE -- GISTEMP ONLY USES DE BILT!]. Meteo Consult are above all happy that the riddle has been solved. For fun they have also calculated what an extra half degree in De Bilt would have meant for this summer: 5 extra summery days and 2 tropical ones.

  2. DeWitt Payne said

    I would expect the maximum date as well as area and extent to be much less sensitive to temperature than the minimum date. Heat loss in the winter is mainly radiative to space and ghg forcing in the arctic is minimal as the tropopause height is so low. Any difference in cloud cover in the winter would probably have a large effect. Is there any data on that?

  3. DeWitt Payne said

    Also, 100,000 km2 as a cutoff seems a little severe as the JAXA data has a number of days when the change in area was greater than 100,000 km2. In 2007, the EWMA smoothed rate exceeded 100,000 km2/day for 13 of 15 days starting July 3.

  4. Jeff Id said

    #3 good info. I could do some more experimenting but what would you suggest for a reasonable cutoff?

  5. DeWitt Payne said

    Max and min for the JAXA extent data are 271406 and -201875, but those seem a little high. I did COUNTIF in Excel on the JAXA data and an upper limit of 250,000 still rejects 3 points. A lower limit of -170000 rejects 2 points. I haven’t tried calculating rates from the NSIDC data so I don’t have those differences. What did you do about the only every other day before 1987 thing?

  6. Jeff Id said

    #5 The sliding filter took care of infilling. I’ll try your numbers.

  7. Crashex said

    Thanks for posting the plots I suggested.

    The results indicate that extent and area are diverging with a progressive reduction of the summertime density or concentration to go with the trend in physical area. Interesting. Admittedly, not what I expected from scanning through the CT plots. I had expected to see the ’09 average concentration had recovered back to the mean (or higher).

    Can’t quite understand how having 75-80% of the area at 95-100% concentration would end up with an average concentration for the overall region below 75%. Guess my “visual averaging” needs work.

  8. Jeff Id said


    It was a good suggestion but it took time before I was happy with the code. These posts take a long time and are a bit unpopular. It’s still worth it to me. One of the best things about it was that I was able to replicate the cryosphere work nearly perfectly. This is the first time I’ve seen it that close from my own work.

  9. DeWitt Payne said

    Now if I could just figure out where Cryosphere Today gets its flakey extent data. I think I have a lead, but I’m still working on the details.

  10. Jeff Id said

    #9 You’re kind of the iceman. What ‘flaky’ extent plots are you referring to. The mainpage is only area that I saw.

  11. Crashex said

    Dewitt: The concentrations illustrated at that site are dramatically different than the CT plots. See,

    The “ice map” illustrates the A/E value and the relative volume distribution of concentrations that are used to calculate the Area from the extent. A great find. These concentration values make sense for the quoted Extents and Areas, with a predominant volume of 65-85% concentrations; substantially different than the predominent 95 to 100% concentration distribution illustrated at CT “high” color plots. A matching CT plot should be largely Green, NOT Magenta.

    Now, which one of the maps is accurate? If you believe the CT plot, the actual Ice Area is substantially greater then the quoted values.

  12. DeWitt Payne said


    The flaky CT numbers are related to the big drops in extent for 2007 and 2008. Look at the seasonal sea ice graph. There are other problems with the series in other years when compared to NSIDC extent data. Chapman says they use mid-month data to compute the seasonal and annual averages. The question is whose mid-month data. I’ve been able to exactly match a few of the CT seasonal numbers by the proper combination of data from the National Ice Center (link in my post above), which are spaced at two week intervals, but not always on the same date each year. The other piece of evidence is that CT hasn’t updated the chart through winter 2008 and the 2008 chart from the National Ice Center is missing data from November and December.

  13. DeWitt Payne said


    Your link showed an average concentration of 72% on 9/24. The concentration calculated from CT area and JAXA extent for the same date is 70%. That’s close enough for me. The false color scheme is very different from what CT uses and is even more non-linear. I don’t think it’s worthwhile to try to compare false color charts that use different color schemes.

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