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DMI and GISS Arctic Temperatures: Hide the Increase?

Posted on 17 October 2010 by Peter Hogarth

SkS Note: Peter Hogarth has done us a great service by writing three level of rebuttals for the skeptic argument "DMI measurements show a cooling Arctic". This blog post is the Intermediate Version. However, if you want to ease yourself into the subject, you might want to kick off with the Basic Version first. Then if you're stout of heart, you might be ready to sink your teeth into the Advanced Version which features the trademark Hogarth detailed approach.

A recent WUWT article by Frank Lansner, August 5th 2010 has the heading “DMI polar data shows cooler Arctic temperature since 1958”. Peter Berenyi also posted a similar chart here on SkS (which sparked my interest). Frank Lansnser goes on to show data from Goddard Institute of Space Science (GISS) July polar views and compares this with graphics of Danish Meteorological Institute (DMI) data for July 2010 to cast doubt on the validity of the GISS gridded values in the Arctic region. This follows on from similar points made by Steve Goddard, and another article by Harold Ambler which tries to show how DMI is based on more data measurements than GISS, again providing a setting to raise questions about the reliability of GISS gridded values in the Arctic.

Similar claims that the DMI data shows Arctic “cooling” or highlights problems with other temperature data sets (eg from GISS, which mostly interpolates over the Arctic ice) appear on other websites. It appears that such sites regard the DMI data as a standard.

This post seeks to correct the public misunderstandings that these articles may cause, primarily about the claim of arctic “cooling” but also about comparisons between the DMI 2m Arctic absolute temperature time series and GISS temperature anomaly data from the Arctic region.

The Danish Meteorological Institute (DMI) Arctic temperature data is the output of the latest operational model as used for weather forecasting by the European Centre for Medium-Range Weather Forecasts (ECMWF). At present this output is an average of all model points at 2m height on a 0.5 degree grid over the most northerly part of the Arctic, above 80N. Because the number of land stations in the World Meteorological Organization (WMO) list above 80 degrees North is very small indeed (a handful), data inputs for the model must be supplemented by other sources for high resolution meteorological work. The models assimilate inputs from weather stations, drifting buoys, radiosondes, aircraft, vessels and since the 1970s, high coverage infra-red and microwave satellite based sensors. The models allow this high resolution satellite data to be used to interpolate between the sparse but very accurate observations from land stations, which form a network of absolute temperature value “tie points” - allowing calibration of the fine scale overall satellite derived relative changes.

DMI recommend that the 2m air temperature data should not be compared with overall Arctic temperature estimates from other data sets, which generally cover a wider area (usually above 65N) where more land station data is available.

We will now examine the claim of cooling “melt season” temperatures. Most of the area above 80N is (currently) still covered in permanent sea ice. In the Arctic Summer when the surface ice is melting, it is known that the air temperature close to the surface is limited by this ice melt temperature to just above zero degrees C, (Rigor 2000). This is why the Summer air temperatures have not varied much over the entire instrumental period. This maximum temperature “clipping” effect is clearly seen on all arctic data sets from Arctic buoy data to individual station data to satellite data.

Clearly high Arctic Summer surface temperatures just above zero are not really an indication of anything except proximity to a melting ice surface. To claim that the Arctic is cooling is misrepresenting the data.

It is also evident from these High Arctic data sets that the average temperatures in the Winter, Spring and Autumn periods have generally increased over the measurement period. It appears that the overall seasonal cycle is riding on a gradually warming average value, but peak positive excursions are being limited by the ice melt temperature in Summer.

It would be intuitive that such seasonal warming patterns would show up clearly in the overall DMI temperature anomaly trend, and this is the case. If we plot the entire daily DMI temperature data, and then a 365 day rolling average, we end with a positive trend of 0.383 degrees C per decade.

Figure 1: DMI daily temperature values, annual average and linear trend over the entire record period

Thus the reality is that the annual average Arctic surface temperature as indicated by DMI has risen at rates around twice the global average over the past 50 years, which is entirely consistent with other Arctic data sets, including the data from GISS. This annual temperature anomaly trend (red) gives clearer context to the Lansner chart (green).

Figure 2: DMI summer melt season temperatures and annual DMI temperature anomaly as well as five year running averages

The Goddard Institute of Space Science (GISS) global surface temperature anomaly time series is based on observations from publicly available observational data sets rather than models. Its primary usefulness is as an indicator of global or large scale regional temperature changes. The measurements used by GISS are gridded at either 1200km or 250km resolution, with appropriate weighting in grid cells containing both land and ocean. The SST data where available is used up to 100km from any coast, but data from any source is extended to a maximum radius of 1200km if no other measured data points are present within this range.

For the high Arctic, we have already noted that there are relatively few land stations, (a handful above 80N), and most of this area is currently still covered by permanent sea ice. A study using data from Polar drifting ice buoys showed that near surface air temperatures over the pack ice are relatively homogenous, with a CLS (correlation length scale) of 900-1000 km, see (Rigor 2000). Obviously SST can not be used in this region, as the sea surface is frozen. In open Ocean SST tracks variations in Air temperature, but this is not the case near the transitional and mobile ice “boundaries”. This is one reason why GISS does not currently use SST data in the seasonal ice region above 75N, even when this data is seasonally available (as is increasingly the case due to diminishing trends in ice extent and better coverage due to satellite data).

This means in the Arctic region, GISS data is relatively coarse grained, as individual grid cells above 80N may include station data interpolated out to as much as 1200km, and are likely to show the higher short term variability which is characteristic of data from individual Polar stations.

However, given all of the above, and the significant differences in horizontal resolution, and methodology, and the caveats and cautions from both DMI and GISS, how do annually averaged time series compare? The DMI data is the official data (not extracted from DMI graphics as Lansner and others have done).

Figure 3: Annual DMI and GISS Arctic temperature anomalies and trends

Here the annual average values for each year have been plotted for both the polar “zonal” GISS data (64-90N) and the DMI Arctic data, and the trends calculated for both data sets for the full DMI period. At this resolution the correlation is reasonable, and the 50 year gradients are statistically indistinguishable. These trend figures also match those from a recent comprehensive surface station based study of the Arctic which gives 0.364 degrees C/decade from 60-90N over this same period (Bekryaev 2010).

The Lansner article is thus misleading. On average relatively strong Arctic warming has occurred (rather than cooling) as indicated both by the GISS and DMI data. The GISS zonal Arctic temperature trends are consistent not only with the DMI Arctic trends but also the trends from other recent Arctic surface temperature studies (see the advanced version for more details).

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Comments 101 to 140 out of 140:

  1. Albatross: ...it is evident in their Fig. 1c. that the strongest warming during the summer (JJA) is not at the surface but concentrated between 850 and 950 hPa... Now that's interesting. I've been puzzling over what might forestall or even reverse an increase in temperature at the surface. Bearing in mind the clipping effect which seems pretty obvious from graphs, what could also help drive down statistics would be more frequent, deep or persistent temperature inversions. Superficially at least, it seems that warming above the surface would help drive an inversion process. Albatross continues: Given the stable stratification of the low-levels, it is difficult for the warmer air to mix down, thereby resulting in a slower rate of warming immediately at and above the surface during the summer. This is beginning to sound entirely mundane. Another smoking gun?
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  2. Hi Doug, Perhaps it is b/c it is late and I'm tired, but could you please elaborate on this: "This is beginning to sound entirely mundane." Thanks. So sorry to be dim.
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  3. Not at all, Albatross. If this is about temperature inversions then this is much ado about nothing, or worse if one is a selective skeptic. The bottoms of inversions are little worlds all of their own, and of course such a beast is going to neatly reflect the "clipping effect" alluded to earlier. If anything, hardened, more persistent or more frequent inversions could well be seen as confirmatory of change, unless somebody can explain why upper air is warming for natural reasons.
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  4. As a matter of fact, the "clipping effect" ought to be nicely amplified or highlighted in a regime undergoing a shift to exaggerated inversions. "Cooling," yes, but a case of being careful of what we wish for.
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  5. @FLansner: "Archiesteel, in the article I dont just write "the Arctic is cooling" as you imply." Well, that's the implication, isn't it? That DMI shows cooling while GISS shows warming? Isn't that the entire point of your blog post? The name of your blog directly refers to a contrarian mantra - now are you saying that all this time you really agreed that the Arctic, overall, has been warming at a rate greater than the rest of the world? Are you going to do a blog post about that as well? "And if i somewhere in the comments did so(???), im sure most peoble here knows by now that we are talking about DMI summer melt season 80N-90N trends (!)" Well, since we all agree that this is about melt season only, and does not change the fact that, overall, the Arctic is warming, then what was the point of coming here to argue about it? "But im happy you dont think the ½ degree cooling trend 1991-2010 summermelt 80N-90N is surpricing." [...] "correction: "is not surpricing" I'm confused now. You're happy I don't think the cooling is not surprising? That a double negative. Am I suprised by the cooling? Well, it's certainly interesting, but others here have provided some interesting hypotheses as to why this could be. Others dispute the cooling, so there's clearly no consensus about this. So, interested? Sure. Surprised? Not really. Concerned this could be an argument against AGW? Not in the least.
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  6. Albatross, ok the title has been shortened and it does compromise the content - until one reads the article. Heres how I wrote: http://hidethedecline.eu/pages/posts/colder-arctic-temperatures-in-the-melt-season-vs.-giss-temperatures-188.php Ha! now I better understand this fuzz :-) K.R. Frank
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  7. @FLansner, how do you explain what you wrote in the comments section of that blog post: "The end of the global warming movement seems to take more than good arguments and data - first when temperatures (due to the ongoing Solar low activity) reach temperatures so low than no adjustments can hide it, when the ice grows massively, then this night mare of pseudo science will pass away. What a relief, and as you say, then we have to fight with many decades of colder times when we will remember the good old warm days. Thanks for your words!" You clearly seem to indicate that the "cooling trend" is general in that comment. Perhaps you should consider publishing a retraction on your blog?
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  8. "Bibliovermis at 14:16 PM on 22 October, 2010 I don't find a trend of melt season cooling during an annual warming trend surprising either. The "missing" heat can reasonably be concluded to be going into the enthalpy of fusion of the increased melting rate. " I agree totally! It has been one of the possible explanations, and its nice that we now can take a more scientific look at these thing in stead of just ignoring data. My original purpose was to show descrepancy with GISS data 80N-90N that comes from their land based data projected 1200 km over water and ice. And then of course my aim was simply to show the DMI data for people to know and considder. I personally did not expect a cooling trend incentral Arctic while in the melting season at the same time the bulk of the Arctic lost a great amount of ice. For me it was surpricing, but not impossible. K.R. Frank
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  9. Archiesteel, you write: "You clearly seem to indicate that the "cooling trend" is general in that comment. Perhaps you should consider publishing a retraction on your blog? " ??? I should retract... a comment?? (that was a new one...!) Heres the comment again: "The end of the global warming movement seems to take more than good arguments and data - first when temperatures (due to the ongoing Solar low activity) reach temperatures so low than no adjustments can hide it, when the ice grows massively, then this night mare of pseudo science will pass away." To me this is a general comment, and yes my impression is, that too much of the alarmist foundation is based on pseodu-science and pseudo data. In this context I have shown you GISS pseudo data by projecting temperature from land over sea and ice. Its grotesk. We have seen how UHI has been "measured" from London and suburbs. Grotesk. we have seen how Cryosphere ice has been adjusted massively in the year 2000. What happened in year 2000? And when these drops of weak science just keep coming in thousands, then one day even I got sceptic. I was believing "Alarmist" until around jan 2008. K.R. Frank
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  10. FLansner wrote : "I was believing "Alarmist" until around jan 2008." What's your definition of an "alarmist" ? I ask because perhaps you were the only one who believed in things the way you claimed to before Jan 2008 - a definition would help determine your beliefs. What did you believe and what evidence can you show that gives an idea of what your beliefs were before Jan 2008 ?
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  11. Jmurphy: I think i was overwhelmed by the low Arctic ice extend sep 2007. And i just trusted in the "consensus". But then i found out that in the same period the Antarctic ice extend anomaly (around 2007-8) not only set a max record of around +2 mio sq km, but this record war almost TWICE the anomaly ever measured since 1979. And I noticed that the medias was quiet about this. Then I had to dig down in things. Another thing: I was going "bla bla bla" about my global warming opninion at a party Eastern Europe, and then it turned out that NO ONE else shared my opnions that global warming was very real. It turned out that people thought western countries where acting like embarresing fools! So I was a little shocked, and had to check things out. K.R. Frank
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  12. FLansner wrote : "I think i was overwhelmed by the low Arctic ice extend sep 2007. And i just trusted in the "consensus". But then i found out that in the same period the Antarctic ice extend anomaly (around 2007-8) not only set a max record of around +2 mio sq km, but this record war almost TWICE the anomaly ever measured since 1979." It sounds like you were someone in search of something to believe in : first it was the low Arctic extent which convinced you to believe one thing, then a low Antarctic (sea-ice ?) extent convinced you to believe something opposite. That doesn't make sense to me, because I think it best to look at long-term trends and to look at all the evidence as a whole - not just one piece in isolation. Perhaps you were unsure of what you actually believed before Jan 2008 (as you stated previously), and will go back to believing something else in a few years time ? As I suggested, look at the long-term trends of all the evidence. I would also suggest a read of this thread (Is Antarctica Losing or Gaining Ice) from Skeptical Science, where you will see the difference between land and sea ice, and how the big picture looks.
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  13. Hi Jmurphy! If you look at my site www.hidethedecline.eu, the A-Z, then you will see that i am of course interested in long term trends. Here in a little blog, i just gave you a few examples, hope you understand this. Antarctica is one just of endless examples of how data and results are changed more and more in line with the global warming hypothesis: http://hidethedecline.eu/media/antarctic%20air%20temperature%20at%20lower/aag.jpg The individual modification of data (temperatures, tree proxy data, ice areas etc.etc.), change in viewpoints etc. coming from the "alarmist" site may very well be 100% correct. Just like the one you link to now. The problem is, that statistically all the many many modifications has far too much a trend, a trend toward supporting global warming hypothesis. This is one of tha main problems that creates skeptics. But speaking of "long term trend and Antarctica, Look: http://hidethedecline.eu/media/antarctic%20air%20temperature%20at%20lower/aaf.jpg and http://hidethedecline.eu/pages/posts/antarctic-ice-melt-95.php K.R. Frank Lansner
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    Moderator Response: If your own hypothesis to account for global warming diverges from science and relies instead on conspiracy theories, you'll need to find another thread to carry on the discussion. Use the search box at upper left. Similarly, if the topic you choose to discuss is now Antarctica, use the search box, find a thread discussing the particular feature of Antarctica you have in mind, then carry on there.
  14. Sorry FLansner, I won't be increasing the traffic to your site. Please provide the original sources for your claims and state what you think they are claiming - or hiding/not claiming, according to you.
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  15. @FLansner: "I should retract... a comment?? (that was a new one...!)" You don't have to retract anything, but it's hard not to make a link between your opinion that overall temperatures are going down (i.e. what's implied in the comment) with the subject of the article (i.e. Arctic cooling during melt season). The second does not in any way validate the first. "To me this is a general comment, and yes my impression is, that too much of the alarmist foundation is based on pseodu-science and pseudo data." You're welcome to your own opinion. You are not welcome to your own facts. The Arctic has been warming at twice the global rate over the past decades. Those are the facts. "In this context I have shown you GISS pseudo data by projecting temperature from land over sea and ice. Its grotesk." The word is spelled "grotesque", and the GISS data is not "pseudo data," it's different data. It shows a warming Arctic overall, *just* like the DMI data. That's probably why the DMI itself agrees the Arctic has been warming considerably. "We have seen how UHI has been "measured" from London and suburbs. Grotesk." Off-topic. Take it to the UHI thread, where people will be happy to show you why you're wrong. "And when these drops of weak science just keep coming in thousands, then one day even I got sceptic. I was believing "Alarmist" until around jan 2008." There's nothing alarmist about learning real science. I suggest you become skeptical about your own skepticism and actually read the articles on this site. They represent the *real* science about Climate Change, unlike the tripe you'll find on WUWT and (sorry) your own blog. "I think i was overwhelmed by the low Arctic ice extend sep 2007. And i just trusted in the "consensus". But then i found out that in the same period the Antarctic ice extend anomaly (around 2007-8) not only set a max record of around +2 mio sq km, but this record war almost TWICE the anomaly ever measured since 1979." What are you talking about? Sea ice extent is still on a decreasing trend, and sea ice volume is "diving", to use a term you favor. See Has Arctic sea ice returned to normal? for more info.
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  16. Oh, and I would still like the data you used to generate your graph. Why have you not provided it yet?
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  17. Hi, I should like to do a reconcilation of the DMI data and the data Frank Lanser has produced from reading the graphs from DMI. The next step is to understand the DMI process behind the the data. I amlooking forward links to the data. Regards Klaus Flemløse
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  18. Hi Doug, Thanks for your clarification. I have been thinking about the inversion; I presented just one hypothesis. But there could be other factors--either acting individually, acting in combination to produce the inversion. Someone should look at sounding data from Alert (82.5 N)-- I checked this morning and the University of Wyoming site has upper-air sounding data going back to circa 1977 for Alert. Pity that we do not have long-term in-situ observations from near the pole like they do from Amundson-Scott base....but of course a Arctic counterpart is just not possible. Anyhow, I'm tiring of Frank's conspiracy theories-- sounds like he may have caved to peer-pressure and it is clear from his posts here that he does not grasp the (sometimes counter intuitive) science. For example, the difference between sea ice and land ice, the fact that it is going to be decades before the Antarctic sea ice starts to respond to AGW and that Manabe et al. did an excellent of predicting the current evolution of the Arctic and Antarctic sea ice way back in 1992. When the sea ice eventually starts melting out en mass north of 80N during the summer (next 5-10 years, although there were signs of that starting to happen this past summer as shown on Neven's site), this latest little attempted distraction that WUWT dreamed up will be completely irrelevant, just like the vast majority of their other distractions.
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  19. The domain name "hidethedecline" does smack somehow of presupposition, true enough, Albatross. Regarding inversions, it's sort of comical that I was scratching my head over what actually might produce a cooling signal during certain times of the year in certain regions of the Arctic, while sitting in the fog we always experience during this time of year here where I live. Different kinds of fog...
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  20. Hi everyone, NOAA just posted its "Arctic report card for 2009/2010". You can view it (or download it) here Pretty sobering stuff...
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  21. Frank, The very name of your site is a conspiracy notion. You started the name calling with terms such as "warmies", alarmist & believers. Indignation does not trump moderation. This page is on the topic of DMI data, not on the notion of widespread malfeasance in the scientific community.
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  22. Ok, Bikliovermis, it was just not my intension to do name calling. Skeptics are called skeptics, but what can we call the other fraction? I have seen "Alarmists" , "warmies" etc etc, but whats is the correct term?? "Conspiracy": I think that some people in good intension has exaggerated. But im not allowed to say more here. Antarctic: I was asked about how/why i turned skeptic, and Antarctic was a key explanation here. And im just not used to blogs so strict on the topic. And then is would like to defend my site hidethedecline that is under attack in coments, but its outside this blog. So back to the subject: As I see it DMI data, mostly ERA-40 data shows that GISS data over the Arctic are not accurate. My original article also showed that GISS temperatures projected over ocean matches Hadley SST poorly. Any objections when all comes to all? K.R. Frank
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  23. @FLansner: "As I see it DMI data, mostly ERA-40 data shows that GISS data over the Arctic are not accurate." ...and yet both GISS and DMI show the same warming trend, as demonstrated above. How do you respond to this? Your site is under attack because the science presented on it is of shoddy quality. You were right before caving in to peer pressure from your friends, who were wrong on the science. Here, however, is a lot of scientific literature about the subject. I suggest you stop posting and start reading instead.
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  24. Also, you have been asked repeatedly: could you provide the data you used to generate your graphs? Thanks.
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  25. archiesteel at 07:33 AM on 23 October, 2010 "Also, you have been asked repeatedly: could you provide the data you used to generate your graphs?" Archiesteel, i have really been extreeeemly busy, so my comments here have been written in time i dont have. And i think you can see, that i have had plenty of comments that i should considder in this and other blogs. Im not sure what you look for, as my results as described on my site is not 100% accurate. Here are yearly values: http://hidethedecline.eu/media/BLANDET/DMIIS.xls But as i understood Peter Hogarth, he has actually got his hands on DMI numbers up to 2009 and alittle beyond. And Peter i would like very much to see those data :-) THen, Archiesteel you write: "...and yet both GISS and DMI show the same warming trend, as demonstrated above. How do you respond to this?" ?? Are you back to yearly numbers again or??? Please, I have shown trends 80N-90N in summer months DMI (ERA-40) data: http://hidethedecline.eu/media/GlobalIceExtend/fig1.jpg VS GISS 80N-90N summer data: http://hidethedecline.eu/media/GlobalIceExtend/fig2.jpg So 80N-90N, summer data does NOT show a match between GISS and DMI. You must be thinking of yearly data whoch was not what my article was about. Please lets move forward now. you write "Your site is under attack because the science presented on it is of shoddy quality" Well, feel free to argument on any topic mentioned whereever and whenever you want. until then, its very easy for you just to come with claims like that out of thin air. Im in for a debate on ANY topic in the climate debate. K.R. Frank
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  26. I missed the part where Frank answers Archiesteel's question in 124. Frank, can you provide the data you used to generate your graphs?
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  27. @FLansner: what is your obsession with melt season data? Why exclude data from the rest of the year? It seems to me (and others, apparently) that the goal of this exercise was that there is an overall cooling trend - at least that's what the comment you posted in that article tends to indicate. As for the data, I was asking about the data you used to make your graphs. Perhaps I haven't been entirely clear, so let's try to establish a few things. Since you're a busy man, I'll try to keep it to yes/no questions: Do you agree that, overall, the Arctic has been warming up over the past decades? Do you agree that, despite alleged discrepancies in summer temperatures, yearly figures from both the GISS and DMI provide the same temperature increase, and as such are both useful when trying to determine overal warming trends? Did you produce the graphs on your site, and if so do you still have the link to the official data you used (not a link to a file hosted on your own server - I mean the original data from the DMI)? I still think the science on your site is shoddy compared to what's found here, but of course that is an opinion. Feel free to disagree with it - after all, we are all entitled to our opinions, aren't we?
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  28. FLansner at 08:16 AM on 23 October, 2010 Klaus Flemløse at 02:50 AM on 23 October, 2010 Albatross at 09:51 AM on 22 October, 2010 (and thanks also the many others who have commented). I have concentrated my efforts on the two points of 1) possible pixel counting errors in the Lansner data, and 2) possible bias steps in actual DMI data. This highlights significant problems with the Lansner chart. My summary based on the best available evidence is that Summer Arctic temperatures are increasing slightly, the Lansner chart contains errors and any conclusions based on this chart are likely to be incorrect. 1) I used an evaluation version of a commercial chart conversion software package to carefully create a “pixel counted” version of the DMI daily data for the past few years. I then compared this with the real DMI data. Some of the Summer daily values were as different as -0.98 or +0.84 degrees C. Difference values in Winter are much larger, but the re-generated overall charts looked very similar visually. Because the “above zero degrees C” only covers a few days, and it is above a threshold, any errors have high impact here, especially as the data is extracted from a different DMI chart for each year, each with potential scale and offset errors. I have concluded that "pixel counting" is not an appropriate method for analysing trends or data in this case. The Lansner chart has large differences from the correct DMI values and it appears the conversion of numerical data to images and then pixel counting from these images is easily capable of creating bad data. 2) I obtained daily ERA-Interim 2m air temperature data from 1989 to 2009 gridded for 80.25N to 90N. The ERA-Interim uses identical raw data inputs to the operational models used in DMI, but is a re-analysis, where a great deal of attention has been paid to systematically resolving small bias differences (particularly between different satellite sensors), so that the re-analysis can be used for climatology purposes and trend analysis (Dee 2009, ECMWF Newsletter). The absolute temperature plots of both ERA-Interim and DMI for 2008 (or any other year in the overlap period) indicate that the underlying raw data is almost identical. I used the daily ERA-Interim >80N data to look at the Summer melt above zero degrees C in exactly the same way as we have treated the DMI data. Results are plotted for daily minimum air temperatures greater than zero degrees C and also daily maximum air temperatures to look at possible differences. The ERA-Interim trends over the period 1989 to late 2009 for both Tmax and Tmin are identical and positive. This means it is likely that bias steps are affecting the real DMI melt season data. The two operational model transitions in DMI at 2002 and 2006 are identified with crosses below, but there are other points where new satellite data streams are assimilated where bias errors have been identified and addressed comprehensively in ERA-Interim. A rolling 365 day average plot was then generated based on the daily data from DMI and ERA-Interim, which highlights the small bias steps in the DMI series which are likely to be related to the changes briefly described in the “advanced” article. The ERA-Interim >80N 2m air temperature trend from 1989 to 2009 is 1.27 degrees C/decade. Based on the most comprehensive data set we currently have, it appears GISS is underestimating the recent high Arctic temperature trends, and the Arctic is not currently “cooling” through the melt season.
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  29. Hi Peter! At first glimpse your work appears brilliant, i will dig into it as soon as i get a little time. I just want to comment fast: The general picture, that the dive in DMI data might be caused by my pixel counting is flat wrong. Just check out years in the DMI link: http://ocean.dmi.dk/arctic/meant80n.uk.php 1991, 1993-4 shows temperatures above average in the melting period while 2010 shows temperatures clearly below average. So the essence here has nothing to do with my pixel counting that could lead to a little marginal error in both directions. So therefore as i said earlier, either DMI´s data in melt season are pretty useless or else we have had a cooling in the meltperiod 80N-90N from 1991 and foreward. And both options to me are surpricing and "hard to swallow". If you are correct above, then i believe that DMI´s presentations contains rather fundamental errors. It simply doens make sence to present melting temperatures warmer than average in 1991 and colder than average in 2010 if this has nothing to do with reality. I think i will forward your work to DMI, perhaps? K.R. Frank Lansner
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  30. @FLansner: when accused of pixel counting, you pointed to graphs and suggest we eyeball them as confirmation of your thesis. Basically, you just proved the accusation. Instead of eyeballing, which can be misleading, why not do as Peter did and use actual data to produce charts using the appropriate software?
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  31. Peter, you ought to think about updating your main post w/that "reanalysis." A shame to have it buried in the 3rd page of comments... Nice work. BTW, if you're looking for a decent chart/plotting package without any encumbrances, take a look at gnuplot if you've not already done so.
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  32. Peter Hogarth, Thank you for your remarks. Frank Lanser has been so kind as to produce an excel sheet with the data behind his temperature graph. You can find it below: http://hidethedecline.eu/media/BLANDET/DMIIS.xls I understand from your latest remarks that you have access to the corresponding data from DMI. I would be pleased if you could provide Skeptical Science readers with the DMI data in excel format. I am looking forward to doing a reconciliation of the two datasets. Regards Klaus Flemløse
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  33. Klaus Flemløse at 05:18 AM on 25 October 2010 Thanks. I will post the Excel values in a few days if I have somewhere to post them here! I will be out of e-mail range over next week. Anyway, whilst seeing if there was a nice publicly available version of DMI I have found a website called Climate Sanity which has also created yet another “pixel counting” numerical version of DMI (through some of 2009), along with a relevant article (I will not pass judgement on the overall site!). I have also checked this data and was interested to see how good a match it is to DMI. The overall averages and trends seem very well matched. My own attempt at "pixel counting" gave errors quite similar to Franks (but in different places). I have calculated the above zero degrees average for all three data sets using Franks table. The overall trend of the difference between the Lansner and DMI values is -0.02 degrees C/decade. Whilst this is not really significant, we can see below that most of the significant errors seem to be in recent years.
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  34. Peter Hogarth at 06:30 AM on 25 October, 2010 Thank you Peter Hogarth This is what I whant to see. Looking forward to read the excel sheet with DMI data. Regards Klaus Flemløse
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  35. Hi Peter and klaus :-) I did not expect acurracy, but im not sure why the latest years should have mor descrepancy than the other years. Here my 2010 point: http://hidethedecline.eu/media/BLANDET/dmi2010.jpg -a value less than +0,4 deg C appears correct still, so im not sure what to make of this. But :-) There is a decline in temperatures of perhaps 0,5 K 1991 - 2010 -and this is something quite else than the GISS trend GISS 80N-90N summer data: http://hidethedecline.eu/media/GlobalIceExtend/fig2.jpg GISS shows no sign of cooling trend, only warming for summer 1991-2009 80N-90N. And of course yearly anomalies are very interesting´indeed, but yearly anomalies does not make errors in summer anomalies go away. K.R. Frank
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  36. Peter @129 and 133, Thanks for this Peter-- I realise that it is easy for me and others to talk hypotheticals, but another story entirely to actually track down the data, undertake the analysis and then write it up. Great work. Peter "My summary based on the best available evidence is that Summer Arctic temperatures are increasing slightly, the Lansner chart contains errors and any conclusions based on this chart are likely to be incorrect. Based on your findings and those of Screen and Simmonds (2010) I concur with that assessment. "I have concluded that "pixel counting" is not an appropriate method for analysing trends or data in this case. The Lansner chart has large differences from the correct DMI values and it appears the conversion of numerical data to images and then pixel counting from these images is easily capable of creating bad data." FWIW, I would concur with that assessment as well. It seems that the alleged "cooling" is an artifact of a combination of issues with the DMI data and Lansner's methodology and/or analysis. I would also like to second what Doug wrote @133. It may be worth bringing this to the attention of DMI as well...the poor match that you show between ERA-interim and DMI (for the melt season) is rather troubling. Just one example in addition to the "step" issues, something odd seems to have happened with the DMI data between 1991 and 1995.
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  37. I now have the updated 2010 ECMWF T1279 model (used by DMI since January 2010) daily 2m temperature values for >80N, (courtesy of DMI). From this data the average Summer “above zero” temperature is 0.48 degrees C for 2010. Although this is indeed a relatively low value, it is from the first Summer data from the new T1279 model time series, and as DMI have pointed out this model change alone could easily account for small bias steps (similar to those seen elsewhere in the series). It is obviously too early to say yet for trends from the T1279 model. If the Lansner “pixel count” errors (-0.23 degrees C for 2009, -0.14 degrees C for 2010) are also factored in we can explain the apparent Summer "cooling" as an artifact due to a combination of these two errors. Bias errors are discussed (with respect to corrections applied to different overlapping satellite sensor data) in some of the references in the advanced article. The ERA-Interim does attempt to resolve these bias differences. The daily ERA-Interim re-analysis values are not readily available for Summer 2010 yet. Given the relatively low variability of Summer temperature values from 1989 to date and the very small positive summer “above zero” trend of 0.1 degrees C/decade in the ERA-Interim daily "above zero" data there is no reason to expect large deviations for summer 2010 values. The Summer monthly ERA-Interim values for >80N (JJA) give what is statistically speaking a flat line trend between 1989 and 2009. Given that melt season temperature rises as well as falls are constrained by the ice melt temperature (whilst the ice exists) this is to be expected.
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  38. I have updated all appropriate charts in all posts with the new DMI data. The overall DMI average trend increases slightly from 0.376 to 0.383 degrees C/decade. I also calculated trends for the difference between the Lansner and DMI Summer "above zero" data, which was 0.024 degrees C/decade. Whilst this error may seem small, it effectively doubles the real trend which is most likely due to small bias errors in transitions between models.
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  39. Great work as always Peter. Thanks!
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  40. My thanks to Klaus for further statistical analysis and valuable input, and also to Pavel for pointing out (elsewhere) that the former USSR "NP" Arctic data was of course from drifting manned stations rather than buoys! I have now corrected this mistake (which appeared in the original advanced version).
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