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Rob Dekker
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I'm sorry, that should read as a dip from the 30's to the 60's as the most profound finding in September extent, preceded by a higher extent earlier. Other months are also interesting. August is remarkably variable pre-1950, while October, November and December are remarkably flat. Time to look into the details of the methods they used.
And the report is here : I have not looked at the data and methods yet either, but figure 1 shows ice extent from 1850-present. Seems to collaborate your findings of an uptrend in September from the early 50's to the end of the 60's, but put in a wider context of a 'flat' and higher extent before that.
And we have not even included the other side of the Arctic : The Nordic seas, Baffin Bay, the Canadian Arctic, and the Beaufort. Now I understand why Walsh is taking his time coming up with a pan-Arctic estimate before 1953.
Thanks Diablo, I've looked through the extent files from Mahoney et al, and yes, it seems clear that the greatest challenge is how to find the best methodology to estimate the missing data in these temporal/spacial sparse data sets of the 30's and 40's and equally important : to estimate an error margin. In that respect, I have to admit that at this point, I do not understand exactly how you, nor Mahoney have done this for the pre-1953 period.
Sorry. That is 38 MJ/m^3.
VaughnA, interesting reasoning. For your question 1, an upper bound would be the heat value of methane, which is something like 1000 btu/ft^3 (some 18 MJ/m^3). For question 2, you would need to know the "density" of methane release in certain areas of the Arctic, as well as the heat insulation value of the water and ice above. I have not looked into that, but maybe this helps as a starting point to see if your theory has merit.
Hi Diablo, ACSYS and DMI both have good coverage over the Nordic seas over the 1935 - 1953 period, so it would be a great addition to your work. Mahoney et al 2008 describes a method (using longitudinal slices) that could work very well for ACSYS, since that data set deals with latitudinal ice edges. Incidentally, that paper also analyzed the very same AARI data set, so it is interesting to compare with your findings. Mahoney find a statistically significant DECREASE in summer ice extent in summer during the 1935 - 1953 period, while your graph suggest no trend or maybe a slight uptrend. Do you know why that is ?
Neven said : All I can say that increasing Arctic SIA seems likely in the coming week because of winds pushing the ice edge towards the Atlantic, and a cold anomaly (finally!) in the Sea of Okhotsk. Agreed. Seems like things are getting back to normal in the Arctic after a number of freek storms. Even DMI north-of-80 is returning to more 'average' temperatures :
Hi Diablo, Starting with that last note by Walsh, I think the AARI data you analyzed is providing a wealth of data, specifically about the Siberian side of the Arctic, which was not well covered by the Walsh and Chapman 2001 data that was at the core of the HadISST data set. Since you adjusted that data set using AARI (after compensating for Meier et al 2012's adjustment), I have no issue with your 1953-and-later assessment of the Arctic. Your work helped in fine tuning Meier et al's work in reconstructing Arctic sea ice extent over that period. You ask : Why are you so sure that the extent values during 1935-1939 must be necessarily much higher than ours? No necessarily. But I argue that there is a 800 k km2 discontinuity between 1952 and 1953 in your data set, even WITHOUT any (AARI or other) ice observations. Why are you so sure that the upward trend since 1935 to 60s can't be right? I did not say any of that. I'm just saying that you cannot declare a "statistically significant" uptrend in ice extent between the 30's and the 70's if you introduced it yourself by choosing a "climatology" from 1935-1952 that is 800 k km2 below the 1953 numbers you use. The choice of climatology before 1953 should not matter if there are enough ice observations before 1953. So you could have chosen a climatology that levels out at 7.8 M km2 at 1953, so it nicely blends in with the adjusted gridded HadISST around that period. If you make the AARI adjustments on THAT climatology, you could show how much the Siberian side of the Arctic creates a 'trend' between the 30's and the 70's. OR you could have stuck with the 7 M km2 climatology you choose for 1935-1952 and made AARI adjustments on that stretching on to 1978. That would show how AARI shows a trend as well. But you can't do both, because then the trend is pre-determined by your input (the temperature graph in your case). If the upward trend is an artifact of our methodology, why a fully different methodology (new Walsh) obtains almost the same upward trend? Walsh' findings are preliminary, and please note that there are still some odd irregularities in his graph as well around the 20s. Other researchers such as Vinje 2000, Polyakov et al 2003, Johanessen et al 2004, and Divine & Dick 2004, all show a steady decline that started in the 19th century, with possibly a 'hold' or a mild dip in the 30's, but it would be hard to call that "significant", followed by accellerated trends in the 90's and 2000's that we all agree on. Thanks for your work Diablo. And I promise that I'll give future publications the same scrutiny that I gave yours. Be it from Walsh or anyone else :o)
Thanks guys. Yeah. 2006 seems to have been pretty bad too. Yet that "double pincher" move around Franz Josef Land appear unprecedented. Either way, are there higher resolution images of Bremen's AMSR recordings ?
D-Luke thank you for that entry. I love RadioLab, and it would be great if they would do a piece on climate change or the great Arctic meltdown that we are witnessing. Maybe apart from the theoretical arguments, it would be good to include a concrete example of what is really happening. Today. Such as this : which shows that there is a place north of Svalbard, where we can sail to 83 deg North, without encountering ice. In the dead of winter. Did that ever happen before ?
Diablo, You are right. For the 1953-1978 period, HadISST "scalar" adjustments (as per Meier 2012) were done based on the overlapping period 1972-1978 of satellite observations. Yet, HadISST over the full 1953-1978 period were based on non-satellite ice observations, mostly from the Atlantic and Canadian/Alaska side of the Arctic. Notably few observations from the Siberian side. So when you adjust that record on the "gridded" form based only on ice-concentration, you may have erased some real ice observations, and thus you AARI adjustments may have been double-counted. You think that the upward trend from 1935 to 60s and 70s is an artifact created by our methodology. Do you agree ?
Thank you Diablo, for your extensive explanations. I think you did a great job in trying to reconstruct ice extent in the Arctic back to 1935. I have some concerns with your methods, summarized as follows : 1) You use a different 'baseline' for the 1935-1953 period than for your 1953-1976 period, which causes an artificial discrepancy : Imagine you did not do any AARI adjustment at all. In that case, your series will show a flat line from 1935-1953 at 6.994 M km2 and then suddenly jump to the Meier et al 'adjusted' value of 7.8 M km2. That is an 800 k km2 discrepancy which is the cause for your conclusion that there is a "significant" uptrend between 1935 and 1978. While in fact that uptrend has nothing to do with ice observations, and is only caused by your choice of 'baseline' (climatology) over that period. 2) By creating that climatology using temperature data, you are polluting the signal with temperature info, and by adjusting HadISST on concentration, you are even overruling any ice observations with your temperature signal. Result is that your ice extent numbers have more to do with the known temperature graph that you used as an input than with ice extent observations. That all said, it is mighty hard to choose a good climatology in an era that has sparse data, so I do not envy you. It would be best if we could incorporate more ice observations, rather than relying on an assumption of SAT-SIE links. I understand that Walsh is working on that and I also would recommend that you reconsider some observations that you currently left out : - It turns out that the DMI 1935 map has a decent overlap with AARI charts from August and September, and is pretty consistent in the overlap. That puts some confidence that maybe the other DMI observations are also reliable. It would be interesting to incorporate these DMI findings into your work. - There are more other observations over the 1935-1978 period, for example the ice edge data from the Norwegians. That data shows a mild dip around the 1940's but not significant. I would be happy to help out find more data sets that could further restraint the (arbitrary) choice of a baseline gridded product, and even help out finding better methods to homogenize different data sets.
I'm sorry, Diablobanquisa. In my prior post I ask for the correlation between SAT and your SIE numbers, for the 1953-1978 range, but I meant to say the 1935-1953 range. That is the period that you used your own climatology, based on SAT, and my point is the SAT-SIE link breaks over that period with sparse data. If the SAT-SIE correlation over that 1935-1953 period is weak, you cannot draw conclusions about trends between that period and later periods.
Thanks Diablobanquisa for your continued replies. Let me first answer your question: You asked: Why should it be significantly different during 1935-1952? (there are obvious physics linking SIE and SAT). Yes, there are obvious physics linking SIE and SAT. And your regression analysis over the satellite era confirms that (with correlation of r=0.9). But the problem for the 1953-1978 period is that you are working with sparse data sets, both for temperature observations and SIE observations. And that can break the correlation to the point where even the trend is not clear. For example, can you please determine the correlation between your SAT data (HATCRUT4 April-Sep 70+ deg) and your final SEI numbers over the same period 1953-1978 ? I suspect that you get much lower correlation than during any time during the sat era (where you obtained 0.9). I still do not understand how you obtained your 1953-1978 numbers. You write : The data for the years of this period is a combination of AARI with adjusted HadISST. No climatologies involved. How did that work exactly ? On this graph : HadISST gridded hangs around 9.9 M km2 for 1953, and (non-gridded) Meier et al logs in at about 7.9 M km^2 for 1953, while your estimate is about 7.2 M km2. Did you obtain that number (7.2) only by doing AARI adjustment on the HadISST gridded product ? Or did you do something more ?
One more question, this one about the temp - SIE correlation : You choose April - Sept HADCRUT4, 70 - 90 deg as your temperature reference. Could you tell us a bit more about that choice ? Did April - Sept give the best correlation with Sept SIE ? I'm curious, because SIPN is looking for better ways to predict Sept SIE based on data earlier in the year.
Ah. Now I understand. In my words : You created your own gridded climatology for the 1935-1952 period, by using 1985-2002 sat images since that period matches the temperature range of 1935-1952. On that brand new gridded climatology map you then applied the gridded AARI observations for the Kara and the Siberian Sea, and that is how you obtained your 1935-1952 extent numbers. Doublecheck : So if you would not have applied AARI we would have seen a flat line at 6.994.000 km2 in your series, from 1935-1952. Did I get that right ? If so, I think that is very creative but it raises a couple of comments and a few questions. Let me do the questions first : 1) Why did you only apply AARI observations ? Why not other observations that Walsh and Chapman included in their 2001 paper ? 2) Which gridded climatology did you use for the 1953-1978 period ? And how do you argue that these two periods, with two different gridded climatologies, are still "consistent" ? And may I add that the correlation numbers between temp and SIE are indeed remarkable. You may be onto something there.
Apologies for being so skeptical about the 30's extent numbers. But here is another reason why : You post the September 1935-1944 median ice extent numbers in this graph : Note that it looks like the North-West Passage is virtually open. And this is the "median", where your earlier years show even less ice. If that were really the case, why did the first NW Passage (after Amundsen's 1906 partial traversal) not happen until 1942 by Larsen ?And it took him 2 years to get through.
Diablobanquisa, thank you for your patience with me. I understand the confidence intervals graph now. It is for the trend, not the confidence in the data itself. But the actual determination of the early data is still a mystery to me : Neven wrote: 'Rob, if I've understood correctly, they extrapolate the correlation between SAT and sea ice cover (during the satellite era, I assume), constrained by historical data for the Siberian regions as provided by AARI. Is that correct, Diablo?' Yes, Neven, it's absolutely correct. I'm probably just slow, but how exactly does that work ? Could you possibly explain how you obtain an example year (such as 1935) ?
jgnfld, as Neven said : As a statistic it's somewhat interesting, but it doesn't convey all that much information about the individual health of both polar regions, let alone their sub-regions. It's like stating that because on average the human race decreases in weight, that therefor obesity is not a problem, and hunger is non-existent.
Also, I see you calculated confidence intervals for the series back to 1944 : but not before that. Why not ?
Diablobanquisa, since you state "we decided not to use DMI maps" I am still wondering exactly which data you used to reconstruct the 1935 (and the 30's in general) sea ice extent. From your block I read : En tercer lugar, extendemos la serie hasta 1935 combinando los datos de AARI con una climatología seleccionada en base a la correlación entre temperatura y banquisa But what does that mean exactly for 1935 or any year in the 30's ?
Kevin O'Neill said If you mean the jet stream is the tail, yes she's looking at the tail, but not because she's ignoring the rest of the elephant. Otherwise I have no idea what you mean. Thank you Kevin. Very well said.
Maybe we should carry this discussion to the "North Pole temperature anomaly (big)" thread, but this latest influx of heat apparently reaching the NP was predicted both by ClimateReanalyser and by DMI for the past 5 days. Interestingly enough, this latest anomaly does not yet seem to show up in the buoy data. Legendary buoy 300234062785480 located between Svalbard and the NP is still hovering around -15 C : and buoy 300234062788470 just behind the NP is still logging in at -30 C : Also DMI's "north-of-80" temp tool is not yet showing exceptional temps Let us check in a day or two, because it seems that this latest wave of heat from the Atlantic is just a bit late. After all, Climate ReAnalyser and DMI are forecast tools.
I'm still skeptical of the low numbers for the early part of the series in both your and Walsh graphs, because of two reasons : 1) The August DMI charts which show more ice in more places than August satellite years that ended up well above 7 M km^2 in September, and 2) The discontinuity visible in the Walsh extend graph (page 17) : Prior to 1935 the extend is sharply higher. But I am fully aware that I have not gathered enough data to contest your or Walsh' findings. Thus I would like to complement you on the work you have done. It's an excellent piece of work, sustained by clear graphs and arguments in your article and your comments alike. Thank you, Diablobanquisa, for presenting your findings to us with this much detail and reasoning.