This is Rob Dekker's Typepad Profile.
Join Typepad and start following Rob Dekker's activity
Join Now!
Already a member? Sign In
Rob Dekker
Recent Activity
viddaloo, I have had my reservations of using Cryosat for sea ice. After all, it is quite hard to determine freeboard at 1 cm accuracy (for 10 cm ice thickness accuracy) from hundreds of km up in space. Honestly, I have more trust in the models (like PIOMAS) that use temperature data to determine ice growth and thickness. But since Cryosat data does come out consistent with PIOMAS this puts a bit more trust in BOTH Cryosat AND PIOMAS model.
Toggle Commented Nov 26, 2016 on Sabbatical (I hope) at Arctic Sea Ice
Etienne, your graph goes through 2013, but the latest data (through 2015) shows that coal consumption is on the decline : Not sure if that decline will be sustained, but it suggests that countries around the world are finding better ways to generate electricity. The tar sands in Alberta are capped by pipeline transport, so as long as the Keystone XL is not built (and oil prices stay low) tar sand production cannot increase.
Toggle Commented Nov 23, 2016 on Sabbatical (I hope) at Arctic Sea Ice
NeilT, P-Maker, I'm with you guys. Yes, Obama did a lot of good to reducing carbon emissions, and Yes, Trump may revert some of that. But either way, Trump is not concerned about climate change, so there is a good chance he will not spend much effort on fighting science. There will be plenty other stuff to keep him busy.
Toggle Commented Nov 11, 2016 on PIOMAS November 2016 at Arctic Sea Ice
Temperatures above 80 deg N are really extraordinary : Looks like some 15 C above normal. I wonder when it starts freezing up there...
Neven, in the Arctic Sea Ice Graphs, many graphs are sourced from Crosphere Today, which still (after almost 9 months now) uses a disfunctional data source. May it be time to eliminate these graphs for the time being ?
Extent is exceptionally low for the date, according to Jaxa: On the other hand, winter DID kick in at places in the Arctic. Obuoy 14 registers (in the CAA) -25 C :
Thanks Diablo, It is remarkable how closely the post-1935 September reconstructions match. Especially the difference between your and my reconstruction is surprising, since we used different methods, and had only AARI observations in common. Apologies for being so skeptical at the start of this thread. Regarding the full 1850-present reconstruction, Walsh and his team deserve all the credit. All I did was take out the suspect Kelly fields and filled them in with a regional match-and-merge spatial/temporal fill-in algorithm. In that regard, I feel that my best contribution to this work is my August reconstruction : My August reconstruction simply matches much better with the September numbers from Meiers, you and Walsh own numbers, so if anything came out of this analysis, it is the hope that Walsh et al takes the Kelly fields source out of the next version of their historical Arctic sea ice extent reconstruction and replace it by their spatial/temporal fill-in algorithm. I'm still disappointed that I have not been able to come up with a statistically sound method to determine "uncertainty" in the reconstruction, but if I find a method, I'll surely post it here. All in all, it has been marvelous thread, and I appreciate your clarity of insight and attention to detail from you, Diablo. If you ever think of publishing another paper, please let me know and I'd be happy to contribute. Neven has my contact info.
Jeff, thanks for your comment. However, I have not seen ANY year freezing 200+ km2 per day between Oct 21 and Oct 31. The largest freeze over that period was 2007, which went from 6.55 to 8.12 (a 1.57 increase). What makes you think that 2016 is going to go much faster than that ?
Final note : Because of the "open water" bias of my fill-in algorithm, I consider my September reconstruction a lower bound for ice extent since 1850. Maybe the difference with Walsh' original which is (for pre-1900) more based on a fixed 'climatology', the difference between the graphs is an indication of the uncertainty in observation.
Second plot here is for the entire 1850-present period, for the month of September : Notice that with my fill-in algorithm, there appears a small uptrend from 1850 to about 1900. I'm not sure if that is real, but I suspect it is not. After all, with very sparse observations my algorithm tends to amplify the 'open water' area ('open-water bias' as explained earlier) and with the very sparse observations of the pre-1900 era, that effect may amplify. Another indication that that 'up-trend' in the 19th century is not real is the August-minus-September graph plotted in blue : before 1900 the difference between August and September appears to go up, which is very unlikely to be realistic. In all, for the full 1850-present period, I prefer my August reconstruction (presented earlier). There are more observations in August, and it results is a robust and realistic result, especially when you analyze individual years as I did in this thread.
September historic reconstructions are more difficult than August, because of the sparse observations available. But since this thread started with Diablo's reconstruction for September 1935 - present, I owed a September reconstruction using my Match-and-Merge spatial/temporal fill-in algorithm over that period. Note that I started with the Walsh reconstruction, then removed Walsh's spatial/temporal fill-in source, and I removed the Walsh&Johnson source, but let the other observations (such as the Navo yearbooks, the Dehn collection, AARI, DMI etc) stand. Then I let my match-and-merge algorithm fill it the rest. Here is the result : Click for a larger image. First thing to note is that the September reconstruction more closely follows Walsh reconstruction than for August. That's probably since September does not use Kelly fields, and this suggests that the August Kelly fields in Walsh reconstruction are really no good. Second, I wanted to get some sort of "uncertainty" metric for these reconstructions, and the best I could come up with is to plot the difference between August and September. Remember that both months are based on independent observations, so if there is a wild difference between the months, then there is probably a large uncertainty in the reconstruction. But as you can see, the difference between August and September is rather stable (hovers around 900 k km^2) and this gives confidence that the uncertainty in the August and September reconstruction is rather small (maybe in the order of a few hundred k km^2 SD). Finally, let's compare the reconstructions. Diablo, I do not have the numbers for Meier et al and your reconstruction, so could you please provide a 'final' overview plot of how our reconstructions of Arctic sea ice in September from 1935 to present day differ ? If you need my exact numbers for 1935-1978, please let me know and I can send them to you (if I know your email) or post them here.
It really does not want to freeze up there in the high North, does it ?
Do I see this right ? IJIS reports that 2016 at this time has overtaken 2012 and is thus currently again (since July) the lowest on record for the day :
Thanks Diablo for posting the HadISST2 data. Indeed that series seems already in need of an update. At least they could update with the new Walsh data, but considering that we found some significant issues with that as well (most notably the Kelly fields issue and the Walsh&Johnson high bias) they may want to wait until Walsh updates his reconstruction. Meanwhile, I'm running (as we speak) the September numbers through for the whole series. Then we can finally compare Meier et al, your numbers, Walsh reconstruction and my numbers and compare them. That would be a nice finale to this very long thread :o)
Photobucket is back up, so here is my latest 1850-2013 reconstruction, which omits the Walsh&Johnson source (over the 1953-1978 period) and replaces it by fill-in using my match-and-merge algorithm. This reconstruction was done to avoid any bias that my match-and-merge algorithm may have. As you can see, the match-and-merge algorithm did not substantially change the reconstruction, and if anything, made it more plausible, since some of the extreme spikes during the 70's are now mellowed out and more consistent with Diablo's and Meier et al.
It just does not want to freeze that much in the far North, does it ?
Toggle Commented Oct 14, 2016 on The 2016 melting season in images at Arctic Sea Ice
I ran the 1953 to 1978 period excluding the Walsh&Johnson source, instead letting my match-and-merge algorithm fill in the missing data from the remaining sources (Navo yearbooks etc) and the result is very encouraging : The reconstruction still shows the 'hill' around the 70's that we have become accustomed to, but the sharp peaks and valleys in the 70's are less pronounced. Overall, for averages, not much of a change with the graph I showed above with the bias-adjusted Walsh&Johnson source. That is really good news, since it tells my algorithm is doing realistic fill-ins even when taking out a dominant 'field' source like Walsh&Johnson. Unfortunately, there are some known issues with Photobucket today which means I can't show you the graph. Maybe it is time to start a 'forum' topic on this work, or, Neven, will you still be posting a new ASIB post on the Walsh historic sea ice reconstruction ?
Thanks Diablo, The purpose of running without Walsh&Johnson source over the 1953-1978 period is to avoid any 'bias' in my match-and-merge algorithm when comparing to the period before 1953. The reconstruction is running as we speak, and I will report on it tomorrow. Yes, it is possible that there will be "cross-contamination" from that, but remember that my match-and-merge algorithm uses analogs only if they 'fit' locally. So it should be fairly insensitive to exactly which analogs we feed them as long as there is some analog that matches locally. My concern with reducing the analogs to the post 1979 period is that even the best analogs will underestimate the pan-Arctic ice extent because after 1979 ice extent was lower than in some prior periods. I will show you a pre-1900 reconstruction tomorrow to show what I mean. Maybe I should actually extend the 'analog' set by including July maps into the August assessment, just so we have some analogs that match with the higher extent in the pre-1930 reconstructions.. Yet, varying the analog period is good advice, if only to see how sensitive (or not) it is. I will run some experiments to see how that affects the reconstruction. Which kind of brings us to the final frontier : How can we get some "uncertainty" margin into these reconstructions ? I wish I paid more attention during "statistics" class in college...
In the graph below, I added the regional ice extent over the 1850-2013 period by sector : - Russian sector from the Kara to Bering Strait - American sector from the Bering Strait to Baffin Bay - Atlantic sector from the Greenland sea and the Barents Click the image for a larger version. Noteworthy is that the 'dip' in ice extent from the 30's to the early 70's is apparent in all three sectors. So it seems that this dip (and the subsequent hill in the 70's) is pan-Arctic, although it seems most pronounced in the American sector. It seems that Arctic sea ice follows the temperature over that 30's to 70's period, just like Diablo concluded from his work. Although it is interesting that pre-1930, ice extent remains rather flat, although Arctic temperatures were certainly on the rise there. Also note the irregularities around 1970, especially for the Atlantic sector. One reason for these spikes is that "bad apple" in August 1972 that I reported about a few comments back, but it is not the only spike. Note that the pre-1953 reconstruction heavily relies on my Match-and-Merge algorithm, while the post-1953 reconstruction relies on the original Walsh sources, including the Walsh&Johnson source that we already had to adjust for concentration bias. To be totally fair, the last reconstruction I will make will be one where I ignore the Walsh&Johnson source in the 1953-1979 period, and let my Match-and-Merge algorithm do the work. That would be a fair comparison between pre- and post-1953 reconstruction, and I'm curious how pronounced the 'dip' remains with that. And after that I really will wait for Neven's post about the Walsh reconstruction, since this thread has become way too long already a long time ago :o)
Wayne, regarding your reference, it simply STATES that the water was 1.0 C when it retained the snow that fell on it. You don't know that, and basic physics suggests that that water was -1.8 C, with no heat to spare that could melt the snow. Of course that water was -1.8 C, since it was surrounded by ice. If it were any warmer than -1.8 C, it would have quickly melted some ice and cooled down to -1.8 C. The point is that water surrounded by ice (as in the heavily dispersed ice pack this year) ALWAYS cools down to -1.8 C. If it were warmer, it would melt some ice and then drop to -1.8 C. There is physically no way in which the water between the floes would be any warmer than -1.8 C given the salinity in the Arctic.
wayne said : Remember, snow does not mix with colder water, its more like brined out sea ice melting last because its melting point point is close to 0 C. Here is one suggestion : Put a glass of salt water in your freezer, salty enough not to freeze, and then put some snow on top of it. According to you it should last, but it does not. It will melt. Great suggestion not supported by evidence. : What are we looking at here ? And how did they obtain these numbers ? And why are there no numbers on the ice free parts of the Arctic ?
Wayne said : Michael Sweet: "Snow will not remain frozen if it falls into -1C sea water at 1.035. " Nature seems to contradict your statement: Wayne, I'm not convinced at all. Michael Sweet has a point that ice in contact with salt will melt unless the water is colder than -1.8 C. That is basic physics. The fact that the Arctic north of 80 C froze over rather quickly this year suggests that the water was cold (-1.8C) likely because it opened up only recently and did not have time to warm up. Now the ice edge encounters water that has been 'open' for months, and that water is warmer than -1.8C and thus requires time before it releases its heat, and thus the rate of freezing slows down. Nothing magical about it.
Of course, with the highly dispersed ice cover in 2016, the "area" number gives a better measure of the state of the ice, and that number (2.81 M average over September) is in 2nd place, after 2012.
Toggle Commented Oct 5, 2016 on ASI 2016 update 7: minimum time at Arctic Sea Ice
Regarding that 4.72 number for NSIDC-monthly, or 5th place (after 2012, 2007, 2011 and 2015), I did not see that one coming. Especially since the minimum was 2nd place (only after 2012) and average of ice extent based on daily numbers for both Jaxa and NSIDC turns out to be 3rd place : Jaxa average extent over September based on daily numbers : 2016: 4.39 2015: 4.51 2011: 4.46 2007: 4.18 which puts 2016 in 3rd place (after 2012 and 2007). NSIDC average extent over September based on daily numbers : 2016: 4.50507 2007: 4.26727 2011: 4.56133 2015: 4.61577 which also puts 2016 in 3rd place after 2007 and 2016. The big difference for the NSIDC monthly number of 4.72 seems to originate from the somewhat unorthodox method of ranking each pixel by their average ice content over the month, and counting them as ice 'extent' if that pixel shows 15% average ice over the month. So when a pixel has 100% ice concentration during only 15% of the time (5 days) of the month, it gets counted in full for that extent number. While it would only add 15% for the daily average over the month. With the rapid refreeze, there were a lot of pixels that fit that metric and that is why the overall number pumped up to 4.72.
Toggle Commented Oct 5, 2016 on ASI 2016 update 7: minimum time at Arctic Sea Ice