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Chris Reynolds
UK
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I've been looking at Beaufort/Chukchi/East Siberian Seas, a region I call the BCE region. For the BCE region, the 2007 to 2012 period has an average September extent 14% of that for the 1980s. For comparison with the whole Northern Hemisphere extent, 14% of the 1980s average would be 0.979M km^2, which fits the commonly accepted definition of below 1M km^2 for which the Arctic be considered virtually ice free in September. Therefore BCE can be considered virtually ice free in September for the period 2007 to 2012.
Neil, I get where you're coming from: "Politics is the art of the possible..." Must be a right wing thing (I'm by leaning a small government, free market democracy, libertarian). Throughout this discussion my most frequent unvoiced thought has been how many people would vote for radical action on AGW? The fact that I am the only person of those I know, who doesn't drive anymore speaks volumes. In managing people I have found that most people respond better to encouragement than to criticism.
Toggle Commented 7 days ago on Bill McKibben nails it at Arctic Sea Ice
Good post Neven, Fingers crossed for clear open skies and lots of melt ponds. Enjoy your holiday.
Dean, The latest snow cover is from Rutgers. http://climate.rutgers.edu/snowcover/chart_vis.php?ui_year=2013&ui_week=18&ui_set=0 But that only takes us up to early May. At that time there was snow there. However there is MODIS. https://earthdata.nasa.gov/labs/worldview/?p=arctic&l=MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2015-05-17&v=-6701056,-3824582.481450516,3784704,1631289.5185494842 And that does indeed show a lot of snow free land in the region of greatest warming as you suspect.
Toggle Commented May 18, 2015 on Don't forget the ASIG at Arctic Sea Ice
Stan, Thanks, the price fell after 2008 but then did rise to higher levels before the recent collapse. http://blogs.lse.ac.uk/europpblog/files/2015/01/oilpricechart20002015.jpg It's been years since I followed the issue closely enough and had misremembered. But I stand by my reading that the people investing in what seems like uneconomic prospects (in this case Shell) aren't idiots. They're playing a long game. I didn't discuss it above but as you raise it, I suspect a bubble in some of the mainland US investment - expectations losing touch with reality (like the DotCom bubble).
Toggle Commented May 16, 2015 on Bill McKibben nails it at Arctic Sea Ice
Jim, You'll find this amusing. http://dosbat.blogspot.co.uk/2015/05/the-bitter-irony-of-paul-holmewood.html I think I stumbled on that site via one of your comments.
Toggle Commented May 16, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
JD Allen, While looking at market data I came across a particular firm that had invested in licenses to exploit shale as in the north of England (IGas). Now this firm has invested a stack of cash into licenses for fracking (IIRC the biggest in the UK - but don't quote me on that). However their actual exploratory drilling programme is very leasurely, unlike Caudrilla. Such firms, and Shell in the Arctic, are playing a long game. They are buying up licenses, knwing full well that whilst the oil glut persists it won't be economically viable. But the oil glut, and accompanying low prices, will not persist. Between 2005 and 2008 oil prices increased exponentially as declining oil supply (e.g. Venezuela and others peaking) met with soaring demand (China and the economic bubble created by cheap credit - e.g. in the OECD). In 2008 the 'credit crunch' hit, possibly triggered in part by high oil prices in the US. In the wake of that, oil prices slumped and have not risen as high as in the 2005 to 2008 period. Now prices are kept low by a combination of lower demand (OECD demand level since 2008), and increased supply. In the past Saudi Arabia would have cut supply to raise prices, this time they have not (US/EU vs Russia game?). Furthermore the increase in prices had supported an explosion of fracking and exploitation of new smaller oil fields. What the investors in UK gas fracking and Shell in the Arctic are doing is reflecting sentiment regards future energy supply. The levelling of conventional oil supply since 2005 has continued. The increase in oil supply since then has mainly been due to non conventional supply and new fields. A substantial number of the world's oil producing nations are post peak, those that are not have little leeway to increase production to make up for those in decline. The fundamentals remained geared to high oil price, and those investing in leases for new oil/gas fields know this. We are in a lull in prices, they will go up again. Those holding licenses for exploration and exploitation will move forward substantially then. Some may be investing in production at a loss now in the hope of catching the upswing in oil prices with fields ready to ramp up production around an existing infrasctructure.
Toggle Commented May 16, 2015 on Bill McKibben nails it at Arctic Sea Ice
Jim, "You're on Chris, assuming that you're happy with "below 1M km^2 on any day before December 31st 2022"." OK, but to be clear, were I to see a sub 1M km^2 in December when it had been higher in September, my first thought would be that force majeur may need to be invoked. That would be beyond 'unusual weather'. Maybe we need to add a 5 standard deviation level as a demarcation between 'unusual weather' and force majeure. That could be tricky though so would need to be discussed.
Toggle Commented May 16, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Jim, Regards a bet. Rather than blather I'll simply say I'd rather not take your money, although I am happy to fleece denialists. However, if you want to 'test my mettle' with regards my confidence in a long tail. I would suggest: Your proposition is that CT Area will drop to below 1M km^2 on any day before 2022. I challenge this proposition, 2 exceptions: 1) Days with data coverage problems that could feasibly affect the outcome are excepted. 2) Force majeur is excepted, by this I do not except unusual weather (whether provably related to AGW or not). Should you choose to imply this provision in the event of exceptional weather related loss of ice, I leave to your discretion. So as a test of my confidence: If your proposition succeeds I owe you £1000.00 to be paid within one month of the day in question. If your proposition fails you owe me £1.00 which you can pay to the charity of your choice. Monetary values are the value of pound sterling as of the date of settlement. This asymetric bet is merely intended to indicate my confidence in my previously asserted position (That we face a long tail, not a fast crash).
Toggle Commented May 16, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Jim, Vid's gone? I've just logged in and can see he's no longer a member. Thanks, I shall resume commenting at the forum. I've been too busy today to give your offer of a bet at my blog consideration. I'll ponder tonight. Try Arctic-GRO http://www.arcticgreatrivers.org/ The data is a bit patchy, and doesn't go back very far, but covers the main rivers seen in the graphic at the top of that page. Also ARDAT. http://mather.sfos.uaf.edu/~jwhitefield/river/ That's a climatology of river discharge. See this abstract: http://utexas.influuent.utsystem.edu/en/publications/a-new-river-discharge-and-river-temperature-climatology-data-set-for-the-panarctic-region(d9c3baa3-7b3c-4a04-a376-a6061a0c9e8d).html Unfortunately due to the sparse data and lack of coverage before 2007 I haven't been able to do anything really useful with it. Sorry, no live data for Siberia, as far as I have found.
Toggle Commented May 15, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Jim, Susan, Thanks I will read FOOW's article next. Jim, As you're doubtless aware Vidaloo 'persuaded' me the forum just wasn't fun any more, I've not been back since. That Mackenzie River flow is similar to what data I've been able to find for the Siberian Arctic. Thanks for that graph. It is worth noting however that even 2013 and 14 had large flows in that plot, although this year looks like an early start. If you have river temperature data then temperature X flow might be more useful, degC m/s. Kris, Thanks for that page. Navegante, Indeed I have said that, but I think it is mainly the whole Beaufort/Chukchi/ESS region. Relevant here is one approach I looked at for using April volume to predict September extent, looking at regional and sub regional relationships. Looking at Beaufort shows a very variable progression of volume loss, and a very poor linear fit to September extent. This is because Beaufort is the outflow of winter transport of thicker ice out of the Central Arctic. The variability of the Beaufort high imprints itself onto the transport of MYI into Beaufort, this in turn impacts September extent by affecting summer open water formation efficiency. So yes Beaufort has turned into a killing zone for MYI, but not every year is a masacre.
Toggle Commented May 14, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Rob, I have found the same problem with every method I have tried, not just this year, but last year too. The summer weather is the killer and I don't see how anyone is going to get past it. Using peripheral seas volume I get a sigma of 0.62. If I take the residuals from that model I can get a R2 of 0.45 for a linear fit to temperature at 500mb. Incorporating the temperature/residuals relationship means my sigma for the hindcast drops to 0.43. But I cannot predict temperature from April. Anyway here is one of the hindcast plots. https://c4.staticflickr.com/8/7695/16988968294_151f3d1953_o.png 'Actual' is actual NSIDC September extent, 'Model' is model based on the relationship between April volume and September Extent, 'Adjusted Model' is the same as Model, but with the temperature adjustment. The improvement in recent years using 500mb temperature is marked.
Jim, I have been looking at that Beaufort situation in a hopefull sort of way. But checking Beaufort extent, the open water there is not without precedent, and although I haven't done the numbers, looking at a plot of extent, early season open water has no relationship to the state at minimum. I was wondering about an early season open water leading to ice abedo feedback - like we saw in Laptev last year. But it seems the dominant issue in Beaufort is MYI - not a factor in Laptev. Susan, Not sure about unusual heat transport at present (I must revisit the El Nino - Arctic issue again). But what Fish Out of Water article at Daily Kos?
Toggle Commented May 13, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Wayne Kernochan, Granted irreversibility is mainly a theoretical argument. As there is scant evidence the human forcing (notably CO2 emissions) will reduce, the pack will transition. However with Bifurcations often comes rapid transitions. This paper suggests that this is not likely. As earlier suggested by Tietsche et al, this also means that a succession of catastrophically good melt weather might make what looks like a crash. But as the linear relationship between AGW and sea ice loss suggests, when such a run of good melt weather summers is followed by a succession of more normal summers (like 2013 and 2014), the ice will recover. So the first virtually ice free state may be followed by what looks like a recovery.
Navegante, That's not what I am reading in what Rob is saying. But I agree that the following from Rob is a fair summary: "This Wagner and Eisenman paper shows that if you take heat latitudial heat transport and seasonal variation into account, that the "biforcation" behavior of the SCM and EBM models disappears." Wagner and Eisenman state that: "This result may help to reconcile the discrepancy between low-order models and comprehensive GCMs in previous studies. Specifically, it suggests that the low-order models overestimate the likelihood of sea ice “tipping point”." My reading of the whole paper leads me to the conclusion that the bifurcation seen in various EBM/SCM (Energy Balance Model/Single Column Model) studies is actually an artefact of these simple models, i.e. it is not real. By combining the two types of model into an intermediate complexity model the bifurcations disappear. And this intermediate complexity model is more like the more complex GCM type models. Where Rob suggests that: "Meanwhile the paper suggests that seasonally ice free conditions in the Arctic may occur at lower temperature increase than previously thought." I'm not sure I agree with this. Wagner & Eisenman state that: "The model becomes seasonally ice-free at 2 C of warming, and it becomes perennially ice-free at 6 C (Figure 4b). These values compare with comprehensive GCM results from Armour et al. (2011), who find the complete loss of winter and summer ice to occur at 4degC and 7degC, respectively." Note that in stating seasonal and perennially ice free, the authors imply three states in the transition. 1) Perennially ice covered. - NOW. 2) Seasonally ice free. 3) Perennially ice free. Armour et al "The reversibility of sea ice loss in a state-of-the-art climate model" use CCSM3 to find their result, and it is higher than Wagner & Eisenman's intermediate complexity model. But it should be noted that Mahlstein and Knutti published a paper in 2012 entitled "September Arctic sea ice predicted to disappear near 2degC global warming above present." Here's a graphic from their paper. http://1.bp.blogspot.com/-yBoKKsILj_8/VUUWeiaGd9I/AAAAAAAABz4/idkzqNywQnc/s1600/M%26K.png This conclusion is based on observed data, with the utilisation of data supported by a suite of GCMs, also the use of observations to adjust GCM data. However their results show the 2degC is from observed temperature, and extent, with the GCMs producing temperatures of around 3 to 4 degC global warming for a seasonally sea ice free Arctic. So I conclude not that the Wagner & Eisenman suggests a lower temperature, it doesn't, it agrees with earlier results, rather the agreement between Wagner & Eisenman and Mahlstein & Knutti might be coincidental. The observed data used by Mahlstein & Knutti is extrapolated substantially to give the 2degC GW for an ice free September, also the Wagner & Eisenman paper is a simple version of what is going on in a GCM - so this lower temperature for summer ice free state might itself be an artefact of simplicity, much as the Wagner & Eisenman paper shows bifurcations to be an artefact of the simplicity of EBMs and SCMs.
PS, Neven, coincidentally three days ago I had to ban one from my blog. Must be the state of the moon or something.
Toggle Commented May 11, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Good call Neven, Keep the signal to noise ratio high. People might find this of use. "An Early Warning for Summer Sea Ice Crashes?" http://dosbat.blogspot.co.uk/2015/05/an-early-warning-for-summer-sea-ice.html "If June 10 to 30th average compactness is around 0.7 for a given year, a large summer melt can be anticipated, but is not guaranteed, over the following summer."
Toggle Commented May 11, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Cincinatus, Wrong. NSIDC Extent is calculated as being the sum of the areas of grid cells for which concentration (from satellite) exceeds 15%. The product I use is from Wipneus, who gives a regional breakdown using the Cryosphere Today regions, as I do for PIOMAS. Both of our independent calculations agree with NSIDC Extent and PIOMAS volume for the whole domains. I also have and use code to process gridded NSIDC Concentration data, so I am not about to take lessons from you, especially in view of how wrong you get everything. Wrong. The ice state map you point to is a production of ice analysts, they may use cocentration from satellites, but they also use other products like MODIS. I struggle to see how that plot is at all relevant to your abortive criticism of me. Note that analysts findings tend to be conservative with regards ice state because they don't want to lead shipping into areas that are worse than what they state in their charts. Wrong. The Drift Age Model, the animated gif of ice age, tells you nothing at all about thickness! That model parcels up ice into grid boxes, tracks the movement of ice as dictated by winds, and assigns an age to a grid box as the oldest age of ice exceeding 15% area of the grid box. It is not a model like PIOMAS, it does not contain ice physics, the ice in the model neither thickens nor thins. Wrong. I used NCEP/NCAR reanalysis to examine Jim's statement about Beaufort, averaging over 1 to 7 May 2015. For that period the average temperature over Beaufort is between 260 and 270 Kelvin, 273 Kelvin is approximately 0 degC, 271.2 Kelvin is -1.8degC, which is the freezing point of sea water assumed in sea ice modelling papers like Thorndike 1975. The average air temperature in NCEP/NCAR is below that of the ice/ocean interface. The ice is thin enough to allow a potential heat flux through (e.g. HYCOM Cice, and my previous calculations on the issue). However that aside, fundamentally; as the air/ice(or snow) interface is colder than the ice/ocean interface net heat flux is from ocean to atmosphere. Wrong. Your pompous, self-regarding explanation is crap. Surface atmospheric temperatures in Beaufort are below freezing, therefore aside from the continual melt/freeze on a local scale at the ice/ocean boundary, there is no melt happening. ...Which leads on to clear evidence that you don't even know what a temperature anomaly is! Jim's map shows an anomaly of 3degC, yes? Going back to NCEP/NCAR, the climatological average temperature (1 to 7 May) for that region is of the order of -10degC, a +3 degC anomaly gives -7degC. As -7 is below -1.8 there is no melt. I'd draw you a picture, but I doubt it would help Alarmists? Wrong again!!! You've used that smear before. I assume you mean it to apply to everyone commenting here, myself as well. Yet I have done a series of blog posts on why it is not likely that we will see a rapid crash to zero of Arctic Sea ice, but we will instead see a long tail of sea ice and a slow transition. e.g. http://dosbat.blogspot.co.uk/2014/12/the-slow-transition-arctic-ocean-energy.html http://dosbat.blogspot.co.uk/2015/01/the-slow-transition-thickness-growth.html http://dosbat.blogspot.co.uk/2015/01/the-slow-transition-mono-modal-spike.html I have also been critical of those claiming we face an imminent methane catastrophe. http://dosbat.blogspot.co.uk/2012/02/arctic-methane-imminent-abrupt-and.html So in implying that everyone here is an alarmist, you are wrong. Demonstrably so. If you disagree with my analysis of PIOMAS gice, fine. The raw data is available here: http://psc.apl.washington.edu/zhang/IDAO/data_piomas.html When you have done your own analysis let me know what you find. Without such a retort you have started up a smokescreen of fallacies because you don't like my conclusions, this is infantile. In my recent post about ice state in April I concluded that finding this MYI export amounted to little in PIOMAS was a surprise to me and forced me to change my opinion about its importance. http://dosbat.blogspot.co.uk/2015/05/april-2015-status-part-2.html Your response to the same evidence was to throw a hissy fit.
Toggle Commented May 11, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Jim, Regards the Beaufort warming. It is a shallow structure, anomaly (NCEP/NCAR) is limited to below 800mb, having the hallmark of heat release from the thinner ice in Beaufort as a result of the recent transport westward from Banks Island. It may be below zero but it isn't cold enough to have grown very thick ice and the ocean is venting heat. This may also explain the whorl of warmth into the central pack, as there is an adjacent low.
Toggle Commented May 10, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Neven, Not really a stupid question, and I am going off personal judgement, for all that my judgement is informed by data. For ice to register as extent not a lot of ice is needed. For NSIDC (and the 'industry standard') it is 15% concentration. 1/6 is equivalent to 16.7%, so a sea region with only 1/6 of sea ice cover counts towards extent. That is very sparse. The question then becomes whether there is enough MYI to keep concentration up to 1/6 over Beaufort/Chukchi and the East Siberian Sea (BCE area) by the coming September. There may be. But the last time we saw that very strongly was in 2010, and then the MYI export/presence was far stronger than this year. And in 2010 we saw very sparse ice over a large area that just didn't melt out. Ice many metres thick in April won't melt out unless it is dispersed in open water. Where it is surrounded by a mass of thinner ice it will be 'protected' by the sea surface temperature being pegged down to 'zero' by the surrounding melting first year ice. This acts to keep heat flux from ocean to ice down because it reduces the temperature gradient from ocean to ice. Of course, both MYI and FYI melt when they coexist, but MYI has a greater ratio of volume to surface area, and it is only through surface area that a heat flux can pass (this is why species spanning the mid lattitudes to the Arctic tend to be large the further north their range is - natural selection breeds for volume / surface area being large so they can keep warm in winter). Once the surrounding first year ice melts in a dispersed field of MYI the ocean can start to warm under the sun (or backradiation from clouds) and then the mass of MYI can be more effectively attacked as the warmer ocean generates a stronger heat flux from ocean to ice. While working out my prediction for this year I got distracted and did the groundwork for a blog post ready on the collapse of the Beaufort Gyre Flywheel. Here is one of the graphics. https://c1.staticflickr.com/9/8867/16875312773_7c5f679125_o.png Blue and red are plotted on the left side axis (April PIOMAS volume km^3). They show volume for ice above and below 3.3m thick (PIOMAS gice). The green trace is plotted on the right side and shows September average extent (M km^2) for Beaufort/Chukchi/East Siberian Sea (BCE). Bare with me, this is relevant to what I am saying. The BCE region is the region into which the Beaufort gyre draws ice from the Central Arctic, in the 'old Arctic' it would cycle ice through those seas until the following winter when the ice would be drawn into the transpolar drift and returned to the central Arctic. This plot shows the transition from the old Arctic to the new Arctic. As the volume of thicker ice declines due to thinning in the Central Arctic it reduces resistance to melt in the summer. So as the thickest ice volume declines it increases 'open water formation efficiency', which is why September extent tracks the decline in ice over 3.3m thick. Meanwhile, first year ice (covered by the gice thickness bands under 3.3m thick) declines at a far more modest rate because it re-grows each season (Bitz & Roe). So (IMO) what we see in the BCE region is a loss of protection from thicker MYI in the summer leading to a increase loss of extent, more open water, more ice albedo feedback and the further loss of MYI. The BCE region becomes a killing ground for ice exported out of the Central Arctic due to the Beaufort gyre, rather than an ageing and stabilising flywheel for the pack. This is of course a positive feedback. This process has been accompanied by a decline in September average compactness. In the East Siberian Sea September compactness for the 1980s was an average of 0.720, compactess for 2005 to 2014 was 0.419. (For the lurkers - Compactness is Area / Extent)
Toggle Commented May 10, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Neven, In my second April Status post I have concluded that the export into Beaufort/Chukchi and towards the East Siberian Sea, is not likely to be as strong a factor as we saw in 2010. Considering the following graphic, which uses PIOMAS sub grid thickness distribution(gice) for 30 April: http://2.bp.blogspot.com/-nwVG3Oh1QIA/VUpPYcFE7dI/AAAAAAAAB3E/NUoBpiGlSuM/s1600/Arctic%2BBasin.png The two regions, peripheral and Central are shown in this graphic. http://2.bp.blogspot.com/-jzYP7cMbtFI/VUpoVvpGkYI/AAAAAAAAB5Y/FBDbOkGOQwE/s1600/Arctic%2BBasin%2Bmap.png In 2010 the presence of ice volume over 3.3m thick was 2.81k km^3, by far the largest post 2007 volume for ice >3.3m thick. As we saw in that year it retarded the summer extent loss causing a persistent tongue of ice in September in the East Siberian Sea. In the second half of that graphic it can be seen that in 2010 ice volume in the Central Arctic was very low for both greater and less than 3.3m thick bands. This was due to the massive export over winter. This year in the Central Arctic volume of ice thicker than 3.3m thick is the highest for the post 2007 period. While thick ice volume is normal-to-low for the peripheral seas. I had been watching this export over the past few months and had suspected that it would keep September extent up in Beaufort/Chukchi/East Siberian Sea. Having seen the PIOMAS numbers I now doubt that it will play a strong role. The export seems to be rather dispersed. I'm changing my prediction method because the high volume in the Central Arctic had biassed my earlier prediction high. In mid March I predicted 5.20 million kmsq +/-0.63 million kmsq, that has now changed downwards. I don't want to make a firm prediction yet, that will follow later this week. But based on the range of numbers I'm getting, my expectation is for a minimum in September of mid range to low levels for the post 2007 period, uncertainty due to the unprecedented state in PIOMAS has widened my range. However as you say, weather is a major factor.
Toggle Commented May 10, 2015 on 2014/2015 Winter analysis at Arctic Sea Ice
Navegante, I think we are talking about different defintions of tipping points. Amidst the ongoing forcing of climate change, yes a reversal is more unlikely (difficult even?) than an advancement. What I mean by a tipping point is explained here, in paragraphs 3 to 6. http://dosbat.blogspot.co.uk/2015/05/is-arctic-sea-ice-like-cup-or-ball.html I don't think the Arctic has 'tipped over' like a cup. I think it is a ball rolling down a slope.
Nevagante, Mmm, I'm not convinced it does contain hysteresis. The 2010 loss event involved a large loss of volume, resulted in a change to the seasonal cycle (in PIOMAS) and I don't think the 2011 and 2012 minimae were coincidences, I think they were largely caused by the 2010 volume loss event. Yet conditions now seem to have largely wiped out the 2010 event. No evidence of strong hysteresis for a volume loss event of similar magnitude and impact as 2007, instead it was quietly reversed five years later. What acts against reversal of such events is the trend of regional warming, and the after effects persist, the more global warming plays a role in sustaining the impacts.
Robert, For the 4m and above thickness band, April 2015 volume is 2992.6km^3, you'd need to go back to 2002 to substantially beat that. And you'd need to go back to 1997 as one of the last years of a period when volume for ice that thick regularly exceeded 3000km^3. What is happening over the last few years is significant and important, I disagree that it is 'within the noise'. Graphing those thickness bands in pairs is rather revealing. 4m and above together with 3 to 3.9m: Both decline - the volume loss has mainly come from thick ice. 3 to 3.9m and 2m to 2.9m - they behave very differently, 3 to 3.9 declines throughout, while 2m to 2.9 rises then falls. Now for the interesting pair.... 2 to 2.9m and 1 to 1.9m. In recent years these start to 'dance' together, it looks like they're almost mirror images of each other. This is because these thickness bands straddle the thickness of around 2m thick, which is typical thickness one would expect for growth of new ice from open water in September to ice in April. So variations in how much ice thickens moves bulk volume from one thickness band to another. As it goes up in one, so it goes down in another. The base data from which I calculate those bands is in 10cm increments. In that finer data the transition of the two behaviours happens about 2.2m. I've uploaded a couple of graphs they should be apparent from the above. 2m and 3m https://farm9.staticflickr.com/8729/17381420841_cab87e74c2_o.png 1m and 2m https://farm8.staticflickr.com/7714/17195536529_bb794c8d7c_o.png So above 3m there is constant decline (until the recent uptick), while 1m to 2m start to mirror each other. Why? Here is where I get to a feedback that I think will dominate the remainder of this decade, and probably most of next. That recent mirroring in 1m and 2m thick bands suggests a wall is being hit, I think it is. The following is a plot of gice - the PIOMAS sub grid thickness distribution. It's a plot I've done for a blog post I'm working on. While the above stuff is all for the grid box effective thickness. Gice is the 'hidden' distribution of thickness that PIOMAS uses within the grid box, so a grid box reporting ice 2m thick doesn't just have ice 2m thick, it contains a wide range of thicknesses. The thickness bands can be seen on the horizontal axis of the following graph. https://farm8.staticflickr.com/7748/16761477493_cf95c5d74a_o.png The critical detail is this: The thicker ice declines as can be seen by the movement from dark blue (early years) to light blue (recent years), but look at the behaviour of thinnest ice. There is very little change in the ice below 1.46m thick. This is December ice, in December, even within a grid box that has ice at the end of the September, there is open water that freezes and forms new ice. The lack of change at the thinner side of the gice profile is the because of the thermodynamic thickening of sea ice. It is this that forms the 'surface' that forces the recent mirroring in the 1m/2m thickness bands. As I have been arguing in some detail since last summer (I was 'outed' in responding to a comment by Neven), the thickness growth feedback is in the process of becoming dominant and will avert a crash in Arctic sea ice leading instead to a 'long tail' of summer sea ice persistence well into next decade at least. I have discussed the thickness growt feedback in detail here: http://dosbat.blogspot.co.uk/2015/01/the-slow-transition-thickness-growth.html
Oops, this makes more sense for the quoted part of the above comment: "if I use the demarcation of above 3.3m thick, there is an April 2015 volume of 1.48k km^3 (for ice over 3.3m thick) for the peripheral seas of the Arctic Basin (Beaufort round to Laptev), this is the second lowest volume in the post 2007 period. Whereas for the Central Arctic region, sub grid thickness volume over 3.3m thick is 5.87k km^3, that is the highest in the post 2007 period and is 3.6 standard deviations above the 2007 to 2014 average April volume for sub grid thickness ice over 3.3m thick."