NSIDC Extent continues to show a relatively flat maximum, however I am not convinced that this means anything strong for the coming melt season. Indeed the early peak suggests that a new record is not likely, as discussed previously. However it does no more than suggest, and as I have no idea what the mechanism might be there, I will not factor that into considerations of the coming melt season.
The record of 14.54km^2 on February 2015 (NSIDC) looks increasingly certain. The following graphic shows sector extents, the sectors as defined in this post. Being contained within the Arctic Basin the Siberian and Alaskan sectors are flat (almost). The Pacific Sector (Okhotsk & Bering) remains on a bumpy plateau, but the Atlantic (Laptev, Barents, Greenland) and Canadian (Baffin, St Lawrence, and Hudson Bay) are both falling away from their peaks.
As usual, to make the results comparable with DMI I have calculated average surface temperatures north of 80degN for September to March. These are presented as anomalies (differences) from the NASA GISS baseline of 1951 to 1980.
Winter 2015 confirms the visual impression of a rapid rise of temperature starting in about 1995 and ending about 2006. This has been followed by a period of far lesser rise in temperature. But before passing that over, the rise of over 4 degrees C is staggering. Looking at the steepest rate of warming, I have taken the averages of two ten year periods, 1985 to 1994 (1.0degC) and 2006 to 2015 (4.7degC) this is an increase of 3.7degC, which happened in ten years.
Subtracting the 1951 to 1980 average from the 2015 period shows that the warming is spread over the Arctic Ocean towards Siberia and around the Atlantic Ocean ice edge.
So the astonishing warming seen between those two periods is shown to be a surface hugging feature with warming higher in the atmosphere being around a quarter of that at the surface. This is potentially indicative of two processes, one is heat flux through ice increasing as ice thins, the other is the decline of the surface temperature inversion typical of Arctic winters over the pack. With regards the latter effect, it is difficult to disentangle the decline of the inversion as this would itself be disrupted by an increase of heat flux as the ice thins. Either way, it seems to me, given the geographical distribution of warming seen in the preceding map, that the cause of the warming is sea ice decline.
I have read opinions that if the rate of winter warming keeps up we will see virtually sea ice free conditions early next decade. If we see the previous rate of warming resume then this is feasible. However my reading of the situation is that as the ice has thinned it has hit a situation of diminishing returns, Once the ice tends to a first year state the warming rate reduces. So further rapid winter warming due to ice loss seems to me unlikely to be as fast as it was between the 1990s and 2000s.
PIOMAS data is now available, as usual here is a map plot of thickness from the gridded thickness data.
This shows a thickening over the 2m threshold into Beaufort, as shown in my previous post on the matter, the Drift Age Model shows a substantial transport of multi year ice into this region. I suspect this means higher survival prospects in Beaufort, Chukchi, and possibly the East Siberian Sea in the coming summer.
Because people may find it interesting, I post an animated gif of September 2014 to March 2015 below.
And now for the usual plot of regional volume, which remains high in the Central Arctic region, but not convincingly high elsewhere. Note that the black trace for Central Arctic is on a scale four times as great as that for the rest of the regions.
Using the PIOMAS main series of volume from the Polar Science Centre's website, the volume as of 31 March 2015 is 24.036k km^3, this is 1.397k km^3 above that for the same date last year. Volume is virtually the same as that for 31 March 2010, 24.053k km^3. At present I am using the monthly gridded PIOMAS data (heff files), for these March volume is 23.207k km^3, which is 1.419k km^3 above that of March 2013. The Central Arctic is 1.337k km^3 above the volume in March 2013, so accounts for most of the increase in volume.
Looking at thickness/volume breakdowns, the increase in the Central Arctic for grid boxes reporting over 4m thick is 2.082k km^3, which is offset by reductions in thinner categories of ice. The increase for grid boxes reporting over 4m thick for the whole PIOMAS model domain is 2.094k km^3. So the picture seen throughout the autumn and winter is maintained: The volume increase is mainly due to the thickest ice in the Central Arctic.
Breaking the March PIOMAS gridded data down into five thickness bands shows that virtually all of the increase of volume is from grid boxes over 4m thick. One must go back to 2002 to find a greater volume of ice in that thickest category for March. However it is worth pointing out that for the whole PIOMAS domain, in 2008 volume for grid boxes over 4m thick was 2.188k km^3, but by March 2009 that had dropped to 0.437k km^3.
Despite the increased volume much of the pack remains relatively thin compared to past decades, this leads to a faster rate of thickening through the autumn and winter. This is shown in the volume gain from the previous year's minimum to 31 March. This year's volume gain was similar to last year and low for a post 2007 year, but remains hight compared to previous years. 2014's autumn winter gain behaviour was very much a post 2007 behaviour.
The March thickness distribution for 2015 largely follows the 2007 to 2014 pattern, apart from the substantial volume increase for grid boxes over 4m thick.
So near the end of the volume cycle for 2014/2015 the impact of 2010 seems to have been largely erased, but the impact of the 2007 volume increase remains largely intact. General conditions regards the PIOMAS data, and HYCOM and Drift Age Model images, suggest to me that there is little prospect of a new record or even extent near that of 2007 or 2011 in September 2015. Of course weather conditions similarly exceptional to 2007 could mean record losses, however I don't consider it sound to prognosticate on the basis of the inherently unpredictable.
Such unpredictable factors merely add to the 'noise' in the predictive model used, or need to be accepted as outliers for which prediction fails. In making my 2015 prediction for average September sea ice extent I will be taking the latter approach. To get in early for this year's SIPN (of course I can't actually enter it until June), here is my prediction for the 2015 September sea ice extent:
5.20 million kmsq +/-0.65 million kmsq.
The method uses March PIOMAS volume for the Arctic Ocean, and is totally statistical with no heuristic adjustment this year. Based on the hindcast from 1979 to 2014 the method is 81% successful, I have decided to accept a level of failure to predict hindcast years.
Here is the hindcast.