As of May 31st the 2016 trend line is lowest on the graph. A sea ice volume decrease of 3037 km3 during the month of May was enough to overtake 2011 and increase the lead over every other year in the 2007-2016 period, except for 2010 and 2012, which both recorded massive volume losses during May. 2016 has a very small lead now over 2011 (162 km3) and 2012 (270 km3). The gap with last year has grown to a whopping 2180 km3.
Here's how the differences with previous years have changed since last month:
Wipneus' version of the PIOMAS volume graph also shows how close the 2011, 2012 and 2016 trend lines are:
The trend line on the PIOMAS sea ice volume anomaly graph has now dipped well below the linear trend, moving towards the 2 standard deviation zone where it hasn't been since 2013:
As for thickness, I still can't use Cryosphere Today sea ice area data for my crude thickness calculation (PICT), as they haven't switched to the new SSMIS-based data yet (it's still in the calibration phase) and so I've decided to use reliable AMSR-2 based data as provided by JAXA (via ADS-NIPR). I divide PIOMAS volume by JAXA sea ice extent to get average thickness that I can then compare to previous years. I've decided to use a serious acronym this time: PIJAMAS.
Here's the graph:
One would intuitively guess that when volume is low, average thickness is low too. But when the ice cover is even lower - and JAXA SIE was much lower than previous years at the end of May - the volume gets spread out over a smaller area, and thus average sea ice thickness is now higher than other years from the post-2010 era.
The thickness plot from the Polar Science Center is showing the exact same thing:
Another interesting piece of information has been added to the PIOMAS website, a thickness anomaly map that shows where this year the ice is thicker/thinner compared to the 2000-2015 average:
This reminded me of the volume distribution comparison maps that Wipneus produces every month and shares on the Arctic Sea Ice Forum. Because this year is so close to 2011 and 2012, I decided to have a look at the differences with these two years (red means there is more ice now than there was then, blue the reverse):
As you can see, according to the PIOMAS model there is more ice this year mainly in the Central Arctic and in the East Siberian Sea, the difference being more pronounced in 2011. Sea ice volume is practically on a par with 2011 and 2012 as of the end of May. These are also the years that ended in the lowest September volume and extent numbers.
If we assume that volume in the Central Arctic doesn't matter for the September sea ice extent minimum (as it didn't melt in 2011 and 2012 when sea ice volume was lower there), this means that sea ice volume is lower outside of the Central Arctic, in the regions that do matter for the outcome of the melting season.
As eyeballing only gets you so far, I asked Chris Reynolds about this (be sure to check out his latest blog post on PIOMAS and other data) and he was so kind as to send me the PIOMAS volume numbers for the Central Arctic and the rest of the Arctic:
This year is on a par with 2011 both within and outside of the Central Arctic region, but looking again at Wipneus' thickness difference map, it's clear that the East Siberian Sea will play crucial role in the race between 2011 and 2016. This region is in the middle of a heatwave as we speak, and the ice surface is showing extensive melting, according to satellite images and other data (I'll have more on this next week).
As for 2012, this year there is 1000 km3 less sea ice volume in the regions outside of the Central Arctic. That's a lot of ice - almost 10% - that doesn't need to melt for this year to end on a par with 2012. Most of this difference is situated in the American-Pacific side of the Arctic, where the ice pack opened up at record speed this year and large stretches of open water are in the process of warming up, next to and within a large part of the ice pack that is looking increasingly patchy.
According to both PIOMAS and CryoSat the ice seems to be thicker in the currently warm East Siberian Sea than it was in 2012, but in contrast to 2011, there's also somewhat thicker ice on the Atlantic side of the Arctic. The Atlantic seems to be bringing warmer ocean currents to the Arctic this year, so it remains to be seen what will happen to that ice. All in all, 2016 looks to have a slight advantage over 2012, when it comes to potential melting in the regions outside of the Central Arctic.
This is all fine and well, speculating is fun, but June was when 2012 laid the basis for its record breaking melt, due to almost perfect weather conditions for melting. June has been more modest this year so far, but there's three more weeks left to go. We'll know next month whether this year will have been able to keep up with 2012's breakneck pace.