After starting the year as the lowest on record, the 2013 trend line is now 425 and 901 km3 above those of 2011 and 2012 respectively. It doesn't come as a complete surprise, given the slow start to the melting season (see ASI 2013 update 1), but is remarkable nonetheless.
The various area and extent graphs on the ASIG (Arctic Sea Ice Graphs page) are a bit in disagreement, but it seems that the sea ice cover is greater than in previous years, and this could be the main reason for the difference in volume. There is simply more ice right now.
Here is Wipneus'
version with the calculated "expected" 2013 values (dotted
lines), based on the same date values of 1979-2011 and an exponential
A caveat from Wipneus: "Note that the statistical error bars are quite large."
Nevertheless, the anomaly trend line has dropped well into 2 standard deviation territory and it'll probably stay there for a while now:
Interestingly, average thickness has now dropped below previous years when compared to last months's update. I crudely calculate the ice pack's average thickness by dividing PIOMAS (PI) volume numbers with Cryosphere Today (CT) sea ice area numbers. There's more thin ice at the fringes that hasn't started melting yet (probably because of cloudiness and colder than average temperatures) which means the average thickness goes down:
Here's average thickness for May 31st in metres, with change from last month between brackets:
- 2005: 2.33 (+0.17)
- 2006: 2.31 (+0.19)
- 2007: 2.16 (+0.15)
- 2008: 2.29 (+0.25)
- 2009: 2.14 (+0.11)
- 2010: 1.95 (+0.08)
- 2011: 1.86 (+0.04)
- 2012: 1.83 (+0.07)
- 2013: 1.79 (+0.01)
If you want to have a look at the data yourself, you can download the spreadsheet I use and update from GoogleDrive.
Average thickness has hardly gone up in the past month. It will probably hover around this value until the end of June and then start dropping.
The thickness graph from the Polar Science Center is showing 2013 slightly above 2012 this time:
All in all this is a very interesting development, especially if this year doesn't bottom out below last year's volume record. It could mean that either winter weather still has enough of a punch to restore the ice pack to the state it was in the previous year. Or it could even mean that some negative feedbacks have started to kick in and we see a sort of plateau in coming years. Not a deceiving extent/area plateau of the 2007-type, but a volume plateau, until continued warming pushes the boundaries even further.
But it's too early for speculation, as the melting season has just started and we are bound to see the steep volume drop that we have witnessed every year since the spring of 2010. If you want some high-quality speculation though, I highly recommend reading the Dosbat blog, as Chris Reynolds has been one of the people who have been putting most thought into volume developments and what it means for the near future (for instance in this Summer Acceleration blog post).
Update June 8th:
Wipneus reports that PIOMAS gridded thickness data has also been updated. Here's the thickness map he has produced:
And this one compares May this year with that of 2012:
You can compare this comparison to the one posted in April. Thanks, Wipneus!