A couple of things were missing from the 2015/2016 winter analysis posted a few days ago, and so I've decided to present them in this separate blog post. Most of these images come from the website of NSIDC research scientist Andrew Slater.
Another way to express how warm or not-cold the Arctic has been this winter, is through so-called freezing degree days. The NSIDC explains it as follows in the All About Sea Ice segment of their website:
The relationship between thermodynamics and sea ice thickness can be thought of most simply in terms of freezing degree days (FDD), which is essentially a measure of how cold it has been for how long. The cumulative FDD is simply daily degrees below freezing summed over the total number of days the temperature was below freezing.
In other words, the sum of the number of days below 0 °C multiplied by the temperature for each day. Edit April 5th: I came up with a better explanation in the comments below. Here's a graph from the +80N 2m Tair page on Dr. Slater's website that shows this year's FDD compared to those of other years:
What can I say? This year's trend line is not only way outside of the percentile zones, it's falling off the chart. This comparison obviously corresponds well with the temperature charts and anomaly distribution maps I used in the 2015/2016 Winter analysis. But let me repeat that this isn't necessarily telling us anything about the coming melting season. As you can see, the blue line representing FDD preceding the 2011 melting season is rather high, but that melting season still managed to equal 2007, record holder at the time. Conversely, the yellow line is low, but the 2014 melting season turned out to be a second rebound year after the 2012 record breaking melting season.
Even though we don't know what will happen this coming melting season, we do know that those anomalously warm/non-cold temperatures have had a marked effect on the ice pack. As mentioned in the 2015/2016 Winter analysis the increase in sea ice volume so far this year is the lowest on record (PIOMAS will probably be updated in the coming week and I'm expecting March increase to be lower than the average of the past decade).
When it comes to sea ice extent and area, Cryosphere Today reported the lowest Arctic sea ice area maximum on record, as did the NSIDC for their Sea Ice Index (extent), and JAXA sea ice extent had the second lowest maximum on record (just 16K more than last year's record). As we can see on the JAXA SIE and CT SIA graphs this year's trend line is still the lowest of all in the 2007-2016 period: