Epiphyte,
Your statements are in quotes.
1. The trends for March and May crossed in 2009. Before then, there was consistently more ice in May than in March, since then there has consistently been less ice in May than there was in March - including last year, which was well above the trend for both months.
This crossing is due to the PIOMAS spring volume loss, which involves anomalous loss of volume from around 20 April to around the solstice. I shall shortly be blogging further on why this anomaly should be viewed as a result of thinning, particularly in the Central Arctic since the 2010 volume loss event.
2. According to PIOMAS there has since 2009 been a consistent 1M km3 volume gain Mar-Apr , and it has always been lost Apr-May, again regardless of trend.
Again, an effect of the PIOMAS spring volume loss anomaly, prior to 2010 the Apr-May volume loss was substantially lower.
3. Backing up to January , and roughly eyeballing the graph, PIOMAS has never come up with a Jan-Feb volume increase of less than ~2.5 Mkm3, or a Feb-Mar increase less than ~2Mkm3
So if PIOMAS stays true to form, the Feb number will be >= 21M, and under better-than-existing worst case conditions the the March number will be >= 23M and the April number will be >= 24M
Jan to Feb; The average increase is 2.74, the min is 2.23, but broadly correct. At 3.01 the 2015 jan Feb increase was above average but substantially less than the post 2012 increase of 3.52, which was driven by the thickness growth feedback.
Feb to Mar: Quite a few years were below 2Mkm^2, 1978, 1979, 1980, 1984, 1987, 1989, 1990, 1992, 1993... sorry I got bored with that list. 2015 was 1.75, not unusal. Lower September extent leads to greater growth - the growth thickness feedback again.
In other words, the January number is high enough to guarantee that the April number will be more than a million km3 *higher* than it was in 2014, absent worse than existing worst-case behavior in February and March.
Yes, it was 1.31 higher.
So we just lived through Feb - and to my eyes at least it looked as though it might indeed have have been the worst ever. Assume that PIOMAS cuts it's previous worst-case Feb growth in half (i.e. from ~2.5 to ~1.25m). If it did that the Feb number would be the same as it was last year.
Sorry, you lost me here, but February volume was 23.21, Jan Feb gain was 3.01 not unusual, Feb to Mar gain was 1.75 - towards the lower end of the distribution. 1993 (1.74), 1995 (1.52), were lower making 2015 Feb to Mar gain the third lowest on record.
Looking at the actual area today it is essentially the same as it was this time last year - so If PIOMAS does come up with a 50% cut in Feb volume growth over 2014 (which itself was very low), it might be a plausible number - albeit an unprecedentedly bad February for the arctic - but only if the avg. thickness is also now the same as this time last year. This seems a stretch given the weak winter and the low thickness estimates. If the ice is actually thinner, then PIOMAS would need essentially zero Feb growth to avoid coming up with an incredible number for Apr/May.
I'm sorry but I really don't get how you conclude Apr/May was/would be an 'incredible' i.e. unbelievable number. The PIOMAS April volume was as I said above 1.31 higher than in 2014, but area would be uninformative as this is concentrated in the thicker ice of the Central Arctic.
If, OTOH, PIOMAS comes in with the same (already low) Feb & Mar growth that it did in 2014, it can only end with a modeled March-May volume >1m km3 higher than it was last year, which would IMO be astonishing if true, because it would imply faster Feb growth than 2014, on top of thicker ice than 2014, in the presence of higher temperatures than 2014.
February 2015 was colder than 2014, I have attached a difference plot, so the high volume increase from Jan to feb is to be expected.
So all in all, I'm wondering if this might be the year when PIOMAS last-meter uncertainties finally cause it to part company with directly observable reality.
It might be that I am tired (very), but I don't see how this conclusion follows.