That's Obvious

Tamino is doing a sea ice series (Pt 1, Pt 2, Pt 3) which started, what else, with a provocation from Jeff Condon, owner operator of Bishop Hill some other blog

What Condon’s essay really illustrates is how fake skeptics fool themselves into thinking they have real evidence.

The gist is a re-definition of sea ice area to include only what Condon calls “annual” or “single-year” ice area. This isn’t done by determining which ice is really 1st-year and which isn’t — it’s done by noting that every year, almost all of the Arctic sea ice south of latitude 72N melts away, so the new definition is “sea ice south of latitude 72N.” That’s for the northern hemisphere, for the southern the definition of “annual” is: all the sea ice.

Eli leaves it to the gentle bunnies to go read the various ins and outs, esp a comment by Jeffey

The 72 degree mark was the northernmost divider for non-annual ice. It was identified by using data. Shame that. As you know, but managed to fail to point out, the Antarctic ice melts almost completely every year. Adding them together shows a picture of how regions which don’t support multi-year ice are reacting to global warming. In other words – Most of the ice on Earth. I found it interesting to see a minimal trend and concluded nothing much from it. As I told Nathan, nobody is taking away your end-of-the-world sandwich boards gentlemen.

Now Eli is not as swift as he used to be, but if you want first year ice, hell, just subtract the minimum ice area each September from the ice area in the following twelve months till you hit a new minimum.  It's a lot easier than getting the ice south of 72 degree, and Eli was not alone in spotting this (Ron Broberg at a minimum was another).  So the Rabett wrote a polite letter to the Cryosphere Today folks and got the data for the ice area and the anomaly and did the dirty

UPDATE:  Prettified and a bit clarified.  The green line is, as it was, the difference between the lowest sea ice area in September and the sea ice area in the following year until a new minimum is reached.  Also made the lines a bit thicker for reading.

There are some interesting things here.  For one, the simple way to get the first year ice, tells you how much ice lasted for two or more years (called old ice here, which is not quite the normal, where old ice is reserved for multiyear ice).  The interesting thing is how parallel the decrease in teh old ice is to the anomaly, but if you think about this, it's not so strange, because most of the first year ice does not survive, esp the more southerly.  Thus, the anomaly is basically a disappearance of old ice.  Second, the first year ice area jumps about until the big melt of 2007, after which it takes a big jump.  Makes sense, the old ice melted out, and usually the Arctic pretty much freezes over every winter.  This winter may be different because the western end of the Arctic was pretty ice free this year.

Someone, might even try to match the peaks of the first year ice to the NAO.