Friday, March 09, 2012

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.


J Bowers said...

"owner operator of Bishop Hill"

You mean The Air Vent? Bishop Hill is Andrew Montford's. It's easy to get free market extremists mixed up.

EliRabett said...

Yeah, whatever. Mostly Eli stays out of those swamps

dbostrom said...

"Just for the record, summer ice depends mostly on how much is blown out of the arctic basin – something that used to be textbook information. While there really doesn’t appear to be that much going on, anecdotal information can be more dramatic."

--Richard "Automatic Iris" Lindzen

Michael Tobis said...

"subtract the minimum ice area each September from the ice area in the following twelve months till you hit a new minimum" ???

Do you mean, subtract the minimum from the immediately succeeding maximum?

If you do, that makes sense to me. If you don;t, please explain.

Anonymous said...

@tobis : maybe he meant "from the maximal ice area in the following twelve months", aka he hinted as his algorithm : you take the lowest September value and then you do a simple maxima research for the following 12 months.
A senior high school exercise, except that our carrot distributor was less lazy than I was when I ran across Jeff's nonsense :]


Anonymous said...

So the problem is that the light green first year sea ice area sometimes goes below zero... because the light green isn't really "first year sea ice" but rather "excess sea ice above the minimum", which is equal to first year sea ice up until some older ice melts... at which point, it isn't anymore...


owlbrudder said...

MMM, You have me confused (not difficult, my synapses are not ageing well).

If you take the maximum (presumably winter) and subtract the following minmum (presumably summer), the difference may include some melted multi-year ice, so does not represent the actual first-year ice only. On the other hand, if you take the minimum away from the following maximum, surely it must be only first-year ice?

It'll probably become clearer after my next cup of coffee, but I'm puzzled right now ...

Anonymous said...

owlbrudder: it is entirely possible that I am the one who is confused here. But I'll try to explain my reasoning in a bit more depth:

First: I'm basing my analysis on this sentence: "just subtract the minimum ice area each September from the ice area in the following twelve months till you hit a new minimum", and the corresponding green line in the graph. So this implies that for every day after the minimum, up until the new minimum, there is a calculation of "first year ice". This includes the day before the new minimum... and if that day is _less_ than the first minimum, then the calculation of "first year ice" can be negative, which is clearly not physical.

Second, even looking just at the day _after_ the first minimum... there has been an increase of ice, but you don't know that there hasn't been a continued melt of old ice. So even that number may not exactly correspond.

So... I think what we have here is a lower bound on first year ice: the number provided by (current ice minus previous minimum) must be less than or equal to (current first year ice). The "less than" comes from melting of non-first-year-ice, which might happen a bit after the first minimum, but will happen a bunch in the months leading up to the new minimum...

Does that make sense?


Anonymous said...

Er. Also, my guess is that the technical definition of "first year ice" may involve "ice less than a year old" such that it is not a near-zero number the day after the minimum... but my previous comment was made assuming that our "new ice since the last minimum" metric was the only one that counted.


Anonymous said...

Dr. Jay Cadbury, phd.

I think a graph of sea ice that starts at 1979 doesn't really tell us much. We know that the ice has been lower than this before, nothing new here.

Kevin O'Neill said...

Dr. Jay Cadbury, phd.

I think a graph of sea ice that starts at 1979 doesn't really tell us much. We know that the ice has been lower than this before, nothing new here.

Oh really? *Much* lower? When? 48 million years ago?

We know there was reduced sea ice at the end of the HCO - we don't know how much less because of conflicting evidence. While the eastern side appears to have been ice-free, Ellesmere Island had more ice and the western arctic also appears to have had more ice.

Even if we grant there was less ice at the end of the HCO than *today* - what would lead us to believe that *today* is going to be the minimum for this era? Nothing.

Besides, Kinnard et al show sea ice going back 1450 years, not starting in 1979.

EliRabett said...

MMM more or less gets it, but there is also the point that the difference between the ice at the max and the ice at the previous min IS the total of the first year ice.

The problem with looking after the max is that you get some melting of the multiyear ice as well as some non melting of the first year. Still, all and all it ain't bad.

Update coming.

Kevin O'Neill said...

the difference between the ice at the max and the ice at the previous min IS the total of the first year ice.

I think it only sets a lower boundary for FYI. It neglects any ice at Min that also subsequently melts before Max.

Assume 5million km^2 at min. 15million at max. That means at least 10million FYI. But if at some point in the winter (say when it reaches 10 million) all 5 million km^2 that were hanging around at Min up and paddle off through Nares Strait and are immediately nuked by voracious Baffin Bay waters - then we'd actually have 15 million km^2 of FYI at Max.

Realistically, the flux through Fram Strait can be fairly large (1 to 3mil km^2 during winter??), but that will include ice of all ages. Still, I'm willing to bet some burnt pizza crusts that your formula only sets a lower boundary for FYI.

a_ray_in_dilbert_space said...

Hypothesis: Dr. Jay Cadbury is a dinosaur who has been hiding in somebody's closet and is secretly agitating to restore the climatic conditions that prevailed during the Cretaceous.


Anonymous said...

I agree with Kevin (and my previous comment). The new red line is a lower bound on first-year ice formed.

I also think that the "Cadbury-dinosaur" theory is intriguing, and fits much of the evidence... =)


owlbrudder said...

MMM et al, thanks for the clarification. I think I understand now what you are driving at: further melting of multi-year ice can be occurring after minimum extent is recorded, so the observed difference in extent is a close approximation, but not the whole enchilada.

a_ray, I disagree on the grounds that dinosaur skeletons exhibit cranial volume in which a brain once resided, whereas I find no equivalent evidence in our resident chocolate blockhead.