Guest post by Steven Goddard
NSIDC Arctic Ice Extent Just a few pixels from “average”.
May 1st is May Day . “Mayday” is a universally understood distress call signifying that an aircraft or other vessel is headed on a collision trajectory. 2009 Arctic ice extent is on a collision trajectory with normal, which could be disastrous for AGW alarmists. “May Day” is an international holiday celebrated on May 1. In the Soviet Union it celebrated the worker’s “liberation” from capitalism, though they hadn’t yet thought up “cap and trade” at that time.
I have more news to report about the ongoing mystery of why NSIDC shows Arctic ice extent much closer to the 1979-2000 average than NANSEN is to the 1979-2007 average. It should be the other way around.
Dr. Walt Meier at NSIDC has again graciously responded to further questions:
Dr. Meier:
It is possible that there could be inconsistency in the Nansen data. I’m not familiar with their processing. I am confident that our dataset is consistent. However, it may simply be due to the ice conditions. Most of the time, the differences between algorithm should be an offset – though this offset can vary over the course of the year (particularly summer vs. winter). However, there can inconsistencies in this depending on the character of the ice cover.
My suspicion is that much of this is due to the Bering. The ice in the Bering is very broken up and, basically, on its last legs. It could be that our algorithm is more sensitive in picking up the ice than the Nansen algorithm. Or it could be that our algorithm is overly sensitive and is not catching open water.
Remember that the threshold for ice extent is 15%. So if you have low concentration ice, even small differences in the algorithms can result in relatively large differences in extent. If Nansen consistently shows 5% less ice that NSIDC, when there is 90% ice, that makes no difference, but where there is ~15% ice, it can make a difference. From other imagery, it looks like there is a lot of area with concentrations in the ballbpark of 15%.
Me:
If it were due to Bering Strait ice, I would expect to see a convergence between the two data sets as the Bering ice melts. It looks to me like they are actually diverging over the last week or two though?
Any ideas from the readers?
UPDATE: Dr. Meier just responded, minutes after posting this article:
Dr. Meier:
It is the Bering Sea, not the Strait and as it begins to melt, with all the old, broken up, sparse ice, you see the divergence. As it melts out completely, I expect that we’ll see things go back to being more consistent.
Addendum from Anthony:
A question to Dr. Meier: When are we going to see a date/time stamp on the NSIDC imagery? NANSEN has one.
This NSIDC graphic above is one of the most widely displayed and quoted on the net today, yet it lacks this most basic feature found in many scientific images presented for public consumption.
I realize the curve itself is marked against the x axis, but it is not easy to determine an exact date. Science is exacting, it would seem prudent to add a date/time stamp. Otherwise, the appearance of exacting science presented to the public is one of sloppiness, IMHO.
Flanagan (03:13:29) :
Well, NASA satellite measurements just revealed there are very large parts of deep-arctic zones that are covered with very thin ice layers. This is especially striking if one takes a look at the sea ice concentration rightnow
http://arctic.atmos.uiuc.edu/cryosphere/NEWIMAGES/arctic.seaice.color.000.png
There are some immense patches of low-concentration ice right in the middle of the Arctic basin, which I never observed before at this time of the year. Even the multi-year ice that drifted in the Barents sea is beginning to melt now. Given the wind pattern we had, we might well be heading for a new record.
The use of colors in the linked image is “unusual.” Black appears in more than one place on the spectrum. I suspect the black areas near the pole are the 95% band, not one of the lower ones.
E.M.Smith (13:08:03) :
“So the fact that this May 1st is the same more or less as the average of all other May firsts (which is what is shown on the May 1st date of the average curve) is very useful. It says that we are absolutely normal for arctic ice.”
This is the problem with ignoring standard statistical tests. “Normal” is a vague and somewhat loaded word, misleading when used to mean “the average of period showing a strong trend down.” Esp so when looking at a short-term series of such noisy data.
Which is why I suggested alternative and more commonly used methods to show the trend. The NSIDC gives one such: Average Monthly Sea Ice Extent. The graph of March numbers is here:
http://nsidc.org/images/arcticseaicenews/20090406_Figure3.png
It will be interesting to see the April graph. I suspect it will be similar, suggest that the trend might be reversing — but that it is too early to say for sure.
Fabius Maximus
“Normal” is a vague and somewhat loaded word, misleading when used to mean “the average of period showing a strong trend down.”
Since the bell-curve is called the “normal” distribution, it is not very far fetched to call values in the interval [mean plus/minus standard deviation] “normal”.
Example: An IQ between 85 and 115 is “normal”.
Alexej: Exactly. That sort of analysis would give meaningful results. But it is too seldom done, as we see in this case. We don’t know if there is a statistically significant trend in article ice extent (or area). And we do not know if recent years indicate a change in the trend. All we have are pretty pictures (like the spaghetti graphs so loved by many climate scientists.
This is state-of-the-art statistics pre-1650 (before Fermat and Pascal). Absurd that on such a weak foundation the newspapers warn about the end of the world.
“Average Monthly Sea Ice Extent.”
You’re fashionably late for the party but we’ve beaten this dead horse, buried it and then dug it up many, many times over.
In particular, the preference for a linear trend of cyclic data is ripe for abuse by the presenter, causes arguments over the base period, etc.
IMHO, this area of investigation, sea ice area/extent/thickness/age is one of the fat butt of climate research; certain to devolve into trivial controversy.
Let’s hope things don’t turn into a real mayday. If the sea ice situation, over the next few years, gets into the realm last experienced during the LIA, there will be quite a few mayday calls going out from ships striking icebergs in the North Atlantic.
Joe Romm posted the following comment back in January
http://climateprogress.org/2009/01/27/nsidc-arctic-sea-ice-drops-below-2007-levels/#comment-44543
Hmm! “The day by day meanderings of Arctic sea ice extent are not overly meaningful yet, but I think they are worth reporting because it bugs the deniers to see any evidence whatsoever that the world is not undergoing global cooling”
I was somewhat amused and certainly not “bugged” to see that the NSIDC image has continued to update itself through to May.
Actually ‘MAYDAY’ is the international call for immediate help and has nothing to do with collision. If in n trouble but not immediate danger the call would be ‘Pan Pan’.
It comes from the French, M’aidez, ie, help me! Pan Pan comes from Panne which means a mechanical breakdown.
Just thought I would let you know.