Sea Ice News Volume 3, #2

kadaka (KD Knoebel) says:
March 20, 2012 at 12:38 am
Long-Term Ice Variability in Arctic Marginal Seas;
Polyakov et al. J Climate 2003, 2078-2085
Examination of records of fast ice thickness (1936–2000) and ice extent (1900–2000) in the Kara, Laptev, East Siberian, and Chukchi Seas provide evidence that long-term ice thickness and extent trends are small and generally not statistically significant, while trends for shorter records are not indicative of the long-term tendencies due to large-amplitude low-frequency variability. The ice variability in these seas is dominated by a multidecadal, low-frequency oscillation (LFO) and (to a lesser degree) by higher-frequency decadal fluctuations. The LFO signal decays eastward from the Kara Sea where it is strongest. In the Chukchi Sea ice variability is dominated by decadal fluctuations, and there is no evidence of the LFO. This spatial pattern is consistent with the air temperature–North Atlantic Oscillation (NAO) index correlation pattern, with maximum correlation in the near-Atlantic region, which decays toward the North Pacific. Sensitivity analysis shows that dynamical forcing (wind or surface currents) dominates ice-extent variations in the Laptev, East Siberian, and Chukchi Seas. Variability of Kara Sea ice extent is governed primarily by thermodynamic factors.
Like the sprinkling of salt on the back of a slug,
so is the confronting of climate apparatchiks with evidence of climatic oscillation and cycles
The reaction is predictable and entertaining!

I am wise enough to understand the saying, “Do not argue with a fool lest onlookers cannot tell the difference.”
Kadaka has certainly said enough to give a pretext to those who want to ignore available but inconvenient evidence to do so.
I have said enough so that people who want their opinions to be guided by the evidence know the evidence is available and where to find it.
Kadaka only raises one substantive issue where he says, “I’ve seen on satellite-based extent maps before, there can be significant areas of open water or minimal concentration contained within the outer boundaries of the Arctic sea ice.” Sea ice extent is defined as the area in which sea ice represents 10% (or 15% depending on the study) or more of the surface area. It is very clear that prior to 1978 (if you look at the detailed data) Walsh and Chapman provide, they do not have that information inside the ice edge. It is also clear from the 1978 onwards that areas within the ice pack with sea ice concentrations as low as 60% are not uncommon. What you do not find is large areas of open water or with sea ice concentration below 20%. For that reason, the sea ice extent data from Walsh and Chapman are reasonably reliable,while the sea ice area data from the same source are not.
I have, of course, exclusively discussed sea ice extent. Kadaka, in turn, seems unable to distinguish between the two. If he disagrees, he need only provide an example of less than 20% sea ice concentration in the Arctic sea ice wholly enclosed by areas of greater than 20% sea ice concentration from within the satellite era. He will, of course, find a few such areas which do not have naval access to the Atlantic of Pacific Ocean when the ice has melted away from parts of the Russian coastline, or withing the straits of the Canadian Archipelago, but such instances where observed and occur throughout the Walsh and Chapman record, and hence are not germane.
I will confidently predict that he will not find even one such instance where the area of low sea ice concentration enclosed represents even 10% of the total sea ice extent. He will certainly not find sufficient to suggest this is a major source of error in Walsh and Chapman’s record.

From Tom Curtis on March 20, 2012 at 11:30 pm:

I am wise enough to understand the saying, “Do not argue with a fool lest onlookers cannot tell the difference.”

Therefore you should not argue with yourself in public.

Kadaka has certainly said enough to give a pretext to those who want to ignore available but inconvenient evidence to do so.

Which you have shown yourself remarkably able to do even without the purported pretext.

I have said enough so that people who want their opinions to be guided by the evidence know the evidence is available and where to find it.

And of the evidence you have provided, I have shown how the paths keep leading back to Walsh and Chapman, which has serious caveats that restrict that data and work derived from it from claiming the authoritativeness you insist on ascribing to it.

Kadaka only raises one substantive issue…

Actually I raised several, but go on anyway.

Sea ice extent is defined as the area in which sea ice represents 10% (or 15% depending on the study) or more of the surface area.

Gee, let me refer to the definitions of extent and area on the IARC-JAXA Sea Ice Page (I miss those updates):

Definition of sea-ice cover (extent and area)
* The area of sea-ice cover is often defined in two ways, i.e., sea-ice “extent” and sea-ice “area.” These multiple definitions of sea-ice cover may sometimes confuse data users. The former is defined as the areal sum of sea ice covering the ocean (sea ice + open ocean), whereas the latter “area” definition counts only sea ice covering a fraction of the ocean (sea ice only). Thus, the sea-ice extent is always larger than the sea-ice area.

With 10% concentration, a cube of solid ice a meter to a side yields the same extent as a square meter of slush of at least 10% ice concentration. For area a square meter of 10% slush is recorded as 1/10 of a square meter. In both cases the cube is still a larger amount of ice than that in the slush. Neither metric properly represents the amount, the volume, of ice, but area comes closest.

I have, of course, exclusively discussed sea ice extent. Kadaka, in turn, seems unable to distinguish between the two. (…)

Dang, here I though I was clear enough that an idiot could follow. Guess I was wrong. As I said: “Thus with the pre-1953 data one can calculate higher amounts of sea ice than what was actually there.” “A frequent bone of contention is if there was less Arctic sea ice circa pre-1979, you’re actually addressing if there could have been more by establishing an upper limit.” I was talking about amounts of sea ice, the volume, with area being the closest metric.

(…) If he disagrees, he need only provide an example of less than 20% sea ice concentration in the Arctic sea ice wholly enclosed by areas of greater than 20% sea ice concentration from within the satellite era. (…)

Actually I do disagree with your assertion I don’t know the difference between area and extent, and all I really had to do was show that I know. I’ve been on this site over two years, the difference has come up and been discussed many times in the past.
In any case, my focus was the pre-1953 data, and I’ve established it has problems, Walsh and Chapman have noted it has problems, therefore that derived from that data has problems. You’ve even admitted there are problems: “For that reason, the sea ice extent data from Walsh and Chapman are reasonably reliable,while the sea ice area data from the same source are not.” Thus it is hard to know if the amount of Arctic sea ice was more or less pre-1953.
Caveats on the W&C dataset are further detailed by Chapman, see the “Expert User Guidance” section:
http://www.cgd.ucar.edu/cas/guide/Data/walsh.html

The temporal and spatial inhomogeneities in the data sources that went into the construction of this dataset require that any historical analysis of the data is done with caution and an understanding of the limitations of the data.
There are three periods for which the sources of the data change fundamentally:
1972-1998: Satellite period – hemispheric coverage, state-of-the-art data accuracy
1953-1971: Hemispheric observations – complete coverage from a variety of sources. The observational reliability varies with each source, but is generally accurate.
1870-1952: Climatology with increasing amounts of observed data throughout the period.
Because most of the direct observations of sea ice (1870-1971 period) are from ships at sea, they are generally the most complete near the ice edge. The conditions north of the ice edge are often assumed to be 100% covered during this period. The satellite era has shown otherwise with concentrations between 70-90% frequently occurring well north of the ice edge in the post-1972 data. For this reason, we recommend using a measure of ice extent, when doing historical comparisons of hemispheric sea ice coverage for periods which include data prior to 1972. This is done by assuming that all grid points with ice concentrations greater than some threshold (15% is commonly used) is assumed completely covered by sea ice.

Got that? North of the boundary, 100% was assumed. So amount of ice would be overestimated. To compare with modern satellite data, as best one can, treat the modern as if extent was area (100% ice). In other words, overstate the modern amounts of ice to compare with the old data. So Walsh and Chapman is not a definitive source for determining if there was more or less sea ice in the past, likewise that derived from it.

I will confidently predict that he will not find even one such instance where the area of low sea ice concentration enclosed represents even 10% of the total sea ice extent. He will certainly not find sufficient to suggest this is a major source of error in Walsh and Chapman’s record.

I admit I have neither the skills, time, nor the connection speed for such a search, and the tricky area calculations have been a source of notable contention on this site before. Do you have any idea how long it takes to download a single Cryosphere Today map on dial-up?
But the University of Bremen, following the AMSR-E loss, now has SSMIS-derived maps:
http://www.iup.uni-bremen.de:8084/ssmis/index.html
The small Sep 2011 to date animation allowed me to home in on two interesting times, and there are detailed-enough small png files of individual dates in the archives. From Oct 25 to 30, 2011, there’s a significant area between about 120° and 135°E that gets encircled. When going by shipping reports and observations from the shore, such would have been missed.
Then there’s the start of the animation, Sep 1, 2011. Look at the outer boundary, the bits of open water and large areas of low concentration contained within that boundary. For the old W&C data, all that contained area would be considered 100% ice. It only takes a look to know that’d be more than a 10% overstatement right there. Sep 5 map, same thing, actually could be worse.
And I’ve found those by briefly looking at less than a single year of satellite-era maps.
I suppose if you don’t mind working with the worst available metric, where a million square kilometers of 20% slush is the same as a million square kilometers of multi-year sea ice several meters thick, then you likely won’t see much difference. But for those of us who prefer more realistic measurements of reality, who would prefer to know the actual amounts of sea ice or at least as close to them as possible, Walsh and Chapman will continue to be problematic.