Guest post by Steven Goddard
I have been noticing in recent weeks that NSIDC extent is much closer to their 1979-2000 mean than NANSEN is to their 1979-2007 mean. This is counter-intuitive, because the NANSEN mean should be relatively lower than NSIDC – as NANSEN’s mean includes the low extent years of the 2001-2007 period. Those low years should have the effect of lowering the mean, and as a result I would expect the NANSEN current extent to be equal to or above the 1979-2007 mean.
I overlaid the NANSEN graph on top of the NSIDC graph below, and it is easy to see how large the discrepancy is. In fact, the NSIDC mean sits at about one standard deviation below the NANSEN mean – which makes little sense given their base time periods. It should be the opposite way.
(Note – the NANSEN and NSIDC measuring systems are not identical, and I had to make a shift along the Y-axis to line them up. However, the X and Y scales are identical for both graphs in the overlay image.)
Nansen uses a different algorithm to calculate the sea ice extent. The algorithms differ in the way combine the raw data together to estimate extent. As long as one uses the same algorithm, the stories are all the same, but the details can differ, more so at certain times of year. When there is a diffuse, broken up ice edge and melt is starting is one such time.
I suspect the Bering Sea is probably the region resulting in most of the differences. While our algorithm shows the region has mostly “ice-covered” the ice cover there is very fragmented, broken-up, and thin.
….
The other thing that’s important to mention is that I was referring simply to discrepancy between how close the current lines are to climatology. However, there is also generally an “offset” between algorithm outputs – a bias or mean difference between the algorithms that is fairly consistent throughout the record. That is why NSIDC’s climatology is different than the Nansen climatology.
The important thing to remember is that there is a good consistent record from the passive microwave data as long as you consistently use the same algorithm and the same processing. But you can’t mix and match products.
In addition to the cracks in the antarctic ice, there are now cracks in the Australia governments stand on climate change.
http://www.theaustralian.news.com.au/story/0,25197,25406747-11949,00.html
Walter,
You said that 2008 was a record high year for the Antarctic ice pack… Here is the graph from CT:
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.south.jpg
Maybe I’m looking at it wrong, but it appears that 2007 was the record high for SH ice…
Thanks,
Mike
” But something odd happened with the NANSEN data on December 13, 2008 ”
Does anyone know the whereabouts of James Hansen on the date in question? 😉 jk
NANSEN — Hansen, rhyming,…. hmmm, something’s up there… 😉
Looking at the Sea ice graphs that Anthony kindly displays on the RHS of his webpage can anyone provide a reason behind the persistent annual small “blip” in June? This appears to suggest a small regular annual increase at a time when ice is melting fastest. Quite strange.
The notorious base line of 1979 – 2000 cannot be considered normal. It is just an arbitrary reference period with no foundation for anything. We really do not know what “normal” arctic sea ice coverage is.
Another thing that seems odd… CT has the SH Sea Ice Area at 1,227,000 sq. km. ABOVE the 1979-2000 mean, while NSIDC has the SH Sea Ice EXTENT just barely meeting the 1979-2000 average. Now I know that area and extent are different but isn’t that a pretty big difference?
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.365.south.jpg
http://nsidc.org/data/seaice_index/daily.html
On the Arctic Roos, I know it’s the Arctic and not the Antarctic… however even though the area and extent ARE very different numbers, they are still each about the same distance from the mean…
http://arctic-roos.org/observations/satellite-data/sea-ice/ice-area-and-extent-in-arctic
Mike
“What Is Normal Arctic Ice Extent?”
The earth spent most of the last half million years in an ice age. By that standard “normal” would mean ice covering most of Canada and much of the northern US. Under “normal” conditions the place where I’m sitting right now would be under 1/2 mile of ice. I think I prefer the abnormal conditions of the Holocene.
From a statistical standpoint, I don’t see a real problem with -2000 instead of -2007. The data in that region is fairly consistent with little variation. Since the point of contention is the recent history (the last decade), it’s nice to have a control signal outside the area in question.
In addition, if you move the end points for the 79-00 readings, the average stays fairly consistent (and flat). ‘choosing’ end points close to the 2007 minimum (or even specifically choosing a certain point) can distort the results drastically. Whenever a signal is comparing specific results to itself, you have to be very skeptical of the results and examine the comparison very carefully.
I’ve seen quite a few graphs of this ice coverage data [media bias supporting the ‘polar bears are dying’ standpoint] which don’t go much beyond 2007 – even though we have quite up-to-date daily data – disingenuous to say the least.
It’s pitiful that whenever the facts don’t fit the premise they are summarily dismissed (as the antarctic data has) on a whim. It wouldn’t surprise me to see that the sea ice coverage doesn’t matter; it’s now the volume that’s monumentally important (data which can be distorted or massaged and thrown out with a “don’t bother with the boring details, you wouldn’t understand it: our top scientists have assured us we are all going to die”)
Out of curiosity, I went back to the original story as covered here by Anthony on 13 December:
http://wattsupwiththat.com/2008/12/13/something-is-rotten-in-norway-500000-sq-km-of-sea-ice-disappears-overnight/
NANSEN’s explanation, which was later added to the post, seems weak as it cites changes from 22 October when in fact they began 11 September. It may very well have been a small error that kept compounding, though NANSEN never said that explicitly, but ever since then I’ve been a bit dubious about NANSEN. Dr. Meier makes a good point when he says, “The important thing to remember is that there is a good consistent record from the passive microwave data as long as you consistently use the same algorithm and the same processing.”
Personally, my favored source is IARC-JAXA. The comparisons this September should be most interesting.
Heat or no heat the maximum winter ice extent has no real significance in my opinion as the arctic is constrained by landmass. An increase in the ice extent/area as opposed to the last few years at maximum melt in mid september is what we want to see. In view of the reported increase in ice thickness and changed weather/circulation patterns in the arctic as opposed to the 2007 season this looks increasingly likely in my view.
Saying that ( fingers crossed ) we dont want to see too much of a dip in temperatures in the coming years – not good for nature in general and certainly not for us human saps. The alarmists are not worth dying for just to make a point – not that we have any control over anything anyhow.
Mark T said “Do you mean “it seems weird that it hasn’t immediately rebounded to above normal conditions in just 1 year“?
Sounds a little weird, actually, when you put it in this context.”
Shouldn’t be all that weird really. Snow melt in mountains can be lengthened by a strong winter and cooler spring, likewise snow melt can be quicker and earlier if the conditions are warmer over the winter and spring. In some mountainous areas, snow can last well into summer months specifically because it’s on the northern slope and away from direct sun.
True, sea ice can last up to a few seasons – it’s rare in mountains for that – so it’s not a perfect analogy, but given the homogenous nature of the Arctic sea ice compared to mountain ranges, the analogy doesn’t seem all that far-fetched and it seems like cooler winters and lower sun energy would have a more widespread effect across the whole…
How long would you postulate the “lag” be for a “rebound?”
@Cassanders, there must be meteorological and current data available to compare from year to year?
Moving the goalposts. That’s what the media does and their information is provided by, or filtered through various so-called science organizations.
This past year we’ve been hearing about how Arctic ice is on a steady decline which will inevitably lead to an ice-free summer in the very near future. In fact, the decline in relation to recent years ended in 2007. It has been coming back rapidly this past winter and spring. So what does the media do now?
They either continue to report on the 2007 ice year, or, if they have been told by a flood of e-mails pointing to the current data which has the ice on this date above the previsous high for this date back to 2003, the previous highest in this time frame. (In fact, yesterday, Apr 28th, the extent of Arctic ice as reported by JAXA was 245,000 km² above 2003 and getting very close to the 1979-2000 mean).
So does the AGW crowd concede? You’ve got to be kidding! They simply move the goalposts. Now they say that it is the ice volume that counts and most of the present ice is 1-year ice and the Polar ice sheet is much thinner than normal. Thus the ice volume is a lot lower.
But now we have the real measurements obtained this month by the Alfred Wegener Institute for Polar and Marine Research (featured in an article on WUWT a day or two ago) that measured the ice thickness with a sophisticated electromagnetic sensing device attached to a revamped C54 (DC3) and towed about 20m above the ice. Their route crossed the Pole and they ran several legs in various directions from the Pole. (I know, all of the routes ran southward, but at different longitudes). What did they find?
The first reports said that the ice thickness at the North Pole was about twice the amount they expected to find. Since the volume varies as the cube of the thickness, what do the AGWers do now. They’ve already backed the goalposts up to the grandstands.
The answer is bait and switch. They’ll probably shift their reportage to the Catlin expedition. This is a highly publicized trek by 3 grossly unprepared publicity seekers whose equipment failed early-on and any data they may have collected will be of little, if any scientific value. Nevertheless, they will be lionized by the media, especially the BBC a co-sponsor, for their daring and acumen as they dutifully report in regard to the ice situation that “It’s worse than we thought”.
As a matter of fact, if the AGW community had an emblem, their motto would be “It’s worse than we thought”.
Reply: Small point of correction. If you vary only one axis of a solid, ie the thickness and not the width or length, (just z, not x or y) the volume change would be directly proportional or simply double, not proportional to the cube of the variance. ~ charles the moderator.
BTW – Steve, perhaps you could do a post to explain to everyone how the adjustments are made by IARC-JAXA in June & October. There was an explanation in a comment awhile back on an earlier sea ice post but I guess not everyone reads the comments.
This is a bit off topic, but I thought you should see it. Re the assumptions of AGW Truth!!! Look at this drivel–especially the chart.
http://www.sciam.com/article.cfm?id=limits-on-greenhouse-gas-emissions
MarcH said…
“Looking at the Sea ice graphs that Anthony kindly displays on the RHS of his webpage can anyone provide a reason behind the persistent annual small “blip” in June? This appears to suggest a small regular annual increase at a time when ice is melting fastest. Quite strange.”
I’m glad you have seen this too. I brought this up on a previous thread a month-or-so ago bit it was never explained. I ‘seriously’ doubt the ice is actually doing what the graph is supposed to say that it is. Can someone please address this issue?
Thanks,
Jeff
OceanTwo (16:57:38) said “From a statistical standpoint, I don’t see a real problem with -2000 instead of -2007.”
Although this argument may be correct and there may not be a “real problem”, the more words required to explain the data the more the data should be questioned.
ak
We don’t know how much of an effect the quiet sun should have, Lief thinks not that much it seems, but, it sure wouldn’t be large this quick. Thermal inertia is huge and input change small.
Hey Anthony,
I know this is completely off topic but I had a discussion a while ago with a guy called Foinavon (I think) about climate’s sensitivity to CO2. I think it was to do with Hansen having nailed the sensitivity/gain, g, to 3.
One of the papers I referenced was by John Christy and was, at the time, not published, hence Foinavon was not interested. Apparently this has now been published and is available to view at http://www.nsstc.uah.edu/atmos/christy_pubs.html.
It seems quite interesting as it purports to show that CO2’s forcing has no feedback. I.e. a doubling of CO2 leads to at most 1 degree C rise in temperature or that if there is a positive feedback mechanism it must be balanced currently by an existing negative feedback. The negative feedback cannot be due to aerosols, as the IPCC claims, because of Chylek(2007)
These results puts CO2’s forcing well below all existing models and well below any disaster scenario.
Cheers
Steve
Re my prior comment:
Charles: You’re right, I should have kept the x and y axes constant leaving any change in the z axis directly proportional to the volume.hat was I thinking?
Notice that if you look at the values of the averages for now, they both are 14 million square kilometers. But the current values are quite different. If one value is presently larger, the average should also be larger unless what they’re measuring happens to be currently affected by the differences.
Incidentally, in our current glacial averages, “normal” extent might actually be around London or Manhattan. 🙂
MarcH & JeffK
I believe the little blip on the chart was identified as a period when they change to a different filter on the satellite. It was on a previous thread.
Mike86
Aron @14:12:47
Being as the Grauniad is a British rag, that should be “… stick your two fingers up to them”.
Steven,
Have I missed something here?
Has there been some reasonable explanation of the data differences as seen in the blink comparator or not?
Clearly NANSEN and NSIDC are different data sets and shouldn’t be expected to exactly track, but when a public data set changes that radically – someone has some explaining to do.
Has no explanation been forthcoming in the last four months?