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.
As always if you don’t like the outcome just move the goal post.
Blatant lies:
http://www.guardian.co.uk/environment/2009/apr/28/climate-change-poles
“In the past four years, air temperatures have increased, sea ice has declined sharply, surface waters in the Arctic ocean have warmed and permafrost is in some areas rapidly thawing.”
Note the use of alarmist language “sharply” and “rapidly”
I appreciate the answer from Meier, but I am not sure it goes to the heart of the discrepancy. What am I missing?
Mike
Also, according to CT the Global Sea Ice Anomaly is now 765,000 sq. km. which is a large enough area to contain, Virginia, West Virginia, Louisiana, Mississippi, Ohio, Maine and Pennsylvania. Oh yeah Rhode Island and D. C. will fit in there too…
Also,
I wonder if Dr. Meier would comment on why these side by side graphs are using different comparison years… 2007 in Arctic vs. 2008 in Antarctic?
http://nsidc.org/data/seaice_index/daily.html
I posted this as a public note on Facebook:
“Read this article by the Guardian’s John Vidal (a man who enjoys lying so much that he probably has bought himself a golden throne to go with his ego)
http://www.guardian.co.uk/environment/2009/apr/28/climate-change-poles
Sounds frightening doesn’t it? Let’s take a look at just one sentence of it:
“In the past four years, air temperatures have increased, sea ice has declined sharply, surface waters in the Arctic ocean have warmed and permafrost is in some areas rapidly thawing.”
Notice the use of alarming language designed to create public hysteria. Now let’s take a look at how Arctic Ice is really doing according to the National Snow and Ice Data Center (NSIDC).
http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png
As you can see, arctic ice is in a very healthy state. It’s been growing yearly for the past few years and is almost back up to its long term average. So where did John Vidal get the idea that ” sea ice has declined sharply, surface waters in the Arctic ocean have warmed and permafrost is in some areas rapidly thawing”???
The Guardian lies every single day. It’s that simple. Their agenda is to force you to believe the world is going to end unless you change your ways and conform to their mind controlling, soul destroying socialism.
Stick your middle finger up to them. Go enjoy your lives and live the way YOU want to live.”
“nearly large enough to place California inside”
YIKES !!!
Ring the alrm bells !!!!
Has any one told Mr Waxman that CA was moved North and then apparently melted ? Or did it evaporate ? I always have trouble keeping those two in order.
Just out of curiosity, why doesn’t NSIDC use the 1979-2007 average?
Why would you accept just 15% coverage as full coverage. Maybe 85% sea ice would classify as coverage; but 15% ice coverage is open water to me.
George
Shouldn’t the ice be above normal given the lull that the Sun has been in and the low(er) temperatures experienced across the region this past winter? It seems weird that given those factors it’s still below the average.
It seems weird that given those factors it’s still below the average.
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.
Mark
@ak
Recall that there are still heat stored in the sea. IF the “large” areas of young ice continues to thaw slower than the previous years, I would think it is reasonable to look for connections to sun and air temperature.
(But as I have stated earlier, I think the interannual variation between ice area minima is more sensitive to wind and currents than thawing, per se).
Cassanders
In Cod we trust
Following years will have to take into account the area covered with ice over Canada..:)
We have only tracked Arctic sea ice extent for 30 years. How do we have enough of a sample to know?
It’s only 30 years. That’s a lot in human terms, but that’s a meaningless fraction of the number of years since just the last ice age.
Off topic but I just saw on Fox news where Antarctic ice is starting to break up and they don’t know why it’s happening but for sure of course it’s due to the warming.I didn’t think Antarctic mattered any mores???
Dr.Meir: 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.
Perhaps I am too fool to understand, but, why the need of an algorithm?
Why not just a picture?…You know, those images taken by a thing called a camera..
I’m sure the choice of 1979 to some recent year as the span to average for comparison is based mostly on the fact that we don’t have any satellite-based coverage or extent measurements from any earlier than 1979. But what is the basis for assuming that this particular 20+ year period is long enough to cover all of the natural variation in the ice pack?
Isn’t it possible that recent low excursions are simply part of the natural variation and not an issue at all?
If we don’t know if the reference period is “normal”, it isn’t particularly honest to call excursions from it “abnormal” after all.
The approaching minimum will make things easier. At Boulder, new age scientists will measure ice deep from below 🙂
That is peculiar that the NANSEN mean is higher than the NSIDC mean.
Makes no sense.
It’s good to have Dr. Meier accessible and so responsive.
Perhaps he stops in here on occasion.
So I have a few questions for him.
1) Why couldn’t, and hasn’t, the NSIDC adapted it’s mean from their current 1979-2000 mean to a 1979-2007 mean?
2) Will the Dr. acknowledge that in doing so would reduce the NSIDC mean?
3) With 30 years of record why are none of the most recent 9 years included in computing the mean?
4) Wouldn’t removing any 9 year period from calculating the mean make that mean a poor representation and basis for comparison?
Risking the wrath of persons intent on directing the forces of Nature against me, I venture to say that the normal extent of Arctic sea ice is whatever it is at the moment. Persons with skins thinner than my Early Girl tomatoes and whose theme song might be Cole Porter’s “I’ve Got You Under My Skin,” might find fault with that observation. But as has been said, nobody disagrees that Nature is the norm.
Adolfo,
Good questions. In winter the Arctic is dark; covered with clouds, and the ice is fractured and interspersed with open water. Visible wavelength photography is out of the question, so satellites use microwave data and organisations like NSIDC calculate the extent (area of the sea with greater than 15% ice concentration.)
George E. Smith (14:19:31) :
Why would you accept just 15% coverage as full coverage. Maybe 85% sea ice would classify as coverage; but 15% ice coverage is open water to me.
===============================================
You can use any number if you apply it consistently, so use 50% or 92% or 27% it will make little to no difference over the entire time series.
Please note that at the ice edge ice must reach several centimeters thickness before becoming translucent and rise above the surface as nilas, also in rougher water frazil condense until pressure forms cakes of slush that get pushed together to produce pancake ice. So 15% Coverage does not mean 85% Ice Free, means pancake or non dark nilas covering 15% of the area.
> Mike Bryant (14:08:47) :
> Also, I wonder if Dr. Meier would comment on why these side
> by side graphs are using different comparison years… 2007
> in Arctic vs. 2008 in Antarctic?
I think it’s because those are the record years of interest in each hemisphere. 2007 was a record low year for the Arctic ice pack. 2008 was a record high year for the Antarctic ice pack (not widely covered by the MSM; it goes against their AGW religion).
I have a question for Anthony or anybody else. Where on the NSIDC website do you find plottable data for the mean and current (or other) year? Rather than rely on the cramped graph at the IARC-JAXA website, I have a nice spreadsheet graph at home of IARC-JAXA data that fills my 24″ 1920×1200 monitor. I’d like to be able to reproduce the NSIDC graphs at home. Direct URLs to the data please. I’ve tried plowing through http://nsidc.org/data/docs/noaa/g02135_seaice_index/index.html and I sea stuff about monthly data, dailiy image files, and shapefiles. I want daily text data. Help.
Fox News just reported on the “Unexpected Eisdicke” study Anthony posted yesterday-it was brief but they mentioned that an expected ice thickness of 2 meters turned out to be 4 meters. The Goracle has a problem handling this one !!!!!!
O/T, but couldn’t resist this from my RSS feed:
http://briefingroom.typepad.com/the_briefing_room/2009/04/bill-mckibben-pulls-out-of-global-warming-tv-debate.html
Speaking of ice, I’ve done some more reporting on Catlin and interviewed Kenn Borek Air v.p. of operations Sean Loutitt regarding the eventual removal of the currently underfed expedition team members.
Story here:
http://talkingabouttheweather.wordpress.com