You may recall the guest post from Jeff Id of the Air Vent I carried about a week ago called Global Sea Ice Trend Since 1979 – surprising
In that post, a note of correction was issued because that we were led to believe (by Tamino) that the entire post was “invalidated” due to an error in accounting for ice area very near the pole. Both Jeff and I were roundly criticized for “not reading the documentation”, which was one of the more civil criticisms over there at Tamino’s site.
After further investigation It turns out that the error was in NSIDC’s public documentation, and they have issued a correction to it. Even more importantly the correction now affects NSIDC’s own trend graph, and they are considering how to handle it.
This episode illustrates how citizen science can be useful. Sometimes people too close to the science they publish can make mistakes, (we’ve all been there) which is why peer review of papers is important. But “web review” in this day and age of instant publication is equally important. It also illustrates how mistakes, however embarrassing initially, can be useful if you learn from them and study the cause. There is no shame in mistakes if they are corrected and you learn from them. But, the blogospheric noise of angry and sometimes juvenile criticism (on both sides) really isn’t useful as it often masks the real issue. The key is to put that aside and find the truth behind the error. Jeff has done that. His update follows below.
Merry Christmas to everyone! – Anthony
Based on The Air Vent post carried by Watts Up With That, the National Snow Ice Data Center has issued several corrections to the documentation of their sea ice area time series.
Guest post by Jeff ID
Most will remember my earlier post which plotted global sea ice trends. After initially concluding that the global ice level wasn’t decreasing measurably Tamino pointed out a problem in my analysis. After issuing my corrections, thanks and apologies to Tamino and the um…..thousands of readers of Watts Up With That, I went back to work investigating what was really happening to the ice area time series.
It was actually quite lucky that Tamino mentioned the step in the data and criticized me for not reading carefully (something which was mentioned in several comments on the various threads). When I first learned of it, I found the criticism was based on an entirely different set of ice area data with different source documentation. Still, I checked closely and found the tiny step in the time series and was convinced that I had missed something. I had spent a huge amount of time learning the data before I made my post so it was frustrating to say the least. Understand, I used several resources to check my work; not the least of which was the National Snow Ice Data Center (NSIDC) anomaly graph which has the same shape as the one I generated.
The first graph below is from the NSIDC website, the second is my calc. Differences in the noise between the two are explained by the daily resolution used in my graph compared to what my eyes tell me must be monthly data for their plot. They also seem to have an additional year (2007) in their data plot which is not available in the bootstrap time series I used.
After reading everything with great care, this graph and a similar one for the SH were used to verify my results before my original post. This paragraph below used to be on the NSIDC website describing the data of these time series.
In computing the total ice-covered area and ice extent, pixels must have an ice concentration of 15 percent or greater to be included; thus, total ice-covered area is defined as the area of each pixel with at least 15 percent ice concentration multiplied by the ice fraction in the pixel (0.15-1.00). Total ice extent is computed by summing the number of pixels with at least 15 percent ice concentration multiplied by the area per pixel. Sea ice concentrations are assumed to be 100 percent around a circular sector centered over the Northern Hemisphere pole (known as the pole hole) which is never measured due to orbit inclination. The Southern Hemisphere also has a pole hole; however, it does not affect this sea ice data set; since only land is under this hole. For SMMR, the hole is 611 km in radius and is located poleward of 84.5 degrees north. For SSM/I, the hole is 310 km in radius and is located poleward of 87 degrees north.
After checking this for about the hundredth time along with the rest of the extensive documentation, I wrote to the NSIDC and asked them to confirm that the area anomaly for the NH wasn’t corrected another way. Several emails back and forth later they confirmed that the area anomaly wasn’t accounted for. I then pointed out that the graph above and the paragraph in the data description were in error. After a short time, the NSIDC replied that they had their sea ice team was reviewing the data and planning an immediate update to their site.
That same day the site was corrected to read:
In computing the total ice-covered area and ice extent with both the NASA Team and Bootstrap Algorithms, pixels must have an ice concentration of 15 percent or greater to be included. Total ice extent is computed by summing the number of pixels with at least 15 percent ice concentration multiplied by the area per pixel, thus the entire area of any pixel with at least 15 percent ice concentration is considered to contribute to the total ice extent. Total ice-covered area is defined as the area of each pixel with at least 15 percent ice concentration multiplied by the ice fraction in the pixel (0.15-1.00). There is a circular section over the Northern Hemisphere pole (known as the pole hole) which is never measured due to orbit inclination. For the purposes of ice extent, pixels under the pole hole are always considered to be at least 15 percent. For total ice-covered area, the pixels under the pole hole are not used. The Southern Hemisphere also has a pole hole. However, it does not affect this sea ice data set because there is only land under this hole. For SMMR, the hole is 611 km in radius and is located poleward of 84.5 degrees north. For SSM/I, the hole is 310 km in radius and is located poleward of 87 degrees north. Note: The difference in pole hole areas between SMMR and SSM/I results in a discontinuity in the Northern Hemisphere ice-covered area time series across the instrument transition.
Link HERE. They are still considering how to handle the area anomaly graph.
Since this changes how you interpret area data substantially, there is no easy method for updating the trend graph. Still, the step in the data is quite small as shown below.
It occurs right after 1987.5 which corresponds to the 87 July/August boundary which is different from tamino’s reference. If we assume worst case that the NH hole in the data was 100% filled with ice (it wasn’t), the calculation from before produces a slight downslope in comparison to the flat trendless line in my original post. The result is only a trend equaling a 4% reduction in global sea ice over a nearly 30 year period. Not exactly disastrous either way. I am going to continue my work on this by matching (regressing) the last two years from other sites on the end of the data. With the recent global cooling, it should be interesting to see where global sea ice is today.
I need to offer thanks to Anthony Watts for putting the original post on his blog. His professionalism was commendable in handling this matter quickly and transparently. IMO this openness to correction is lacking on several AGW blogs. I also need to thank the NSIDC (particularly, Dave, Molly and the Sea Ice Team) who really blew me away with their responsiveness and professional demeanor in making these corrections.
“” Mark (07:32:10) :
Don’t know if anybody has posted this yet but according to the NSIDC, this years ice extent area is now less than 2007-2008 area.
http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png
Seems kind of odd how all of a sudden, the line flattens out…
REPLY: Yes it does seem odd. But since nobody seems to have a clear picture as to why, I’m not going to speculate. It will shake out, patience. – Anthony “”
Well ho hum; no big deal.
I should remind everyone that it was the SUMMER meltback of 2007 that was of world record extent; all the way back to 1979.
Then in OCOBER of 2007, there was the world record ice regrowth; as I recall something like 58,000 square miles per day for at least 10 days straight; as recorded on WUWT.
So by dec 2007, arctic sea ice was pretty much ordinary and nothing to write home about.
so now it is late Dec 2008 and we are below 2007.
So what we are right in the range of normal variation; so nothing to panic over.
Who or what is TAMINO. ?
Only Tamino, I ever heard of was the pansy hero in Mozart’s “The Magic Flute.”
REPLY: Google “Tamino” and “Open Mind” and you’ll find him. – Anthony
david:
Jeffs calculation was based on the “worst case”, i e that the area between 310 and 611 km from the pole was 100% ice-covered at all times before 1987. This makes the downward trend (4 %) artificially large. Since we actually have no information about ice in this area, the only way to get comparable figures before and after 1987 would be to remove this area for the time period after 1987, which means identifying the affected pixels and removing them from each day’s count for 21 years, a non-trivial task. Note that the problem only applies to ice area, ice extent is unaffected since we can safely assume that each pixel within the pole-hole contains more than 15% ice at all times.
Steve Keohane,
If, in the 80s the sea ice was in places that are now land, I guess the sea level must have been much higher in the 80s than now! The Arctic ocean bucks the trend!! 🙂
http://i44.tinypic.com/330u63t.jpg
I’m still curious if the Hudson Bay and the outlet of Ob river in Russia are even larger in the 80s version than in a real photo. In other words, is the 80s version also “doctored up”? That might be a litter harder to tell.
Looking at the comparisons at Cryosphere Today it has become obvious that the earlier Sea Ice “photos” have been “corrected” to appear that there was more Sea Ice, while the newer “photos” have been “corrected” to show less sea ice. As Steve said, it is most apparent in the Hudson Bay and the outlet of Ob river in Russia. If you look at any sea ice free month, you can see the shape of the Ob River outlet (shaped like a boot), In the years that show snow, this outlet becomes a tiny string of sea ice, whereas in the in the earlier years where the snow was not shown, the sea ice in the “boot” becomes much larger than the actual river.
I hereby call for Cryosphere Today to archive this ridiculous set of “photos” and replace them with the originals. Please make the archived “photos” available as well as the originals. This is a disgrace.
Perhaps the land is still rebounding from the last ice age.
James A (07:54:30) :
Why does the NSIDC highlight the arctic ice extent data and not have the antarctic ice extent data readily available?
They get equal billing here:
http://nsidc.org/data/smmr_ssmi_ancillary/area_extent.html
By the way the current Cryosphere maps are higher resolution than was used in the 80’s.
I have a question about the 1979 start date for these ice studies. I have a book from NASA (NASA SP-489, Arctic Sea Ice, 1973-1976: Satellite Passive-Microwave Observations) covering the mid 1970’s Arctic ice. Why is this data not used in any of their trend lines for ice cover in the Arctic?
Dennis as I recall the coverage wasn’t as consistent, the data is included in the CT database I think.
The following graph includes that data for the Antarctic:
http://www.grida.no/publications/other/ipcc%5Ftar/?src=/climate/ipcc_tar/wg1/fig2-16.htm
Somewhat OT.
hernadi-key (02:57:18) :
…
3. Beer Gets More Expensive
In April, the Associated Press reported that global warming was going to hit beer drinkers in the wallet because the cost of barley would increase, driving up the price of a pint.
…
Just wait til the AGW crowd realizes that most baking, all ale/beer brewing, and all fermentation of wine which involves yeast – which, to the best of my knowledge, they all do – produce CO2. Then wait for the inevitable demand for carbon credits, or even banning, of those activities.
Home brewing will probably once again be made illegal.
– Sigh –
Somewhat OT.
hernadi-key (02:57:18) :
“…
3. Beer Gets More Expensive
In April, the Associated Press reported that global warming was going to hit beer drinkers in the wallet because the cost of barley would increase, driving up the price of a pint.
…’
Just wait til the AGW crowd realizes that most baking, all ale/beer brewing, and all fermentation of wine which involves yeast – which, to the best of my knowledge, they all do – produce CO2. Then wait for the inevitable demand for carbon credits, or even banning, of those activities.
Home brewing will probably once again be made illegal.
– Sigh –
Apologies for the double posting above.
Sea ice fluctuates wildly. If it’s more or less than last year, it means little.
Look at the longer term trends!
Dr.Walt Meier,
Can you please explain a couple of things on the Cryosphere Today “Compare side-by-side images of Northern Hemisphere sea ice extent” product, please?
Why does the snow in the more recent dates cover areas that were previously sea inlets, fjords, coastal sea areas, islands and rivers? (Water areas, most easily discernible in the River Ob inley
Why does the sea ice in the older images cover land areas? (Land areas, most easily discernible in River Ob inlet)
See this overlay: http://i44.tinypic.com/330u63t.jpg
Looking forward to your answer,
Mike Bryant
I have sent these questions to Dr Chapman at CT.
Dr William Chapman,
Can you please explain a couple of things on the Cryosphere Today “Compare side-by-side images of Northern Hemisphere sea ice extent” product, please?Why does the snow in the more recent dates cover areas that were previously sea inlets, fjords, coastal sea areas, islands and rivers? (Water areas, most easily discernible in the River Ob inleyWhy does the sea ice in the older images cover land areas? (Land areas, most easily discernible in River Ob inlet)See this overlay: http://i44.tinypic.com/330u63t.jpgLooking forward to your answer,
Mike Bryant
i have a friendly suggestion to make this site more user friendly. if the posts were numbered where the dates are out to the right, it would be easier to remember where you left off and come back. i know there is a time stamp, but simply numbering the posts would be even easier.
Phil
Thanks. The information that I have from NASA SP-489 is interesting. There is a pronounced increase in the ice from 1973 to 75 and then a drop in 76. The data was not daily data but monthly in the NASA publication.
I am currently hunting for the old Nimbus 2″ Analog data tapes as I have the last surviving tape drives in the world that are functioning and will play that data.
Steve Keohane and Mike Bryant
I checked the Ob River outlet on Google Earth and found some interesting photos posted near the town of Sabetta. At 71-16′-35.97″ N and 72-10′-27.98″ E, there is a photo posted of a Russian Nuclear Powered Ice Breaker at work. This is a location that seems to be indicated as a non sea ice area on the Cryosphere site. There are other interesting photos of other ice breakers at work, clearly on frozen sea ice, as well as some land based photos that show the shoreline near Sabetta. Also, though I can’t say with precision, the town seems to have been there for a while since some of the photos are dated back 13 years or so and it has a name. If the shoreline were moving one direction or the other, I suspect Sabetta would be threatened.
Bob Lucas,
You are correct sir. On December 25 1980, Sabetta was under floating sea ice! On December 25 2008 (yesterday) however, they were under snow, and the snow apparently has also raised parts of the River Ob’s bottom to ground level where snow has been deposited on it! Who’d a thunk it? This Global Warming thing really is bad! How do those few Sabettans cope? Are they Climate refugees?
Mike Bryant,
Yes, very perplexing. But there are obvious discrepancies with CT that need to be addressed.
Google Earth is a good tool to the extent that it can provide the same perspective as Cryosphere Today, at the same general scale. As I pointed out, it also has imbedded photos and other information that can be useful. Plus, someone could contact the photographer of these shots of Sabetta, to see how accurately her Lat&Long was recorded for each shot. Recall she has 4 shots of ice breakers in action off the coast tis year and last year (that is apparently now land), one way or another she found a way to visit the location for the photo.
Finally, those ice breakers off of Sabetta, surely weren’t on dry land. They were there for a purpose.
I’ve done a cursory check of the other arctic areas that have changed sea coast designations and there are other pieces of imbedded information in Google Earth at some of these other locations that might be worthwhile. Its worth looking.
So… let me bite at your final question. Are they Climate refugees? No! Only in modeled virtual reality. At home, they are at peace, living day to day life. Entirely oblivious to this discussion and anything having to do with any changes that are supposed to have occurred in their lifestyle. Can you imagine any people better suited to describe the potential effects of the wrath of nature?
Nice to meet you Mike. I’ve been tracking the technical basis of this issues for a couple of years, but only today jumped into your discussion.
JimB (05:22:01) :
OT…but here’s a great new business opportunity, and if we hurry, we can get in on the ground floor.
http://www.foxnews.com/story/0,2933,472785,00.html
“Travelers will enter their destination into the kiosk, which will calculate the amount of carbon dioxide for which they are responsible and the cost of offsetting it. After swiping their credit cards, they would get a receipt listing the exact carbon-reducing projects their money went to.”
Wonder what the overhead is per transaction
I’ll have a guess at something close to 100%
Bob Lucas & Mike Bryant: Whether the depictions are accurate or not isn’t necessarily the issue. Phil pointed out that the more recent depictions are more accurate, and I would tend to agree, based on the more realistic depiction of the outlet of the river Ob into the Arctic Sea. Fine. What concerns me is that this is a pixel counting business. The background image of the earth is the same in the CT plats 1979 to today. My main concern is the apparent change in the designated shoreline. Has a more ‘realistic’ depiction changed the line of demarcation for the maxiumum ice extent? Has the added snow impinged in that same line? For continuity, and accuracy in comparing any two times in the measurement series, I personally would want as little change as possible in the the whole dataset (pixels) over time. Presenting a more “accurate/realistic” depiction is meaningless if the depiction changes the measurement. In all of the AGW bruhaha, there is a peculiar bias that any and all adjustments only go in one direction, to support the AGW hypothesis, and I hope this is not another, moving the ice extent limit down so that it can never exceed the past extent.
Steve,
I see what you mean. They could change the images but keep the data the same. I wonder who would be the best person to make sure this doesn’t happen? Wouldn’t it be ironic if the images that they posted for a biased comparison, turned out to be the thing that makes them correct the pixel counting routines?
Mike Bryant
Steve and Mike,
” My main concern is the apparent change in the designated shoreline.” Your point is that they can change the designated shoreline without changing the background image? If correct, your concern would be valid. But wouldn’t that practice be the equivalent of changing the actual shoreline, and wouldn’t that be equivalent to changing the base map?
This is why I went to Google Earth, to see if I could see any apparent changes to the shore line in this area from the 1980 map. What I found is that the shoreline depicted by Google Earth looks alot more like that of the 1980 CT depiction of the ice limit line than that of 2008. An adjustment of the designated shore line, as it looks like occurred sometime between 1980 and 2008, would not match the original base map, nor would it match today’s actual shoreline, nor would it be supportable. But it would arbitrarily constrain the pixel count of allowable sea ice.
At least in the case of the area around Sabetta, the actual shoreline certainly appears to be much further inland than shown on the 2008 image. Since Sabetta is obviously an on-going shoreline settlement, the designated shoreline in the 2008 image would appear to be wrong, afterall, no one operates ice breakers on solid ground. Unfortunately, at the scale depicted by the CT images, it would not be possible to determine how wrong.
Perhaps, the appropriate entity, could be asked to compare the Latitude and Longitude of known shoreline settlements like Sabetta, to the L & L of the designated shoreline used in the current pixel counting routines. Or, simply be asked to divulge the L & L’s of the designated shoreline. These figures could easily be checked against the L & L displayed at any point by Google Earth.
Steve and Bob … I don’t know if you saw this but it appears that there are changes taking place at CT… See this
http://igloo.atmos.uiuc.edu/cgi-bin/test/print.sh?fm=12&fd=24&fy=2008&sm=12&sd=25&sy=2008
Adjacent days with very different snow!